The pituitary gland is an important hormonal gland located in the brain. Hormones are little chemical messengers that travel throughout the body to send signals to other tissues or organs. Hormones usually have a longer and more dispersed effect of signal in comparison to neurotransmitters, as they travel in the bloodstream to all parts of the body. The endocrine system is comprised of these hormone releasing glands, the pituitary being one of the most important, getting the name the “master gland”.
The pituitary gland is divided into two parts with separate functions and physiology, the anterior pituitary and the posterior pituitary. The pituitary as a whole is connected to and controlled by the hypothalamus. The posterior pituitary can almost be said to be an extension of the hypothalamus and contains nervous tissue, itself not being a true gland. The posterior pituitary is also called the neurohypophysis, because it is made up of neural tissue, and is further divided into three parts: the median eminence; the infundibulum; and the posterior lobe, the biggest and most important part of the neurohypophysis.
Neurons with cell bodies in the hypothalamus pass down a stalk in a bundle called the hypothalamo-hypophyseal tract into the posterior lobe. Hormones are made in the hypothalamus and travel through these neurons to the pituitary.
The anterior pituitary, also called the adenohypophysis, differs from this as it contains no neuronal connection to the hypothalamus but linked still by blood vessels. The anterior pituitary is a true gland; it produces, stores, and releases hormones.
This release of hormones however, is controlled and regulated by the hypothalamus. The anterior pituitary is also bigger in size than the posterior portion, making up about three quarters of the total pituitary size. The two parts that make up the anterior pituitary are the pars tuberalis, and the pars distalis, also known as the anterior lobe.
Although the posterior pituitary is not a true gland, it does release two different hormones: oxytocin and vasopressin (antidiuretic hormone). Both of these hormones are produced in the hypothalamus but stored in the posterior pituitary. Oxytocin (OT) is mainly produced in the paraventricular nuclei of the hypothalamus while antidiuretic hormone (ADH) is mainly produced in the supraoptic nuclei in the hypothalamus. OT effects sexual function in the body, such as sexual arousal and orgasm. ADH increases water retention by the kidneys and reduces urine production.
The anterior pituitary makes and secretes main six hormones. The release of which are controlled by the hypothalamus. These hormones are also produced and stored in the anterior pituitary, which differs from the production of posterior pituitary hormones. The six hormones are: follicle-stimulating hormone (FSH); luteinizing hormone (LH); thyroid stimulating hormone (TSH); adrenocorticotropic hormone (ACTH); prolactin (PRL); and growth hormone (GH), also known as somatotropin.
FSH stimulates sperm production in males and ovarian sex hormones in females needed for the development of follicles for eggs. LH is needed for release of an egg in females, as well as progesterone secretion. In males, LH stimulates testosterone secretion. TSH, also called thyrotropin, stimulates the thyroid and release of thyroid hormone, which regulates many bodily functions such as metabolic rate. ACTH stimulates the release of many other hormones that regulate glucose, protein, and fat metabolism. PRL has an important role in lactation in females. GH is the most produced hormone in the pituitary. GH promotes mitosis and cell differentiation, thus controlling cell growth throughout the body.