Unit 1 – Lesson 1: The Lymphatic and Immune Systems

Vocabulary study set detailing the anatomy, cellular components, immune lines of defense, lymphoid organs, immunoglobulin classes, transplant types, and clinical disorders of the human lymphatic and immune systems.

Lymph

Excess tissue fluid collected from interstitial spaces that is carried by lymphatic vessels.

Lacteals

Specialized lymphatic capillaries located in the small intestine that absorb lipids.

Chyle

Lymph fluid passing through lacteals that has a milky-white appearance due to an increased fat content.

Lymphatic Capillaries

Close-ended microscopic vessels made of overlapping simple squamous epithelium forming flap-like minivalves, lacking a basement membrane, and absent from the central nervous system, bone marrow, epidermis, and cartilage.

Right Thoracic Duct

The lymphatic duct that drains lymph from the right upper limb and the right half of the head, neck, and chest, emptying into the right subclavian vein.

Thoracic Duct

The large lymphatic vessel that collects lymph from the left side of the upper body and all regions below the diaphragm, emptying into the left subclavian vein.

Lymph Nodes

Small, rounded or kidney-shaped organs less than $1\text{ inch}$ long distributed along lymphatic vessels that filter lymph and house macrophages and lymphocytes.

Germinal Centers

Central areas within lymph node follicles containing rapidly dividing lymphocytes.

Afferent Lymphatic Vessels

Vessels through which lymph enters a lymph node.

Efferent Lymphatic Vessels

Vessels through which filtered lymph exits a lymph node.

White Pulp

Splenic lymphatic tissue surrounding central arteries within the spleen that provides immune surveillance and protection.

Red Pulp

Splenic tissue associated with veins, consisting of a fibrous network filled with macrophages, red blood cells, and enlarged capillaries through which blood passes before exiting the spleen.

Thymus

A bilobed, roughly triangular endocrine and lymphatic gland in the superior mediastinum where pre-T cells mature into functional T cells.

Thymosin

A hormone produced by the thymus that facilitates the maturation and programming of T lymphocytes.

Palatine Tonsils

Paired masses of lymphoid tissue located on each side of the posterior opening of the oral cavity.

Pharyngeal Tonsil

A lymphoid mass located near the internal opening of the nasal cavity; commonly referred to as the adenoids when enlarged.

Lingual Tonsil

Lymphoid tissue located on the posterior surface of the tongue.

Peyer's Patches

Clusters of mucosa-associated lymphatic tissue (MALT) embedded within the wall of the ileum of the small intestine that capture and destroy bacteria.

Lymphedema

Tissue swelling caused by the accumulation of interstitial lymph fluid, commonly resulting from cancer, surgical lymph node removal, or filariasis.

Lymphadenopathy

The swelling or enlargement of lymph nodes or glands in response to infection, tuberculosis (scrofula), or cancer.

Lymphoma

A cancer of the lymphatic system characterized by malignant transformation of lymphocytes within lymph nodes and other lymphoid organs.

Innate Immunity

Nonspecific defense mechanisms where the body recognizes and destroys certain pathogens with a response that remains identical upon each subsequent exposure.

Adaptive Immunity

Specific defense mechanisms characterized by specificity and memory, where the immune response improves each time a specific pathogen is encountered.

Chemotaxis

The directional movement of white blood cells toward an area of infection in response to chemical signals released by pathogens or injured cells.

Natural Killer (NK) Cells

Nonspecific defensive cells capable of lysing and destroying virus-infected cells and cancer cells without prior antigenic stimulation.

Rubor

Redness, one of the four classic signs of acute inflammation resulting from vasodilation and increased blood flow.

Complement Proteins

A group of at least $20$ plasma proteins that damage foreign cell membranes, enhance inflammation, and coat pathogens to facilitate phagocytosis.

Opsonization

The process of tagging foreign entities, such as bacteria or viruses, with complement proteins to enable phagocytes to recognize and engulf them.

Interferons

Proteins secreted by virus-infected cells that bind to receptors on adjacent healthy cells to hinder viral multiplication.

Pyrogen

A fever-producing substance released by white blood cells that resets the hypothalamic thermostat to an abnormally high temperature exceeding $37.5\,^{\circ}\text{C}$ ($98.7\,^{\circ}\text{F}$).

Humoral Immunity

Antibody-mediated adaptive immunity provided by antibodies present in bodily fluids that target extracellular pathogens.

Cellular Immunity

Cell-mediated adaptive immunity that directly targets and destroys virus-infected cells, cancer cells, and foreign tissue grafts.

MHC I

Major histocompatibility complex molecules found on all nucleated cells in the body, critical for organ transplantation matching.

MHC II

Major histocompatibility complex molecules found on antigen-presenting cells (macrophages and B cells) used to present antigens to helper T cells.

Immunocompetence

The ability of a lymphocyte to recognize and respond to a specific antigen by binding to its surface receptors.

Plasma Cells

Antibody-secreting cells derived from activated B lymphocytes, possessing a characteristic clock-face or spoke-wheel nuclear chromatin pattern.

IgM

The largest immunoglobulin class, capable of fixing complement and serving as the primary antibody produced upon initial antigen contact.

IgA

An antibody class present primarily in mucus, saliva, tears, and other bodily secretions.

IgG

The abundant immunoglobulin class capable of crossing the placental barrier and fixing complement.

IgE

An immunoglobulin class that binds to mast cells and basophils, triggering release of histamine during allergic responses.

Cytotoxic T Cells

Effector T lymphocytes that kill virus-infected and abnormal body cells by releasing perforin and cytokines.

Perforin

A toxic chemical released by cytotoxic T cells that creates holes in target cell membranes to cause direct cell lysis.

Helper T Cells

T lymphocytes that stimulate proliferation of B cells and cytotoxic T cells and recruit other immune cells by producing cytokines.

Regulatory T Cells

Specialized T cells that release suppressive chemicals to halt immune activity and prevent unchecked immune responses.

Autograft

A tissue graft transplanted from one anatomical site to another within the same individual.

Isograft

A tissue graft transplanted between genetically identical individuals, such as identical twins.

Allograft

A tissue graft transplanted between genetically non-identical individuals of the same species.

Xenograft

A tissue graft harvested from an animal donor of a different species and transplanted into a human, which is never successful.

Multiple Sclerosis

An autoimmune disorder characterized by antibody destruction of the myelin sheath insulating the white matter of the brain and spinal cord.

Myasthenia Gravis

An autoimmune disorder in which autoantibodies attack acetylcholine receptors, disrupting neuromuscular communication.

Systemic Lupus Erythematosus (SLE)

A systemic autoimmune disease in which the body develops autoantibodies against its own DNA, causing widespread damage to the kidneys, heart, lungs, and skin.