Endocrine System Review:
Questions and Answers
1. Distinguish between endocrine glands and exocrine glands.
Exocrine glands retain their connection to the epithelial surface, which may be
external (for example, sweat and tear glands) or internal (for example, the pancreas
and salivary glands), using a duct.
Endocrine glands: do not have ducts but are full of blood capillaries; secrete
hormones directly into the blood, for example, thyroid, adrenal, and pituitary glands
2. Define or describe hormone, target cell, hypersecretion, and hyposecretion.
Hormone: A chemically active substance secreted by a group of cells to regulate the
functions of other cell types.
Target cell: A cell that has specific receptors (binding sites) for a particular hormone.
Hypersecretion: excessive production of a hormone.
Hyposecretion: inadequate secretion of a hormone.
3. Explain the mechanism of action of nonsteroid hormones.
Hormone-receptor interaction (first messenger), Enzyme activation, Release of the
second messenger, Effects on cellular function
4. Describe the mode of action of steroid hormones.
They move along the cytoplasm and into the nucleus where they bind to a receptor
(lock-and-key model).
5. Describe and provide an example of a negative feedback mechanism involved in
the regulation of hormone release.
An increase in the level of blood glucose stimulates the secretion of insulin by the
pancreatic beta cells. Because insulin facilitates the uptake of glucose by cellular
organisms, the blood glucose level is returned to its base, normal level, and any
surplus gets stored as glycogen in the liver.
6. Define the concept of a positive feedback loop in endocrine control, and provide
a suitable example.
Oxytocin, which is the hormone released during the process of labor, stimulates
uterine contractions that lead to the further release of oxytocin. The build-up must
be rapid because it enables the process of labor to proceed quickly, thus
safeguarding the health of the mother and baby.
7. Explain the difference between prostaglandins and hormones. List some
physiological processes that can be influenced by prostaglandins.
Prostaglandins are the cause of starting inflammation and formation of a blood clot
within the injured tissue while the hormones are the main class of growth and
developmental regulatory molecules, metabolism, and reproduction.
Prostaglandin roles:
Stimulating the inflammatory response and fever production, and pain in tissue
damage. Prostaglandins are generated due to the flow of white blood towards the
area of tissue damage.
Blood clotting occurs following a vessel damage. Thromboxane is a category of
prostaglandins that favors the clotting of blood.
Induction of labor. Prostaglandins such as PGE2 are accountable for the contractions
of the uterus, which bring about labor.
Prostaglandins also serve roles in other systems, such as the gastrointestinal tract,
kidneys, and bronchi.
8. Describe the structure of the pituitary gland and its location.
The Pituitary gland is a two-lobed gland that secretes important hormones, the two
lobes are:
Adenohypophysis: the anterior lobe, made up of glandular tissue which produces
and secretes several hormones and Neurohypophysis: the posterior lobe (neural
tissue) that receives, stores, and releases hormones from the hypothalamus and this
gland is found in the diencephalon.
9. Name the four tropic hormones released by the anterior pituitary gland and state
briefly their function.
Thyroid-Stimulating Hormone (TSH):
Stimulates the thyroid gland to release thyroxine (T4) and triiodothyronine (T3),
which regulate metabolism.
Adrenocorticotropic Hormone (ACTH):
Stimulates the adrenal cortex to release glucocorticoids, mainly cortisol, that help
the body respond to stress and regulate metabolism and inflammation.
Follicle-Stimulating Hormone (FSH):
In females, stimulates growth of ovarian follicles and release of estrogen. In males, it
supports spermatogenesis in the testes.
Luteinizing Hormone (LH):
In females, it induces ovulation and causes the secretion of progesterone. In males,
it activates the Leydig cells of the testes to secrete testosterone.
10. Describe the role of growth hormone.
It promotes growth by speeding up protein anabolism - Speeds up fat catabolism
and slows down glucose catabolism, and then, by slowing down glucose catabolism,
tends to raise blood glucose to a level greater than normal (hyperglycemia).
11. Outline the function of ADH.
It attaches to V2 receptors on the principal cells of the collecting ducts and distal
convoluted tubules.
Via adenylate cyclase/cAMP induces the production of specific proteins into the
luminal membrane and enhances the permeability of the cell to water.
Enhanced membrane permeability to water allows back diffusion of free water,
leading to elevated urine osmolality (concentrates urine).
