The Pituitary Gland
The pituitary gland (also known as the 'hypophysis') is one of the glands of the endocrine system, which consists of several glands whose function is to produce and release ('secret') chemical 'messengers' called hormones. The hormones then move around the body via blood vessels to reach 'target cells' that have receptors that recognise the specific hormone molecule(s) able to regulate the activity of that particular cell and hence the tissue or organ of which it is a part.
The pituitary gland has been called the 'master gland' of the human endocrine system because it secrets some hormones that control other endocrine glands by stimulating them to release specific hormones. However, the pituitary gland itself also has a 'master', which is the hypothalamus, the region of the brain that regulates the interaction of the endocrine system and the nervous system.
So, some of the hormones secreted by the pituitary gland ...
- control other endocrine glands by secreting hormones that stimulate certain other endocrine glands e.g. adrenal glands, to release their hormones (that is, hormones that are not synthesized in the pituitary gland),
while other hormones secreted by the pituitary gland ...
- act directly on target cells in the body e.g. human growth hormone (HGH), which acts on cells in many parts of the body.
Location of the Pituitary Gland
As shown in the diagram on the right, the pituitary gland is small gland (typically just over 1cm in adults) located at the base of the skull.
Its location may be described as:
"Approximately in the centre of the head, behind the bridge of the nose, below the base of the brain, near the optic nerves".
A shorter and also accurate description is:
"At the base of the brain, inside the sella turcica - which is a depression located towards the centre of the superior surface of the sphenoid bone".
The pituitary gland hangs in two parts called 'lobes' that rest in and are protected by the pituitary fossa*, which is also called the sella turicica, and is a deep saddle-shaped depression in the superior (i.e. upper) surface of the sphenoid bone immediately below the pituitary gland. The sphenoid bone is a wedge-shaped bone that been described as resembling "a bat with wings extended" (Gray's Anatomy), see the image below.
Structure of the Pituitary Gland
The pituitary gland hangs from the base of the brain and is attached to the hypothalamus (part of the brain) by a short stalk-like structure called the infundibulum and also known as the infundibular stem and the pituitary stalk, which consists of many nerve fibres (axons).
How many lobes does the pituitary gland have ?
The pituitary gland is often described as consisting of two lobes, the anterior lobe ('adenohypophysis') and the posterior lobe ('neurohypophysis'). As their names suggest, the anterior lobe is located in front of, i.e. "anterior to" the posterior lobe.
Some more detailed descriptions of the pituitary gland state that it consists of three lobes:
- the anterior lobe of the pituitary gland (also called the adenohypophysis)
- the intermediate lobe of the pituitary gland,
- the posterior lobe of the pituitary gland (also called the neurohypophysis)
However, whereas in some animals the three lobes of the pituitary are distinct, in humans the intermediate lobe is only a few cells thick and is often considered part of the anterior pituitary lobe - it is useful to include this information if mentioning the intermediate pituitary in descriptions for introductory anatomy courses.
It is important to distinguish between the anterior and posterior lobes of the pituitary gland because they have different structures. Although both the anterior and posterior lobes of the pituitary gland secret important hormones, only the anterior lobe produces ('synthesizes') the hormones it secretes. The posterior pituitary gland receives hormones that were synthesized in the hypothalamus and stores them in neurosecretory vesicles called 'Herring Bodies' before secreting them into the bloodstream.
Hormones released by the Pituitary Gland
The above notes are part of a general description of the human endocrine system likely to be appropriate for first-level courses such as AS and A-Level Human Biology, ITEC Anatomy and Physiology, and other introductory courses in Health Sciences.