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Module 2

1. Module 2

1.23. Page 4

Lesson 3

Module 2—The Endocrine System

The Adrenal Cortex—Regulating Long-Term Stress

 

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The sadness experienced by the woman in this picture, who may have lost a loved one, can stimulate the long-term stress response and potentially harmful effects.

© Fouquin/shutterstock

Cortisol, which is produced by the adrenal cortex, is thought to be the most important glucocorticoid in humans. It is primarily concerned with glucose metabolism during periods of long-term stress, such as engaging in athletic competition and writing Diploma Exams. It also plays a role in increasing blood pressure when it works in concert with the sympathetic nervous system and the release of epinephrine and norepinephrine by the adrenal medulla. After a time, the stress responses fade, and normal conditions are restored in part by the parasympathetic nervous system. In the Student Stress lab your partner slowly returned to normal after you had stressed him or her out. If the stress-producing stimuli persist, the danger to the body can include an excessively high metabolic rate, high blood pressure, and an elevated heart rate for a prolonged period of time—or long-term stress responses. This is particularly damaging for the circulatory system and is a contributing factor in increasing the risk of heart attacks and atherosclerosis, which you studied in Biology 20.

 

cortisol: also called hydrocortisone or cortisone; involved in enhancing short-term stress responses and in stimulating conversion of protein and fat into glucose

 

Cortisol is secreted in highest amounts in humans and is produced by the adrenal cortex in response to stimulation by ACTH.

 

glucocorticoids: a group of hormones produced by the adrenal cortex, of which cortisol is of prime importance; influence glucose metabolism from protein and fat and immune function by suppressing inflammation

 

long-term stress responses: responses, mainly stimulated by cortisol, which are of long duration


 

Cortisol also acts to suppress inflammation, and is sometimes used in the treatment of arthritis and allergies. Side effects, such as reducing immune system effectiveness, limit its usefulness.

 

You can further your understanding of the role that cortisol plays in returning the body to  homeostasis by reading pages 453 and 454 of your textbook or by watching the following video segments of “The Adrenal Glands and the Gonads: Stress and Sexuality: Vital to Life.” Whichever you choose to do, make notes to support your understanding and file them in your course folder for later review.

 

If you choose to watch the videos, you may be required to enter a username and password to access the videos. Contact your teacher for this information.

  • “Adrenal Cortex”
  • “Bio Fact: Glucocorticoid Hormones”
Regulating Cortisol Release

 

Cortisol is secreted in response to ACTH when the anterior pituitary is stimulated by releasing hormone from the hypothalamus. Secretion is decreased by negative feedback exerted on the anterior pituitary and the hypothalamus, as outlined in the general regulatory pathway of tropic hormones in “Figure 13.10” on page 441 of your textbook and in the following segment of “The Adrenal Glands and the Gonads: Stress and Sexuality: Vital to Life.”

  • “Adrenocorticotropic Hormone”

This is one of the more simple feedback loops that you will study in this module. The information that you have learned about cortisol could be easily summarized in a well-labelled feedback loop diagram for your course folder.

 

Self-Check

 

Use the following information to answer the next four questions, remembering that your responses must include well-explained steps that follow a sequential order of the events. After checking your answers, file them in your course folder. Consult with your teacher if you do not understand any questions or answers or if you need feedback about the detail of your responses.

 

Due to tiny tumours growing in Emily’s anterior pituitary, she overproduces ACTH, which, in turn, stimulates oversecretion of cortisol. The cortisol maintains a high metabolic rate by burning protein and fat; constricts her blood vessels, causing an increase in her blood pressure; and causes her heart to race constantly.

 

SC 4. Draw a feedback loop that would illustrate this disruption in Emily’s production of cortisol.

 

SC 5. Before treatment, Emily’s blood glucose was abnormally high. Explain how this situation could have been the result of overproduction of cortisol.

 

SC 6. Emily’s heart rate and blood pressure were elevated around the clock. Explain why this is a potentially life-threatening situation.

 

SC 7. Emily was very prone to infections, such as colds, laryngitis, and bronchitis. Explain why this was probably the result of elevated cortisol levels.

 

Check your work.
Self-Check Answers

 

SC 4. The feedback loop should illustrate the positive feedback in the tropic regulatory pathway for cortisol and aldosterone. It should resemble the one shown below, but could be drawn horizontally rather than vertically. Boxes could be placed around the words hypothalamus, anterior pituitary, and adrenal cortex.

 

A flow chart containing four vertically organized boxes is shown. Downward arrows connect the boxes. The upper most box is titled “hypothalamus,” and the arrow from this box is labelled “releasing hormone.” The second box is titled “anterior pituitary,” and the arrow form this box is labelled “ACTH.” The third box is titled “adrenal cortex.” The fourth fox is titled “cortisol/aldosterone.” Within the fourth box is an upward arrow. Two additional arrows extend from the fourth box. One is to the first box, and the other is to the second box. Both of these additional arrows are labelled “positive feedback.”

 

SC 5. Cortisol stimulates the decomposition of proteins, amino acids, and fats, as well as the conversion of the products of their breakdown into glucose. Too much cortisol would accelerate this process and explain why Emily’s blood had an elevated glucose level.

 

SC 6. An increased heart rate and high blood pressure lead to increased risk of heart attack, stroke, aneurysms (bursting of blood vessels), and kidney damage, which are all life-threatening situations.

 

SC 7. Inflammation is the immune system’s response to injury and invasion by micro-organisms. It directs the body’s defences to block off the area, kill the invaders, dispose of dead and damaged tissue, and begin the process of repair. During inflammation, the blood supply to the area is increased and the area becomes red and warm. The walls of the blood vessels become leaky and the area swells. White blood cells flock to the area to kill the bacteria or viruses that are present, and they release chemicals that continue the inflammation. Cortisol decreases the inflammatory response. If the inflammatory response is decreased by elevated levels of cortisol, the invading micro-organisms are not killed and the person becomes sick with  a cold, laryngitis, bronchitis, pneumonia, and so on. Also, the person may become ill more often if the inflammatory response is dampened.