CH: 20 ~ The lymphatic system and immunity

unit ~ ch 20 ~ quick checks in the slide's pdf

 What are the two main components of the lymphatic system?

• Lymphatic vessels

• Lymphatic tissues and organs

Blind-ended tubes that collect and transport lymph

Lymphatic vessels

Include lymphoid follicles, tonsils, lymph nodes, spleen, and thymus.

Lymphatic tissues and organs

What are the major functions of the lymphatic system?

1. Fluid balance

2. Fat absorption

3. Immune defense

Returns excess interstitial fluid to the bloodstream, helping maintain blood volume and pressure.

Fluid balance

Lacteals in the small intestine absorb dietary fats and transport them to the blood.

Fat absorption

Lymphoid organs filter pathogens from lymph and blood and house or support the maturation of immune cells.

Immune defense

is clear, colorless fluid formed when interstitial fluid enters lymphatic capillaries. It is similar to blood plasma but contains much less protein

Lymph

How does lymph move through the lymphatic vessels?

Lymph moves through a low-pressure system without a central pump.

• Valves

• Skeletal muscle contractions

• Smooth muscle contractions

Define: Valves, Skeletal muscle contractions, Smooth muscle contractions

• prevent back flow

• compress lymphatic vessels

• the walls of collecting vessels

Describe the structure and function of lymphatic capillaries.

• Blind‑ended, one‑way system

• Loosely overlapping endothelial cells open with pressure

• Allow fluid, proteins, macrophages, immune cells in

• Lacteals absorb dietary fats

Trace the pathway of lymph circulation.

Interstitial fluid → lymphatic capillaries → collecting vessels → lymph trunks → lymphatic ducts → veins.

drains the lower body and the left side of the upper body. It receives lymph from the cisterna chyli and empties near the left jugular and subclavian veins.

 thoracic duct

drains the upper-right side of the body and empties near the right jugular and subclavian veins.

 right lymphatic duct

Describe the basic structure and cellular composition of lymphatic tissue.

Reticular connective tissue containing:

• Macrophages

• B & T lymphocytes

• Dendritic cells

• Reticular cells (produce reticular fibers)

engulf pathogens and debris.

Macrophages

carry out adaptive immune functions.

B & T lymphocytes

present antigens to lymphocytes.

Dendritic cells

produce reticular fibers.

Reticular cells

lymphoid tissue that protects mucous membranes exposed to pathogens. It is found in the digestive and respiratory tracts, as well as in parts of the genitourinary tract.

(mucosa‑associated lymphatic tissue)

MALT

where is MALT found?

• Tonsils

• Peyer’s patches (ileum)

• Appendix

1. Surround the oral and nasal cavities; their crypts trap pathogens and debris.

2. Aggregated lymphoid nodules in the ileum of the small intestine.

3. A blind-ended projection from the large intestine containing lymphoid tissue

1. Tonsils

2. Peyer’s patches (ileum)

3. Appendix

Encapsulated, bean-shaped structures along lymphatic vessels. They filter lymph and contain macrophages, dendritic cells, B cells, and T cells. Lymph enters through afferent vessels and leaves through efferent vessels at the hilum.

Lymph nodes

The largest lymphoid organ. Its red pulp removes old red blood cells; its white pulp filters blood and contains immune cells.

Spleen

An organ in the superior mediastinum that supports T-cell maturation. It is most active during childhood and gradually atrophies in adulthood.

Thymus

What roles do surface barriers play in immunity?

• Skin: keratin barrier; acidic sebum

• Mucous membranes: mucus traps pathogens

• Other: stomach acid, normal flora

1. Keratinized layers create a physical barrier; acidic sebum discourages pathogen growth.

2. Mucus traps pathogens and debris.

3. Stomach acid kills many ingested pathogens, while normal gut bacteria compete with harmful microbes.

1. Skin

2. Mucous membranes

3. Other

 is your body’s first responder — fast, general, and always ready, no memory

Innate immunity

your special forces — slower to mobilize but precise and long‑lasting, has memory

Adaptive immunity

What roles do phagocytic cells play in innate immunity?

