Chapter 20: Endocrine Glands

Endocrine Glands SUMMARY OF KEY POINTS Pituitary Gland

• The pituitary gland has two major parts: the posterior part called the pars nervosa develops as a downgrowth of the developing brain and is attached in the hypothalamus by the infundibulum.

• The anterior pituitary includes the large pars distalis, the pars tuberalis that surrounds the infundibulum, and the thin pars intermedia adjacent to the pars nervosa.

• Blood vessels of the hypothalamic hypophyseal portal system are important in carrying peptide factors from hypothalamic neurons to cells of the anterior pituitary where they control cell secretion.

• This portal system includes a primary capillary plexus in the infundibulum and lower hypothalamus and a secondary plexus in the pars distalis, connected by portal veins and draining to the hypophyseal vein.

• Endocrine cells of the anterior pituitary can be called acidophils, basophils, or chromophobes based on their general staining properties; the latter lack secretory granules and stain poorly.

  • Acidophils and basophils can be identified as to which pituitary hormone they produce using immunohistochemistry and antibodies against specific hormones.

  • Acidophils are primarily somatotrophs producing somatotropin (growth hormone), or lactotrophs (or mammotrophs) producing prolactin (PRL).

  • Basophils include gonadotrophs producing FSH and LH and thyrotrophs making TSH.

  • A third type of basophil is the corticotroph, synthesizing POMC that is cleaved by proteases to make ACTH and β-LPH.

• The hypothalamic hypophyseal tract includes bundles of nerve axons that run from supraoptic nucleus (SON) and paraventricular nucleus (PVN) in the hypothalamus to the posterior pituitary.

• Hypothalamic neurons in the SON synthesize vasopressin/ADH and those of the PVN synthesize oxytocin, both of which are stored in axonal dilations called Herring bodies before release to capillaries in the posterior pituitary.

• The adrenal cortex of each adrenal gland consists of three concentric zones, all histologically distinct but with cells producing steroid hormones and all drained by the same system of capillaries.

  • The most superficial zona glomerulosa has round clusters of cells producing mineralocorticoids such as aldosterone regulating electrolyte levels.

  • The wider, middle zona fasciculata has elongated strands of cells producing glucocorticoids such as cortisol, which regulates several aspects of carbohydrate metabolism.

  • The innermost zona reticularis has a network of cells making the weak androgen DHEA that is converted to testosterone in men and women.

• The adrenal medulla contains neural crest-derived chromaffin cells synthesizing either epinephrine or norepinephrine that regulate the stress response.

• Pancreatic islets of Langerhans are small clusters of pale cells embedded within the exocrine tissue; they have primarily β cells making insulin, α cell (glucagon), and δ cells (somatostatin).

• The thyroid gland consists mainly of spherical follicles composed of simple epithelium of thyrocytes surrounding a lumen with thyroglobulin.

• Thyroglobulin is a large glycoprotein in which tyrosine residues are iodinated as precursors of the thyroid hormones thyroxine and tri-iodothyronine, which are released when the precursor ...