What is the pituitary gland
Our bodies are regulated by hormones which are chemicals that allow communication between different cells and parts of the body. Endocrine glands release hormones into the bloodstream.Hormones regulate many functions in our bodies, including mood, growth and development, tissue function, and metabolism. Hormones are typically produced by endocrine glands and together these glands are referred to as the endocrine system. The study of this system is called endocrinology. The pituitary gland is sometimes referred to as the master gland and abnormalities in this gland can have a serious affect on the health of patients. The gland sits at the base of the brain and is roughly the size and shape of a bean (Figure 1). The pituitary is directly under the optic nerve which transmits information from our eyes to our brains (Figure 1, Figure 2 and Figure 3). A pituitary adenoma can cause the gland to grow abnormally and press onto the optic nerve and onto important areas of the brain which surround the gland (Figure 4). This is why patients with pituitary adenoma often experience impaired vision and headaches. Pituitary adenomas are benign tumours and are typically slow growing. A pituitary adenoma may be present for several years before the patient becomes aware of symptoms. Pituitary adenomas are generally not malignant tumours. Such tumours are called pituitary carcinomas and are very rare. However, pituitary adenomas can have a serious affect on a patientís health as they can cause pressure on brain structures surrounding the gland. Some adenomas also interrupt the normal function of the pituitary gland. This can cause the gland to produce excessive amounts of active hormones which can lead to the patient being hormonally imbalanced.
The pituitary gland, also known as the hypophysis, lies immediately beneath the hypothalamus, resting in a depression of the base of the skull called the pituitary fossa, also called the Turkish saddle (sella turcica) (Figure 1).The pituitary gland is composed of two distinctive parts:
- The anterior pituitary or adenohypophysis is composed of cells that secrete hormones, such as growth hormone, prolactin, adrenocorticotropic hormone (ACTH), thyroid stimulating hormone (TSH) as well as luteinising hormone (LH) & follicle-stimulating hormone (FSH).
- The posterior pituitary or neurohypophysis contains nerve cell axons reaching down from the hypothalamus and they release oxytocin and vasopressin.
- The pituitary stalk connects the hypophysis to the base of the brain, to the hypothalamus.
The best way to see the pituitary gland is with MRI. Figure 2 and 3 shows an MRI scan of a normal pituitary from the side and from the frontal view. Please click on the figures to see an enlarged image. Figure 4 shows a large pituitary adenoma from the side.
The function of the pituitary gland
The function of the pituitary gland is to release hormones to the body to regulate various functions such as growth and sexual functions. The pituitary is regulated by the hypothalamus via another set of hormones (Figure 5).
|Growth hormone||GH||Growth hormone controls our rate of growth and also regulates our metabolism. Growth hormone enables the body to grow and reproduce and it is essential for good health throughout our lives. Growth hormone is also of considerable interest as a drug used in both humans and animals, and there are problems of abuse of growth hormone in sport.|
|Prolactin||PRL||Prolactin is found in both men and women. Its principal function is to initiate and sustain lactation which is the process of producing and releasing breast milk.|
|Adrenocorticotropic hormone||ACTH||ACTH stimulates the adrenal gland to produce other substances including cortisol. Cortisol controls a number of functions and is particularly important in times of illness and stress. Hormones often have a knock-on effect initiating important processes in other glands and organs.|
|Thyroid stimulating hormone||TSH||TSH stimulates the thyroid gland. Thyroid stimulating hormone tells the thyroid gland to produce thyroid hormones which are needed by the body. The thyroid controls how quickly the body uses energy, makes proteins, and also regulates how sensitive the body should be to other hormones.|
|Luteinising hormone & Follicle-stimulating hormone||LH and FSH||Luteinising hormone and follicle-stimulating hormone are both regulating functions of the gonads (ovary and testis). They are not necessary for life but are essential for reproduction. Together they stimulate the reproductive organs and initiate puberty which enables children to develop into sexually mature adults. In women these hormones control ovulation and are essential for a normal menstrual cycle and for fertility. In men, these hormones stimulate the testes to produce sperm.|
|Vasopressin||AVP or ADH||Vasopressin (also called anti-diuretic hormone, ADH) is one of the hormones of the posterior pituitary. This hormone has a key role in the regulation of water, glucose and salts in the blood. Its single most important effect is as an anti-diuretic hormone. It is released when the body is dehydrated and sent to the kidneys where it concentrates the urine and conserves water.|
|Oxytocin||Oxytocin||Oxytocin is a posterior pituitary hormone. Oxytocin is an important hormone and is largely associated with female reproduction. It is released in large amounts during labour. It is also important after labour in the establishment of maternal behaviour and bonding between mother and child. Oxytocin can also affect our feelings and moods and is present in both men and women.|
The effects of these hormones show that the endocrine system is an information signal system like the nervous system. The endocrine system is connected to the nervous system through the pituitary gland via the hypothalamus. The hypothalamus is an extremely complicated region of the brain. It releases hormones which in turn stimulate or inhibit the activity of the pituitary gland. Disease in the hypothalamus can also adversely affect the function of the pituitary gland.
|Growth hormone-releasing hormone||GHRH||GHRH is a hypothalamic peptide that stimulates both the synthesis and secretion of growth hormone.|
|Somatostatin||SS||SS inhibits growth hormone release from anterior pituitary. Analogues of somatostatin is used for the treatment of acromegaly and certain other types of tumours as well.|
|Corticotropin-releasing hormone||CRH||CRH is secreted by the hypothalamus in response to stress and it stimulates ACTH.|
|Thyroid stimulating hormone||TRH||Thyrotropin-releasing hormone (TRH) stimulates the release of thyroid-stimulating hormone and prolactin by the anterior pituitary.|
|Gonadotrophin-releasing hormone (also called Luteinizing hormone-releasing hormone (LHRH))||GnRH||GnRH causes the pituitary gland to make and release luteinizing hormone (LH) and follicle-stimulating hormone (FSH). These hormones are involved in reproduction.|