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Lymph
Clear fluid derived from interstitial fluid that carries white blood cells and waste.
What does lymph contain?
Water, dissolved solutes, small proteins, and lymphocytes.
What color is lymph typically?
Clear to pale yellow.
Lymphatic capillaries
Smallest lymph vessels that absorb interstitial fluid.
Where are lymphatic capillaries located?
Between cells in most tissues except avascular areas like the CNS and bone marrow.
What type of cells form the walls of lymphatic capillaries?
Overlapping endothelial cells with flaplike valves.
Why do lymphatic capillaries have flaplike valves?
To allow fluid and debris in but prevent backflow.
What anchors lymphatic capillaries to surrounding tissue?
Anchoring filaments.
What causes lymph to enter lymphatic capillaries?
Increased interstitial fluid pressure.
What moves lymph through lymph vessels?
Skeletal muscle contraction, respiration, and smooth muscle in vessel walls.
Do lymphatic vessels have valves?
Yes, numerous one-way valves.
What prevents backflow of lymph?
Valves inside lymphatic vessels.
What structures do lymphatic vessels pass through?
Lymph nodes.
What are lymphatic trunks formed by?
The merging of multiple lymphatic vessels.
What do lymphatic trunks drain into?
Lymphatic ducts.
What are the two lymphatic ducts?
Right lymphatic duct and thoracic duct.
What does the right lymphatic duct drain?
Right side of head, neck, thorax, and right upper limb.
What does the thoracic duct drain?
Left side of body and both lower limbs.
Into what vein does lymph return to blood circulation?
Subclavian vein.
What are the two categories of lymphoid structures?
Primary and secondary lymphoid structures.
What are primary lymphoid structures?
Sites of lymphocyte formation and maturation (red bone marrow, thymus).
What are secondary lymphoid structures?
Sites of immune response activation (lymph nodes, spleen, tonsils, MALT).
Where is red bone marrow located?
In spongy bone of axial skeleton and ends of long bones.
What is the function of red bone marrow?
Produce formed elements including lymphocytes.
What unique step occurs in T-lymphocyte maturation?
They migrate to the thymus for selection.
What is the thymus?
Bilobed organ behind the sternum where T cells mature.
What happens to the thymus with age?
It shrinks and becomes fatty (involution).
What is the main function of the thymus?
T-cell maturation and selection.
What are lymph nodes?
Small encapsulated structures that filter lymph.
Where are large clusters of lymph nodes found?
Cervical, axillary, and inguinal regions.
What is the function of lymph nodes?
Filter lymph and activate lymphocytes.
What is the spleen?
Largest lymphatic organ located in upper left abdomen.
What are the main functions of the spleen?
Filters blood, stores platelets, destroys old RBCs, and activates lymphocytes.
What are tonsils?
Masses of lymphoid tissue around the pharynx.
Name the three main tonsil groups.
Pharyngeal, palatine, and lingual tonsils.
What is the function of tonsils?
Trap and remove pathogens entering through mouth or nose.
What are lymphatic nodules?
Clusters of lymphocytes without a capsule.
Where are MALT tissues found?
Mucosa of GI, respiratory, urinary, and reproductive tracts.
What are Peyer's patches?
Large collections of MALT in the ileum of the small intestine.
How do Peyer's patches differ from other MALT?
They are larger and monitor intestinal bacteria.
What are the five major classes of infectious agents?
Bacteria, viruses, fungi, protozoa, and multicellular parasites.
What is a prion?
Infectious protein that causes misfolding of other proteins.
What disease do prions cause?
Creutzfeldt-Jakob disease or mad cow disease.
What are leukocytes?
White blood cells involved in immune defense.
Name the five leukocyte types.
Neutrophils, eosinophils, basophils, lymphocytes, monocytes.
Where are leukocytes found?
Blood, lymph, and body tissues.
What are cytokines?
Small proteins released by immune cells for communication.
How are cytokines similar to hormones?
They act as signaling molecules but locally and transiently.
Cytokines
Small proteins released by immune cells for communication.
Innate Immunity
Nonspecific defense present at birth.
Adaptive Immunity
Specific defense developed after exposure to antigens.
Physical Barriers to Infection
Skin, mucous membranes.
Chemical Barriers to Infection
Acid, enzymes, and antimicrobial proteins.
Biological Barriers
Normal flora competing with pathogens.
Nonspecific Internal Defenses
Cells, chemicals, inflammation, and fever.
Innate Immunity Cells
Macrophages, NK cells, dendritic cells, neutrophils.
Interferons
Antiviral proteins produced by infected cells to warn neighbors.
Complement System
Group of plasma proteins enhancing immune reactions.
Classical Complement Pathway Activation
By antigen-antibody complexes.
Effects of Complement Activation
Opsonization, inflammation, and cell lysis.
Inflammation
Localized response to injury or infection that brings immune cells to the area.
Redness in Inflammation
Increased blood flow (hyperemia).
Heat in Inflammation
Increased metabolic activity and blood flow.
Swelling in Inflammation
Fluid leaking into tissues (exudate).
Pain in Inflammation
Chemical mediators stimulating nerve endings.
Benefit of Inflammation
Removes debris and pathogens, begins repair.
Exudate
Fluid and immune cells leaking out during inflammation.
Fever
Abnormally high body temperature.
Fever Trigger
Pyrogens released by leukocytes or pathogens.
Benefits of Mild Fever
Inhibits pathogen growth and speeds metabolism.
Risks of High Fever
Protein denaturation, seizures, brain damage.
Antigen
Substance that triggers an immune response.
Antigenic Determinant
Specific site on antigen recognized by antibody.
Immunogenicity
Ability of an antigen to trigger an immune response.
Factors Affecting Immunogenicity
Size, complexity, and foreignness of antigen.
Hapten
Small molecule that becomes antigenic when attached to a carrier protein.
T-Lymphocyte Receptors
T-cell receptors (TCRs).
B-Lymphocyte Receptors
Membrane-bound antibodies (BCRs).
Antigen-Presenting Cells (APCs)
Cells that display antigens to T cells.
Three Major Events in Lymphocyte Life
Formation, activation, and effector response.
T-Lymphocyte Formation
In red bone marrow.
T-Lymphocyte Maturation
In the thymus.
Positive Selection in T-Cell Maturation
T-cells that recognize MHC survive.
Negative Selection in T-Cell Maturation
T-cells reacting strongly to self-antigens are eliminated.
Central Tolerance
Elimination of self-reactive T cells in thymus.
Naïve T-Lymphocytes
They have not yet encountered antigen.
T-Regulatory Cells (T-regs)
Cells that help maintain immune tolerance and prevent autoimmunity.
Helper T-Cell Activation
Antigen presentation and IL-2 signaling.
Cytotoxic T-Cell Activation
Antigen presentation plus IL-2 from helper T-cells.
IL-2 Function
Promotes proliferation of T-cells and B-cells.
B-Cell Activation Difference
B-cells bind antigen directly and require T-cell help.
Lymphocyte Recirculation
Constant movement of lymphocytes through blood, lymph, and tissues.
Effector Response of Helper T-Cells
Release cytokines that stimulate other immune cells.
Cytotoxic T-Cell Killing Mechanism
Release perforin and granzymes causing apoptosis.
T-Cell Immunity Type
Cell-mediated immunity.
Plasma Cells Role
Produce and secrete antibodies.
Antibody Titer
Measure of antibody concentration in the blood.
Antibody Regions
Antigen-binding site and Fc region.
Major Classes of Immunoglobulins
IgG, IgA, IgM, IgE, IgD.
IL-2
Stimulates proliferation of T- and B-lymphocytes.