LESSON 18 cortas

The trabeculae in the spleen are composed of fibroblasts, collagen fibers, elastic fibers, and smooth muscle fibers. They provide passage for arteries, veins, lymphatics, and nerves into the spleen.

The white splenic pulp is made up of periarterial lymphoid sheaths and lymphoid follicles, surrounded by a network of reticular fibers and cells. It is mainly composed of T cells, interdigitating cells, B cells, follicular dendritic cells, and macrophages.

Central arteries are muscular arteries that supply the lymphoid structures in the spleen. They branch repeatedly to form trabecular arteries and then periarterial lymphoid sheaths.

Capillaries in the white splenic pulp receive blood from central and follicular arteries and are surrounded by splenic cords, which are mostly made up of macrophages.

Venous sinuses are dilated and tortuous ducts that collect capillary blood. They are surrounded by splenic cords, where macrophages filter blood and remove old erythrocytes.

The marginal zone is a transition zone between the white and red splenic pulp, consisting of a framework of reticular fibers and cells. It is occupied by specialized B cells and macrophages.

There are three theories suggesting either closed or open circulation, and the anastomosis of capillaries with the venous system is a subject of controversy.

The spleen's parenchyma consists of three zones or compartments: white splenic pulp, red splenic pulp, and the marginal zone. It is involved in immune responses and blood filtration.

The spleen capsule is lined by a mesothelium, which is thickened at the hilum. It allows for arteries, nerves, veins, and lymphatic vessels to enter the spleen.

The collagen fibers of the trabeculae continue into a three-dimensional network of reticular fibers that are argyrophilic and formed by reticular cells of stellate morphology.

Macrophages play a crucial role in the spleen by filtering blood, removing old erythrocytes, and participating in immune responses.

The hilum of the spleen is thickened and allows for arteries, nerves, veins, and lymphatic vessels to enter the spleen.

The four major functions of the spleen as a secondary lymphoid organ are: A. Haematopoietic function, involving the formation and maturation of red blood cells; B. Haemocatheretic function, which is the physiological and controlled destruction of blood cells; C. Immune function, where B and T cells are stimulated to give rise to humoral and cellular immune responses; and D. Mechanical function, acting as a blood store and releasing stored blood into circulation during stress or disease states.

The spleen is a parenchymatous organ consisting of a stroma (capsule, trabeculae, and reticular fibers and cells) and a parenchyma generically called 'pulp'. The stroma is surrounded by a capsule of dense connective tissue, containing smooth muscle fibers and elastic networks. The parenchyma, or 'pulp', has a pulpy appearance macroscopically when cut.

The haematopoietic function of the spleen involves the process of formation and maturation of red blood cells. Additionally, in disease states, leukocytes, erythrocytes, megakaryocytes, and platelets can also be produced.

As a secondary lymphoid organ, the spleen plays a role in immune function by stimulating B and T cells in response to antigens, leading to humoral and cellular immune responses, respectively.