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, 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.

* As stated on features and markings on bones, the term "fossa" is usually used to describe and refer to a shallow depression on the surface of a bone.

 

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.

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

from the Anterior Lobe of the Pituitary Gland Adrenocorticotrophic hormone (ACTH) - targets the adrenal glands (to produce cortisol, to control metabolism and has ant-inflammatory effects) Follicle-stimulating hormone (FSH) - targets the ovaries (in women, to produce ova for fertilization and to increase production of oestrogen) and the testes (in men, to produce sperm) Human growth hormone (HGH) is sometimes called simply "growth hormone" - targets cells in many parts of the body e.g. to increase height in children and to regulate muscle and fat in both adults and children. Luteinizing hormone (LH) - targets the ovaries (in women, to trigger ovulation) and the testes (in men, to produce testosterone) Melanocyte-stimulating hormone (MSH) is also known as intermedin - targets the brain Prolactin (PRL) - targets the breasts (to produce breastmilk but is also present in non-pregnant women) Thyroid-stimulating hormone (TSH) - targets the thyroid gland (to produce triiodothyronine and thyroxine) from the Posterior Lobe of the Pituitary Gland Antidiuretic hormone (ADH) - targets the kidneys (to decrease the volume of urine they produce) Oxytocin - targets the breasts (to release breastmilk) and uterus (to contract during childbirth) Note that, unlike the anterior lobe of the pituitary gland, the posterior lobe does not synthesize hormones. It stores and releases hormones. So, according to this table*, how many different hormones does the pituitary gland produce ? The answer is 7 (seven), not 9 (nine), because only the hormones secreted by the anterior lobe are also produced in the pituitary gland. The hormones secreted by the posterior lobe of the pituitary gland are synthesized in the hypothalamus. *Other lists may vary slightly e.g. in the level of detail and the names used for some hormones.

Note: Hormones secreted by the anterior and posterior lobes of the pituitary gland are listed (above) in alphabetical order. The numbers shown on the left of each of the hormones listed are for reference to these lists and because some people find it easier to learn lists by also remembering how many items are listed. These hormones are not produced or secreted in the order(s) or in quantities corresponding to these numbers.

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.