ENDOCRINE SYSTEM

Endocrine system 

The endocrine system is the system of glands, each of which secretes a type of hormone directly into the bloodstream to regulate the body. The endocrine system is in contrast to the exocrine system, which secretes its chemicals using ducts. It derives from the Greek words "endo" meaning inside, within, and "crinis" for secrete. The endocrine system is an information signal system like the nervous system, yet its effects and mechanism are classifiably different. The endocrine system's effects are slow to initiate, and prolonged in their response, lasting from a few hours up to weeks. The nervous system sends information very quickly, and responses are generally short lived. Hormones are substances (chemical mediators) released from endocrine tissue into the bloodstream where they travel to target tissue and generate a response. Hormones regulate various human functions, including metabolism, growth and development, tissue function, and mood. The field of study dealing with the endocrine system and its disorders is endocrinology, a branch ofinternal medicine.

Features of endocrine glands are, in general, their ductless nature, their vascularity, and usually the presence of intracellular vacuoles or granules storing their hormones. In contrast, exocrine glands, such as salivary glands, sweat glands, and glands within the gastrointestinal tract, tend to be much less vascular and have ducts or a hollow lumen.

In addition to the specialised endocrine organs mentioned above, many other organs that are part of other body systems, such as the kidney, liver, heart and gonads, have secondary endocrine functions. For example the kidney secretes endocrine hormones such as erythropoietin and renin.

The endocrine system is made of a series of glands that produce chemicals called hormones. A number of glands that signal each other in sequence are usually referred to as an axis, for example, the hypothalamic-pituitary-adrenal axis.

pituitary gland

In vertebrate anatomy the pituitary gland, or hypophysis, is an endocrine gland about the size of a pea and weighing 0.5 grams (0.018 oz) in humans. It is not a part of the brain. It is a protrusion off the bottom of the hypothalamus at the base of the brain, and rests in a small, bony cavity (sella turcica) covered by a dural fold (diaphragma sellae). The pituitary is functionally connected to the hypothalamus by the median eminence via a small tube called the infundibular stem (Pituitary stalk). The pituitary fossa, in which the pituitary gland sits, is situated in the sphenoid bone in the middle cranial fossa at the base of the brain. The pituitary gland secretes nine hormones that regulate homeostasis.

The pituitary gland consists of two components: the anterior pituitary (or adenohypophysis) and the posterior pituitary (or neurohypophysis), and is functionally linked to the hypothalamus by the pituitary stalk (also named the "infundibular stem", or simply the "infundibulum"). It is from the hypothalamus that hypothalamic tropic factors are released to descend down the pituitary stalk to the pituitary gland where they stimulate the release of pituitary hormones. While the pituitary gland is known as the 'master' endocrine gland, both of the lobes are under the control of the hypothalamus; the anterior pituitary receives its signals from the parvocellular neurons and the posterior pituitary receives its signals from magnocellular neurons.

Hypothyroidism 

Hypothyroidism  is a condition in which the thyroid gland does not make enough thyroid hormone.

Iodine deficiency is often cited as the most common cause of hypothyroidism worldwide but it can be caused by many other factors. It can result from a lack of a thyroid gland or from iodine-131 treatment, and can also be associated with increased stress. Severe hypothyroidism in infants can result in cretinism.

A 2011 study concluded that about 8% of women over 50 and men over 65 in the UK suffer from an under-active thyroid and that as many as 100,000 of these people could benefit from treatment they are currently not receiving.

Gigantism

Gigantism is abnormally large growth due to an excess of growth hormone during childhood, before the bone growth plates have closed.

Causes

The most common cause of too much growth hormone release is a noncancerous (benign) tumor of the pituitary gland. Other causes include:

• Carney complex
• McCune-Albright syndrome (MAS)
• Multiple endocrine neoplasia type 1 (MEN-1)
• Neurofibromatosis

If excess growth hormone occurs after normal bone growth has stopped, the condition is known as acromegaly.

Symptoms

The child will grow in height, as well as in the muscles and organs. This excessive growth makes the child extremely large for his or her age.

Other symptoms include:

• Delayed puberty
• Double vision or difficulty with side (peripheral) vision
• Frontal bossing and a prominent jaw
• Headache
• Increased sweating
• Irregular periods (menstruation)
• Large hands and feet with thick fingers and toes
• Release of breast milk
• Thickening of the facial features
• Weakness

Treatment

In pituitary tumors with well-defined borders, surgery is the treatment of choice and can cure many cases.

For situations in which surgery cannot completely remove the tumor, medication is the treatment of choice. The most effective medications are somatostatin analogs (such as octreotide or long-acting lanreotide), which reduce growth hormone release.

Dopamine agonists (bromocriptine mesylate, cabergoline) have also been used to reduce growth hormone release, but these are generally less effective. Pegvisomant, a medication that blocks the effect of growth hormone, may be used.

