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The Endocrine System
Hypothalamus
Thyroid
gland
Adrenal
glands
Testicles
(men)
Pineal gland
Pituitary gland
Parathyroid
gland
Pancreas
Ovaries
(women)
Endocrine System (I)
 Cells, organs, and functions in the human
or animal body are regulated practically every
day by the endocrine system.
 Structurally, the endocrine system is a
collection of ductless glands that secrete
chemical messages known as hormones.
 Main function of the endocrine network is
to maintain homeostasis of and long-term
control in the body by means of chemical
signals. It works in parallel with the nervous
system to control many body functions.
Endocrine System (II)
 The glands that make up the (human’s)
endocrine system are hypothalamus, pituitary,
thyroid, parathyroid, adrenals, pineal body,
pancreas, ovaries, and testicles.
 The primary function of these glands is to
synthesize and secrete hormones.
 Acting as body’s messengers, hormones
transfer information and instructions from one
set of cells to another; the shape of each
hormone molecule is specific and can bind to
certain cellular receptors only.
Human Endocrine System
major glands
Hypothalamus, Pituitary
 The hypothalamus is located below the
thalamus, in the lower center part of the brain;
beneath this gland is the pituitary, which has
the size of a pea. Together, these two glands
control many other endocrine functions.
 Hormones from the two glands are crucial
to pregnancy, birth, lactation, and a woman’s
menstrual cycle, including ovulation.
 Growth hormone and antidiuretic hormone
are also crucial hormones secreted by the
anterior and posterior pituitary, respectively.
(Para)Thyroid, Adrenals
 Thyroid is located in the front and middle
of the lower neck; thyroxine and T3 are two
important hormones from this gland.
 Located within each of the thyroid lobes
are a pair of tiny oval-shaped glands called
parathyroid; hormones from this gland are the
most important regulator of serum calcium.
 The two adrenals are each situated atop of
each kidney; their corticosteroid and catecholamine hormones play an important role in
metabolism, the immune system, and stress.
Pineal, Pancreas
 The pineal body is located near the center
of the brain, having the shape of a tiny clone;
its hormone melatonin has significant effects
on reproduction and daily physiologic cycles,
most notably the circadian rhythms.
 Pancreas has both exocrine and endocrine
functions; its bulk is a ducted gland secreting
digestive enzymes into the small intestine. Its
endocrine function is by means of its many
small clusters of endocrine cells, from which
the hormones glucagons and insulin play an
important role in regulating blood sugar level.
Ovaries, Testicles
 The female ovaries and the male testicles,
responsible for many sex characteristics, are
referred to as the gonad glands or sex organs.
 Female ovaries synthesize the hormones
estrogen and progesterone in varying amounts
depending on where in her cycle a woman is.
 Testicular production of the sex hormone
testosterone (a principle androgen) begins
during fetal development, continues for a
short time after birth, nearly ceases during
childhood, and then resumes at puberty.

How does the Endocrine system work
The endocrine system is regulated by feedback in
much the same way that a thermostat regulates
the temperature in a room. For the hormones that
are regulated by the pituitary gland, a signal is
sent from the hypothalamus to the pituitary
gland in the form of a “releasing hormone,” which
stimulates the pituitary to secrete a “stimulating
hormone” into the circulation.
Endocrine (continued)
The stimulating hormone then signals the target
gland to secrete its hormone. As the level of this
hormone rises in the circulation, the hypothalamus
and the pituitary gland shut down secretion of the
releasing hormone and the stimulating hormone,
which in turn slows the secretion by the target
gland. This system results in stable blood
concentrations of the hormones that are regulated
by the pituitary gland
Feedback control

Feedback control is a homeostasis
mechanism used by the body to maintain
a constant internal environment. If the
brain receives impulses to communicate
there is too much or too little of a
substance, then impulses are sent to the
relevant organs to return the situation to
normal
How is feedback seen
Temperature control
 Body fluids

Temperature control

Since the human body maintains a
constant body temperature, therefore
there must be ways in which the body
adjusts its internal processes as the
external temperature changes.