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:::Index>Profound Human World>Knowledge Acquisition>Internal Regulation> The
Function of Endocrine Glands
The Function of Endocrine Glands
Glands of the human body, like sweat glands or tear glands, have specialized ducts to
transport the substances secreted, like sweat glands expel sweat to the skin surface,
and tear ducts transport tears to the eye. But hormones secreted by endocrine glands
are transported through the whole body by the bloodstream, and every communication
between each endocrine gland is conducted through hormonal levels in the blood.
The commander of all endocrine glands is the hypophysis, located below the brain.
Hormones secreted by the pituitary gland include growth hormone that affect the
metabolism of saccharides, proteins and fats in the body, therefore affecting body
metabolic function. For growing children, this will affect their height; any form of
gigantism or dwarfism is caused also by long-term anomaly in growth hormone
secretion. The hypophysis also secretes adrenocorticotropic hormone, which
stimulates the epinephrine to produce epinephrine, and thyroid-stimulating hormone
affects the thyroid gland; the hypophysis also secretes luteinizing hormone and
follicle-stimulating hormone. These last two hormones stimulate the growth and
maturation of sexual glands; during puberty, the dormant ovaries and testis begin to
develop under the influence of these two hormones, which also affect the
development of secondary sexual characteristics, and the production of eggs and
sperms.
Adrenal glands are situated above the kidneys, and secrete epinephrine, which can
be considered a protective net for body emergencies. During major and severe stress
situations, epinephrine is produced in large quantities, increasing blood sugar levels,
heart rate and dilating blood vessels, putting the body in the best condition to face
crisis, and do things that normally should be impossible. It had been reported that
during a fire, a small woman was able to transport a very heavy fridge out of the
house, but afterwards it took 5 grown men to return this fridge to its original place;
this is all due to epinephrine. Therefore during Olympic trials, athletes have to submit
to drug tests; because of the concern that somebody may use epinephrine-based drugs,
causing unfairness in the competition.
Thyroid glands are located at the sides of the trachea and can be divided into thyroid
and parathyroid glands. They secrete thyroxine, which affects the metabolism of the
whole body. For growing children, insufficient thyroxine production affects mental
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and body development. Parathyroid hormones are very important for the balance of
electrolytes like calcium and phosphorus, and therefore affect bone development.
Iodine is a very important element of thyroxine: insufficient consumption of iodine
lowers thyroxine in the body, and causes thyroid swelling. At present all
commercialized salt contain iodine, to prevent deficiencies.
Pancreatic islets are specialized tissues located in the pancreas; unlike the digestive
enzymes secreted by the pancreas, hormones secreted by the pancreatic islets circulate
in the bloodstream, and affect blood sugar balance in the body. There are two types of
hormones: insulin lowers blood sugar levels, while glucagon raises blood sugar levels.
After every meal, the body digests the food, raising blood sugar levels and stimulating
insulin production. Insulin converts blood saccharides into glycogen, to be stored in
the liver. Insulin’s part in blood sugar lowering is very important, because if
production is insufficient or lacking, blood levels will skyrocket, causing diabetes.
Glucagon’s function is just the opposite: when blood sugar levels are low, insulin
production diminishes, while glucagons secretion will increase, promoting the
conversion of glycogen to blood sugar, to be used by the body. Therefore, when we
are hungry, we fell light-headed, experience tremor and clamminess; but after a while
these condition improve, because of glucagon releases saccharides in the blood.
Testis and ovaries are reproductive organs, but they are also important endocrine
glands. During puberty, luteinizing hormone and follicle-stimulating hormone
stimulate male testes to produce androgens, inducing the development of secondary
sexual characteristics, maturity of sexual organs and sperm production; in females, the
ovaries begin to produce estrogens, inducing the development of breasts, secondary
sexual characteristics and menstrual cycles.
Reviewed by：Zhang, Yong-Ta、Lu, Yu-Ling professor
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