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SBI4U
Endocrine System
Use information from Chapter 8 (p370-399) to answer the following questions.
1. Compare exocrine and endocrine glands, in terms of description and products.
Endocrine: glands that secrete chemicals directly into the bloodstream;
product = hormones
Excocrine: glands that secrete chemicals through ducts into a body cavity or on
to a surface; products = digestive enzymes, sweat, etc.
2. (a) Briefly describe how von Mering and Minkowski established that a hormone was
responsible for regulating blood sugar.
They removed the pancreas of healthy dogs and found that they lost weight
rapidly and became fatigued. Analysis of their urine showed that it contained
glucose while the healthy dogs’ urine did not. This experiment was used later as
proof that the pancreas contained a hormone responsible for glucose regulation
(b) The above experiment is typical of the “classical” approach to medical
experimentation. Explain why this approach has limited effectiveness.
This type of approach is a very blunt instrument; involving removal of an organ
or gland. The problem is that many glands produce more than one type of
hormone, and often their effects are interconnected. It is difficult to sort out one
specific hormone’s function by using this type of approach.
(c) What technological advances have improved our recent understanding of the
endocrine system?
Radioactive tracers, chemical analysis equipment (i.e. spectroscopy,
spectrophotometry & gas chromatographs), high-powered microscopes
3. Although hormones are sometimes sent into the bloodstream far away from their target
sites, they don’t act upon any cells except for the target. How are hormones able to be so
specific?
Target cells have receptors on their membranes that are specific to a hormone.
Also, the numbers of receptors differ depending on the activity of the hormone
and type of cell.
4. How can blood sugar levels be increased, and what advantage does this give in times
of stress?
Glycogen must me metabolized into glucose (taken out of storage). This gives a
readily available source of energy, so body tissues can carry out respiration and
make more ATP, meaning that whole-body responses can occur more quickly.
5. A number of laboratory experiments were conducted on mice, which have a similar
endocrine system to humans. Summaries of the experiments are provided in Table 2.
(a) In procedure 1, identify the gland that was removed and explain why the levels of
ACTH increased.
The adrenal cortex has been removed. Cortisol exerts a negative feedback
response that normally decreases the ACTH in the blood. If cortisol is not
produced by the adrenal cortex, ACTH cannot be used, so ACTH levels rise.
(b) In procedure 2, identify the hormone that was injected and explain why blood
sugar levels decreased.
Insulin has been injected. Insulin increases the permeability of the cells to
glucose. Glucose diffuses from the blood into the body’s cells, decreasing blood
glucose levels.
(c) In procedure 3, identify the hormone that was affected and explain why urine
production increased.
ADH was affected. ADH is produced in the posterior pituitary and is normally
carried in the blood. If blood cannot move from the posterior pituitary to other
regions of the body, ADH also cannot move. ADH signals to the body to
reabsorb water from the nephron. No ADH = less water re-absorption, resulting
in more urine.
(d) In procedure 4, identify the hormone that was injected and explain why blood
glucose levels increased.
Glucagon was injected. Glucagon stimulates the conversion of glycogen into
glucose in the liver and muscles. Glucose diffuses into the blood
Table 2
Procedure
1
Gland removed
2
3
4
Hormone injected
Blood flow from the
posterior pituitary reduced
Hormone injected
Observation
Urine output increased; Na+ concentration in urine
increased; ACTH blood level increased
Blood glucose levels decreased
Urine production increased
Glycogen converted to glucose in liver; blood
glucose levels increased
6. Cortisone, a drug chemically very similar to cortisol, is often prescribed as an antiinflammatory. Why would doctors be hesitant to prescribe it for a long duration of time?
It increases the metabolic rate and increases blood sugar. Both of these
responses are safe in the short term, but dangerous to sustain over long periods
of time. These lead to common side effects including mood changes, bone
deterioration, weight gain, etc.
7. What is a goiter and why does it create a problem?
A goiter is an enlargement of the thyroid gland. Since it is located in the throat
area, it can interfere with the trachea and esophagus, creating difficulty with
breathing, swallowing and voice, and can also lead to compression of blood
vessels in the neck.
8. (a) What is EPO, and what advantage does it give athletes?
Erythropoietin. EPO boosts red blood cell production, increasing transport of
oxygen to the tissues. More oxygen = more energy = better performance. This is
what our friend Lance Armstrong has been taking! Injecting EPO and then
later filtering out your blood is sometimes referred to as blood doping.
(b) In what environmental situation might EPO levels naturally rise in the body?
EPO is a type of growth hormone that occurs naturally in the body. When
exposed repeated to low atmospheric oxygen levels, more EPO is produced by
the adrenal cortex as past of a negative feedback mechanism. People living at
high altitudes (where oxygen levels are low) naturally have higher EPO levels,
and thus more red blood cells.
(c) How has EPO been used medicinally?
EPO has been used as a treatment for anemia (low red blood cell count or poor
oxygen distribution).
(d) How is EPO dangerous?
High RBC count leads to blood that is thick and difficult for the heart to pump.
Blood clots easily and the heart becomes overworked.
9. Explain why a marathon runner would be unlikely to take growth hormone or anabolic
steroids.
Marathon runners need improved oxygen delivery systems, but not increased
muscle mass, which is what growth hormone and anabolic steroids deliver.
10. (a) Using LH and testosterone as examples, explain the mechanism of negative
feedback.
LH is released from the pituitary gland at puberty, acting on the testicular cells
to produce testosterone. Testosterone itself increases sperm production. Once
high levels of testosterone are detected by the hypothalamus, LH production is
inhibited. This is negative feedback
(b) Give an example of a negative feedback system found in the female reproductive
system.
FSH stimulates the production of estrogen via follicular development. As
estrogen rises, a message is sent to the pituitary to stop production and secretion
of FSH
11. Describe how the corpus luteum forms in the ovary.
The corpus luteum is formed by follicle cells that previously surrounded the
dominant follicle cell but remain in the ovary after release of the secondary
oocyte. The corpus luteum secreted the hormones estrogen and progesterone. If
pregnancy does not occur, the corpus luteum degenerates after about 10 days.