Download The Endocrine System

The Endocrine System
The endocrine system is comprised of various diverse glands that work together and
alone to maintain the body's ability to function. Each endocrine gland-the thyroid,
pancreas, pineal, thymus, ovaries, testes, adrenals, and parathyroid--produce and secretes
hormones. These chemical messengers work within the body, exciting or inhibiting
various tissues regarding metabolism, growth and reproduction.
The coordinator of the endocrine system is the anterior pituitary gland, found at the base
of the brain. The hypothalamus sends special hormones called releasing factors to the
pituitary instructing it how to manage the other endocrine glands. Then with its own set
of directive hormones, the anterior pituitary guides the body's glands. The anterior
pituitary also releases prolactin, a breast-feeding hormone, and growth hormone. The
posterior pituitary, a neighbor but unrelated to the anterior pituitary, is responsible for
two hormones: antidiuretic hormone (ADH) and oxytocin. ADH helps to maintain arterial
blood pressure by reabsorbing water from your kidneys. Oxytocin contracts the uterus
during childbirth and causes milk letdown during breast-feeding.
Each endocrine gland plays a distinct role in the body, but these actions overlap and
therefore affect each other.
Adrenal Glands
Sitting astride each kidney is a triangular shaped adrenal gland. The adrenals are divided
into two distinct parts, the outer region of the adrenal called the adrenal cortex and the
small inner section called the adrenal medulla. All adrenal hormones are ruled by
adrenocorticotrophic hormone (ACTH) from the anterior pituitary.
1. The adrenal cortex - produces and secretes three kinds of steroid hormones. The
first type, called mineral corticoids, includes aldosterone, which maintains normal
blood pressure by balancing sodium, potassium and fluid levels. Secondly, the
adrenal cortex makes small amounts of sex hormones, namely testosterone and
estrogen. The glucocorticoids, cortisol and corticosterone, regulate blood
pressure, support normal muscle function, promote protein breakdown, distribute
body fat and increase blood sugar as needed. This hormone class is most noted for
its anti-inflammatory properties, hence the popularity of artificial cortisone as a
medication. Dehydroepiandrosterone (DHEA), a steroid hormone, is also
produced by the adrenals. Researchers used to think DHEA only acted as a
reservoir for the body to produce other hormones, like estrogen and testosterone.
DHEA also appears to have it's own role, but at present that role is unclear. It is
suspected that it affect the heart, body weight, nervous system, immunity, bones
and other systems
2. The adrenal medulla - is derived from the same primitive tissue as the ganglion
cells of the sympathetic nervous system and as a result its hormones tend to act
largely on the nervous system. The medulla's hormones, epinephrine (also called
adrenalin) and norepinephrine, are also controlled by the sympathetic nervous
system during fear or stress. The body reacts to these hormones with a "flight or
fight" response: pounding heart, dilated pupils and high blood pressure.
Thyroid and Parathyroid
The two lobes of your thyroid gland straddle your windpipe. Using two hormones,
triodothyronine and thyroxin, the thyroid regulates various enzymes that dominate energy
metabolism. Calcitonin, a blood calcium-lowering hormone, is also released by the
thyroid. Thyrotrophin from the anterior pituitary keeps thyroid hormones balance. Just
under the thyroid are four small parathyroid glands that emit parathormone (PTH). The
parathyroid hormone acts on your digestive system, bones and kidneys to control
phosphate and calcium metabolism. Without this regulation, the bone and nerves are
impacted. Too little PTH and a convulsive, twitching condition called tetany ensues. Too
much PTH leads to high blood calcium and eventually a bone softening disease called
osteitis fibrosa cystica.
Thymus
Located just behind your breastbone and just below the thyroid the thymus is an
irregularly shaped member of both the endocrine and immune systems. Relatively large
in childhood, the thymus grows until the teen years, and then shrinks with age. Fat
replaces active lymphatic tissue. Thymosin, thymopoeitin and serum thymic factor are
thymus hormones, which oversee several immune operations. Before and shortly after
birth, an infant's thymus gland preprocesses T-lymphocytes, the white blood cells in
charge of cellular immunity. This type of immunity, the kind not controlled by
antibodies, shields your body from yeast, fungi, parasites, viruses, cancer and allergies.
Thymopoeitein also activates circulating T-cells in the body.
Pineal Gland
Although part of the endocrine system, the pineal gland isn’t a gland in the true sense.
The pineal gland is a neuroendocrine body that translates nerve messages into hormonal
output--namely melatonin. The pineal hormone level peaks in the body at around
midnight. Babies are born with very little melatonin in their system however; levels rise
with age, top out in childhood and then slowly decline with years. The pineal gland and
melatonin are thought to keep your biological clock ticking. External cues like
temperature and light, as well as endogenous messages such as emotions guide the pineal
gland. In this way sleep, mood, immunity, seasonal rhythms, menstruation and even
aging are regulated.
Pancreas
The pancreas is a slender gland about the size of a finger located behind the stomach and
next to the liver and gallbladder. It produces 2 1/2 pints of digestive enzyme-containing
fluid each day; amylase for starch, lipase for fat and protease for protein and deposits
these into the small intestine.
The Islets of Langerhans rule the pancreases better known hormones, insulin and
glucagons. These opposing hormones work together keeping the blood sugar in balance.
Glucagons works together with epinephrine, growth hormone and glucocorticoids to
prevent the blood glucose from dropping too low by promoting glycogen breakdown.
Insulin controls high blood sugar by enhancing the uptake and utilization of glucose by
your muscles and body fat.
Testes
Two testes, located in a mants scrotum, produce sperm and testosterone. This sex
hormone is responsible for men having deeper voices, beards and increased musculature.
Testosterone, also responsible for sex organ development, is produced in the testes under
the direction of gonadotrophins from the anterior pituitary. Testosterone also enhances
libido in both sexes.
Ovaries
In females, two ovaries, linked to the uterus via fallopian tubes, produce ovum as well as
estrogen and progesterone. These female hormones endow women with their feminine
traits: large breasts and hips, soft skin and a menstrual cycle. During pregnancy, the
placenta also produces progesterone, taking over from the ovaries. This allows pregnancy
to proceed normally, as well as prepare a woman's breasts for nursing her baby.