• Macrophages: Engulf pathogens and debris, release antimicrobial chemicals, and present antigens to T cells.

• Neutrophils: Rapidly recruited from blood; engulf and destroy pathogens, especially bacteria.

• Eosinophils: Help defend against parasites by releasing damaging chemicals.

What roles do non-phagocytic cells play in innate immunity?

• atural killer (NK) cells: Destroy certain virus-infected and cancerous cells.

• Dendritic cells: Present antigens to activate adaptive immune cells.

• Basophils and mast cells: Release inflammatory mediators such as histamine; mast cells are important in allergies.

 group of more than 20 plasma proteins, produced mainly by the liver. They circulate mostly in inactive forms and become activated through a cascade of reactions. Complement supports both innate and adaptive immunity.

complement system

What are five main effects of the complement system?

• Cell lysis (MAC)

• Enhanced inflammation

• Virus neutralization

• Opsonization

• Immune‑complex clearance

1. The membrane attack complex (MAC), which includes C5b, forms pores in target-cell membranes.

2. Complement proteins stimulate basophils and mast cells to release inflammatory mediators.

3. Complement components can bind to and block certain viruses.

4. C3b coats pathogens, making them easier for phagocytes to bind and engulf.

5. C3b helps remove antigen–antibody complexes from circulation through phagocytosis.

define these definitions

1. Cell lysis (MAC)

2. Enhanced inflammation

3. Virus neutralization

4. Opsonization

5. Immune‑complex clearance

coating of a pathogen with molecules such as C3b or IgG. The coating helps phagocytes recognize and bind to the pathogen, making phagocytosis more efficient.

Opsonization

signaling proteins produced by immune cells that regulate immune responses.

Cytokines

Attracts phagocytes to infection sites, increases their activity, and stimulates further cytokine release.

Tumor necrosis factor (TNF):

Help inhibit viral replication inside host cells.

Interferons

Signal between leukocytes and can stimulate neutrophil production, NK cells, interferon production, and T-cell activation.

Interleukins

innate response to tissue injury caused by factors such as trauma, pathogens, toxins, heat, or chemicals. It involves inflammatory mediators and the arrival of phagocytes to contain threats and clear damaged tissue.

inflammatory response

What steps occur in part 1 of the inflammatory response?

Tissue damage → mediator release → vasodilation → permeability → pain → chemotaxis.

What are the four cardinal signs of inflammation?

• Redness

• heat

• swelling

• pain.

What steps occur in part 2 of the inflammatory response?

Macrophages respond → neutrophils (margination, diapedesis) → monocytes → leukocytosis → pus formation.

Movement of immune cells toward chemical signals from an injury or infection.

Chemotaxis

Immune cells adhere to the inner wall of blood vessels near the affected tissue.

Margination

Immune cells squeeze between endothelial cells to leave the blood and enter the tissue.

Diapedesis

A body temperature above the normal range, generally about 36–38°C (97–99°F).

Fever

Describes a person who has a fever.

Febrile

How is fever generated, and what is its purpose?

1. Pyrogens reset hypothalamic set point

2. shivering

3. temperature rises.

Purpose: enhances immune response; slows pathogen growth.

are fever-producing chemicals released by damaged cells or certain bacteria. They act on the hypothalamus to raise its temperature set point, triggering responses such as chills and shivering.

Pyrogens

List the cells involved in cell-mediated immunity.

• Helper T cells (CD4)

• Cytotoxic T cells (CD8)

When do these T cells respond?

They respond primarily to:

• Cells infected with intracellular pathogens (viruses, intracellular bacteria)

• Cancer cells

• Foreign (non‑self) cells, such as transplanted tissue

• T cells form in bone marrow.

• They migrate to the thymus to mature.

