Diplomate, Board Certification of Emergency Medicine
Chairman, Department of Emergency Medicine Ma'ayenei Hayeshua
Hospital
As far as the body is concerned, the boss in the physical
sense is the brain. To allow us to function, it usually
communicates via electrical pathways called the nerves.
However another pathway is chemical. By releasing chemicals,
the brain is able to influence many systems at once instead
of just the end organ that the nerve activates in an
electrical pathway. These chemicals are called hormones and
this release of chemicals is called the endocrine system.
The main players here are the following organs: the
hypothalamus and the pituitary at the base of the brain, the
thyroid and the parathyroid glands in the neck, the pancreas
in the abdomen, the ovaries and the testes in the pelvis, and
the inner and outer portion of the adrenal glands, which sit
just above the kidneys. The pineal gland as well is located
in the brain.
The hypothalamus is the initiator of a hormone release. It
releases hormones called releasing factors that order the
pituitary to release its hormones. The pituitary hormones
influence most of the other organs above, so you can see what
an important organ a pituitary is. Stroke, tumor, trauma, or
loss of blood in childbirth (a syndrome called Sheehan's
Syndrome) all can cause damage to the pituitary with the need
for lifelong supplements of many different hormones.
The pituitary doesn't only influence other endocrine organs
to release hormones; it also has some direct effects as well.
These are the two hormones called growth hormone and
Prolactin.
Growth hormone stimulates growth, and as such the absence of
this hormone will result in short stature -- so called dwarfs
or midgets. This hormone persists throughout adulthood and
does play a role in the release of sugars in the blood, but
its full role is still not understood.
Prolactin is what stimulates the release of milk. It
antagonizes another hormone, estrogen, but not completely.
What this means is that about 70% of women will not get
pregnant while they are nursing. Prolactin is stimulated by
nursing -- the more demand for milk, the more that is
produced, and vice versa. Prolactin also causes the uterus to
contract, producing less bleeding after pregnancy, and also
stimulates the release of fatty acids into the milk. These
fatty acids are usually not used unless a severe starvation
state exists (indeed, in a fast, the body will break down
essential proteins for energy before touching its fat
stores), but in nursing they are released, which results in a
welcome weight loss for women who are after pregnancy.
Prolactin is present in males but in lesser amounts, and
again, for reasons that are not understood.
May you all have a good week, and continue to write me in
care of the Yated.
A message from Glaxo, sponsor of this column. I'm very
excited that Zyban has finally made it to these shores. Zyban
has been proven to help end the smoking habit, and is
recommended by the American AHCPR as an approved aid to
ending this destructive habit. (2 million people died of
smoking related diseases last year.) Think of Zyban to help
you kick the habit.
