Anatomy and Physiology 2e - Chapter 21: The Lymphatic and Immune System

Vocabulary flashcards covering the anatomical structures, cellular pathways, organs, complement cascades, and antibody classes of the lymphatic and immune system from OpenStax Anatomy and Physiology 2e, Chapter 21.

Lymphatic Capillaries

Microscopic, blind-ended vessels interlaced with cardiovascular arterioles and venules that feature overlapping endothelial cells anchored by collagen fibers, which open like flaps to permit fluid entry when surrounding tissues swell.

Thoracic Duct

The major lymphatic duct that begins at the cisterna chyli and drains lymph from both lower extremities, the abdomen, the left thorax, the left upper extremity, and the left side of the head and neck into the left subclavian vein.

Right Lymphatic Duct

A major lymphatic drainage vessel that collects lymph exclusively from the right side of the head and neck, the right upper extremity, and the right thoracic region, emptying into the right subclavian vein.

Hemocytoblast

A multipotent hematopoietic stem cell in red bone marrow that differentiates into either myeloid or lymphoid stem cells to generate all formed elements of the blood and cells of the immune system.

Thymus

A primary lymphoid organ situated superior to the heart within the mediastinum, consisting of lobules divided by trabeculae into an outer cortex and inner medulla where T lymphocytes mature.

Germinal Center

A distinct histological region within lymphoid follicles of lymph nodes, tonsils, and the spleen comprising rapidly dividing B lymphocytes surrounded by a mantle of T cells and accessory cells.

Marginal Zone

The specialized region of the spleen located between the red pulp and the white pulp that sequesters particulate antigens from the bloodstream and presents them to lymphocytes.

White Pulp

The lymphoid tissue component of the spleen arranged around central arterioles, composed of lymphocytes, macrophages, and germinal centers that mount adaptive immune defenses against blood-borne antigens.

Red Pulp

The splenic tissue made of venous sinuses and arterial capillaries where circulating blood is filtered and aged or damaged red blood cells are broken down.

Pharyngeal Tonsil

A single lymphoid organ located in the posterior-superior wall of the nasopharynx, also commonly known as an adenoid.

Palatine Tonsils

Paired masses of lymphatic tissue situated on lateral sides of the pharynx, covered by non-keratinized stratified squamous epithelium and invaginated by deep tonsillar crypts.

Histamine

A chemical signaling molecule released by mast cells and basophils upon tissue injury that stimulates local vasodilation and vascular permeability, recruiting phagocytes and causing erythema, edema, warmth, and pain.

C3 Convertase

An enzymatic complex assembled from complement fragments C2 and C4 during the classical complement pathway that cleaves native C3 into fragments C3a and C3b.

Membrane Attack Complex (MAC)

A transmembrane pore assembly formed by complement components C5b, C6, C7, C8, and C9 that perforates target pathogen cell membranes, allowing water to enter the hyperosmotic cytoplasm and causing cell lysis.

Antigen-Presenting Cell (APC)

A phagocytic cell, such as a dendritic cell or macrophage, that ingests extracellular pathogens, processes antigens via lysosomal enzymes, and presents the resulting peptide fragments on surface MHC molecules to naive T cells.

Major Histocompatibility Complex (MHC)

A family of cell surface proteins featuring a peptide-binding cleft that presents endogenous or exogenous antigen fragments to T cell receptors to trigger adaptive immune responses.

Variable Region

The amino-terminal ends of the heavy and light chains of an antibody molecule that form the antigen-binding sites, exhibiting unique structural diversity to match specific antigens.

Fc Region

The constant 'tail' region of an antibody composed of heavy chain constant domains that binds to specific cell surface receptors on phagocytes, mast cells, or basophils, or initiates complement activation.

Immunoglobulin M (IgM)

A pentameric antibody containing \text{\mu} heavy chains and $10$ antigen-binding sites that makes up $6\%$ of serum antibody; it is the primary antibody produced during initial immune responses, is most potent at complement fixation, and functions as a monomeric B cell receptor.

Immunoglobulin G (IgG)

A monomeric antibody with \text{\gamma} heavy chains that accounts for $80\%$ of serum antibodies; it is the dominant antibody of secondary immune responses, promotes opsonization, neutralizes toxins, fixes complement, and crosses the placenta.

Secretory IgA

A dimeric antibody joined by a secretory component with \text{\alpha} heavy chains and $4$ antigen-binding sites that represents $13\%$ of serum antibodies and confers mucosal immunity in secretions like tears, saliva, colostrum, and mucus.

Immunoglobulin E (IgE)

A monomeric antibody with \text{\epsilon} heavy chains present at trace levels ($0.002\%$ of serum antibodies) whose Fc stem binds to mast cells and basophils to mediate allergic reactions and defense against parasites.

Immunoglobulin D (IgD)

A monomeric antibody with \text{\delta} heavy chains constituting approximately $1\%$ of serum antibodies that serves primarily as a membrane-bound antigen receptor on naive B lymphocytes.

Clonal Selection

The process by which an antigen binds specifically to a mature, naive B cell receptor, triggering its activation and proliferation into a clone of antibody-secreting plasma cells and long-lived memory B cells.

Secondary Immune Response

A rapid, elevated immune reaction triggered by re-exposure to a previously encountered antigen, driven by memory cells that rapidly produce higher titers of high-affinity antibodies compared to the primary response.

M Cells

Specialized epithelial cells in the follicle-associated epithelium of Peyer's patches and nasal-associated lymphoid tissue that transport luminal antigens across the intestinal barrier to underlying dendritic cells and lymphocytes.