12. Describe the roles of oxytocin and prolactin.
PRL: Stimulates breast development during pregnancy and milk release after the
baby is born
Oxytocin: Stimulates pregnant uterus to contract - May initiate labor - Stimulates
glandular cells of the breast to release milk into ducts - Promotes social bonding
13. Describe the role of the hypothalamus in the endocrine system.
The production of ADH and oxytocin actually occurs in the hypothalamus, and
nervous stimuli for it are accountable for provoking regulation of posterior pituitary
secretions.
14. Describe the distinction between T3 and T4. What is special about the thyroid
gland?
T3 works in fetal bone and connective tissue development, resting respiratory rate
regulation, induction of alertness, growth hormone secretion, ovarian cycle, and
protein synthesis, while T4 works in muscle and heart function, weight management,
bone strength, and aiding brain development.
Thyroid gland is the sole endocrine gland that holds significant quantities of its
hormones (T3 and T4) in a proteinous substance called colloid extracellularly. The
gland is the sole organ requiring iodine in hormone synthesis and hence is the sole
critical nutrient for iodine. Both calcitonin, which is involved in the regulation of
calcium, and metabolic hormones (T3 and T4) are secreted from the gland.
Additionally, it is the largest pure endocrine gland of the body and is well
vascularized, which results in an extremely efficient delivery of hormones.
15. Identify the hormones secreted by the various zones or regions of the adrenal
cortex.
Zona glomerulosa: Mineralocorticoids (Aldosterone)
Zona fasciculata: Glucocorticoids (hydroCortisol)
Zona reticularis: Androgens (Small amounts of male hormones (androgens) secreted
by the adrenal cortex of both males and females)
16. Describe the role of Aldosterone.
It balances Na+ by minimizing the removal of Na+ from the body. It stimulates the
reabsorption of Na+ by the distal tubule and collecting duct of the kidneys.
Stimulates the active secretion of potassium from the tubular cell into the urine. - It
also stimulates sodium & potassium transport in sweat glands, salivary glands, &
intestinal epithelial cells.
17. Describe the role of glucocorticoids.
They play a vital role in metabolic regulation by increasing blood glucose levels via
gluconeogenesis, inhibiting inflammation and immune responses, and aiding the
body's response to stress. They also impact blood pressure and the balance of fluids.
Analytical Reasoning:
18. Explain why a second messenger system is necessary for nonsteroid hormones
but not necessary for steroid hormones.
A secondary messenger system is required for nonsteroid hormones due to their
insolubility in lipids, which makes them unable to cross the cell membrane. These
hormones instead bind to receptors on the surface of target cells, which in turn
stimulates the activation of a secondary messenger (e.g., cAMP) in the intracellular
milieu to stimulate a response. In contrast to other hormones, steroid hormones
exhibit lipid solubility, thus enabling them to easily cross the cell membrane and
bind to intracellular receptors. Because of this characteristic, they have a direct
effect on gene expression without utilizing a secondary messenger.
19. Select a physiological process, i.e., the regulation of glucose or calcium
concentration in the blood, and describe how hormone interactions assist in
bringing about homeostasis.
The metabolic breakdown of blood glucose is regulated by the balance between
glucagon and insulin. Insulin is secreted by the pancreas in reaction to increased
concentrations of blood glucose, stimulating the uptake of glucose by cells and
promoting the deposition of excess glucose as glycogen in the liver.
For low blood glucose levels, the pancreas secretes glucagon, which has the effect of
breaking down glycogen to glucose and back into the bloodstream. The balance of
these hormones provides homeostasis by regulating blood glucose concentrations
within an acceptable range.
20. What would be the physiological effects on the body following the removal of
the thyroid gland?
If the thyroid gland were eliminated, the body would be deprived of thyroid
hormones (T3 and T4), which are necessary for the regulation of metabolism, heart
rate, body temperature, and growth. Consequently, the patient would suffer from
symptoms such as fatigue, weight gain, intolerance to cold, depression, and a
decline in physical and mental functions. Moreover, because the thyroid also
produces calcitonin, calcium homeostasis would be mildly disturbed, although the
parathyroid glands regulate this.
21. If a doctor discovered that a patient had very low thyroxine levels but high TSH
levels, would the patient's problem be with the thyroid gland or the pituitary gland?
Explain your answer
The defect is in the thyroid gland. It is also called primary hypothyroidism. The
pituitary gland is functioning properly, and it secretes more TSH to encourage
thyroid function. The thyroid gland does not appropriately respond by not
producing sufficient thyroxine and hence shows that the defect is in the thyroid
gland itself.