SOMAPL1E

Lymphatic System & Immunity

OBJ 2703 — Components & Functions

Identify the major components of the lymphatic system and their functions.

Question 1

The lymphatic system has four structural components. Which answer correctly lists all four?

ALymph nodes, spleen, thymus, and red bone marrow

BLymphatic vessels, lymph fluid, lymphocytes, and lymphoid tissues and organs

CAfferent vessels, efferent vessels, lymph nodes, and the thoracic duct

DB cells, T cells, NK cells, and plasma cells

ELymph fluid, lymph nodes, the spleen, and MALT

Question 2

The lymphatic system has three primary functions. Which answer correctly identifies all three?

AProducing red blood cells, filtering plasma, and destroying pathogens

BProducing, maintaining, and distributing lymphocytes; returning tissue fluid to blood; and distributing hormones, nutrients, and waste products

CFiltering lymph in lymph nodes, producing antibodies, and storing iron

DCirculating lymph, filtering blood, and activating T cells

EProducing lymphocytes, producing platelets, and transporting fats

Question 3

The thoracic duct and the right lymphatic duct are the two large collecting structures of the lymphatic system. The thoracic duct drains which regions of the body?

AThe entire right side of the body above and below the diaphragm

BThe right side of the body above the diaphragm only

CThe lower abdomen, pelvis, lower limbs, and the left half of the head, neck, and chest

DThe upper body only, on both sides

EThe entire left side of the body and the lower right side

Question 4

Lymphatic capillaries begin as blind pockets in peripheral tissues. Their endothelial cells overlap to form a one-way valve. This design allows which substances to enter?

AWater molecules only — proteins and cells are too large

BFluids, solutes including proteins, viruses, bacteria, and cell debris

CRed blood cells and white blood cells only

DOnly substances smaller than 1 nanometer

EFluids and small molecules, but not pathogens

Question 5

The spleen is the largest lymphoid organ in the adult body. How does it differ functionally from a lymph node?

AThe spleen filters lymph; lymph nodes filter blood

BThe spleen filters blood; lymph nodes filter lymph

CThe spleen produces T cells; lymph nodes produce B cells

DThe spleen is not a lymphoid organ; it belongs to the cardiovascular system

EThe spleen only stores blood; lymph nodes perform all immune functions

Question 6

The thymus reaches its greatest size relative to body size in the first year or two after birth and its maximum absolute weight at puberty (30–40 g). What happens to the thymus after puberty?

AIt doubles in size to support adult immune function

BIt gradually decreases in size

CIt transforms into the spleen

DIt maintains its size throughout adult life

EIt migrates to the abdominal cavity

Question 7

Lymphoid nodules differ from lymphoid organs in one key structural way. What is that difference?

ALymphoid nodules contain T cells only; lymphoid organs contain B cells only

BLymphoid nodules are not surrounded by a fibrous capsule; lymphoid organs are encapsulated

CLymphoid nodules are connected to blood vessels; lymphoid organs are not

DLymphoid nodules cannot change in size; lymphoid organs can expand

ELymphoid nodules contain only macrophages; lymphoid organs contain lymphocytes

Question 8

The tonsils are a type of lymphoid tissue. How many tonsils are usually present in a healthy person, and where are they located?

ATwo — one on each side of the throat

BThree — one pharyngeal, two palatine

CFive — one pharyngeal (adenoid), two palatine, two lingual; all in walls of the pharynx

DFour — two palatine and two lingual

ESix — distributed throughout the digestive and respiratory tracts

Question 9

Roughly 3.6 liters of lymph flow through the lymphatic system per day. What would happen if the thoracic duct were suddenly blocked?

AThe spleen would immediately compensate by producing more lymph

BThere would be a rapid and potentially fatal decline in blood volume

CLymph would back up but blood volume would be unaffected

DThe right lymphatic duct would automatically take over full drainage

EInterstitial fluid would decrease because lymph cannot enter tissues

Question 10

The base of the thoracic duct is an expanded, sac-like chamber. What is its name?

Question 11

A patient presents with massive swelling and fluid accumulation in the left leg after surgery. Lymphatic drainage from that limb is blocked. Which term describes this condition, and what is its direct cause?

ALymphadenopathy — caused by chronic lymphocyte overproduction

BLymphedema — caused by accumulation of interstitial fluid unable to drain through blocked lymphatics

CAnaphylaxis — caused by allergen entry into the lymphatic vessels

DEdema — caused by excessive blood plasma production

ELymphocytosis — caused by too many lymphocytes in the swollen tissue

Question 12

Dietary lipids absorbed by the digestive tract do not typically enter the bloodstream through blood capillaries. How do they reach the general circulation?

AThey are broken down into water-soluble fragments and cross the intestinal capillary walls directly

BThey travel along lymphatic vessels and reach the bloodstream when those vessels drain into the venous system

CThey are stored in the mesenteric lymph nodes until needed

DThey are converted to glucose by the liver before entering the circulation

EThey are phagocytized by macrophages and transported via the spleen

OBJ 2704 — Lymphocytes

Communicate the importance of lymphocytes and identify where they are found in the body.

Question 1

There are approximately one trillion lymphocytes in the body. What percentage of circulating white blood cells do lymphocytes make up?

A5–10 percent

B20–40 percent

C60–70 percent

D80–90 percent

E50–60 percent

Question 2

The three classes of circulating lymphocytes are T cells, B cells, and NK cells. Which statement correctly matches each class to its approximate percentage and primary function?

AT cells = 5–10%, cell-mediated immunity; B cells = 80%, antibody-mediated immunity; NK cells = 10–15%, immunological surveillance

BT cells = 80%, cell-mediated immunity; B cells = 10–15%, antibody-mediated immunity; NK cells = 5–10%, immunological surveillance

CT cells = 50%, B cells = 40%, NK cells = 10%; all perform the same function

DT cells = 10–15%, B cells = 80%, NK cells = 5–10%; all provide cell-mediated immunity

ET cells = 80%, B cells = 5–10%, NK cells = 10–15%; T cells produce antibodies

Question 3

Where do T cells and B cells originate, and what determines which path they take during development?

ABoth originate in the thymus; whether they become T or B cells depends on antigen exposure

BBoth originate from hemocytoblasts in red bone marrow; lymphoid stem cells that remain in the marrow become B cells, while those that migrate to the thymus become T cells

CT cells originate in the spleen; B cells originate in the thymus

DT cells originate in lymph nodes; B cells originate in red bone marrow

EBoth originate in the spleen and migrate to their respective organs for maturation

Question 4

Most of the body's trillion lymphocytes are NOT found in the blood. Where is the majority of the lymphocyte population located?

ACirculating in the bloodstream at all times

BWithin lymphoid organs or other tissues throughout the body

CStored exclusively in the red bone marrow

DConcentrated in the liver

ELocated only in the spleen and thymus

Question 5

The hormone collectively known as thymosins stimulates lymphocyte stem-cell divisions and T cell maturation. Where are thymosins produced?

Question 6

NK cells perform immunological surveillance. What makes NK cells different from cytotoxic T cells when it comes to attacking abnormal cells?

ANK cells require prior antigen sensitization; cytotoxic T cells do not

BNK cells respond much more rapidly and do not require prior sensitization; cytotoxic T cells must be activated through antigen presentation first

CNK cells kill only bacteria; cytotoxic T cells kill only cancer cells

DNK cells produce antibodies; cytotoxic T cells destroy cells physically

ENK cells are found only in lymph nodes; cytotoxic T cells circulate in blood

Question 7

NK cells kill abnormal cells by secreting a protein that creates large pores in the plasma membrane. What is this protein called?

Question 8

Roughly what percentage of lymphocytes survive for 4 years, and how long can some individual lymphocytes last?

A50% survive 4 years; some last up to 10 years

B80% survive 4 years; some last 20 years or more

C20% survive 4 years; most live less than one year

DAll lymphocytes are replaced every 4 years

E60% survive 4 years; none last more than 10 years

Question 9

Some cancer cells avoid destruction by NK cells despite displaying abnormal antigens. This ability of cancer cells to go undetected is called:

AImmunological tolerance

BImmunological escape

CImmunological surveillance

DClonal suppression

EAntigen masking

Question 10

A patient has a tumor in the mediastinum that is compressing and destroying the thymus. Over time, which lymphocyte population would be most severely affected and why?

AB cells, because the thymus produces thymosins that directly stimulate B cell production in the marrow

BT cells, because the thymus is the site where lymphoid stem cells mature into T cells under thymosin stimulation

CNK cells, because NK cells require thymic maturation to become functional

DAll lymphocytes equally, because all types originate in the thymus

EPlasma cells, because plasma cells are stored in the thymic medulla

OBJ 2705 — Nonspecific Defenses

Communicate the body's nonspecific defenses and how each one functions.

Question 1

The body has seven major categories of innate (nonspecific) defenses. Select all seven from the list below.

Select ALL that apply, then click Submit.

APhysical barriers

BPhagocytes

CImmunological surveillance

DMemory cells

EInterferons

FComplement system

GInflammation

HFever

IAntibody production

Question 2

Physical barriers are the first nonspecific defense. Which feature of the skin makes it an especially effective barrier against pathogen entry?

AThe skin is extremely thin, allowing rapid detection of pathogens

BA keratin coating, multiple layers of cells, and a network of desmosomes locking adjacent cells together

CThe skin contains large numbers of macrophages that destroy pathogens on contact

DThe outer layer of the skin is saturated with IgG antibodies

EThe skin secretes strong acids that kill all pathogens on contact

Question 3

Two general classes of phagocytic cells are found in the body. What are they, and which specific cell types make up each class?

AMicrophages (neutrophils and eosinophils) and macrophages (derived from monocytes)

BMicrophages (basophils and mast cells) and macrophages (lymphocytes)

CPhagocytes (neutrophils) and non-phagocytes (eosinophils and basophils)

DFree macrophages (circulating) and fixed macrophages (tissue-resident); both derived from lymphocytes

EMicrophages (T cells) and macrophages (B cells)

Question 4

Macrophages found in the central nervous system have a special name. What are they called?

