The pituitary gland is the master endocrine gland. It produces small quantities of hormones (thyroids, adrenal glands etc.), that cause the target organ to release the final active hormone e.g. T3 and T4, Adrenaline, oestrogen and testosterone. The gland sits within the sella turcica in the body of the sphenoid bone, and receives hormonal influence from the hypothalamus.
The pituitary gland is the master endocrine gland of the human body. It produces a range of hormones from its anterior lobe/adenohypophysis (ACTH, TSH, LH and FSH, PL, GH) and posterior lobe/neurohypophysis (Oxytocin and Vasopressin/ADH). The production of these hormones is under the influence of the hypothalamus that releases small concentrations of hormones into the portal system of the pituitary. These hormones influence the anterior pituitary. Hormones of the posterior pituitary are produced by the hypothalamus itself, and stored/released from the posterior pituitary. It is located within the cranial cavity, and sits within its own space, known as the sella turcica, meaning Turkish saddle. The name originates from the appearance of the Turkish saddle, which had 4 posts at each corner. The Turks were therefore able to ride and swing their swords simultaneously during battles. The anterior and posterior clinoid processes of the sphenoid bone reciprocate the four posters of the saddle. The sella turcica is covered in dura mater in life, and the pituitary is connected to the hypothalamus above by the pituitary stalk, or infundibulum.
The pituitary releases a large number of hormones that then pass into the systemic circulation and reach their target endocrine organs or other tissues where they exert their effects. The blood supply to the anterior pituitary is through the paired superior hypophyseal arteries that arise from the medial aspect of the internal carotid artery. These in turn form the hypophyseal portal veins that lie in the pituitary stalk/infundibulum, which deliver blood to a second venous plexus within the anterior pituitary itself. Hormones from this second plexus are drained into the systemic venous circulation. The posterior lobe is supplied by the inferior hypophyseal arteries, which arise directly from the cavernous section of the internal carotid artery. The lobe drains directly into the systemic venous circulation.
Prolactinoma- This is the commonest pituitary tumour, and arises from the anterior pituitary gland. It causes excess prolactin production causing amenorrhoea, bitemporal hemianopia (if it compressed the chiasm from beneath), may cause milk production, and a lack of secondary sexual characteristics in males, headache and impotence.
Cushing’s disease-This is an ACTH producing tumour of the anterior pituitary. Symptoms are caused by excessive cortisol, with central obesity, buffalo hump, purple striae, bone and muscle wasting etc.
Craniopharyngioma- This tumour arises from pituitary gland embryonic tissue. Symptoms include progressive bitemporal hemianopia and headache.
Pituitary apoplexy- This occurs when the pituitary gland bleeds heavily, or had greatly diminished blood supply. It commonly follows a tumour. Symptoms include sudden headache, double vision and sometimes a third nerve palsy (due to the proximity of the cavernous sinus).
Developmental precursor- Anterior pituitary develops from the upward projecting Rathke’s pouch
Posterior pituitary from a downward ectodermal projection from the developing diencephalon
Blood supply- Anterior pituitary from the superior hypophyseal and portal system, posterior pituitary from the inferior hypophyseal arteries.
Venous drainage- Petrosal sinuses, then the cavernous sinuses.
Remember the two hormones released by the posterior pituitary (oxytocin and vasopressin), and the others are released by the anterior pituitary.
The pituitary gland is the master endocrine gland. It is under the influence of the hypothalamus, and releases small quantities of hormones into the blood stream, which will reach the target organs.
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By Shawn P. Moore, 2005
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