Radiation therapy has also been used to bring growth hormone levels to normal. However, it can take 5 - 10 years for the full effects to be seen and this almost always leads to low levels of other pituitary hormones.

Radiation has also been linked to learning disabilities, obesity, and emotional changes in children. Most experts will use radiation only if surgery and medication fail.

Pituitary surgery is usually successful in limiting growth hormone production.

Acromegaly

Acromegaly is a long-term condition in which there is too much growth hormone and the body tissues get larger over time.

Causes

Acromegaly occurs in about 6 of every 100,000 adults. It is caused by abnormal production of growth hormone after the skeleton and other organs finish growing.

Excessive production of growth hormone in children causes gigantism rather than acromegaly.

The cause of the increased growth hormone release is usually a noncancerous (benign) tumor of the pituitary gland. The pituitary gland, which is located just below the brain, controls the production and release of several different hormones, including growth hormone.

Symptoms

• Body odor
• Carpal tunnel syndrome
• Decreased muscle strength (weakness)
• Easy fatigue
• Excessive height (when excess growth hormone production begins in childhood)
• Excessive sweating
• Headache
• Hoarseness
• Joint pain
• Large bones of the face
• Large feet
• Large hands
• Large glands in the skin (sebaceous glands)
• Large jaw (prognathism) and tongue
• Limited joint movement
• Sleep apnea
• Swelling of the bony areas around a joint
• Thickening of the skin, skin tags
• Widely spaced teeth
• Widened fingers or toes due to too much skin growth, with swelling, redness, and pain

Other symptoms that may occur with this disease:

• Excess hair growth in females
• Weight gain (unintentional)

Treatment

Surgery to remove the pituitary tumor that is causing this condition usually corrects the abnormal growth hormone release in most patients. Sometimes the tumor is too large to remove completely. People who do not respond to surgery will have radiation of the pituitary gland. However, the reduction in growth hormone levels after radiation is very slow.

The following medications may be used to treat acromegaly:

• Octreotide (Sandostatin) or bromocriptine (Parlodel) may control growth hormone release in some people.
• Pegvisomant (Somavert) directly blocks the effects of growth hormone, and has been shown to improve symptoms of acromegaly.

These medications may be used before surgery, after surgery, or when surgery is not possible.

After treatment, you will need to see your health care provider regularly to make sure that the pituitary gland is working normally. Yearly evaluations are recommended.

Pituitary surgery is successful in most patients, depending on the size of the tumor and the experience of the surgeon.

Without treatment the symptoms will get worse, and the risk of high blood pressure, diabetes (high blood sugar), and cardiovascular disease increases.

Thyroid Diseases

Your thyroid is a butterfly-shaped gland in your neck, just above your collarbone. It is one of your endocrine glands, which make hormones. The thyroid helps set your metabolism - how your body gets energy from the foods you eat.

Millions of people in the U.S. have thyroid diseases. Most of them are women. If you have a thyroid disease, your body uses energy more slowly or quickly than it should. A thyroid gland that is not active enough, called hypothyroidism, is far more common. It can make you gain weight, feel fatigued and have difficulty dealing with cold temperatures. If your thyroid is too active, it makes more thyroid hormones than your body needs. That condition is hyperthyroidism. Too much thyroid hormone can make you lose weight, speed up your heart rate and make you very sensitive to heat.

There are many causes for both conditions. Treatment involves trying to reset your body's metabolism to a normal rate

Hyperthyroidism is a disorder that occurs when the thyroid gland makes more thyroid hormone than the body needs. It is sometimes called thyrotoxicosis, the technical term for too much thyroid hormone in the blood. About 1 percent of the U.S. population has hyperthyroidism.  Women are much more likely to develop hyperthyroidism than men.

Hyperthyroidism has several causes, including

·         Graves' disease

·         one or more thyroid nodules

·         thyroiditis, or inflammation of the thyroid gland

·         ingesting too much iodine

·         overmedicating with synthetic thyroid hormone, which is used to treat underactive thyroid

Rarely, hyperthyroidism is caused by a pituitary adenoma, which is a noncancerous tumor of the pituitary gland. In this case, hyperthyroidism is due to too much TSH.

Cushing's Syndrome

Also called: Hypercortisolism 

Cushings syndrome is caused by long-term exposure to too much cortisol, a hormone that your adrenal gland makes. Sometimes, taking synthetic hormone medicine to treat an inflammatory disease leads to Cushing's. Some kinds of tumors secrete a hormone that can cause your body to make too much cortisol.

Cushing's syndrome is rare. Some symptoms are

• Upper body obesity
• Thin arms and legs
• Severe fatigue and muscle weakness
• High blood pressure
• High blood sugar
• Easy bruising

Your treatment will depend on why you have too much cortisol. If it is because you have been taking synthetic hormones, a lower dose may control your symptoms. If a tumor caused it, surgery and other therapies may be needed. Most of the time, Cushing's syndrome can be cured.