Question 5

The complement system consists of how many complement proteins in plasma, and what triggers the initial chain reaction?

A5 proteins; triggered when a T cell detects an antigen

B11 proteins; triggered when a complement protein binds to an antibody on a bacterial cell wall or directly to bacterial cell walls

C20 proteins; triggered by fever

D11 proteins; triggered only by antibody-antigen complexes in the blood

E7 proteins; triggered by tissue injury

Question 6

Fever is defined as a body temperature greater than what threshold, and what type of molecule resets the hypothalamic thermostat to cause fever?

A38.5°C (101.3°F); interferons

B37.2°C (99°F); pyrogens

C39°C (102.2°F); interleukins

D37°C (98.6°F); complement proteins

E38°C (100.4°F); histamine

Question 7

Mast cells play a key role in triggering inflammation. What two chemicals do activated mast cells release, and what is the specific role of each?

AHistamine (clots blood at injury site) and heparin (dilates vessels)

BHistamine (increases capillary permeability, speeds blood flow) and heparin (prevents clotting at the injury site itself)

CPerforin (kills bacteria) and lysozyme (destroys cell walls)

DInterferon (prevents viral replication) and complement (destroys membranes)

EHistamine (activates T cells) and heparin (activates B cells)

Question 8

Interferons are released by virus-infected cells. How do interferons protect cells that have NOT yet been infected?

AThey coat the virus and prevent it from binding to new cells

BThey make the secreting cell and its neighbors resistant to viral infection, slowing spread

CThey destroy the virus directly by cleaving its nucleic acid

DThey activate the complement system to lyse virus particles in extracellular fluid

EThey stimulate B cells to immediately produce antiviral antibodies

Question 9

Complement activation produces four known effects. Which answer correctly identifies all four?

AAttracts phagocytes, stimulates phagocytosis, destroys plasma membranes, promotes inflammation

BActivates T cells, produces antibodies, kills cancer cells, triggers fever

CDestroys membranes, produces interferons, activates NK cells, promotes clotting

DCauses fever, activates B cells, promotes diapedesis, stimulates lymphocyte division

EAttracts phagocytes, destroys red blood cells, promotes fever, blocks viral entry

Question 10

During inflammation, a clot forms around the damaged area — but NOT at the actual injury site. Why not?

AComplement proteins at the injury site destroy clotting factors

BHeparin released by mast cells prevents clotting at the injury site, while a clot forms around it

CThe tissue temperature at the injury site is too high for clotting to occur

DHistamine dissolves fibrin at the injury site

EPhagocytes consume clotting factors before they can form a clot

Question 11

The thick fluid mixture of dead cells, cellular debris, and dying phagocytes that accumulates at an injury site is called:

Question 12

A fever of 39°C (102.2°F) may actually be beneficial to the immune response. Which of the following correctly explains why?

AHigh temperature directly kills all bacteria and viruses in the bloodstream

BIncreased temperature increases the rate of metabolism — cells move faster (enhancing phagocytosis) and enzymatic reactions proceed more quickly

CFever activates B cells, causing immediate massive antibody production

DFever triggers release of complement proteins that directly lyse pathogens

EHigh temperature prevents viral replication by denaturing the viral genome

Question 13

A patient receives a stab wound that introduces bacteria into deep tissue. Place the following inflammatory events in the correct sequence: (1) mast cell activation, (2) tissue damage, (3) phagocyte attraction, (4) clot formation around area, (5) histamine and heparin release.

A3 → 1 → 2 → 5 → 4

B2 → 1 → 5 → 3 → 4

C1 → 2 → 3 → 4 → 5

D2 → 5 → 1 → 3 → 4

E5 → 2 → 1 → 4 → 3

Question 14

A patient with a high fever of 41°C (105.8°F) develops confusion and hallucinations. Based on the textbook, at what temperature do high fevers become dangerous, and what types of CNS problems can they cause?

AOver 38°C; causes excessive sweating and dehydration only

BOver 40°C (104°F); can cause nausea, disorientation, hallucinations, or convulsions

COver 39°C (102.2°F); causes permanent brain damage and coma

DOver 42°C only; anything below this is beneficial without risk

EOver 40°C; primary risk is cardiac arrhythmia, not CNS effects

Question 15

Kupffer cells are a type of macrophage. Where are Kupffer cells located and what is their primary role?

AIn the spleen; they filter antigen-bearing lymph

BIn and around blood channels in the liver; they phagocytize debris and pathogens from blood flowing through the liver

CIn the CNS; they present antigens to activate T cells in neural tissue

DIn lymph nodes; they remove antigens from incoming lymph

EIn red bone marrow; they produce monocytes for distribution

Question 16

A patient on long-term corticosteroid therapy (which suppresses inflammation) develops a bacterial skin infection that spreads unusually quickly through deep tissues. Which nonspecific defense mechanism has been most compromised, and why does that explain the rapid spread?

AFever — without fever, bacteria multiply faster; temperature control is the sole barrier

BInflammation — the normal clot formation that walls off the infected region is suppressed, so bacteria spread without the localized barrier that limits their advance

CPhysical barriers — corticosteroids thin the skin, allowing easy pathogen entry

DComplement — corticosteroids directly destroy complement proteins

EImmunological surveillance — NK cells cannot function without inflammation signals

OBJ 2706 — Specific Resistance

Identify specific resistance and the forms and properties of immunity.

Question 1

Adaptive immunity has four general properties: specificity, versatility, memory, and tolerance. Which property explains why the immune system does not normally attack the body's own healthy tissues?

ASpecificity

BVersatility

CMemory

DTolerance

ENeutralization

Question 2

There are four forms of immunity: naturally acquired active, artificially induced active, naturally acquired passive, and artificially induced passive. A newborn is protected from infections during the first months of life by antibodies from its mother. Which form is this?

ANaturally acquired active immunity

BArtificially induced active immunity

CNaturally acquired passive immunity

DArtificially induced passive immunity

EInnate immunity

Question 3

How does the immune system achieve versatility — the ability to respond to tens of thousands of different antigens it cannot predict in advance?

AEvery lymphocyte can respond to every antigen by producing a universal antibody

BBy producing millions of different lymphocyte populations each with different antigen receptors, and through variability in antibody structure

CBy storing pre-made antibodies for every known pathogen in the spleen

DThrough rapid mutation of lymphocytes in response to new antigens

EThrough non-specific binding of all B cells to all antigens simultaneously

Question 4

A vaccine works because it stimulates active immunity under controlled conditions. A person receives their first tetanus vaccination. Which form of adaptive immunity has just been induced?

ANaturally acquired passive immunity

BNaturally acquired active immunity

CArtificially induced active immunity

DArtificially induced passive immunity

EInnate immunity

Question 5

Tolerance is established during lymphocyte maturation. What happens to B cells or T cells that react to normal body antigens during development?

AThey are stored in the red bone marrow in a suppressed state

BThey are modified to recognize foreign antigens instead

CThey are destroyed — only lymphocytes that ignore normal body antigens survive maturation

DThey become suppressor T cells to prevent autoimmune reactions

EThey mature into memory cells but never activate unless stimulated twice

Question 6

Key distinction: active immunity vs passive immunity. A soldier is bitten by a venomous snake and immediately receives a dose of pre-made anti-venom antibodies. Which form of immunity is this, and what is the critical limitation compared to active immunity?

AActive immunity — but it fails because antibodies from outside sources don't work

BPassive immunity — provides immediate protection but is temporary because no memory cells are produced

CPassive immunity — works permanently because the injected antibodies replicate in the body

DActive immunity — because the antibodies activate the patient's own B cells

EInnate immunity — because the response happens immediately without prior exposure

Question 7

Memory is one property of adaptive immunity. What specific cellular mechanism produces immunological memory?

ACirculating antibodies remain in the bloodstream indefinitely after the first exposure

BSome lymphocytes produced during the initial activation remain inactive as memory cells and respond rapidly upon second antigen exposure

CMacrophages store a chemical record of every antigen they have ever phagocytized

DThe hypothalamus records antigen exposures and adjusts the immune response accordingly

EComplement proteins permanently bind to antigens and tag them for future recognition

Question 8

A soldier is exposed to a pathogen they have never encountered before. Their doctor says, "Your immune system has no prior exposure — the initial response may take up to two weeks to reach peak antibody levels, and you could get sick before it fully develops." This accurately describes which form of immunity, and why is the initial response slow?

ASecondary immune response — slow because memory cells must be recruited first

BPrimary immune response — slow because naive B cells must be activated, differentiate into plasma cells, and then begin producing antibodies

CPassive immunity — slow because injected antibodies must travel to lymphoid organs before working

DPrimary immune response — slow because NK cells must clear the pathogen before lymphocytes activate

EInnate immunity — slow because complement proteins must be synthesized from scratch

OBJ 2707 — Cell-Mediated vs Humoral Immunity

Communicate an understanding of the relationship between cell-mediated immunity and antibody-mediated (humoral) immunity.

Question 1

Cell-mediated immunity and antibody-mediated (humoral) immunity each defend a different battleground. Which statement correctly distinguishes them?

ACell-mediated immunity attacks antigens in body fluids; humoral immunity attacks pathogens inside cells

BCell-mediated immunity is provided by T cells and defends against pathogens inside living cells; humoral immunity is provided by B cells and defends against antigens in body fluids

CCell-mediated immunity uses antibodies; humoral immunity uses cytotoxic cells

DBoth are provided by T cells; humoral immunity is simply the name for T cell activity in blood

ECell-mediated immunity is the only adaptive defense; humoral immunity is a nonspecific defense

Question 2

Why are BOTH cell-mediated and humoral immunity necessary? What can each one do that the other cannot?

AActivated T cells cannot respond to antigens in solution; antibodies cannot cross plasma membranes — so each covers the territory the other cannot reach

BT cells kill faster; B cells kill more thoroughly — speed vs completeness requires both

CT cells respond only to bacteria; B cells respond only to viruses

DT cells work in lymphoid organs; B cells work in peripheral tissues — separate anatomical locations require both

ET cells last weeks; B cells last decades — temporal coverage requires both

Question 3

In the sequence of the immune response, which lymphocyte type is typically activated first when an antigen appears, and what happens next?

