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:::Index>Profound Human World>Knowledge Acquisition>Internal
Regulation>Knowledge of Endocrine System
Knowledge of Endocrine System
Tissues or organs that are composed by cells with secretive functions are called glands.
Substances secreted by some gland cells necessitates of a duct for the excretion of the
substances, therefore these kind of glands are called exocrine glands, as for example
the liver needs bile ducts to transport the bile it secretes to the small intestine. Other
glands do not need special ducts, but use the blood stream to transport their secretions:
these kind of glands are called endocrine glands.
The human body uses hormones secreted by endocrine glands to regulate
physiological functions: too much or not enough, or wrong timing can all cause
distress to the body. Let us review some of the most important endocrine glands in the
human body.
Pituitary gland
The pituitary gland is situated below the brain, and is no larger in size than a pea.
This gland secretes a great variety of hormones, such as: the growth hormone
regulates body growth (weight and height), insufficient growth hormone during
infancy causes dwarfism, whereas overproduction causes gigantism. The pituitary
gland also secretes many other hormones that regulates the secretion of other
endocrine glands, therefore is called the chief commander of the endocrine system.
Gonads
Gonads are different in men and women: males have testes, and females have ovaries.
The testes secrete androgens that promote sperm growth and maturity, therefore
influencing the development of secondary sexual characteristics, such as facial hair
growth, prominent Adam’s apple and deepening voice. The ovaries secrete estrogens
that promote ova growth and maturity, therefore influencing the development of
secondary sexual characteristics, such as wider hips, menstrual cycles and breast
development.
Thyroid gland
The thyroid gland is situated at the sides of the trachea and is shaped like a butterfly.
The thyroid secretes thyroxine, which plays a very important role in the regulation of
growth and metabolism. Hypothyroidism during infancy may cause cretinism, stunt
growth and mental retardation, whereas hyperthyroidism has many symptoms, like
increased appetite coupled with weight loss, irritability, insomnia and loss of memory,
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heart palpitations and shortness of breath.
Adrenal glands
Adrenal glands are situated above the kidneys, and secrete adrenaline. Adrenaline
promotes the conversion of glycogen to glucose, increases blood sugar level, heart
rate, and blood pressure, relaxes muscular blood vessels, inhibits the stomach and
intestinal action, and regulates stress response.
Pancreatic isles
Pancreatic isles are part of the pancreas, and secrete insulin and glucagons. Insulin
promotes cell utilization of blood sugars, or converts blood sugars into glycogen to be
stored in the liver, therefore lowering blood sugar levels. Glucagon promotes the
breakdown of glycogen and raises blood sugar levels. Insulin deficiency causes high
blood sugar levels, causing a disease condition called diabetes.
Reviewed by：Zhang, Yong-Ta、Lu, Ting-Wei professor
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