Chapter 22: Lymphatic System and Immunity

Comprehensive vocabulary deck covering the lymphatic system, lymphocyte types, immune responses, and immune disorders based on the lecture transcript.

Pathogens

Microscopic organisms in the environment responsible for diseases in the human body, such as viruses, bacteria, fungi, and parasites.

Lymphocytes

Cells of the lymphatic system that respond to environmental pathogens, toxins, and abnormal body cells; they are part of the specific defense or immune response.

Immunity

The ability to resist infection and disease.

Lymph

A fluid similar to plasma but without the plasma proteins.

Lymphatic vessels (lymphatics)

The network that carries lymph from peripheral tissues to the venous system.

Lymphatic capillaries

Also called terminal lymphatics, these are the smallest vessels of the lymphatic system which start as pockets rather than tubes and have larger diameters and thinner walls than blood capillaries.

Lymphedema

Severe swelling caused by the blockage of lymph drainage from a limb, which interferes with proper immune system function.

T cells

Thymus-dependent lymphocytes that make up approximately $80\%$ of circulating lymphocytes.

Cytotoxic T cells

T cells that attack cells infected by viruses and are responsible for producing cell-mediated immunity.

Helper T cells

Regulatory T cells that stimulate the function of both T cells and B cells.

Suppressor T cells

Regulatory T cells that inhibit the function of T cells and B cells to control the sensitivity of the immune response.

B cells

Bone-marrow derived lymphocytes that make up $10-15\%$ of circulating lymphocytes and differentiate into plasma cells.

Plasma cells

Cells differentiated from B cells that produce and secrete antibodies (immunoglobin proteins).

Antigens

The identifying parts of any pathogen or foreign compound to which immunoglobin proteins bind.

Antibody-mediated immunity

A chain of events started by the binding of a specific antibody to its specific antigen, leading to the destruction of the target.

NK cells

Natural killer cells that make up $5-10\%$ of circulating lymphocytes and are responsible for immunological surveillance.

Lymphopoiesis

The process of lymphocyte production involving the bone marrow, thymus, and peripheral lymphoid tissues.

Hemocytoblasts

Cells in the bone marrow that divide to produce two types of lymphoid stem cells.

Lymphoid nodule

Connective tissue dominated by lymphocytes, consisting of areolar tissue with a germinal center containing dividing lymphocytes.

MALT (Mucosa-associated lymphoid tissue)

Lymphoid tissue associated with the digestive system, including aggregated lymphoid nodules clustered deep to the epithelial lining of the intestine.

Tonsils

Five lymphoid nodules located in the wall of the pharynx: the left and right palatine tonsils, the pharyngeal tonsil (adenoid), and a pair of lingual tonsils.

Lymph Nodes

Lymphoid organs ranging from $1\,mm$ to $25\,mm$ in diameter that act as filters to purify lymph by removing debris, pathogens, and $99\%$ of antigens.

Hilus

A shallow indentation in a lymph node where blood vessels and nerves reach the node and where efferent lymphatics leave.

Afferent lymphatic vessels

Vessels that carry lymph from peripheral tissues toward the lymph node.

Efferent lymphatics

Vessels that leave the lymph node at the hilus and carry lymph toward the venous circulation.

Antigen presentation

The first step in the immune response where extracted antigens are presented to lymphocytes or attached to dendritic cells.

Lymphadenopathy

Chronic or excessive enlargement of lymph nodes which may indicate infections, endocrine disorders, or cancer.

Thymus

A lymphoid organ in the mediastinum that produces thymosins and deteriorates after puberty.

Thymosins

Hormones produced by the thymus that promote the development of lymphocytes.

Spleen

A fragile lymphoid organ that removes abnormal blood cells, stores iron recycled from RBCs, and initiates immune responses by B and T cells.

Red pulp

The portion of the spleen containing large numbers of red blood cells, fixed and free macrophages, and reticular fibers.

White pulp

The portion of the spleen that resembles lymphoid nodules.

Splenectomy

The surgical procedure performed to remove a ruptured spleen.

Physical barriers

Nonspecific defenses like the skin, mucous membranes, and secretions (sweat, mucus, urine) that keep hazardous materials outside the body.

Microphages

Small phagocytic cells, specifically neutrophils and eosinophils, that leave the bloodstream to fight infections in peripheral tissues.

Macrophages

Large phagocytic cells derived from monocytes that make up the monocyte-macrophage system (reticuloendothelial system).

Fixed macrophages

Macrophages that stay in specific tissues or organs, such as microglia in the CNS or Kupffer cells in the liver.

Free macrophages

Phagocytic cells that travel through the body in the bloodstream, such as alveolar macrophages (dust cells).

Immunological surveillance

The constant monitoring of normal tissues by NK cells to identify and destroy abnormal cells like cancer cells or virus-infected cells.

Immunological escape

A process where some cancer cells avoid detection or resist destruction by NK cells.

Interferons

Proteins released by activated lymphocytes and macrophages that trigger normal cells to produce antiviral proteins which block viral replication.

Complement system

A system of $11$ special plasma proteins that work in cascades to stimulate inflammation, attract phagocytes, and destroy target cell membranes.

Inflammation

A localized response to tissue injury characterized by swelling (tumor), redness (rubor), heat (calor), and pain (dolor).

Mast cells

Cells that release histamine (increasing capillary permeability) and heparin (inhibiting clotting) during the inflammatory response.

Fever

A maintained body temperature above $37.2\,^{\circ}C$ ($99\,^{\circ}F$) caused by pyrogens.

Pyrogens

Agents including pathogens, toxins, and antibody complexes that affect the hypothalamus to raise body temperature.

Endogenous pyrogen

A cytokine released by active macrophages, also known as interleukin-1 (IL-1).

Cell-mediated immunity

Specific defense provided by T cells against abnormal cells and pathogens inside cells.

Innate immunity

Immunity that is present at birth.

Acquired immunity

Immunity developed after birth, categorized as active (adaptive) or passive (transferred).

Specificity

The property of immunity where each T cell or B cell responds only to an antigen with a specific molecular structure.

Versatility

The immune system's property of maintaining many lymphocyte types to fight millions of different potential antigens.

Memory

The property of the immune system where memory cells remain in circulation to provide an immediate response upon repeated exposure to an antigen.

Tolerance

The immune system's property of ignoring antigens recognized as "normal" or "self."

MHC (Major Histocompatibility Complex) proteins

Membrane glycoproteins genetically coded on chromosome $6$ that bind to antigens for presentation to T cells.

CD markers (Cluster of Differentiation)

Receptors found on T cell membranes; CD3 is on all T cells, CD8 is on cytotoxic/suppressor cells, and CD4 is on helper T cells.

Perforin

A protein released by cytotoxic T cells to destroy the antigenic cell membrane.

B cell sensitization

The process where antigens are taken into a B cell and reappear on the surface bound to Class II MHC proteins, preparing the cell for activation.

Antibody titer

The concentration of circulating antibodies in the blood.

Autoimmune disorders

Diseases resulting from the immune system attacking the body's own cells when it fails to recognize "self-antigens."

Allergens

Antigens that trigger inappropriate or excessive immune responses.

Anaphylaxis

A severe Type I hypersensitivity reaction that can cause hives, difficulty breathing, and circulatory collapse (anaphylactic shock).