AB cells activate first and then stimulate T cell activation

BNK cells activate first, destroy the antigen, and then trigger T cell activation

CT cells are activated first (via phagocyte antigen presentation); activated T cells then attack the antigen AND stimulate B cell activation

DPlasma cells activate first and produce antibodies before T or B cells are involved

ET cells and B cells always activate simultaneously at the moment of antigen entry

Question 4

Humoral immunity is named after the word "humor," meaning a liquid. Which of the following most accurately explains why this name applies?

AThe immune response involves water-soluble hormones that dissolve in the bloodstream

BAntibodies occur in body fluids — they defend against antigens dissolved or suspended in body fluids

CThe ancient theory of the four humors classified immunity as a fluid-based phenomenon

DB cells are produced in the liquid environment of the red bone marrow

EAntibodies are liquid at body temperature but solid at room temperature

Question 5

HIV destroys helper T cells. Explain why this causes both cell-mediated AND humoral immunity to fail — even though humoral immunity uses B cells, not T cells.

AHIV also directly destroys B cells, so antibody production stops for an unrelated reason

BHelper T cells are required to secrete the cytokines that activate sensitized B cells — without helper T cells, B cells cannot be fully activated to produce antibodies

CHelper T cells produce antibodies directly; when they die, antibody production stops

DWithout helper T cells, the spleen shuts down and B cells cannot mature

EHIV causes bone marrow failure, stopping production of all blood cells including B cells

Question 6

B cells are responsible for antibody-mediated immunity. What is the name for the antibody-secreting cells that B cells differentiate into upon activation?

Question 7

A patient has a rare genetic disorder that eliminates all T cell function but leaves B cells intact. Which aspects of their adaptive immunity would still function, and which would fail?

ABoth cell-mediated and humoral immunity would fail completely because T cells control all adaptive immune functions

BCell-mediated immunity would fail; humoral immunity would be severely impaired but not completely absent, since full B cell activation requires helper T cell cytokines

CCell-mediated immunity would fail; humoral immunity would be completely normal

DBoth would function normally; T cells are only needed for the first exposure to any antigen

EOnly NK cell activity would be affected; B cells and T cells are independent systems

Question 8

The term "antigen recognition" describes the process by which the adaptive immune response is activated. What is required for antigen recognition to occur?

AThe antigen must enter the bloodstream and bind to complement proteins

BThe antigen must bind to specific receptors on the plasma membrane of a T cell or B cell — each lymphocyte has receptors that recognize only one specific antigen

CA macrophage must consume the antigen before any lymphocyte can recognize it

DPyrogens must first raise body temperature above 38°C to signal antigen presence

EThe antigen must be a complete protein — carbohydrate antigens cannot be recognized

OBJ 2708 — T Cell Types

Communicate the different types of T cells and the role played by each in the immune response.

Question 1

When an antigen triggers the immune response, activated T cells differentiate into four major cell types. List all four.

ACytotoxic T cells, helper T cells, suppressor T cells, and memory T cells

BCytotoxic T cells, plasma cells, NK cells, and memory T cells

CHelper T cells, regulatory T cells, B cells, and memory cells

DCytotoxic T cells, dendritic cells, memory T cells, and macrophages

EHelper T cells, killer T cells, memory cells, and plasma cells

Question 2

MHC proteins are classified as Class I or Class II. Which cells display Class I MHC proteins, and what signal do they send?

AOnly macrophages; they signal that a pathogen has been engulfed

BAll nucleated cells; if they display abnormal, viral, or bacterial peptides, they signal that they are infected or abnormal and should be destroyed

COnly B cells; they signal that antibody production has started

DOnly dendritic cells; they signal that an antigen needs to be eliminated from the blood

ERed blood cells only; they signal blood type compatibility

Question 3

CD markers on T cells determine which class of MHC protein they respond to. Match the CD marker to the correct MHC class and T cell type.

ACD4 responds to Class I MHC (cytotoxic T cells); CD8 responds to Class II MHC (helper T cells)

BCD8 responds to Class I MHC (cytotoxic and suppressor T cells); CD4 responds to Class II MHC (helper T cells)

CCD4 responds to Class I MHC; CD8 responds to Class II MHC; both activate the same T cell types

DBoth CD4 and CD8 respond to Class I MHC; Class II MHC activates B cells only

ECD8 responds to Class II MHC; CD4 responds to Class I MHC; both activate cytotoxic T cells

Question 4

Cytotoxic T cells can destroy target cells by three distinct mechanisms. Which answer correctly lists all three?

AReleasing perforin, secreting lymphotoxin, and triggering apoptosis via cytokines

BReleasing histamine, activating complement, and producing antibodies

CPhagocytosis, releasing interferons, and triggering fever

DReleasing interleukins, activating NK cells, and triggering inflammation

EReleasing perforin, producing IgE, and phagocytosis

Question 5

Helper T cells are the central coordinators of the adaptive immune response. What do activated helper T cells secrete, and what two branches of immunity do those secretions coordinate?

APerforins; they coordinate only cell-mediated immunity

BCytokines; they coordinate both cell-mediated immunity AND antibody-mediated immunity, as well as enhancing nonspecific defenses

CAntibodies; they coordinate both humoral and cellular immunity by binding directly to antigens

DThymosins; they coordinate T cell maturation only

EComplement proteins; they coordinate the nonspecific and specific defense systems

Question 6

Suppressor T cells "put on the brakes" on the immune response. Why do suppressor T cells act AFTER the initial immune response rather than simultaneously with it?

ASuppressor T cells are stored in the spleen and cannot arrive at the site until the initial response is over

BSuppressor T cells are activated more slowly than other T cell types — they dampen the response only after the initial immune reaction has occurred

CSuppressor T cells require a second antigen exposure before they can activate

DSuppressor T cells are produced only after the pathogen is destroyed

EHelper T cells block suppressor T cells until enough antibodies have been produced

Question 7

Antigen-presenting cells (APCs) display foreign antigens on Class II MHC proteins. Which of the following are confirmed APCs according to the textbook?

Select ALL that apply, then click Submit.

AFree and fixed macrophages

BKupffer cells in the liver

CMicroglia in the CNS

DDendritic cells in the skin, lymph nodes, and spleen

ERed blood cells

Question 8

Memory T cells are produced when cytotoxic or helper T cells are activated. What is their function, and when do they become active?

AThey continually patrol the bloodstream, attacking any antigen they encounter

BThey remain in reserve; upon second exposure to the same antigen, they immediately differentiate into cytotoxic T cells and helper T cells

CThey migrate to the thymus and store antigen information there for future responses

DThey remain in reserve but produce low levels of antibodies continuously

EThey suppress the immune response after the first exposure is resolved

Question 9

The cytotoxic mechanism called apoptosis involves genetically programmed cell death. How does a cytotoxic T cell trigger apoptosis in a target cell?

ABy releasing perforin, which ruptures the plasma membrane and causes mechanical cell death

BBy secreting cytokines that activate genes in the target cell's nucleus that instruct the cell to self-destruct

CBy releasing lysozymes that dissolve the target cell's plasma membrane from outside

DBy injecting lymphotoxin directly into the target cell's mitochondria

EBy activating complement proteins that create pores in the target cell membrane

Question 10

A transplanted kidney is rejected by the recipient. Based on the textbook's explanation of MHC proteins, what is the primary immunological mechanism driving organ rejection?

AB cells produce antibodies against the donor's blood type antigens

BT cells recognize nonself peptides displayed on the donor tissue's Class I MHC proteins and destroy the transplanted cells

CComplement proteins activate against donor tissue because it lacks the recipient's blood group antigens

DNK cells detect that the donor kidney does not produce thymosins and destroy it

ESuppressor T cells fail to activate, leaving the immune response uncontrolled against all tissues

Question 11

The chemical that cytotoxic T cells secrete to disrupt the metabolism of a target cell is called:

Question 12

A patient tests positive for HIV. Their CD4 count is critically low. Based on the roles of CD4 T cells in the immune response, predict the complete cascade of immune dysfunction that follows as CD4 cells are progressively destroyed.

AOnly cytotoxic T cell function is lost; B cells and NK cells compensate for all other immune activities

BLoss of helper T cell cytokines → reduced cytotoxic T cell activation (cell-mediated fails) + reduced B cell activation (humoral fails) + suppressor T cells unchecked → immune response suppressed → opportunistic infections + increased cancer risk

CNK cells take over all cytotoxic functions; the only real loss is antibody production

DCD4 loss prevents new T cell production; existing T cells continue to function normally for years

ECD4 loss affects only humoral immunity; cell-mediated immunity is fully preserved through CD8 T cells

OBJ 2709 — Antibody Structure & Function

Identify the structure of antibody molecules and communicate how they function.

Question 1

An antibody molecule has a Y-shape. It consists of four polypeptide chains. Which answer correctly describes those chains?

AFour identical heavy chains — no light chains are present in antibodies

BTwo parallel pairs: one pair of long heavy chains and one pair of shorter light chains

COne heavy chain and three light chains arranged in a Y configuration

DTwo heavy chains and two light chains arranged in an X configuration

EFour light chains — the heavy chain forms the stem and is separate

Question 2

There are five classes of antibodies (immunoglobulins). Which class is the largest, making up approximately 80% of all antibodies, and which is the FIRST class secreted after initial antigen exposure?

AIgA is the largest class; IgE is first secreted

BIgG is the largest class (~80%); IgM is the first secreted after initial antigen exposure

CIgM is the largest class; IgG is first secreted

DIgG is both the largest and the first secreted in all immune responses

EIgD is the largest class; IgA is first secreted

Question 3

The variable segments of the light and heavy chains form the antigen binding sites of the antibody molecule. How many antigen binding sites does a single antibody molecule have?

