Exam 2 Review: Chapter 20: Histology of the Lymph Node
capsule - A fibrous, membranous, or fatty sheath that encloses an organ or body part; the capsule of a lymph node is a thin layer of dense fibrous connective tissue penetrated by various afferent and efferent lymphatic vessels; the capsule of the lymph node separates the inner lymphoid tissue from the surrounding connective tissues and serves as a limiting barrier to prevent diffusion of lymph into the surrounding tissues; it may also serve as a barrier to the spread of infections or cancers that reach the lymph node.
cortex - The outer layer of an internal organ or body structure, e.g., the cerebrum, kidney, adrenal gland, or lymph node; the cortex of a lymph node contains many lymph follicles (dendritic cells surrounding germinal centers) which are separated by connective tissue trabeculae and the cortex contains a branching system of channels which route lymph from the afferent lymphatic vessels to the medulla; antigen-presenting macrophages and T and B lymphocytes in the cortex are involved in immune reactions to specific antigens.
medulla - The inner core of an internal organ or body structure, e.g., the cerebrum, kidney, adrenal gland, or lymph node; the medulla of a lymph node contains medullary cords (thin inward extensions of cortical lymphoid tissue) and lymph sinuses spanned by crisscrossing reticular fibers which act as a filter for the passage of lymph from the cortex to the efferent lymphatic vessels which carry lymph away from the lymph node at the hilus; the medulla also contains many macrophages.
trabeculae - (1) Any of the supporting strands of fibrous connective tissue projecting into an organ and constituting part of the framework of that organ. (2) Any of the fine spicules forming a network in spongy = cancellous bone.
lobule - Any small lobe or subdivision of a lobe of an organ, usually separated by a layer of fibrous connective tissue; the cortex of a lymph node contains lobules which house lymph follicles (dendritic cells surrounding germinal centers) which are separated by connective tissue trabeculae.
follicles - A general anatomical term describing small, often microscopic, structures which tend to be rounded and often consist of concentric layers of cells and sometimes with a central fluid filled cavity; the follicles of a lymph node contain dendritic cells surrounding germinal centers containing antigen-presenting macrophages and T and B lymphocytes involved in immune reactions to specific antigens.
germinal center - The light-staining interior of a lymph follicle which contains a few dendritic cells, some antigen-presenting macrophages and many activated proliferating T and B lymphocytes, particularly B lymphocytes, which are involved in immune reactions to specific antigens.
medullary cord - A thin inward extension of cortical lymphoid tissue (T and B lymphocytes) which is bounded by lymph sinuses in the inner core (medulla) of a lymph node
B lymphocyte = B cell - A functional subclass of lymphocytes (the smaller of the two kinds of agranular leukocytes), originating and maturing in the bone marrow; identified by the specific cell surface markers they express; they function in humoral immunity = antibody-mediated immunity (AMI); they make antibodies = immunoglobulins in a complex process requiring lymphokine stimulation and reaction with a specific antigens, and usually the participation of antigen-presenting macrophages and T lymphocytes = T cells; when actively involved in immune defense they may transform into plasma cells; any one B lymphocyte makes only one specific antibody.
T lymphocyte = T cell - A functional subclass of lymphocytes (the smaller of the two kinds of agranular leukocytes), originating in the bone marrow and and maturing in the thymus; identified by the specific cell surface markers they express; (they do not make antibodies = immunoglobulins); they function in cellular immunity = cell-mediated immunity (CMI); they orchestrates and regulate many of the immune system's responses; several functional subcategories are recognized including memory T cells, helper Th cells, suppressor Ts cells, cytotoxic Tc cells, and delayed hypersensitivity Tdh cells.
macrophage - Any of the large long-lived phagocytic cells derived from monocytes comprising a major component of the diffuse immune system (sometimes called the reticuloendothelial system or, more recently, the mononuclear phagocytic system); these phagocytes from different sites in different organs and tissues have somewhat different properties; in addition to contributing to the killing of microorganisms and tumor cells; they release immune regulatory substances and play a vital role in antigen-presentation leading to the production of antibodies by B lymphocytes and the activation of T lymphocytes.
afferent lymphatic vessel - Any of the delicate thin-walled vascular tubes lined with endothelium and with valves which transport lymph (interstitial fluid = intercellular fluid = tissue fluid) from the tissue spaces into the interior of the cortex of a lymph node by passing the fluid through an opening in the capsule; lymph flow is regulated by Interstitial Fluid Hydrostatic Pressure, the muscular pump in the limbs, the thoracic pump in the chest, and valves which prevent backflow.
efferent lymphatic vessel - Any of the delicate thin-walled vascular tubes lined with endothelium and with valves which transport lymph (interstitial fluid = intercellular fluid = tissue fluid) from the interior (medulla) of a lymph node by exiting through an opening in the hilus and on through the lymphatic circulation; lymph flow is regulated by Interstitial Fluid Hydrostatic Pressure, the muscular pump in the limbs, the thoracic pump in the chest, and valves which prevent backflow.
sinuses - (1) A dilated channel or receptacle containing a fluid; e.g., venous blood or lymph; the sinuses of the lymph node are located in the cortex and the medulla and are separated by the trabeculae and medullary cords respectively. (2) Any of various air-filled cavities in the bones of the skull communicating with the nostrils.
hilus - A depression or fissure where vessels or nerves or ducts enter or exit an organ, e.g., the kidneys, lungs, and lymph nodes; the hilus of the lymph node is where the efferent lymphatic vessels carry lymph away from the medulla lymph node and on in the lymphatic circulation.
Sketch and label:
2. The structure of a lymph node. What kinds of cells are common in lymph nodes and what are their functions.
|[Note: T lymphocytes and macrophages are more common in the outer layer of lymph follicles while B lymphocytes and plasma cells are more common in the inner germinal center of lymph follicles.]|