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 patient’s 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.