Introduction
Ever wonder what controls how much you grow?
Have you ever stopped to wonder why some people are tall and others short? Or how those differences sometimes become extreme in rare cases? The most simple answer is that a persons growth, like MANY things in the body, is regulated by a balance of endocrine hormones released by the brain which work throughout the body. If the balance is disturbed it can lead to an array of problems. In the case of growth, pituitary growth hormone is the endocrine hormone whose balance needs to be kept in check. If the pituitary gland secretes a little more than average, a person becomes taller. If the pituitary gland produces a little less than average, that person will be shorter. If this hormone is produced in significantly below or above average levels, pituitary dwarfism or gigantism may result. To find out more about what causes pituitary dwarfism and gigantism, how these conditions manifest themselves, what symptoms to look for, and how it is treated click on the tabs at the top of the page. Once you've finished, take the quiz to see how much of an expert you've become!
So what are Pituitary Dwarfism and Gigantism?
Pituitary dwarfism is a rare condition caused by a deficit in pituitary growth hormone. It causes the person to be shorter in stature than considered normal, which is defined as an adult height of less than 4 feet 10 inches.(1) Dwarfism usually first presents itself through abnormally low placement on growth charts early in childhood. If the cause of dwarfism is due to only a genetic deficiency in growth hormone, the condition is not usually fatal, and can be greatly improved by treatment if caught early. If, however, the diagnosis is the result of trauma, a tumor on the pituitary gland, or any other risk factors, the prognosis is determined on more of a case-by-case basis.
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Pituitary gigantism is an even more rare condition caused by an excess in pituitary growth hormone which causes the person to be much taller than what is considered normal. Gigantism, like pituitary dwarfism, usually presents itself in childhood. Children with gigantism grow at a faster rate than other children their age, therefore having abnormally high placements on growth charts early in childhood. They also have other physical abnormalities such has large hands, flat noses, etc. that make them stand out from their peers.(6) The most common cause of pituitary gigantism is a tumor in the pituitary gland. The prognosis of gigantism is determined on a case-by-case basis.
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Mechanism of Disease
The main player: pituitary growth hormone
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Pituitary growth hormone, which is also called human growth hormone (hGH), is secreted by the pituitary gland (located in the mid section of the brain). When this hormone is introduced into the body, it causes the cells to grow and divide themselves into additional cells at a faster rate.(2)
The amount of this growth hormone in the body effects just what it sounds like ---growth. Pituitary/human growth hormone is indirectly crucial to the stimulation of cell division and enlargement. It acts primarily through control of insulin-like growth factors (IGF-1 and IGF-2). When growth hormone is present in the blood, it signals the liver to produce insulin-like growth factors. IGF-1 which increases the rate of cell growth, proliferation and protein synthesis in tissues throughout the body. (3)
The amount of growth hormone that is secreted by the pituitary gland is regulated by hormones that come from the hypothalamus:
In children, the hyposecretion (hypo- means below normal or too little) of growth hormone causes pituitary dwarfism while the hypersecretion (hyper- means excessive or too much) of growth hormone causes gigantism. In adults, continued hypersecretion of growth hormone can result in acromegaly.(4) A benign tumor on the pituitary gland is often the cause of the hypersecretion which results in excess growth hormone and IGF-1 in the blood. (3)
Pituitary growth hormone, which is also called human growth hormone (hGH), is secreted by the pituitary gland (located in the mid section of the brain). When this hormone is introduced into the body, it causes the cells to grow and divide themselves into additional cells at a faster rate.(2)
The amount of this growth hormone in the body effects just what it sounds like ---growth. Pituitary/human growth hormone is indirectly crucial to the stimulation of cell division and enlargement. It acts primarily through control of insulin-like growth factors (IGF-1 and IGF-2). When growth hormone is present in the blood, it signals the liver to produce insulin-like growth factors. IGF-1 which increases the rate of cell growth, proliferation and protein synthesis in tissues throughout the body. (3)
The amount of growth hormone that is secreted by the pituitary gland is regulated by hormones that come from the hypothalamus:
- Growth-hormone-releasing hormone (GHRH) travels from the hypothalamus to the pituitary gland and does just what it sounds like it might do and stimulates the release of growth hormone. This results is MORE growth hormone in the body. (4)
- Growth-hormone-inhibiting hormone (GHIH) / Somatostatin (SST) travels from the hypothalamus to the pituitary gland and acts in the opposite way as GHRH and inhibits the release of growth hormone. This results in LESS growth hormone in the body (4)
In children, the hyposecretion (hypo- means below normal or too little) of growth hormone causes pituitary dwarfism while the hypersecretion (hyper- means excessive or too much) of growth hormone causes gigantism. In adults, continued hypersecretion of growth hormone can result in acromegaly.(4) A benign tumor on the pituitary gland is often the cause of the hypersecretion which results in excess growth hormone and IGF-1 in the blood. (3)
The figure above illustrates the effects of the direct vs. indirect actions of pituitary growth hormone in metabolic activity, cell growth, protein synthesis, cartilage and bone growth as well as showing the negative feedback pathway which tells the hypothalamus to produce either GHRH or GHIH as needed. (4)
References: (See "References" tab under Introduction/Mechanisms for full AMA citations)
1) http://www.mayoclinic.org/diseases-conditions/dwarfism/basics/definition/con-20032297
2) http://www.buzzle.com/articles/pituitary-growth-hormone.html
3) Vander's Human Physiology, The Mechanisms of Body Function
4) http://classes.midlandstech.edu/carterp/Courses/bio211/chap16/chap16.htm
5) Video: What is the Pituitary Gland http://m.youtube.com/watch?v=ZfDXSKhNS4I
6) http://www.healthline.com/health/gigantism#Treatment5 http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0002157/#adam_001174.disease.symptoms
1) http://www.mayoclinic.org/diseases-conditions/dwarfism/basics/definition/con-20032297
2) http://www.buzzle.com/articles/pituitary-growth-hormone.html
3) Vander's Human Physiology, The Mechanisms of Body Function
4) http://classes.midlandstech.edu/carterp/Courses/bio211/chap16/chap16.htm
5) Video: What is the Pituitary Gland http://m.youtube.com/watch?v=ZfDXSKhNS4I
6) http://www.healthline.com/health/gigantism#Treatment5 http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0002157/#adam_001174.disease.symptoms