The Histology Guide


Hormones secreted by the Pituitary, Adrenal and Thyroid glands.

Direct action hormones, act directly on non-endocrine tissues.
Indirect action hormones - modulate the secretory activity of other glands (trophic - such as TSH, ACTH, FSH and LH).

Hormones can either be derived from cholesterol (steroid homrones) or be peptide/protein or glycoprotein hormones, or modified amino acids (catecholamines).

Steroid hormones and thyroid hormone are both soluble in lipids, and can diffuse through the plasma membrane, and then bind to intracellular receptors. When this happens, the hormone-receptor complex then binds to DNA sequences called 'promoters' that switch on gene transcription.

The other hormones are water soluble, and must bind to specific hormone receptors in the membrane of target cells. When this happens, this causes activation of a second messenger in the cell such as cyclic adenosine monophosphate (cAMP) or increases the concentration of calcium ions.

The major endocrine compartments of the body are:

Pituitary, Thyroid, Parathyroids, Adrenal cortex and medulla, Pancreatic islets, Pineal, Sex glands (Ovaries and testis), Thymus, Gut enteroendocrine cells, Tracheobronchial neuorendocrine cells, and the Kidneys.


The pituitary produces the direct action hormones: prolactin, ADH and oxytocin. The trophic hormones are TSH, ACTH, FSH and LH.

Thyroid gland

secretes Tri-iodo thyronine (T3), thyroxine (T4) and calcitonin

Adrenal gland

cortex: secretes aldosterone, - regulates absorption/uptake of K+ and Na+ levels in the kidney, and cortisol - raises blood glucose (ACTH dependent), and androgens (sex hormone)
medulla: nor-adrenaline and adrenalin (catecholamines)


endocrine portion of the pancreas: Islets of Langherans secrete peptide hormones insulin and glucagon. They also secrete somatostatin, VIP, and PP (Pancreatic polypeptide). Insulin controls glucose uptake.