It contains several groups of ==neurosecretory cells called nuclei== which produce hormones.
These hormones regulate the synthesis and secretion of pituitary hormones.
These hormones originating in the hypothalamic neurons, pass through axons and are released from their nerve endings.
These hormones reach the pituitary gland through a ==portal circulatory system== and regulate the functions of the anterior pituitary.
The ==posterior pituitary is under the direct neural regulation of the hypothalamus.==
The pituitary gland is located in a ==bony cavity called Sella tursica== and is attached to the ==hypothalamus by a stalk==.
It is divided anatomically into -
The thyroid gland is composed of two lobes which are located on either side of the trachea.
The thyroid gland is composed of follicles and stromal tissues.
The thyroid gland also secretes a ==protein hormone called thyrocalcitonin== (TCT) which regulates the ==blood calcium levels.==
Our body has one pair of adrenal glands, one at the anterior part of each kidney.
The gland is composed of two types of tissues.
Adrenaline and noradrenaline are rapidly secreted in response to the ==stress== of any kind and during ==emergency situations== and are called emergency hormones or hormones of Fight or Flight.
Catecholamines also stimulate the ==breakdown of glycogen== resulting in an increased ==concentration of glucose== in the blood.
The adrenal cortex can be divided into three layers, called:
The adrenal cortex secretes many hormones, commonly called corticoids.
Small amounts of androgenic steroids are also secreted by the adrenal cortex which plays a role in the ==growth of axial hair, pubic hair, and facial hair== during puberty.
Hormones produce their effects on target tissues by binding to specific proteins called hormone receptors located in the target tissues only.
Hormone receptors present on the cell membrane of the target cells are called membrane-bound receptors and the receptors present inside the target cell are called intracellular receptors, mostly nuclear receptors (present in the nucleus).
The binding of a hormone to its receptor leads to the formation of a hormone-receptor complex.
On the basis of their chemical nature, hormones can be divided into groups :
Hormones that interact with membrane-bound receptors normally do not enter the target cell, but generate second messengers (e.g., cyclic AMP, IP3 , Ca++ etc) which in turn regulate cellular metabolism.
Hormones that interact with intracellular receptors (e.g., steroid hormones, iodothyronines, etc.) mostly regulate gene expression or chromosome function by the interaction of the hormone-receptor complex with the genome.
Cumulative biochemical actions result in physiological and developmental effects.