Lymphatic System and Immunity: Key Concepts and Structures

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149 Terms

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Lymph

Clear fluid derived from interstitial fluid that carries white blood cells and waste.

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What does lymph contain?

Water, dissolved solutes, small proteins, and lymphocytes.

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What color is lymph typically?

Clear to pale yellow.

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Lymphatic capillaries

Smallest lymph vessels that absorb interstitial fluid.

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Where are lymphatic capillaries located?

Between cells in most tissues except avascular areas like the CNS and bone marrow.

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What type of cells form the walls of lymphatic capillaries?

Overlapping endothelial cells with flaplike valves.

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Why do lymphatic capillaries have flaplike valves?

To allow fluid and debris in but prevent backflow.

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What anchors lymphatic capillaries to surrounding tissue?

Anchoring filaments.

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What causes lymph to enter lymphatic capillaries?

Increased interstitial fluid pressure.

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What moves lymph through lymph vessels?

Skeletal muscle contraction, respiration, and smooth muscle in vessel walls.

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Do lymphatic vessels have valves?

Yes, numerous one-way valves.

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What prevents backflow of lymph?

Valves inside lymphatic vessels.

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What structures do lymphatic vessels pass through?

Lymph nodes.

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What are lymphatic trunks formed by?

The merging of multiple lymphatic vessels.

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What do lymphatic trunks drain into?

Lymphatic ducts.

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What are the two lymphatic ducts?

Right lymphatic duct and thoracic duct.

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What does the right lymphatic duct drain?

Right side of head, neck, thorax, and right upper limb.

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What does the thoracic duct drain?

Left side of body and both lower limbs.

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Into what vein does lymph return to blood circulation?

Subclavian vein.

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What are the two categories of lymphoid structures?

Primary and secondary lymphoid structures.

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What are primary lymphoid structures?

Sites of lymphocyte formation and maturation (red bone marrow, thymus).

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What are secondary lymphoid structures?

Sites of immune response activation (lymph nodes, spleen, tonsils, MALT).

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Where is red bone marrow located?

In spongy bone of axial skeleton and ends of long bones.

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What is the function of red bone marrow?

Produce formed elements including lymphocytes.

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What unique step occurs in T-lymphocyte maturation?

They migrate to the thymus for selection.

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What is the thymus?

Bilobed organ behind the sternum where T cells mature.

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What happens to the thymus with age?

It shrinks and becomes fatty (involution).

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What is the main function of the thymus?

T-cell maturation and selection.

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What are lymph nodes?

Small encapsulated structures that filter lymph.

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Where are large clusters of lymph nodes found?

Cervical, axillary, and inguinal regions.

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What is the function of lymph nodes?

Filter lymph and activate lymphocytes.

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What is the spleen?

Largest lymphatic organ located in upper left abdomen.

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What are the main functions of the spleen?

Filters blood, stores platelets, destroys old RBCs, and activates lymphocytes.

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What are tonsils?

Masses of lymphoid tissue around the pharynx.

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Name the three main tonsil groups.

Pharyngeal, palatine, and lingual tonsils.

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What is the function of tonsils?

Trap and remove pathogens entering through mouth or nose.

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What are lymphatic nodules?

Clusters of lymphocytes without a capsule.

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Where are MALT tissues found?

Mucosa of GI, respiratory, urinary, and reproductive tracts.

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What are Peyer's patches?

Large collections of MALT in the ileum of the small intestine.

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How do Peyer's patches differ from other MALT?

They are larger and monitor intestinal bacteria.

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What are the five major classes of infectious agents?

Bacteria, viruses, fungi, protozoa, and multicellular parasites.

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What is a prion?

Infectious protein that causes misfolding of other proteins.

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What disease do prions cause?

Creutzfeldt-Jakob disease or mad cow disease.

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What are leukocytes?

White blood cells involved in immune defense.

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Name the five leukocyte types.

Neutrophils, eosinophils, basophils, lymphocytes, monocytes.

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Where are leukocytes found?

Blood, lymph, and body tissues.

