Talk:Draft 2016

Spleen

Thymus Anatomy

left hypochondriac region	almost entirely surrounded by peritoneum adherent to its capsule

Thymus Functions
Immune - filters blood in much the way that the lymph nodes filter lymph. Lymphocytes in the spleen react to pathogens in the blood and attempt to destroy them. Macrophages then engulf the resulting debris, the damaged cells, and the other large particles. Red Blood Cell Removal - spleen (and liver) removes old and damaged erythrocytes from the circulating blood. Blood Reservoir - The sinuses in the spleen also act as a reservoir for blood. In emergencies (haemorrhage) smooth muscle in the vessel walls and in the capsule of the spleen contracts, squeezes blood out of the spleen into the general circulation.

Thymus Structure
afferent splenic artery branches into central arterioles, which are sheathed by white pulp areas. white pulp areas consist of the T-cell zone (also known as the periarteriolar lymphoid sheath, PALS), arterioles and B-cell follicles. arterioles end in cords in the red pulp, from where the blood runs into venous sinuses that collect into the efferent splenic vein. larger arteries and veins run together in connective-tissue trabeculae, which are continuous with the capsule that surrounds the spleen.

Overview - red and white pulp	Overview - blood vessels	Red pulp

Reticular Fibers (type III collagen) act as supporting meshwork (can be seen in Silver stained preparations)

Adult Thymus

Fetal thymus anatomy

Gross Anatomy

Histology

Contains reticular cells but no fibers
Stem lymphocytes
- proliferate and differentiate
- forms long-lived T- lymphocytes
removes auto-reactive T-lymphocytes (negative selection)

‎‎Thymus 1

Reticular cells	Macrophages	Lymphocytes
Abundant, eosinophilic, large, ovoid and light nucleus 1-2 nucleoli sheathe cortical capillaries form an epitheloid layer maintain microenvironment for development of T-lymphocytes in cortex (thymic epitheliocytes)	cortex and medulla difficult to distinguish from reticular cells in (Stain - Haematoxylin Eosin) remove auto-reactive T-lymphocytes	located in cortex and medulla more numerous (denser) in cortex majority are developing T-lymphocytes (= thymic lymphocytes or thymocytes)

{Changes with age Overall Size

Histology

Cortical lymphoid tissue is replaced by adipose tissue (involution)
Increase in size of thymic corpuscles
Thymic corpuscle - (Hassall’s corpuscle) mass of concentric epithelioreticular cells.