like the
nervous system, the endocrine system controls body activities, but it acts much
more slowly. The endocrine glands produce chemical molecules called hormones
and release them into the blood to travel to relatively distant target organs.
PITUITARY GLAND- the pituitary gland is approximately
the size of the grape. It hangs by a stalk from the inferior surface of the
hypothalamus of the brain, where it is snugly surrounded by the “Turk’s saddle”
of the sphenoid bone. It has two functional lobes- the anterior pituitary
(glandular tissue) and the posterior pituitary (nervous tissue).
GROWTH HORMONE (GH)- is a general metabolic hormone.
However, its major effects are directed to the growth of skeletal muscles and long
bones of the body, and thus it plays an important role in determining final
body size. GH is a protein sparing and anabolic hormone that causes amino acids
to be built into proteins and stimulates most target cells to growth in size
and divide. At the same time, it causes fats to be broken down and used for
energy while it spares glucose, helping to maintain blood sugar homeostasis.
THYROID GLAND- the thyroid gland is a hormone
producing gland that Is familiar to most people primarily because many obese
individuals blame their overweight condition on their “glands” (meaning the
thyroid) actually, the effect of thyroid hormones on the body weight is not as
great as many believe to it to be. The thyroid gland is located at the base of
the throat, just inferior to the Adam’s apple, where it is easily palpated
during physical examination. It is a fairly large gland consisting of two lobes
joined by a central mass, or isthmus. The thyroid gland produces two hormones,
one called thyroid hormone, and the other called calcitonin. Internally, the
thyroid gland is composed of hollow structures called follicles, which store a
sticky colloidal material. Thyroid hormone is derived from this colloid.
PARATHYROID GLANDS- the parathyroid glands are tiny
masses of glandular tissue most often found on the posterior surface of the
thyroid gland. Typically there are two glands on each thyroid lobe; that is, a
total of four, but as many as eight have been reported, and some may be in
other regions of the neck. The parathyroid secretes parathyroid hormone (PTH),
or parathormone, which is the most
important regulator of calcium ion homeostasis of the blood. When blood calcium
blood levels drop below a certain level, the parathyroid release PTH, which
stimulate bone destruction cells (osteoclasts) to break down bone matrix and
release calcium into the blood. Thus, PTH is a hypercalcemic hormone (that is,
it acts to increase blood levels of calcium), whereas calcitonin is a
hypercalcemic hormone as they control blood calcium level. Although the
skeleton is the major PTH target, PTH also stimulates the kidneys and intestine
to absorb more calcium (from urinary filtrate and foodstuffs, respectively).
ADRENAL GLANDS- the two bean-shaped adrenal glands
curve over the top of the kidneys. Although the adrenal glands looks like a
single organ, it is structurally and functionally two endocrine organ in one.
Much like the pituitary gland, it has glandular (cortex) and neural tissue
(medulla) parts. The central medulla region is enclosed by the adrenal cortex,
which contains three separate layers of cells.
·
ADRENAL MEDULA- it produces hormone called
epinephrine and norepinephrine which raise blood glucose level; increase rate
of metabolism; constrict certain blood vessels.
·
ADRENAL CORTEX- it produces glucocortoids which
increase blood glucose and mineralocorticoids which promote reabsorption of
sodium and excretion of potassium in kidneys.
PANCREATIC ISLETS- the pancreas, located closed to the
stomach in the abdominal cavity, is a mixed gland. Probably the best-hidden
endocrine glands in the body are the pancreatic islets, formerly called the
islets of Langerhans. These little masses of hormone-producing tissue are
scattered among the enzyme-producing acinar tissue of the pancreas. The
exocrine (enzyme producing) part of the pancreas, which acts as part of the
digestive system. It produces insulin which reduces blood glucose and glucagon
which raises blood glucose.
PINEAL GLAND- the pineal body also called the
pineal gland, is a small, cone-shaped gland found in the roof of the third
ventricle of the brain. The endocrine function of this tiny gland is still
somewhat of a mystery. Although many chemical substances have been identified
in pineal gland, only the hormone melatonin appears to be secreted in
substantial amounts. The levels of melatonin rise and fall during the course of
the day and night. Peak levels occur at night and make us drowsy; the lowest level
occurs during daylight around noon. Melatonin is believed to be a “sleep
trigger” that plays an important role in establishing the body’s day and night
cycle. In some animals, melatonin also helps regulate mating behaviour and
rhythms. In some humans, it is believed to coordinate the hormones of fertility
and to inhibit the reproduction system (specially the ovaries of females) so
that sexual maturation is prevented from occurring before adult body size has
been reached.
THYMUS GLAND- the thymus gland is located in the
upper thorax, posterior to the sternum. Large in infants and children, it
decreases in size throughout adulthood. By old age, it is composed mostly of
fibrous connective tissue and fat. The thymus produces hormone called thymosin,
and during childhood the thymus acts as an incubator for the maturation of a
special group of white blood cells that are important in the immune
response.
·
TESTIS (male)- it produce hormone called androgen's which support sperm formation; development and maintenance of male secondary
sex characteristics.
·
ESTROGENS (female)- it produce hormone called estrogens which
stimulate uterine lining growth; development and maintenance of female
secondary characteristics, and progesterone which promote growth of uterine
lining.
PREPARED BY: LEOMIDEE BUENDIA MW 2:30-4:00
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