Have you ever wondered how our body
achieves internal equilibrium or homeostasis? What system is responsible for
regulating organs and organ systems? And how is it possible to maintain such
balance?
Balance is
important in all aspects of life. In the human body, the existence and maintenance
of a constant environment with respect to functions and the composition of
fluids and tissues (known as homeostasis) depends on the regulation of the
organs and systems. The nervous and
endocrine systems are the two major systems responsible for that regulation.
Today, we’ll focus on the ENDOCRINE SYSTEM.
The word endocrine is derived from the Greek
words endo and krino meaning “within” and to “separate.” This means that
intercellular chemical signals
(molecules released from one location that move to another location to
produce a response) are produced within and secreted from endocrine glands,
but they have effects at locations that
are distinct or away from the glands that secrete them.
These chemical
signals referred to above are called hormones, derived from the Greek word hormon
which means to “set into motion”. Hormones act on tissues at another site in
the body to influence their activity in a specific way. Only certain tissues,
called target tissues, can respond to a certain type of hormone.
When we deal
with the endocrine glands and the hormones they secrete, we are basically
talking about Endocrinology. Endocrinology is the study of the biosynthesis,
storage, chemistry and functions of hormones and the endocrine glands that are
responsible for producing or secreting them; Endocrinology is a world all about
HORMONES. Interesting, isn’t?
Hormones
regulate a lot of processes in our body. Since endocrinology deals with hormones,
let me introduce you to them:
The PITUITARY
GLAND located at the inferior aspect of the brain is divided into anterior and
posterior lobes. The anterior lobe secretes
growth hormone (GH) which affects
growth of bones and muscles, influences protein, lipid, carbohydrate and
calcium metabolism. Prolactin affects
mammary glands to stimulate milk production. Thyroid-stimulating hormone stimulated thyroid hormone production. Adrenocorticotropic hormone (ACTH) stimulates
the adrenal cortex to produce steroids. Follicle-stimulating
hormone stimulates ovaries to develop follicles and secrete estrogen of
stimulates testes to develop seminiferous tubules and perform spermatogenesis. Luteinizing hormone stimulates ovaries
to initiate ovulation and produce progesterone in females or stimulates testes
to secrete testosterone in males. The posterior
lobe secrete oxytocin stimulates
uterine and mammary gland contractions and antidiuretic
hormone (ADH) acts on the distal renal tubule to increase water
reabsorption.
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| Figure 1 The Pituitary Gland Hormones and their Target Tissues |
The THYROID
GLAND, a butterfly shaped gland located in the neck behind the trachea produces
three hormones: T3 and T4 regulate
cellular metabolic activity. Thyrocalcitonin
tones down or lowers calcium level in the body.
PARATHYROID
GLANDS, usually four glands, surround the posterior thyroid tissue secrete parathormone which raises blood calcium
levels by increasing calcium resorption fro kidneys, intestines and bones.
ADRENAL GLANDS
located at the upper poles of both kidneys contain two distinct types of
endocrine tissue: ADRENAL MEDULLA produces the epinephrine or adrenalin which prepares the body for
fight-or-flight response by converting glycogen to glucose. Norepinephrine, another hormone
secreted by the adrenal medulla produces effects similar to epinephrine. The
ADRENAL CORTEX secretes mineralocorticoids
which increase sodium reabsorption and potassium loss, glucocorticoids increase blood glucose and decrease protein
synthesis and the adrenal sex hormones govern
the development of certain secondary sex characteristics.
The PANCREAS, a
slender elongated organ lying horizontally in the posterior abdomen behind the
stomach has both endocrine and exocrine functions. Its endocrine functions are
controlled by the alpha, beta, and delta cells of the islets of Langerhans.
GONADS consist
of ovaries and testes, whose involved
primarily in reproduction.
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| Figure 2 The Major Endocrine Glands and Their Locations in the Human Body |
In order to
maintain balance within the body, a healthy endocrine glands, properly
functioning blood supply to move hormones through the body to their target
tissues, receptor sites on the target cells for the hormones to do their work
and a feedback system to control how and when these hormones are produced and
used are all key ingredients. Disruption in that system can cause major
problems that may require medical intervention.
References:
Seeley, R. et al. Essentials of
Anatomy and Physiology 5th ed. McGraw-Hill Companies,
Inc. New York, 2005. page 278
Hargrove-Huttel, Ray.
Medical-Surgical Nursing 4th ed. Lippincott Williams and Wilkins, Philadelphia,
2005. pages 217-220
images from www.google.com
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