System of Hemopoiesis and Immunogenesis

Comprehensive vocabulary flashcards covering the primary and secondary organs of hemopoiesis and immunogenesis, their histological architecture, cellular components, and immunological functions.

System of Hemopoiesis and Immunogenesis

The body system responsible for producing blood cells (erythrocytes, leukocytes, and platelets) and cells participating in immune reactions (T- and B-lymphocytes, plasma cells, T-killers, and monocytes).

Primary Organs of Hemopoiesis and Immunogenesis

The central organs of the system, comprising the red bone marrow and the thymus.

Secondary Organs of Hemopoiesis and Immunogenesis

Peripheral immune organs including the lymph nodes, spleen, and mucosa-associated lymphoid tissue (MALT).

Red Bone Marrow

A parenchymal organ distributed within spongy bone cavities in adults, weighing $3\text{--}3.5\,\text{kg}$, that produces all blood cells except T-lymphocytes.

Stroma of Red Bone Marrow

Reticular tissue composed of reticular cells and fibers that supports developing blood cells, creates ground substance, and secretes growth factors controlling hemopoiesis.

Sinusoidal Blood Capillaries (Bone Marrow)

Large, thin-walled capillaries lined with porous endothelial cells on a discontinuous basement membrane that allow only mature blood cells to enter the circulation.

Erythroblastic Islets

Clusters of developing erythroblasts located close to the sinusoids in the red bone marrow.

Megakaryocytes

Giant cells situated near bone marrow sinusoids that extend processes into the sinusoidal lumen to release platelets into the bloodstream.

Nurse Cells (Bone Marrow)

Specialized bone marrow macrophages that uptake iron from the circulation and deliver it to surrounding erythroblasts for hemoglobin synthesis.

Yellow Bone Marrow

Inactivated marrow composed of adipose tissue that replaces red bone marrow in the diaphysis of long bones by the age of $18$ years.

Thymus

A parenchymal organ behind the sternum that peaks in size by $10$ years of age ($30\text{--}40\,\text{g}$) and provides a specialized microenvironment for T-lymphocyte maturation before undergoing age-dependent involution.

Epithelial Reticular Cells (Thymus)

Six types of stellate cells joined by processes to form the internal framework of thymic lobules, serving as nurse cells contacting $20\text{--}100$ T-lymphocytes and secreting thymosin and thymopoietin.

Thymic Corpuscles (Hassall's Corpuscles)

Medullary structures composed of concentrically layered epithelial reticular cells that degenerate at their center and enlarge with age.

Antigen-Independent Proliferation and Differentiation

The maturation process of T-lymphocytes in the thymus driven by thymosin and thymopoietin, shielded from external antigens by the blood-thymic barrier.

Blood-Thymic Barrier

A protective structure consisting of capillary endothelial cells, a basement membrane, a perivascular connective tissue sheath rich in macrophages, and epithelial reticular cells.

Accidental Involution of the Thymus

A rapid, reversible reduction in thymic tissue caused by severe, long-term stress wherein corticosteroids induce the death of immature T-lymphocytes.

Lymph Nodes

Bean-shaped secondary lymphoid organs measuring $5\text{--}10\,\text{mm}$ that filter lymph and support antigen-dependent proliferation and differentiation of lymphocytes.

Germinal Center

The central, pale-staining area within a cortical lymphoid nodule containing proliferating lymphoblasts.

Medullary Cords

Parenchymal strands within the medulla of a lymph node composed of B-lymphocytes, reticular cells, and plasma cells.

Paracortical Zone

The thymus-dependent intermediate region of a lymph node containing T-lymphocytes, macrophages, and interdigitating antigen-presenting cells.

High Endothelium Venules

Postcapillary venules deep in the lymph node cortex possessing specialized tall endothelial cells that permit circulating blood lymphocytes to enter the node.

White Pulp

The splenic parenchyma consisting of lymphoid nodules and periarterial lymphatic sheaths (PALS) surrounding central arteries.

Periarterial Lymphatic Sheaths (PALS)

Cylindrical sleeves of lymphoid tissue rich in T-lymphocytes that surround the central arteries within the spleen.

Red Pulp

The blood-rich portion of the splenic parenchyma located between nodules and trabeculae, colored red by abundant erythrocytes.

Ellipsoid Sheathed Capillaries

Splenic capillaries enclosed by specialized arrangements of macrophages that filter blood as part of the closed or open splenic circulation.

Transferrin

A blood plasma transport protein that carries iron (retrieved as ferritin from destroyed red blood cells in the spleen) to bone marrow nurse cells.

Mucosa-Associated Lymphoid Tissue (MALT)

Unencapsulated lymphoid nodules distributed along the gastrointestinal, respiratory, and urogenital tracts acting as the first line of immunological defense.

Plasma Cells

Effector cells derived from stimulated B-immunoblasts, characterized by abundant rough endoplasmic reticulum, that produce and secrete immunoglobulins.

Cell-Mediated Immunity

An immune response directed by antigen-stimulated T-lymphocytes that differentiate into effector subtypes (T-killers, T-helpers, T-suppressors, and T-memory cells) and release lymphokines.

T-Cell Receptor (TCR)

Surface receptor complexes on T-lymphocytes responsible for recognizing specific foreign antigens.