Differentiate between endocrine and exocrine glands.
Endocrine and exocrine glands are two of the different types of glands in the body, and endocrine glands
are the only ones that are considered organs of the endocrine system (Thibodeau, 2010).
Exocrine ducts secrete their products into ducts which then empty into a different surface or cavity of
the body: endocrine glands are ductless and secrete hormones directly into intercellular spaces, where
these hormones then diffuse across membranes and into the blood where they are carried throughout
the body (Thibodeau, 2010).
Endocrine glands are found in the body in specific areas such as the neck (thyroid and parathyroid
glands), cranial (pineal, pituitary and hypothalamus), thoracic (thymus), abdominal (adrenals and
pancreatic islets) as well as pelvic cavity (ovaries and testes) (Thibodeau, 2010).
Exocrine glands are found, for example, in the skin (sweat glands), or under the tongue (salivary glands)
(Thibodeau, 2010).
Define or explain the following terms: hormone, target organ, hypersecretion, and hyposecretion.
Hormone: a substance secreted by an endocrine gland (Thibodeau, 2010)
Mosby’s Pocket Dictionary defines ‘hormone’ as “a complex chemical substance produced in one part of
an organ of the body that initiates or regulates the activity of an organ or a group of cells in another part
of the body. Hormones secreted by the endocrine glands are carried through the bloodstream to the
target organ” (Anderson & Anderson, 1990).
Target Organ: an organ or cell that is acted upon by a specific hormone and then responds to it
(Thibodeau, 2010).
“an organ most affected by a specific hormone: (Mosby’s Pocket Dictionary, Anderson & Anderson,
1990).
Hypersecretion: excessive amounts of a substance being secreted (Thibodeau, 2010).
Excessive amounts of hormones secreted can cause a myriad of problems within the body, such as
overstimulation of the thyroid and adrenal cortex hormones, gigantism or acromegaly, abnormal water
retention, inappropriate lactation in lactating women, hyperthyroidism, hypocalcemia, hypercalcemia,
Cushing Syndrome, premature sexual development, sleep disorders or winter depression, or even
severe hypoglycemia
Hyposecretion: insufficient amounts of a substance being secreted (Thibodeau, 2010).
Hyposecretion can cause a host of problems within the body as well, such as the under stimulation of
the thyroid, lack of sexual development, dwarfism, insufficient lactation in lactating mothers, prolonged
or difficult labour, hypothyroidism, cretinism, myxedema, goiter, hypo/hypercalcemia, Addison disease,
abnormal water loss, spontaneous abortion, and depression of the immune system functions.
Explain why a secondary system is needed for nonsteroid hormones but not for steroid hormones.
Non-steroid hormones are whole proteins, whereas steroid hormones are lipid-soluble, which means
they are able to pass through cell membranes and remain intact.
Non-steroid hormones must first leave the endocrine gland (‘first messengers’) and seek out their
membrane receptor sites on their target organ: they then lock into this site and release their chemical
message which in turn activates a chain of chemical reactions within the target organ cell, in turn
activating the ‘second messengers’ role of facilitating communication within the target organ
(Thibodeau, 2010).
Pick a body function (regulation of glucose or calcium levels in the blood) and explain how the
interaction of hormones is used to help maintain homeostasis.
The thyroid gland plays an important role in the balance of calcium in the blood: its hormones stimulate
cellular metabolism, a function that normal growth and development are dependent on.
The thyroid gland is different from the other endocrine glands in that it does not secrete its hormones
directly into the blood, but rather stores it as a colloid compound that is released only when needed.
There are three hormones that the thyroid gland produces: T4 (thyroxine), T3 (triiodothyroxine) and
calcitonin (CT). T3 and T4 are responsible for the stimulation of body cells to speed up their release of
energy from the metabolism of food. Calcitonin, on the other hand, is responsible for the decrease of
the calcium concentration in our blood. This is accomplished by the calcitonin acting on the bone to
inhibit its breakdown: less calcium then enters the blood.
The parathyroid glands also play a role in the homeostasis of blood calcium levels; PTH (parathyroid
hormone) is released by this gland and is capable of increasing the concentration of blood calcium by
stimulating bone resorbing cells (osteoclasts) to increase the breakdown of bone tissue. This breakdown
causes the release of calcium, which then enters the blood.
Between the calcitonin and the PTH, you can see how these hormones help balance or keep the body in
a state of homeostasis in regards to blood-calcium levels. When these levels are not maintained
properly, it can lead to conditions of too much calcium in the blood (Hypercalcemia) or not enough,
(Hypocalcemia).
References:
Thibodeau, G., & Patton, K. (2010). The Human Body in Health and Disease (5th Ed.) St. Louis, USA:
Mosby, Inc.