• The thymus “screens” T cells and destroys those that cannot recognize antigens.

• Only properly functioning T cells survive and leave the thymus.

T‑cell maturation.

A T cell is immunocompetent when it is capable of mounting a normal immune response to foreign antigens.

immunocompetent

any molecule that can bind to a T‑cell receptor or antibody.

Antigen

an antigen that can trigger an immune response.

immunogen

very small antigens that become immunogenic only when attached to a protein carrier.

Haptens

the specific portion of an antigen that a T‑cell receptor binds.

Antigenic determinant

• Found on nearly all nucleated cells

• Present endogenous antigens

• Interact with cytotoxic T cells (CD8)

Class I MHC

• Found only on antigen‑presenting cells (APCs)

• Present exogenous antigens

• Interact with helper T cells (CD4)

Class II MHC

Produced inside the cell (viral proteins, mutated cancer proteins, intracellular bacteria). Displayed by Class I MHC.

Endogenous antigens

Taken into the cell by phagocytosis (bacteria, debris). Displayed by Class II MHC

Exogenous antigens

T‑cell receptor binds antigen fragment displayed on MHC molecule.

Activation

Only the T‑cell clone that recognizes the antigen is selected to respond.

Clonal selection

Selected clone rapidly divides.

Proliferation

Cells become effector T cells (active fighters) or memory T cells (long‑term immunity).

Differentiation

• Do not kill cells directly

• Secrete cytokines that activate macrophages, B cells, and cytotoxic T cells

• Coordinate and “help” the entire immune response

Helper T cells (TH / CD4):

• Kill infected, cancerous, or foreign cells

• Bind to Class I MHC on target cells

• Release perforins and enzymes to destroy the target cell

Cytotoxic T cells (TC / CD8):

are proteins released by cytotoxic T cells that create pores in target cell membranes, allowing destructive enzymes to enter and kill the cell.

perforins.

List the two components involved in antibody‑mediated immunity.

• B cells

• Antibodies (immunoglobulins)

• B cells form in the bone marrow.

• They mature in the bone marrow, unlike T cells.

• Mature B cells express B‑cell receptors (BCRs) that bind specific antigens.

• Once mature, they circulate and reside in lymphoid organs.

B‑cell maturation.

Describe the structure of an antibody.

• Y‑shaped protein

• Two heavy chains

• Two light chains (2 heavy) (2 light)

• Variable region: binds antigen

• Constant region: determines antibody class and function

• First antibody produced

• Pentamer (5‑unit structure)

• Excellent at agglutination and complement activation

IgM

• Most abundant in blood

• Crosses placenta

• Strong opsonizer

• Dominates secondary immune response

igG

• Found in secretions (tears, saliva, mucus, breast milk)

• Protects mucosal surfaces

• Usually a dimer

igA

• Binds mast cells and basophils

• Important in allergies and parasitic infections

igE

• Found on B‑cell surfaces

• Functions mainly as a B‑cell receptor

IgD

Describe the five basic effects of secreted antibodies.

• Agglutination: clumping of pathogens

• Precipitation: clumping of small antigens

• Opsonization: enhances phagocytosis

• Neutralization: blocks toxins and viruses

• Complement activation: triggers MAC formation

• First exposure to antigen

• Slow (takes several days)

• Mostly IgM

• Weaker response

Primary response:

• Occurs after memory cells are formed

• Rapid and strong

• Mostly IgG

• Long‑lasting protection

Secondary response:

Vaccines expose the body to a safe form of an antigen, triggering a primary immune response and creating memory B cells. Later exposure produces a fast, strong secondary response, preventing illness.

• Live, attenuated vaccines

• Killed vaccines

• Subunit vaccines

Explain how vaccinations induce immunity.

• Body produces its own antibodies

• Long‑lasting

• Occurs through infection or vaccination

Active immunity:

• Body receives antibodies from another source

• Temporary

• Examples: maternal antibodies, antibody injections

Passive immunity