SBI4U



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 |Observation |

|1 |Gland removed |Urine output increased; Na+ concentration in urine increased; ACTH blood level|

| | |increased |

|2 |Hormone injected |Blood glucose levels decreased |

|3 |Blood flow from the posterior pituitary |Urine production increased |

| |reduced | |

|4 |Hormone injected |Glycogen converted to glucose in liver; blood glucose levels increased |

6. Cortisone, a drug chemically very similar to cortisol, is often prescribed as an anti-inflammatory. 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.

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