Pituitary Gland
There are two distinct regions in the gland: the
anterior lobe (adenohypophysis) and the posterior lobe (neurohypophysis).
The activity of the adenohypophysis is controlled by
releasing hormones from the hypothalamus. The
neurohypophysis is controlled by nerve stimulation.
Hormones of the Anterior Lobe (Adenohypophysis)
Growth hormone is a protein that stimulates the growth
of bones, muscles, and other organs by promoting protein
synthesis. This hormone drastically affects the
appearance of an individual because it influences
height. If there is too little growth hormone in a
child, that person may become a pituitary dwarf of
normal proportions but small stature. An excess of the
hormone in a child results in an exaggerated bone
growth, and the individual becomes exceptionally tall or
a giant.
Hormones of the Posterior Lobe (Neurohypophysis)
Antidiuretic hormone promotes the reabsorption of water
by the kidney tubules, with the result that less water
is lost as urine. This mechanism conserves water for the
body. Insufficient amounts of antidiuretic hormone cause
excessive water loss in the urine.
Pineal Gland
The pineal gland, also called pineal body or epiphysis
cerebri, is a small cone-shaped structure that extends
posteriorly from the third ventricle of the brain. The
pineal gland consists of portions of neurons, neuroglial
cells, and specialized secretory cells called
pinealocytes. The pinealocytes synthesize the hormone
melatonin and secrete it directly into the cerebrospinal
fluid, which takes it into the blood. Melatonin affects
reproductive development and daily physiologic cycles.
Pituitary Dwarfism
Definition
Dwarfism is a condition in which the growth of the
individual is very slow or delayed. There are many forms
of dwarfism. The word pituitary is in reference to the
pituitary gland in the body. This gland regulates
certain chemicals (hormones) in the body. Therefore,
pituitary dwarfism is decreased bodily growth due to
hormonal problems. The end result is a proportionate
little person, because the height as well as the growth
of all other structures of the individual are decreased.
Description
Pituitary dwarfism is caused by problems arising in the
pituitary gland. The pituitary gland is also called the
hypophysis. The pituitary gland is divided into two
halves: the anterior (front) and posterior (back)
halves. The anterior half produces six hormones: growth
hormone, adrenocorticotropin (corticotropin), thyroid
stimulating homone (thyrotropin), prolactin, follicle
stimulating hormone, and lutenizing hormone. The
posterior pituitary gland only produces two hormones. It
produces antidiuretic hormone (vasopressin) and oxytocin.
Growth is the body's response to different hormones. The
forebrain contains a small organ called the
hypothalamus, which is responsible for releasing
hormones in response to the body's needs for purposes of
regulation. Growth hormone is produced in the anterior
pituitary gland when growth hormone-releasing hormone
(GHRH), is released by the hypothalamus. Growth hormone
is then released and stimulates the liver to produce
IGF-1. In return, IGF-1 stimulates the long bones to
grow in length. Thus, growth can be slowed down or
stopped if there is a problem making any of these
hormones or if there is a problem with the cells
receiving these hormones.
Causes & Symptoms
Pituitary dwarfism has been shown to run in families.
New investigations are underway to determine the
specific cause and location of the gene responsible for
dwarfism. The human cell contains 46 chromosomes
arranged in 23 pairs. Most of the genes in the two
chromosomes of each pair are identical or almost
identical with each other. However, with dwarfism, there
appears to be disruption on different areas of
chromosome 3 and 7. Some studies have isolated defects
for the production of pituitary hormones to the short
arm (the "p" end) of chromosome 3 at a specific location
of 3p11. Other studies have found changes on the short
arm of chromosome 7.
A child with a growth hormone deficiency is often small
with an immature face and chubby body build. The child's
growth will slow down and not follow the normal growth
curve patterns. In cases of tumor, most commonly
craniopharyngioma (a tumor near the pituitary gland),
children and adolescents may present with neurological
symptoms such as headaches, vomiting, and problems with
vision. The patient may also have symptoms of double
vision. Symptoms such as truly bizarre and excessive
drinking behaviors (polydipsia) and sleep disturbances
may be common.
Diagnosis
The primary symptom of pituitary dwarfism is lack of
height. Therefore, a change in the individual's growth
habits will help lead to a diagnosis. Another diagnostic
technique uses an x ray of the child's hand to determine
the child's bone age by comparing this to the child's
actual chronological age. The bone age in affected
children is usually two years or more behind the
chronological age. This means that if a child is ten
years old, his or her bones will look like they are
those of an eight-year-old child. The levels of growth
hormone and somatomedin C must also be measured with
blood tests.
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