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What are cytokines?

Small proteins released by immune cells for communication.

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How are cytokines similar to hormones?

They act as signaling molecules but locally and transiently.

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Cytokines

Small proteins released by immune cells for communication.

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Innate Immunity

Nonspecific defense present at birth.

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Adaptive Immunity

Specific defense developed after exposure to antigens.

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Physical Barriers to Infection

Skin, mucous membranes.

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Chemical Barriers to Infection

Acid, enzymes, and antimicrobial proteins.

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Biological Barriers

Normal flora competing with pathogens.

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Nonspecific Internal Defenses

Cells, chemicals, inflammation, and fever.

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Innate Immunity Cells

Macrophages, NK cells, dendritic cells, neutrophils.

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Interferons

Antiviral proteins produced by infected cells to warn neighbors.

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Complement System

Group of plasma proteins enhancing immune reactions.

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Classical Complement Pathway Activation

By antigen-antibody complexes.

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Effects of Complement Activation

Opsonization, inflammation, and cell lysis.

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Inflammation

Localized response to injury or infection that brings immune cells to the area.

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Redness in Inflammation

Increased blood flow (hyperemia).

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Heat in Inflammation

Increased metabolic activity and blood flow.

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Swelling in Inflammation

Fluid leaking into tissues (exudate).

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Pain in Inflammation

Chemical mediators stimulating nerve endings.

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Benefit of Inflammation

Removes debris and pathogens, begins repair.

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Exudate

Fluid and immune cells leaking out during inflammation.

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Fever

Abnormally high body temperature.

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Fever Trigger

Pyrogens released by leukocytes or pathogens.

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Benefits of Mild Fever

Inhibits pathogen growth and speeds metabolism.

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Risks of High Fever

Protein denaturation, seizures, brain damage.

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Antigen

Substance that triggers an immune response.

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Antigenic Determinant

Specific site on antigen recognized by antibody.

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Immunogenicity

Ability of an antigen to trigger an immune response.

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Factors Affecting Immunogenicity

Size, complexity, and foreignness of antigen.

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Hapten

Small molecule that becomes antigenic when attached to a carrier protein.

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T-Lymphocyte Receptors

T-cell receptors (TCRs).

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B-Lymphocyte Receptors

Membrane-bound antibodies (BCRs).

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Antigen-Presenting Cells (APCs)

Cells that display antigens to T cells.

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Three Major Events in Lymphocyte Life

Formation, activation, and effector response.

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T-Lymphocyte Formation

In red bone marrow.

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T-Lymphocyte Maturation

In the thymus.

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Positive Selection in T-Cell Maturation

T-cells that recognize MHC survive.

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Negative Selection in T-Cell Maturation

T-cells reacting strongly to self-antigens are eliminated.

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Central Tolerance

Elimination of self-reactive T cells in thymus.

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Naïve T-Lymphocytes

They have not yet encountered antigen.

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T-Regulatory Cells (T-regs)

Cells that help maintain immune tolerance and prevent autoimmunity.

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Helper T-Cell Activation

Antigen presentation and IL-2 signaling.

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Cytotoxic T-Cell Activation

Antigen presentation plus IL-2 from helper T-cells.

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IL-2 Function

Promotes proliferation of T-cells and B-cells.

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B-Cell Activation Difference

B-cells bind antigen directly and require T-cell help.

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Lymphocyte Recirculation

Constant movement of lymphocytes through blood, lymph, and tissues.

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Effector Response of Helper T-Cells

Release cytokines that stimulate other immune cells.

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Cytotoxic T-Cell Killing Mechanism

Release perforin and granzymes causing apoptosis.

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T-Cell Immunity Type

Cell-mediated immunity.

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Plasma Cells Role

Produce and secrete antibodies.

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Antibody Titer

Measure of antibody concentration in the blood.

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Antibody Regions

Antigen-binding site and Fc region.

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Major Classes of Immunoglobulins

IgG, IgA, IgM, IgE, IgD.

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IL-2

Stimulates proliferation of T- and B-lymphocytes.