THE ANTERIOR PITUITARY GLAND
The anterior pituitary gland originates from the roof of the embryo's mouth. It
then attaches itself to the posterior pituitary gland. The anterior pituitary gland is
indirectly connected to the hypothalamus by means of a venous portal system. By
"portal," we mean that the veins carry substances from the capillaries at one point to the
capillaries at another point (hypothalamus to the anterior pituitary gland). In the
hypothalamus, certain chemicals known as releasing factors are produced. These are
carried by the portal system to the anterior pituitary gland. Here, they stimulate the cells
of the anterior pituitary gland to secrete their specific hormones. The anterior pituitary
gland produces many hormones. In general, these hormones stimulate the target
organs to develop or produce their own products. This stimulating effect is referred to
as tropic. Of the many hormones produced by the anterior pituitary gland, we will
a. Somatotropic Hormone (Growth Hormone).
(1) The target organs of this hormone are the growing structures of the
body. This hormone influences such structures to grow. Growth is produced because
cell division is increased--stimulating increased growth of all tissues capable of growing.
This hormone produces an increased utilization of amino acids to produce proteins. It
also causes a renal depression followed by accumulation of sodium chloride and water.
Inhibition of carbohydrate utilization also occurs, producing hyperglycemia.
(2) Unfortunately, the anterior pituitary gland does not always function
properly. For instance, the anterior pituitary gland may produce too much or too little
somatotropin. The hyposecretion of somatotropin in childhood produces a condition
known as pituitary dwarfism that results in a lack of physical development. A 20-year
old person with this disease may have the same physical appearance as a 5-year old
child. Conversely, the hypersecretion of somatotropin in childhood may cause giantism.
This is distinguished by accelerated, undiminished growth. An extreme example of the
results of this condition is a man who has grown to a height of eight feet, 6-1/2 inches
and weighs 375 pounds. This same hypersecretion sometimes occurs in adulthood.
This condition is called acromegaly. In acromegaly, there is no increase in the height of
the person since the epiphyses of the long bones have been fused. However, the
membraneous bones such as the facial bones become enlarged and the person gains
coarse facial features. Other symptoms of acromegaly include enlarged hands, feet,
and internal organs. Hyposecretion of somatotropin in the adult causes a condition
known as Simmond's disease. This disease produces what appears to be advanced
physical senility, although the patient may be quite young.
b. Thyroid-Stimulating Hormone. The thyroid-stimulating hormone
(Thyrotropic Hormone, TSH). stimulates the growth of the thyroid gland. It thus
promotes the growth of the thyroid gland as well as the production and secretion of the
hormones made by the thyroid gland. The secretion of the thyroid-stimulating hormone
as well as the thyroid hormones is controlled by a negative feedback mechanism. That