AOne — located at the base of the Y

BTwo — one at each free tip of the two arms of the Y

CFour — two per arm

DVariable — the number changes depending on the antigen

EUnlimited — the antibody can bind to any number of identical antigens simultaneously

Question 4

Which immunoglobulin class is found in glandular secretions such as tears, mucus, and saliva, and what is its primary function?

AIgG — crosses the placenta to protect the fetus

BIgE — triggers inflammatory reactions in secretions

CIgA — attacks pathogens before they enter body tissues, serving as the first antibody defense at mucous membranes

DIgD — sensitizes B cells in secretions

EIgM — attacks bacteria in glandular secretions

Question 5

When antibody linkage makes antigens clump together on cell surfaces, this is called agglutination. When the same process causes soluble antigens to fall out of solution, it is called:

Question 6

B cell activation requires two steps. What are they, in the correct order?

AActivation by complement, then differentiation into plasma cells

BSensitization (antigen binds to membrane antibodies on the B cell and is displayed on Class II MHC), then activation by cytokines from a helper T cell that recognizes the same antigen

CContact with a cytotoxic T cell, then differentiation into memory B cells

DPhagocytosis of the antigen, then activation by NK cell signals

EAntigen presentation by a dendritic cell, then direct activation by complement

Question 7

IgE plays a specific and important role in allergic responses. What happens when antigen-bound IgE comes into contact with its allergen?

AIgE activates complement and lyses the antigen directly

BIgE bound to mast cells and basophils stimulates those cells to release histamine, heparin, prostaglandins, and other chemicals, causing sudden inflammation

CIgE crosses the placenta and provides passive immunity to the fetus

DIgE neutralizes bacterial toxins by binding to their active sites

EIgE activates NK cells to destroy allergen-bearing cells

Question 8

Opsonization is an antibody function that enhances phagocytosis. Antibodies that perform this function are called:

Question 9

Approximately how many different antibodies can the roughly 10 trillion B cells of a normal adult produce?

A1 million

B100 million

C10 billion

D1 trillion

E10 thousand

Question 10

Which immunoglobulin class is the only one that can cross the placenta, and why is this clinically significant?

AIgM — its small size allows it to pass through the placental barrier

BIgG — this provides passive immunity to the fetus and is also the antibody responsible for hemolytic disease of the newborn in Rh incompatibility

CIgA — found in breast milk, it crosses the placenta to protect the fetus before birth

DIgE — it is the smallest and lightest antibody class

EAll classes cross the placenta equally

Question 11

A patient with a bacterial infection has high circulating levels of IgM but low IgG. What does this antibody pattern tell you about where the patient is in their immune response to this infection?

AThe patient is in the secondary response — IgM always precedes IgG in secondary responses

BThe patient is in the early primary response — IgM is the first antibody class secreted following initial antigen exposure; IgG rises later as the primary response develops

CThe patient has a B cell deficiency — high IgM with low IgG indicates a class-switching failure

DThe patient has been vaccinated — vaccines always produce IgM first regardless of prior exposure

EThe patient has autoimmunity — IgM elevation with low IgG is a hallmark of autoimmune disease

Question 12

A snake venom toxin is injected into a patient. The toxin binds to cell receptors and begins causing tissue damage. If the patient receives anti-venom antibodies, which antibody mechanism would be most effective at stopping the toxin from causing further damage?

AAgglutination — the antibodies clump venom molecules together at the injection site

BNeutralization — antibodies bind to the toxin, making it incapable of attaching to cell receptors

COpsonization — antibodies coat the venom to make it easier to phagocytize

DComplement activation — complement proteins lyse venom molecules

EStimulation of inflammation — the antibodies trigger histamine release to flush the toxin out

OBJ 2710 — Primary vs Secondary Response

Identify the primary and secondary immune responses to antigen exposure.

Question 1

In the primary immune response, how long does it typically take for antibody levels to reach their peak after first antigen exposure?

AWithin 24 hours

B1–2 weeks

C2–4 hours

D3–5 days

E6 months

Question 2

Why is the secondary immune response so much faster and stronger than the primary response?

AThe second antigen is usually weaker than the first

BLarge numbers of memory cells already primed for that antigen respond immediately to even low antigen levels, producing massive quantities of antibodies rapidly

CThe complement system has been pre-activated by the first exposure

DThe liver produces more IgG spontaneously after the first exposure

ENK cells suppress the primary response, allowing the secondary response to dominate

Question 3

In the primary response, which antibody class appears FIRST in the bloodstream after initial antigen exposure?

AIgG

BIgA

CIgM

DIgE

EIgD

Question 4

Vaccination works because it stimulates a primary response under controlled conditions. What is the actual mechanism that PREVENTS disease when the real pathogen is later encountered?

AThe vaccine antibodies remain in circulation and neutralize the pathogen immediately

BThe secondary immune response triggered by the memory cells produced during vaccination is fast and massive enough to neutralize the pathogen before it can cause disease

CThe vaccine permanently raises baseline antibody levels high enough to prevent any infection

DThe primary response from the vaccine is strong enough on its own to prevent future infection

EThe vaccine activates NK cells that remain perpetually vigilant for that specific pathogen

Question 5

Memory B cells do not produce antibodies unless re-exposed to the same antigen. How long can memory B cells survive, enabling a secondary response decades later?

A1–2 years

B20 years or more

C6 months

D5 years maximum

EUntil the same antigen appears — they degrade immediately if never re-exposed

Question 6

Interleukins are the most diverse and important cytokines of the immune system. Which of the following are confirmed functions of interleukins in the immune response?

Select ALL that apply, then click Submit.

AIncrease T cell sensitivity to antigens on macrophage membranes

BStimulate B cell activity and antibody production

CEnhance nonspecific defenses such as inflammation and fever

DDirectly kill cancer cells by lysing their plasma membranes

EHelp suppress immune function and shorten the duration of an immune response

Question 7

A soldier was vaccinated for hepatitis B 15 years ago and never received a booster. They are accidentally exposed to hepatitis B virus today. Predict what will happen immunologically and whether they will develop disease.

ANo immune response will occur because 15 years is too long for memory cells to survive

BA powerful secondary response will occur — memory B and T cells from the vaccination survive 20+ years, will immediately produce large quantities of antibodies, and will likely prevent clinical disease

CA new primary response must occur because memory cells do not persist beyond 10 years

DPassive immunity from the original vaccine will neutralize the virus without activating the immune system

EThe innate immune system will handle the infection; adaptive immunity is not activated by previously encountered antigens

Question 8

Tumor necrosis factors (TNFs) are a group of cytokines involved in the immune response. Which functions do TNFs perform according to the textbook?

Select ALL that apply, then click Submit.

ASlow tumor growth and kill sensitive tumor cells

BStimulate production of neutrophils, eosinophils, and basophils

CCause fever

DIncrease T cell sensitivity to interleukins

EDirectly lyse virus-infected cells by creating membrane pores

OBJ 2711 — Allergies & Autoimmune Disorders

Identify the relation of both allergic reactions and autoimmune disorders to immune mechanisms.

Question 1

There are four types of allergic reactions. Correctly match each type with its mechanism.

AType I = cytotoxic; Type II = delayed; Type III = immediate; Type IV = immune complex

BType I = immediate hypersensitivity (IgE/mast cell); Type II = cytotoxic; Type III = immune complex; Type IV = delayed hypersensitivity

CType I = delayed; Type II = immune complex; Type III = immediate; Type IV = cytotoxic

DAll four types involve the same IgE-mast cell mechanism at different anatomical locations

EType I = T cell mediated; Type II = NK cell mediated; Types III and IV are B cell mediated

Question 2

An autoimmune disorder develops when the immune system attacks normal body tissues. What specific antibodies are produced in autoimmune disorders?

AAllergens

BAutoantibodies

COpsonins

DPyrogens

EInterferons

Question 3

In immediate hypersensitivity (Type I allergy), why does the FIRST exposure to an allergen NOT cause an allergic reaction?

AThe first exposure destroys the allergen before IgE can be produced

BThe first exposure sensitizes — B cells produce IgE that attaches to mast cells, but the reaction occurs only on the second exposure when allergen binds those mast cell-attached IgE molecules

CMast cells cannot bind IgE on first exposure

DThe first exposure activates suppressor T cells that prevent any response

EThe first exposure only activates NK cells, not B cells

Question 4

Anaphylactic shock is a life-threatening Type I allergic reaction. Which sequence of events leads to the dangerous drop in blood pressure?

AIgG binds allergen → complement activated → massive vessel constriction → blood pressure rises dangerously

BCirculating allergen activates mast cells throughout body → massive histamine release → widespread vasodilation and increased capillary permeability → blood pressure falls → circulatory collapse

CT cells attack smooth muscle in all blood vessels simultaneously → vessel constriction → blood pressure rises, then crashes

DIgE destroys red blood cells → blood volume drops → blood pressure falls

EComplement activation lyses endothelial cells → vessel walls fail → massive hemorrhage

Question 5

Multiple sclerosis may be an autoimmune condition. What mechanism of molecular mimicry might cause the immune system to attack myelin sheaths?

AMyelin sheaths contain viral RNA that activates NK cells directly

BSome viruses (measles, influenza) contain amino acid sequences resembling myelin proteins — antibodies targeting those viruses may also attack myelin sheaths

CThe blood-brain barrier blocks suppressor T cells, allowing unchecked cytotoxic T cell activity against neurons

DAutoantibodies mistake myelin's lipid content for a bacterial cell wall antigen

ENK cells in the CNS cannot distinguish myelin from viral-infected cells

Question 6

Poison ivy causes a Type IV (delayed) hypersensitivity reaction. What is the defining feature of this type compared to Type I?

AType IV is caused by IgE; Type I is T cell mediated

BType IV is T cell mediated and produces an inflammatory response 2–3 days after exposure; Type I is IgE/mast cell mediated and occurs within minutes of exposure

CType IV affects the whole body; Type I is localized to the skin

DBoth types are identical in mechanism; only the allergen differs

EType IV involves complement; Type I does not

Question 7

Chronic stress leads to long-term glucocorticoid secretion. Based on the textbook's explanation of the stress-immune response, which specific immune functions are suppressed by prolonged glucocorticoid elevation?

