Endocrine & Lymphatic Systems

Adrenal Medullary parenchymal cells, known as chromaffin cells, arise from neural crest cells, as do the postganglionic neurons of sympathetic and parasympathetic ganglia. Chromaffin cells can be considered modified sympathetic postganglionic neurons, lacking axons and dendrites and specialized as secretory cells.

Reference: Junqueira’s Basic Histology; 14th Edition; Page-438

Oxytocin stimulates milk ejection by acting on mammary gland

-Follicular cells are columnar when stimulated
-Parafollicular cells are larger than follicular cells
-Parafollicular cells produce calcitonin, follicular cells produce T3,T4.

Function of thymus:
1.Production, differentiation and maturation and maturation of T-lymphocytes
2.Secretion of thymopoietin by epithelioreticular cells. Thymopoietin stimulates T cell production.
3.Thymus is essential for development of immunity in early life. 
4. Another main function of the thymus is induction of central tolerance, which along with regulatory T cells prevents autoimmunity

Reference: Junqueira’s Basic Histology; 14th Edition; Page-438

Parathyroid & pancreas are not under pituitary control.

Reference: Junqueira’s Basic Histology; 14th Edition; Page-438

[Ref. Junqueira 15th] 

The thyroid is a highly vascular, butterfly-shaped gland surrounding the anterior surface of the trachea just below the larynx.

Paracortex: 
The region between the cortex and medulla, the paracor­tex or deep cortex does not have precise boundaries but can be distinguished from the outer cortex by its lack of nodules (B-lymphocytes). Paracortex mainly consists of T cells; hence, it is also called thymus-dependent cortex.

It drains all the body except right upper limb and right half of the body above the diaphragm which is drained by right lymphatic duct.

The bone marrow and thymus are called primary/central lymphatic organ because of their function in lymphocyte production and maturation.

***Wall of splenic sinusoids does not have pericytes or smooth muscle cells. Elongated endothelial cells called stave cells line the splenic sinusoids.

Reference: Junqueira’s Basic Histology; 14th Edition; Page-438

A characteristic feature of the pineal gland is the presence of variously sized concretions of calcium and magnesium salts called corpora arenacea, or brain sand, formed by mineralization of extracellular protein deposits.

The parathyroid glands are four small nodules normally embedded in the capsule on the posterior surface of the thyroid gland.