Distúrbios da glândula pituitária

Some of the pituitary gland disorders

Pituitary disorders generally occur when the pituitary gland is either too active or not active enough. Often there is a discrete piece of pituitary gland which leads to the problems, this is called a pituitary adenoma (if it is large it may be called pituitary macroadenoma). These are usually benign, non-cancerous tumours. Pituitary adenomas can cause problems through:

1. Releasing excess of one or more hormone.

2. Not releasing any hormones but pressing on the normal pituitary tissue and thus interfering with normal function; e/ou

3. Causing pressure on nearby structures - for example, pressing on the nerve of the eye, leading to blurred vision or loss of part of the vision.

Conditions where the pituitary gland produces too much of one or more of its hormones include:

• Acromegalia.

• Cushing's syndrome.

• Prolactinoma.

Conditions where the pituitary gland fails to produce enough hormones include:

• Adult growth hormone deficiency.

• Diabetes insipidus.

• Hypopituitarism.

• Pituitary tumours.

• Tumours of, or injury to, the hypothalamus, having a knock-on effect on the pituitary gland.

The diagnosis usually involves hormone blood tests and also brain scans. Hormone blood tests can be taken randomly for some hormones, but others may require specialised testing with substances that should provoke the release or prevent release in certain conditions.

This may require attendance at a day unit and having several hormone blood tests throughout the day. Usually an ressonância magnética of the pituitary gland is undertaken to look for pituitary abnormalities - eg, pituitary adenoma or cysts.

This will depend upon the cause. If there is hormone deficiency then this may need replacement with tablets. If a tumour is discovered as the cause of the problems then pituitary surgery may be required.

This is usually via the nose. If there is a pituitary tumour which is found to be cancerous then radioterapia may be needed after surgery. There may also be a need for lifelong hormone replacement following any treatment.

The pituitary gland is located in the brain and is an endocrine gland. This means that it produces chemicals called hormones. Hormones are chemical messengers which help different organs in the body communicate with each other. The pituitary gland is one part of a messenger system.

The pituitary gland helps to control the body's functions by releasing hormones into the bloodstream. These hormones are transported in the blood to their target. Here they usually cause the release of a second hormone.

The target can either be specialised endocrine glands or other types of body tissue such as groups of cells.

The pituitary gland is sometimes called the master gland because it controls several other hormone-releasing glands. Some of the glands the pituitary gland controls are the thyroid gland, the ovaries, the testicles (testes) and the adrenal glands.

About the size of a pea, the pituitary gland is found at the base of the brain, behind the bridge of your nose. The pituitary gland is very close to another part of the brain, called the hypothalamus.

The pituitary

The pituitary gland has two main parts:

• The part of the pituitary gland at the front, called the anterior pituitary.

• The part of the pituitary gland at the back, called the posterior pituitary.

These two parts release different hormones which are aimed at different parts of the body.

There is also a section between the two main parts, called the intermediate part, which releases a single hormone. The final part of the pituitary gland is the stalk, which connects the posterior pituitary to the hypothalamus.

The body is in a constant state of change. Heart rate, blood pressure and body temperature all change in response to what you do and your surroundings. The body has systems that constantly monitor these and other vital functions. Not only must these systems monitor changes, they must also respond to the changes and help the body to restore balance.

Some of these systems involve the hypothalamus and the pituitary gland. The hypothalamus and the pituitary gland are part of several loops or circuits. The loops include other glands. The hormones produced by each gland complete the loops by travelling in the bloodstream between them.

The hypothalamus receives information from many sources about the basic functions of the body. It uses the information it receives to help regulate these functions. One of the ways the hypothalamus does this involves controlling the pituitary gland. The hypothalamus does this by using its own hormones to communicate with the pituitary gland.

Among the information monitored by the hypothalamus is the level of various hormones in the blood. The hypothalamus has special cells which receive information from the body indicating how much of each hormone is present in the bloodstream.

When these hormones drop below a particular level this stimulates the hypothalamus to release hormones. These hormones travel to the pituitary gland, acting as the signal to the pituitary gland to produce one or more of its hormones.

The hormones produced by the pituitary gland are released into the bloodstream. The bloodstream transports the pituitary hormones to other endocrine glands, such as the thyroid gland.

The pituitary gland hormones may then stimulate their target endocrine glands to produce their own hormones. These locally produced hormones do the actual work of regulating your body.

Take the example of the control of thyroid hormones from the thyroid gland in the neck. The hypothalamus produces a hormone called thyrotropin-releasing hormone (TRH). TRH travels to the pituitary gland and stimulates it to release thyroid-stimulating hormone (TSH).

TSH travels to the thyroid gland and stimulates it to release thyroid hormones, T3 and T4. When levels of T3 and T4 get high enough, levels in the bloodstream are detected by the hypothalamus.

The hypothalamus then knows to stop releasing more TRH. This last part of the loop is called negative feedback and prevents hormone levels from rising too high.

Regulation of thyroid hormones

The anterior pituitary produces hormones that regulate a wide range of bodily activities, from growth to reproduction. Whether a hormone is released by the anterior pituitary is governed by the hypothalamus. There are at least seven different hormones secreted by the anterior pituitary. The posterior pituitary produces just two hormones.

The anterior pituitary hormones

The posterior pituitary makes and releases just two hormones

The Hypophysis Cerebri

From Gray's Anatomy Online

Human Physiology/The endocrine system

From Wikibooks, the open-content textbooks collection

Additional reading information can be found in the 'Further reading' section, below.