Select ALL that apply, then click Submit.

AReduction in inflammation

BLower phagocyte numbers and activity

CInhibited interleukin production

DIncreased NK cell surveillance activity

EWeakened lymphocyte response

Question 8

A patient is diagnosed with insulin-dependent diabetes mellitus (IDDM). Lab work confirms that their immune system has produced antibodies against their own pancreatic islet cells. This is an example of which class of immune disorder, and what is the specific underlying mechanism?

AImmunodeficiency disease — the pancreas fails to produce enough antigens to maintain normal T cell activity

BAutoimmune disorder — the antigen recognition system has malfunctioned; B cells produce autoantibodies that target normal pancreatic islet cells, destroying them

CType I allergy — the pancreas is releasing allergens that trigger an IgE response

DType III immune complex disorder — circulating antigen-antibody complexes deposit in the pancreas

EInnate immune failure — macrophages have mistakenly phagocytized islet cells

OBJ 2712 — Aging & Immunity

Identify the changes in the immune system that occur with aging.

Question 1

As the immune system ages, T cells become less responsive to antigens. What structural change in a lymphoid organ is at least partly responsible for this T cell decline?

AThe spleen enlarges and traps T cells, reducing their circulation

BThe thymus gradually shrinks after puberty, reducing levels of circulating thymic hormones and T cell production and maturation

CLymph nodes become fibrotic and can no longer filter antigens

DRed bone marrow is replaced by yellow marrow, eliminating lymphocyte production

EThe spleen shrinks, reducing the number of NK cells in circulation

Question 2

Aging results in a reduced number of helper T cells. Why does this cause antibody levels to rise more slowly after antigen exposure in elderly individuals?

AFewer helper T cells means fewer cytokines to activate B cells — B cell activation is impaired and plasma cell production is slower

BB cells in elderly individuals cannot produce IgG and can only produce IgM

CFewer helper T cells means complement cannot be activated to destroy antigens

DElderly B cells migrate to the spleen and are unavailable to produce antibodies in lymph nodes

EReduced helper T cells cause the bone marrow to stop producing new B cells

Question 3

The increased incidence of cancer in elderly people is directly linked to a specific decline in the aging immune system. Which declining function explains this increased cancer risk?

ADecreased complement activity — cancer cells are normally lysed by complement

BDeclining immunological surveillance — NK cells and cytotoxic T cells are less active, so tumor cells are not eliminated as effectively before they can spread

CDecreased antibody production — IgG normally prevents cancer cell replication

DIncreased inflammation — chronic inflammatory cytokines directly cause cancer

ELoss of tolerance — autoantibodies accidentally destroy tumor suppressor proteins

Question 4

Why are annual influenza vaccinations specifically recommended for elderly people, given what you know about aging and the immune response?

AElderly people have lost all innate defenses and rely entirely on vaccination for any protection

BBecause both T cell responsiveness and B cell antibody production are reduced with age, the secondary immune response to a viral infection is weaker and slower — annual vaccination re-stimulates memory cells and partially compensates for this decline

CElderly people have never been exposed to influenza and therefore have no memory cells

DThe flu virus mutates so quickly that even young people require annual vaccination, making age irrelevant

EElderly individuals cannot produce IgM, so annual vaccination provides IgM artificially

OBJ 2713 — System Integrations

Communicate the structural and functional interactions between the lymphatic system and other body systems.

Question 1

For all body systems, the lymphatic system provides one universal function. What is it?

ADistributing hormones to all body tissues

BProviding adaptive (specific) defenses against infection and returning tissue fluid to the circulation

CProducing and distributing red blood cells throughout the body

DRegulating the body's metabolic rate through cytokine secretion

EProviding nutrients to all tissues via the lymphatic circulation

Question 2

Muscle contractions assist the lymphatic system. What is the direct mechanical contribution of skeletal muscle to lymphatic function?

AMuscle contractions produce heat that sterilizes lymph before it reaches the thoracic duct

BMuscle contractions help propel lymph along lymphatic vessels, which rely on external compression rather than their own pumping mechanism

CSkeletal muscles produce lymphocytes that supplement those from the bone marrow

DContracting muscles release cytokines that directly activate NK cells

EMuscle fibers physically filter lymph before it enters lymph nodes

★ Final Score

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— Correct— Incorrect— Total

Section Breakdown

The Lymphatic System and Immunity

Martini, Ober, Bartholomew — Essentials of Anatomy & Physiology (Pearson, 2013) · Chapter 14

SOMAPL1EOBJ 2702–271312 Lesson Steps

2702

Medical Vocabulary — The Lymphatic System

Define the medical vocabulary components related to the lymphatic system.

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Word Roots & Meanings

Root / Prefix	Meaning	Example Term
anamnesis	a memory	anamnestic response (the immune system's memory — stronger second response to an antigen)
apo-	away	apoptosis (programmed cell death — the cell is directed "away" from life)
chemo-	chemistry	chemotaxis (a cell's movement guided by chemical signals in surrounding fluid)
dia-	through	diapedesis (white blood cells squeezing "through" capillary walls into tissues)
-gen	to produce	pyrogen (a substance that produces fever); pathogen (an organism that produces disease)
humor	a liquid	humoral immunity (immunity carried by antibodies in body fluids/liquids)
immunis	safe	immune (protected from disease — kept safe)
inflammare	to set on fire	inflammation (localized tissue response with heat, redness, swelling — like being set on fire)
lympha	water	lymph (the clear, water-like fluid that flows through lymphatic vessels)
nodulus	little knot	nodule (a small, rounded mass of lymphoid tissue — like a little knot)
pathos	disease	pathogen (a microorganism that causes disease)
pedesis	a leaping	diapedesis (cells "leaping" through capillary walls — dia = through, pedesis = leaping)
ptosis	a falling	apoptosis (apo = away, ptosis = falling — the cell "falls away" and dies)
pyr	fire	pyrogen (fire-producing — a substance that raises body temperature/sets the thermostat higher)
taxis	arrangement / directed movement	chemotaxis (directed movement in response to chemical signals)

2703

Major Components of the Lymphatic System and Their Functions

Identify the major components of the lymphatic system and their functions.

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Four Components of the Lymphatic System

1. Lymphatic Vessels (Lymphatics)

A network of vessels that begins in peripheral tissues as blind-ended lymphatic capillaries and ends at connections to veins. Carry lymph from peripheral tissues toward the venous system. Contain valves to maintain flow against low pressures.

2. Lymph

The fluid inside lymphatic vessels. Resembles plasma but contains a much lower concentration of suspended proteins. Roughly 3.6 liters per day flow through the system. Breakage of a major lymphatic vessel can cause rapid, potentially fatal decline in blood volume.

3. Lymphocytes

Specialized white blood cells that perform specific defense functions. The primary cells of the lymphatic system. Approximately 1 trillion lymphocytes in the body — most in lymphoid organs and tissues, not in blood.

4. Lymphoid Tissues and Organs

Lymphoid tissues: loose connective tissue dominated by lymphocytes; form lymphoid nodules (not encapsulated). Lymphoid organs: encapsulated; connected to lymphatic vessels. Examples: lymph nodes, spleen, thymus.

Three Primary Functions of the Lymphatic System

Production, maintenance, and distribution of lymphocytes. Lymphocytes are produced in red bone marrow and stored in lymphoid organs. They respond to invading pathogens, abnormal body cells (virus-infected or cancer cells), and foreign proteins.
Return of fluid and solutes from peripheral tissues to the blood. Maintains normal blood volume and eliminates local variations in interstitial fluid composition.
Distribution of hormones, nutrients, and waste products. Substances unable to enter the bloodstream directly can do so via lymphatic vessels. Lipids absorbed by the digestive tract reach the bloodstream this way.

Lymphatic Vessels — Structure

Lymphatic capillaries begin as blind pockets in peripheral tissues. The endothelial cells overlap to create a one-way valve — fluid, proteins, viruses, bacteria, and cell debris can enter but cannot return to intercellular spaces. Larger lymphatics have walls comparable to veins and contain valves.

Lymph ultimately empties into two collecting ducts:

Thoracic Duct

Collects lymph from the lower abdomen, pelvis, lower limbs, AND left half of the head, neck, and chest. Empties near the junction of the left internal jugular vein and left subclavian vein. Base is the expanded cisterna chyli.

Right Lymphatic Duct

Collects lymph from the right side of the body above the diaphragm only. Empties into the right subclavian vein.

⚠ Exam Trap — LymphedemaBlockage of lymphatic drainage from a limb produces lymphedema — interstitial fluids accumulate and the limb becomes swollen and grossly distended. This illustrates that the lymphatic system is essential for maintaining normal fluid balance in tissues.

Lymphoid Nodules

Lymphoid nodules are NOT surrounded by a fibrous capsule (unlike lymphoid organs). They can change in size depending on lymphocyte numbers. Each often has a pale germinal center where lymphocytes are actively dividing. The mucosa-associated lymphoid tissue (MALT) protects the digestive, respiratory, urinary, and reproductive systems — all open to the external environment.

Specific MALT structures: Tonsils (pharyngeal/adenoid, palatine, lingual — 5 total), Peyer patches (clusters of nodules under intestinal lining), appendix (walls contain fused lymphoid nodules).

Lymphoid Organs — The Three Major Ones

Organ	Location	Key Functions
Lymph Nodes	Greatest numbers in neck, armpits, groin. Oval, 1–25 mm diameter, covered by fibrous capsule.	Filter lymph before it returns to veins. At least 99% of antigens removed by fixed macrophages and dendritic cells as lymph passes through. Stimulate T and B cells to initiate immune response. Afferent vessels bring lymph IN; efferent vessels carry it ONWARD.
Thymus	Mediastinum, posterior to sternum. Pink gland with two lobes divided into lobules.	Site of T cell production and maturation. Cortex contains lymphocytes surrounded by cells that secrete thymosins — which stimulate T cell maturation. Greatest size relative to body in first year or two after birth; maximum absolute size at puberty (30–40 g); then gradually shrinks.
Spleen	Wedged between stomach, left kidney, and diaphragm. About 12 cm long, 160 g.	Largest collection of lymphoid tissue in the body. Filters BLOOD (not lymph). Removes abnormal blood cells and components; initiates B and T cell responses to antigens in blood; stores iron from recycled RBCs. Red pulp: large quantities of red blood cells. White pulp: resembles lymphoid nodules.

