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AMA 176 - Anatomy &
Physiology/Medical
Terminology/Pathology 7
Endocrine System
Endocrine System
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Function: an information signaling system (like nervous
system) that uses blood vessels as information channels
(rather than nerves). Glands located all over the body
release chemical messengers called hormones which regulate
specific bodily functions; e.g. growth, puberty, metabolism,
reproduction, etc. Help to maintain homeostasis or balance in
the body.
Hormones: work by binding to sites on various tissues that
recognize them causing the intended biological effect,
somewhat like a lock and key. Each receptor is the lock and
the specific hormone that is attracted to that receptor is
the key that opens that lock and causes the intended
biological effect. (e.g. the pituitary gland secretes growth
hormone that opens the “lock” in bones and tissues and
causes growth).
Structure of the Endocrine
System
Two types of glands:
 Endocrine: secrete hormones into the
bloodstream. (examples: pineal, thymus,
thyroid, parathyroid, adrenal, pancreas,
pituitary, ovaries, testes)
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Exocrine: send chemical substances (tears,
sweat, saliva) via ducts to the outside of
the body. (examples: sweat, mammary,
mucous, salivary, lacrimal (tear) glands)
Pineal & Thymus:
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Pineal: located in the brain. Secretes
melatonin to regulate the body’s
“biological clock”.
Thymus: located behind the sternum.
Produces thymosin and T-cells and is
responsible for immune responses (more
so in childhood, shrinks as we age).
Thyroid:
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Located in the neck.
Secretes thyroxine (tetraiodothyronine)
(T4) and triiodothyronine (T3).
These are hormones synthesized from
iodine from the bloodstream; necessary to
maintain metabolism by helping cells take in
oxygen.
Parathyroid:
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Located on either side of the thyroid in
the neck (four small oval bodies).
Parathyroid hormone (PTH) takes
calcium from bones and puts it into the
bloodstream to help with proper
functioning of body tissues, especially
the muscles.
Adrenal:
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Two small glands on top of each kidney. Composed of two
parts; an inner (medulla) and outer (cortex) portion.
Cortex: secretes corticosteroids (complex chemicals made
from cholesterol)
Cortisol to regulate glucose, fat and protein metabolism
Aldosterone to regulate electrolytes or salts
Androgens and Estrogens to regulate male and female sex
characteristics
Medulla: secretes catecholamines (chemicals made from
amino acids).
Epinephrine to increase heart rate and BP, dilate bronchial
tubes, release glucose and glycogen for more energy – “flight
or fight”
Norepinephrine constricts blood vessels to raise BP)
Pancreas:
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Located near stomach
Made of specialized hormone producing
cells called the islets of Langerhans
that produce insulin and glucagon which
regulate blood sugar levels.
Also secretes digestive enzymes into
the digestive tract.
Pituitary:
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Also called hypophysis; small pea-sized gland
located in brain.
The hypothalamus in the brain sends signals
to cause the pituitary to release or inhibit
many hormones such as growth, thyroid
stimulation, pregnancy, etc.
Basically the pituitary hormones tell other
glands what to do.
Ovaries & Testes:
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Ovaries: located in the lower abdomen in
females. Produce eggs (gamete or ovum) as
well as hormones responsible for female
sex characteristics and regulation of the
menstrual cycle.
Testes: located in the inguinal region of
the male, suspended in the scrotum.
Produce sperm and testosterone
responsible for male sex characteristics.