Lymph Nodes vs Spleen — Key DistinctionLymph nodes filter LYMPH. The spleen filters BLOOD. Both remove antigens and trigger immune responses, but from different fluids.

2704

Lymphocytes — Types, Origins, and Locations

Communicate the importance of lymphocytes and identify where they are found in the body.

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Overview

Lymphocytes account for 20–40 percent of circulating white blood cells. Most of the approximately 1 trillion lymphocytes are found within lymphoid organs or other tissues — circulating lymphocytes are a small fraction. Life spans are long — roughly 80% survive for 4 years; some last 20 years or more.

Three Classes of Lymphocytes

Class	Percentage	Origin	Primary Function
T cells (thymus-dependent)	~80% of circulating lymphocytes	Lymphoid stem cells from red bone marrow → migrate to thymus → mature under thymic hormones (thymosins)	Cell-mediated immunity. Cytotoxic T cells attack foreign cells and virus-infected cells. Helper and suppressor T cells regulate the immune response.
B cells (bone marrow-derived)	10–15% of circulating lymphocytes	Lymphoid stem cells remain in red bone marrow → mature into B cells → enter bloodstream	Antibody-mediated (humoral) immunity. Under proper stimulation, differentiate into plasma cells that secrete antibodies (immunoglobulins). Antibodies bind to specific chemical targets called antigens.
NK cells (natural killer)	5–10% of circulating lymphocytes	Lymphoid stem cells in red bone marrow → mature alongside B cells	Immunological surveillance. Attack foreign cells, virus-infected cells, and cancer cells in normal tissues. Release perforins to kill abnormal cells by creating pores in plasma membranes.

Where Lymphocytes Are FoundLymphocytes are visitors, not permanent residents, everywhere they go — in blood, red bone marrow, spleen, thymus, and peripheral lymphatic tissues. They continuously migrate through tissues, enter blood or lymphatic vessels, and travel to other sites. The bloodstream provides rapid transport for lymphocytes moving between sites.

Origin and Development (Lymphopoiesis)

Hemocytoblasts in red bone marrow produce lymphoid stem cells.

Group 1: Lymphoid stem cells remain in red bone marrow → produce daughter cells that mature into B cells and NK cells.

Group 2: Lymphoid stem cells migrate to the thymus → under influence of thymosins, divide repeatedly → mature into T cells.

All three types enter the bloodstream and migrate to peripheral tissues, including lymphoid tissues and organs.

As they mature, each lymphocyte gains the ability to respond to a specific antigen. NK cells gain the ability to recognize abnormal cells. A dividing B cell produces only B cells, never T or NK cells.

⚠ Exam Trap — NK vs Cytotoxic T CellsBoth kill abnormal cells, but NK cells are part of NONSPECIFIC defense (innate immunity) and respond much more rapidly. Cytotoxic T cells are part of SPECIFIC defense (adaptive immunity) and require antigen presentation and activation before attacking. NK cells do NOT need prior sensitization.

2705

Nonspecific (Innate) Defenses

Communicate the body's nonspecific defenses and how each one functions.

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Classification Objective — 7 CategoriesInnate defenses do NOT distinguish between one threat and another. They are present at birth. Know all seven categories and how each functions. These provide nonspecific resistance.

1. Physical Barriers

Keep hazardous organisms and materials outside the body. To cause trouble, a pathogen must cross an epithelium — either skin or a mucous membrane. Skin: keratin coating, multiple cell layers, desmosomes locking adjacent cells. Secretions: sebaceous and sweat gland secretions flush surfaces, contain lysozymes (destructive enzymes) and antibodies. Mucus, urine, glandular secretions flush open systems (respiratory, urinary, reproductive). Acid pH adds to effectiveness.

2. Phagocytes

Remove cellular debris and respond to invasion. The "first line of cellular defense" — often attack microorganisms before lymphocytes become involved. Two general classes:

Microphages

Neutrophils (abundant, mobile, quick) and eosinophils (target antigens coated with antibodies). Leave bloodstream and enter peripheral tissues subjected to injury or infection.

Macrophages

Large, actively phagocytic cells derived from circulating monocytes. Found in nearly every tissue. The collective system = monocyte-macrophage system (reticuloendothelial system). Special names by location: microglia (CNS), Kupffer cells (liver).

All phagocytic cells can: move through capillary walls via diapedesis (squeezing between endothelial cells); move toward or away from chemicals via chemotaxis.

3. Immunological Surveillance

Constant monitoring of normal tissues, primarily by NK cells. Abnormal cells have different antigens in their plasma membranes. NK cells recognize these abnormal surface antigens. NK cells secrete perforins, which kill abnormal cells by creating large pores in the plasma membrane. Targets: bacteria, cancer cells, virus-infected cells. Immunological escape occurs when some cancer cells avoid detection — they can then multiply and spread without NK cell interference.

4. Interferons

Small proteins released by virus-infected cells, activated lymphocytes, and macrophages. Interferons are cytokines — chemical messengers that tissue cells release to coordinate local activities. They make the secreting cell and its neighbors resistant to viral infection, slowing the spread of virus. Also attract and stimulate NK cells and macrophages. Used to treat some cancers.

5. Complement System

Plasma contains 11 special complement proteins. The term "complement" reflects that these proteins complement the actions of antibodies. Proteins interact in chain reactions similar to the clotting system. Reaction begins when a complement protein binds to an antibody attached to a bacterial cell wall OR directly to bacterial cell walls.

Complement activation causes four effects: (1) attracts phagocytes, (2) stimulates phagocytosis, (3) destroys plasma membranes, (4) promotes inflammation.

6. Inflammation

A localized tissue response to injury. Produces redness, swelling, heat, and pain. Sequence of events:

Tissue damage → chemical change in interstitial fluid → mast cell activation. Mast cells release histamine (increases capillary permeability, speeds blood flow) and heparin (prevents local clotting at injury site).

Histamine stimulates local sensory neurons → pain. Increased blood flow → redness and elevated local temperature → accelerates enzymatic reactions and phagocyte activity.

Increased vessel permeability → clotting factors and complement proteins leave bloodstream. A clot forms around (not at) the damaged area (heparin prevents clotting at injury site itself). Clot walls off the region, limiting spread.

Necrosis: tissue destruction caused by lysosomal enzymes several hours after injury. Dead cells and debris accumulate → pus. An accumulation of pus in enclosed tissue = abscess.

Cytokine release → activation of specific defenses. Clot erosion, pathogen removal, scar tissue formation = tissue repair.

7. Fever

Maintenance of body temperature greater than 37.2°C (99°F). The hypothalamus acts as the body's thermostat. Pyrogens (circulating proteins) reset this thermostat and raise body temperature. Sources of pyrogens: pathogens, bacterial toxins, antigen-antibody complexes, macrophages stimulated by infection.

Benefits of fever: increases metabolic rate (faster cell movement = enhanced phagocytosis; enzymatic reactions proceed more quickly). Risk: high fevers over 40°C (104°F) can damage physiological systems — CNS problems including nausea, disorientation, hallucinations, convulsions.

Key Point — CytokinesCytokines are chemical messengers released by tissue cells to coordinate local activities. Most act only within one tissue; those released by cellular defenders act as hormones affecting cells and tissues throughout the body. Cytokine groups include interleukins, interferons, tumor necrosis factors, phagocytic regulators, and colony-stimulating factors.

2706

Specific Resistance — Forms and Properties of Immunity

Identify specific resistance and the forms and properties of immunity.

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Definition

Specific defenses protect against particular threats — a specific defense may oppose one type of bacterium but ignore all others. Specific defenses develop after birth through exposure to environmental hazards or infectious agents. They produce a state of protection called specific resistance. Adaptive immunity is provided by the coordinated activities of T cells and B cells responding to specific antigens.

Forms of Immunity

Category	Type	How It Arises	Example
Innate (Nonspecific) Immunity	Present at birth	Physical barriers, phagocytes, NK cells, complement, inflammation, fever	Skin preventing pathogen entry
Innate (Nonspecific) Immunity	—	—	—
Active Immunity (adaptive)	Naturally acquired active	Exposure to antigen naturally in the environment; immune response is triggered	Recovering from chickenpox; body produces memory cells against the virus
Active Immunity (adaptive)	Artificially induced active	Deliberate exposure to antigen under controlled conditions (vaccination)	Receiving a flu vaccine — stimulates memory cell production
Passive Immunity (adaptive)	Naturally acquired passive	Antibodies transferred from mother to baby via placenta or breast milk	Newborn protected by maternal antibodies in first months of life
Passive Immunity (adaptive)	Artificially induced passive	Antibodies administered after exposure to combat infection or prevent disease	Rabies antibodies injected after animal bite

⚠ Active vs Passive — Key DistinctionActive immunity: the person's own immune system produces the antibodies and memory cells. Slow to develop but long-lasting. Passive immunity: antibodies are transferred FROM another source — the person never mounts their own immune response to that antigen. Fast protection but temporary — no memory cells are formed.

Four Properties of Adaptive Immunity

Property	Definition	Mechanism
Specificity	A specific defense is activated by a specific antigen and targets only that antigen.	Each T cell and B cell has membrane receptors that bind only one specific antigen. Known as antigen recognition.
Versatility	The immune system can respond to any antigen it encounters — tens of thousands over a lifetime.	Millions of different lymphocyte populations, each with different antigen receptors; variability in antibody structure.
Memory	The immune system "remembers" previously encountered antigens — second response is faster and stronger.	Memory cells produced during the initial response remain inactive until the same antigen appears again. They survive up to 20+ years.
Tolerance	The immune system does not respond to normal body antigens (self-antigens).	B cells and T cells that react to normal body antigens are destroyed during maturation (red bone marrow and thymus). Only cells that ignore "self" survive.

2707

Cell-Mediated vs Antibody-Mediated (Humoral) Immunity

Communicate an understanding of the relationship between cell-mediated immunity and antibody-mediated (humoral) immunity.

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Cell-Mediated Immunity (Cellular Immunity)

Provided by T cells. Defense against abnormal cells and pathogens inside living cells. Involves close physical contact between activated cytotoxic T cells and the target cell. Activated T cells do NOT respond to antigens in solution — they must contact a cell surface displaying the antigen.

Antibody-Mediated Immunity (Humoral Immunity)

Provided by B cells. Defense against antigens and pathogens in body fluids. B cells differentiate into plasma cells that secrete antibodies. "Humoral" = humor, a liquid — antibodies circulate in body fluids. Antibodies cannot cross plasma membranes — they work in fluids, not inside cells.

Why Both Are Needed

Activated T cells cannot respond to antigens in solution (dissolved in body fluids). Antibodies produced by B cells cannot cross plasma membranes to reach pathogens hiding inside cells. The two systems cover different battlegrounds:

Virus hiding inside a cell → cell-mediated immunity (cytotoxic T cells destroy the infected cell)
Bacteria multiplying in interstitial fluids → antibody-mediated immunity (antibodies bind and neutralize/tag them)

Overview of the Immune Response Sequence

An antigen appears in body tissues. Phagocytes engulf and process the antigen.

Phagocytes present the antigen on their surface → T cells are activated first.

Activated T cells attack the antigen directly AND stimulate the activation of B cells.

Activated B cells mature into plasma cells that produce antibodies. Circulating antibodies bind to and attack the antigen.

The RelationshipCell-mediated and humoral immunity are not independent — they cooperate. Helper T cells (activated by antigen presentation) are required to fully activate B cells. Without helper T cells (as occurs in AIDS), both branches of adaptive immunity weaken.

2708

T Cell Types and Their Roles in the Immune Response

Communicate the different types of T cells and the role played by each in the immune response.

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Antigen Presentation — How T Cells Are Activated

T cells are rarely activated by direct contact with free antigens. Activation requires the antigen to be presented on the surface of another cell bound to major histocompatibility complex (MHC) proteins.

Class I MHC Proteins

Found in plasma membranes of all nucleated cells. Bind and display small peptide molecules from inside the cell. If the peptides are foreign, viral, or bacterial → T cells are activated to destroy that cell. Primary signal for: "This cell is infected or abnormal — kill it."

Class II MHC Proteins

Found in membranes of lymphocytes and antigen-presenting cells (APCs). APCs: free and fixed macrophages, Kupffer cells, microglia, and dendritic cells. Signal: "This antigen is dangerous — launch a response against it."

CD markers determine which MHC class a T cell responds to. CD8 T cells respond to Class I MHC. CD4 T cells respond to Class II MHC.

Four Types of T Cells

T Cell Type	CD Marker	MHC Class Recognized	Role
Cytotoxic T cells	CD8	Class I	Directly attack and destroy cells displaying foreign or abnormal antigens. Kill by: (1) releasing lymphotoxin (disrupts cell metabolism), (2) secreting cytokines that trigger apoptosis (programmed cell death), (3) releasing perforin (ruptures plasma membrane). Produce memory T cells upon activation.
Helper T cells	CD4	Class II	Secrete cytokines that coordinate specific and nonspecific defenses. Stimulate both cell-mediated immunity AND antibody-mediated immunity. Required to fully activate B cells. Produce memory T cells and more active helper T cells. HIV targets and destroys helper T cells — their loss paralyzes both branches of adaptive immunity.
Memory T cells	Same as parent (CD8 or CD4)	Same as parent	Produced when cytotoxic T cells and helper T cells are activated. Remain "in reserve." Upon second exposure to the same antigen, immediately differentiate into cytotoxic T cells and helper T cells — producing a faster, stronger response.
Suppressor T cells	CD8	Class I	Dampen the responses of other T cells and B cells by secreting suppression factors. Activated more slowly than other T cells — they act AFTER the initial immune response, "putting on the brakes." Limit the degree of immune response to a single stimulus, preventing excessive immune activity.

⚠ CD4 vs CD8 — Know the PairingCD4 = Helper T cells = Class II MHC = antigen-presenting cells (phagocytes, dendritic cells). CD8 = Cytotoxic T cells AND Suppressor T cells = Class I MHC = infected or abnormal cells. Helper T cells stimulate the immune response. Suppressor T cells slow it down. Both regulatory types are sometimes called "regulatory T cells."

2709

Antibody Structure and Function

Identify the structure of antibody molecules and communicate how they function.

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B Cell Activation — From Sensitization to Antibody Production

Sensitization: Each B cell carries its own specific antibody molecules in its cell membrane. Antigens in the interstitial fluid bind to those membrane antibodies. The antigen enters the B cell by endocytosis and is displayed on Class II MHC proteins on its surface. The B cell is now sensitized.

Activation: A helper T cell that has been activated by the SAME antigen attaches to the MHC-antigen complex on the sensitized B cell and secretes cytokines. Cytokines promote B cell activation, stimulate B cell division, and accelerate B cell development into plasma cells.

Division and Differentiation: The activated B cell divides repeatedly, producing plasma cells (secrete large quantities of antibodies) and memory B cells (remain in reserve for future exposure to the same antigen).

Antibody Structure

An antibody molecule has a Y-shape. It consists of two parallel pairs of polypeptide chains:

Two heavy chains (long) — form the base and stem of the Y
Two light chains (shorter) — paired with the heavy chains

Each chain contains constant segments (the base — only 5 types exist, forming the basis of antibody classification) and variable segments (the free tips of the arms). The variable segments form the antigen binding sites — two per antibody molecule (one per arm of the Y). Small differences in amino acid sequence in variable segments produce different binding site shapes → different specificities. The approximately 10 trillion B cells of a normal adult can produce 100 million different antibodies.

Antibodies bind to specific portions of the antigen's exposed surface called antigenic determinant sites. A complete antigen has at least two antigenic determinant sites (one for each arm). Most environmental antigens have multiple sites; entire microorganisms may have thousands.

Five Classes of Antibodies (Immunoglobulins)

Class	Location / Characteristics	Function
IgG	Largest class (80% of all antibodies); several subtypes; circulates in blood	Resistance against many viruses, bacteria, and bacterial toxins. Only class that can cross the placenta — provides passive immunity to fetus.
IgM	First antibody secreted following initial antigen exposure; levels decline as IgG production rises	Attacks bacteria. Responsible for cross-reactions between incompatible blood types (anti-A and anti-B forms).
IgA	Found in glandular secretions — tears, mucus, saliva	Attacks pathogens before they enter body tissues. First line of antibody defense at mucous membranes.
IgE	Bound to surfaces of mast cells and basophils	When bound IgE contacts its antigen, stimulates mast cells and basophils to release histamine and other inflammatory chemicals. Central role in allergic responses.
IgD	Attached to B cell surfaces	Binds antigens in extracellular fluid to B cells. Can play a role in B cell sensitization.

Six Mechanisms of Antibody Action

Mechanism	How It Works
Neutralization	Antibodies bind to viruses or bacterial toxins, making them incapable of attaching to a cell. The threat is neutralized before it can cause harm.
Agglutination	One antibody links antigens on the surfaces of two different cells together, forming large clumped complexes. Example: clumping of incompatible red blood cells.
Precipitation	When the target antigen is a soluble molecule, antibody linkage creates insoluble complexes too large to stay in solution — they settle out of body fluids.
Activation of Complement	Antigen binding changes the shape of antibody constant segments, exposing complement-binding sites. Bound complement activates the complement system → destroys antigen.
Attraction of Phagocytes	Antigens covered with antibodies attract eosinophils, neutrophils, and macrophages, which phagocytize the pathogens.
Enhancement of Phagocytosis (Opsonization)	Coating of antibodies and complement proteins makes pathogens easier to phagocytize. Antibodies that do this are called opsonins.

Stimulation of Inflammation (7th Mechanism)Antibodies may also promote inflammation by stimulating basophils and mast cells — mobilizing nonspecific defenses and slowing spread of infection to other tissues.

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Primary and Secondary Immune Responses

Identify the primary and secondary immune responses to antigen exposure.

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Primary Response

The body's initial response to first antigen exposure. B cells must be activated and then differentiate into plasma cells before antibody production begins. Slow to develop. Antibody concentrations undergo a gradual, sustained rise — do not peak until 1–2 weeks after initial exposure. IgM molecules appear first in the bloodstream, followed by a slow rise in IgG. Antibody levels then decline (assuming no further exposure). Less effective at preventing disease than the secondary response.

Secondary Response (Anamnestic Response)

Triggered by a second exposure to the same antigen. Memory B cells (and memory T cells) are already primed. They respond immediately — dividing and differentiating into plasma cells that secrete massive quantities of antibodies. IgG rises rapidly to levels many times higher than the primary response. Response is faster and stronger because: (1) numerous memory cells respond to low antigen levels, (2) antibody concentrations remain elevated for an extended period. Memory cells survive for 20 years or more — secondary response can occur decades later.

Why Immunization Works

A vaccine contains dead or inactive pathogen, or antigens derived from it. Administered orally or by injection.

The vaccine triggers a primary response under controlled conditions — stimulating production of memory B cells and memory T cells without causing disease.

When the real pathogen is encountered later, it triggers a powerful secondary response — usually sufficient to prevent infection and disease before symptoms develop.

Key DistinctionIt is the SECONDARY response — not the primary — that actually prevents disease after vaccination. Immunization is effective because it creates memory cells. The primary response alone is too slow to stop disease. The secondary response is fast and massive enough to neutralize the pathogen before it establishes infection.

Cytokines That Coordinate the Immune Response

Cytokine Group	Primary Sources	Key Effects
Interleukins (IL)	Lymphocytes, macrophages, endothelial cells, fibroblasts, astrocytes	Increase T cell sensitivity to antigens; stimulate B cell activity, plasma cell formation, and antibody production; enhance nonspecific defenses (inflammation, fever); some suppress immune function to shorten duration.
Interferons	Virus-infected cells, activated lymphocytes, macrophages	Make infected cell's neighbors resistant to viral infection → slow viral spread. Attract and stimulate NK cells and macrophages. Used to treat some cancers.
Tumor Necrosis Factors (TNFs)	Macrophages, T cells	Slow tumor growth and kill sensitive tumor cells. Stimulate production of neutrophils, eosinophils, basophils; promote eosinophil activity; cause fever; increase T cell sensitivity to interleukins.
Colony-Stimulating Factors (CSFs)	Active T cells, monocyte-macrophage cells, endothelial cells, fibroblasts	Stimulate production of blood cells in red bone marrow and lymphocytes in lymphoid tissues and organs.

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Allergic Reactions and Autoimmune Disorders

Identify the relation of both allergic reactions and autoimmune disorders to immune mechanisms.

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Overview — When Immunity Goes Wrong

The ability to produce a normal immune response after antigen exposure is called immunological competence. Three general categories of disorders result from immune dysfunction: autoimmune disorders, immunodeficiency diseases, and allergies.

Autoimmune Disorders

Develop when the immune response mistakenly targets normal body cells and tissues. The recognition system malfunctions — activated B cells manufacture antibodies against normal body components. These are called autoantibodies. The condition depends on which antigen is attacked.

One mechanism: molecular mimicry — some viruses contain amino acid sequences resembling proteins in the body. Antibodies targeting those viruses may also attack normal tissues. Example: antibodies against measles or influenza viruses may also attack myelin sheaths → neurological complications after vaccination or viral infection; may be responsible for multiple sclerosis.

Risk increases with unusual types of MHC proteins. At least 50 clinical conditions linked to specific MHC structure variations, including: rheumatoid arthritis (attacks connective tissue around joints), insulin-dependent diabetes mellitus (attacks pancreatic islet cells), psoriasis, myasthenia gravis, narcolepsy, Graves disease, Addison's disease, systemic lupus erythematosus (SLE), and chronic hepatitis.

Immunodeficiency Diseases

Either the immune system fails to develop normally or the immune response is blocked. Severe combined immunodeficiency disease (SCID): infants fail to develop either cell- or antibody-mediated immunity. Cannot produce an immune response — even mild infections can be fatal. Treatment: bone marrow transplants or gene-splicing techniques.

AIDS: caused by HIV, a retrovirus that targets helper T cells (via their CD4 membrane protein). Also infects monocyte-macrophage antigen-presenting cells. As helper T cells are destroyed: cell-mediated immunity weakens; antibody-mediated immunity weakens (helper T cells required to activate B cells); suppressor T cells relatively unaffected → excess suppression "turns off" immune response; circulating antibody levels decline; immunological surveillance depressed → cancer risk increases. Even ordinarily harmless microorganisms can initiate lethal opportunistic infections.

Allergies — Four Types

Allergies are inappropriate or excessive immune responses to antigens (called allergens when they trigger allergic reactions). The immune response can destroy normal cells or trigger massive inflammation.

Type	Mechanism	Example
Type I — Immediate Hypersensitivity	First exposure to allergen → B cells produce large quantities of IgE antibodies (no reaction yet — just sensitization). IgE attaches to mast cells and basophils throughout body. Second exposure → allergen binds IgE on mast cells → release of histamine, heparin, prostaglandins, and cytokines → sudden inflammation. First exposure: no reaction. Second exposure: reaction occurs.	Hay fever, environmental allergies (affect ~15% of U.S. population). In severe cases → anaphylaxis: allergen enters bloodstream, mast cells throughout body are activated → widespread vasodilation, capillary permeability increases, smooth muscle in airways contracts → anaphylactic shock can be fatal.
Type II — Cytotoxic Reactions	Antibodies bind to antigens on surfaces of specific cells, activating complement → cell destruction	Transfusion reactions with incompatible blood types (ABO cross-reactions)
Type III — Immune Complex Disorders	Phagocytes cannot rapidly remove circulating antigen-antibody complexes → complexes persist → inflammation and tissue damage, especially in blood vessels and kidneys	Certain autoimmune conditions; some drug reactions
Type IV — Delayed Hypersensitivity	Inflammatory response occurs 2–3 days after antigen exposure; T cell mediated rather than antibody mediated	Contact dermatitis from poison ivy or poison oak

Clinical — AnaphylaxisAnaphylactic shock results from a Type I allergy when the allergen enters the bloodstream. Signs and symptoms: skin swelling/hives (edema in dermis), narrowed airways (smooth muscle contraction), severe fall in blood pressure (extensive peripheral vasodilation). Can be fatal without treatment. Many signs can be prevented by prompt administration of antihistamines — drugs that block the action of histamine. Epinephrine is the primary treatment for anaphylactic shock.

Stress and the Immune ResponseInterleukin-1 (produced early in immune response) stimulates ACTH production by the anterior pituitary → glucocorticoid secretion by adrenal cortex. Anti-inflammatory glucocorticoids may help control the intensity of the immune response. However, chronic stress → long-term glucocorticoid secretion → depressed immune response: reduced inflammation, lower phagocyte numbers and activity, inhibited interleukin production → weakened lymphocyte response → lower resistance to disease.

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Changes in the Immune System with Aging

Identify the changes in the immune system that occur with aging.

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Change	Detail	Consequence
T cell responsiveness declines	T cells become less responsive to antigens. Fewer cytotoxic T cells respond to a given infection. Associated at least in part with gradual shrinkage of the thymus and reduced levels of circulating thymic hormones.	Slower, weaker cell-mediated immune response to infections.
Reduced helper T cell numbers	Because the number of helper T cells also declines, B cells are less stimulated.	Antibody levels rise more slowly after antigen exposure — reduced antibody-mediated immunity.
Increased susceptibility to viral and bacterial infections	Both branches of adaptive immunity are weakened. Vaccinations for acute viral diseases (e.g., flu/influenza) are strongly recommended for elderly people.	A pathogen that would be rapidly controlled in a younger person may cause serious illness in an elderly one.
Decline in immunological surveillance	NK cells and cytotoxic T cells are less active in monitoring tissues for abnormal cells.	Tumor cells are not eliminated as effectively — accounts for the increased incidence of cancer in the elderly.

Overall PatternAging weakens BOTH cell-mediated and humoral immunity. The primary driver is the shrinkage of the thymus — reduced thymosins → reduced T cell production and maturation → reduced helper T cell numbers → downstream weakening of B cell activation. This is the same general mechanism seen (acutely and severely) in AIDS, but occurring slowly and gradually with normal aging.

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Structural and Functional Interactions — Lymphatic System and Other Body Systems

Communicate the structural and functional interactions between the lymphatic system and other body systems.

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The lymphatic system provides adaptive (specific) defenses against infection for all body systems. It also returns tissue fluid to the circulation. Through immunological surveillance, pathogens and abnormal body cells are continuously eliminated throughout the body. Two especially close relationships — between the immune response and the endocrine system, and between the immune response and the nervous system — are active areas of research.

System	What the Lymphatic System Does for It	What It Does for the Lymphatic System
Integumentary	Provides IgA antibodies for secretion onto integumentary surfaces; lymphocytes provide adaptive defense against skin infections	Provides physical barriers to pathogen entry; macrophages in dermis resist infection and present antigens; mast cells trigger inflammation and mobilize lymphatic cells
Skeletal	Assists in repair after bone injuries; osteoclasts differentiate from monocyte-macrophage cell line	Protects endocrine organs in brain, chest, and pelvic cavity; lymphocytes and immune cells produced and stored in red bone marrow
Muscular	Assists in repair of muscle after injuries	Skeletal muscles protect some lymphoid organs; muscle contractions help propel lymph along lymphatic vessels
Nervous	Microglia (CNS macrophages) present antigens that stimulate adaptive defenses; glial cells secrete cytokines; innervation stimulates antigen-presenting cells; some skin conditions (psoriasis) worsen under stress via neural mechanisms	Controls and modulates immune activity; immune response can decline suddenly after even brief emotional distress; nervous system can adjust sensitivity of the immune response
Endocrine	Cytokines from immune cells affect production of CRH and TRH by hypothalamus → TSH by pituitary → increased thyroid hormone → increased metabolism during immune response. Thymus secretes thymosins.	Glucocorticoids have anti-inflammatory effects; thymosins stimulate development and maturation of lymphocytes; many hormones affect immune function
Cardiovascular	Fights infections of cardiovascular organs; returns tissue fluid to circulation (preventing lymphedema)	Distributes WBCs and carries antibodies that attack pathogens; clotting response helps restrict spread of pathogens; granulocytes and lymphocytes produced in red bone marrow; blood vessels transport lymphocytes between sites
Digestive	Lymphocytes in MALT (tonsils, Peyer patches, appendix) protect digestive tract from pathogens ingested with food	Provides nutrients for immune cell metabolism and lymphocyte production
Urinary	Lymphocytes defend urinary tract from infection	Removes metabolic wastes generated by immune activity
Reproductive	Lymphocytes defend reproductive tract; IgA in secretions	Provides nutrients for immune function

The Big Picture — Lymphatic vs Immune SystemThe lymphatic system is an anatomically distinct system with vessels, organs, and cells. The immune system is a broader physiological system that includes the lymphatic system PLUS components of the integumentary, cardiovascular, respiratory, digestive, and other body systems. The immune system is defined by function (defense), not anatomy. The lymphatic system is the primary structural component of the immune system.

Endocrine-Immune Feedback LoopInterleukin-1 (produced during immune response) → stimulates CRH/TRH production by hypothalamus → TSH from pituitary → thyroid hormones increase → accelerated cell and tissue metabolism during immune response. At the same time, interleukin-1 → ACTH from pituitary → glucocorticoids from adrenal cortex → anti-inflammatory effect that controls intensity of the immune response. This bidirectional feedback keeps immune responses effective but prevents them from becoming destructive to the body itself.