Module 2 The Endocrine System

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Reflect and Connect

Stress in moderate doses is a good thing! How is it good? What kinds of activities are carried out better under some stress? Do you think that athletes would do as well as they do if they did not experience the stress of competition that gives them that extra burst of epinephrine? If your heart did not beat a little faster and your breathing rate was not increased at all, do you think you would do as well on an exam? Why do you think “extreme sports” are becoming so popular? Is being too laid back a good thing in some situations? How is too much stress bad for you? Why does a constant accelerated heart rate and constant higher than normal blood pressure lead to heart attacks?

Going Beyond

Hans Selye, a scientist at the University of Montreal, first described the General Adaptation Syndrome or GAS. GAS has three main stages: Alarm, Resistance, and Exhaustion. However, Selye did not regard all stress as bad and even said that some stress was the “spice of life”. Researchers have called this good stress “eustress”. Using library sources as well as the internet, research more about GAS.

Lesson Summary

In this lesson, the following focusing question was explored:

How do the adrenal glands and their secretions affect the body?

Located atop the kidneys, the adrenal gland is really two glands. Similar to the two lobes of the pituitary gland, the adrenal cortex is composed of several layers of secretory cells, while the adrenal medulla is made up of modified nerve cells. Hormones from both parts of the adrenal gland deal with stress. Epinephrine and norepinephrine from the adrenal medulla intensify the “fight or flight” responses of the sympathetic nervous system. The purpose of these responses is to get more oxygen and glucose to the tissues. For example, breathing rate increases and bronchioles dilate so more oxygen can be taken to the lungs. Glucose is synthesized from glycogen. Heart rate, cardiac output and blood pressure are increased so that the increased levels of oxygen and glucose can be delivered to the muscles. Cortisol, from the adrenal cortex, intensifies the fight or flight responses. It increases blood glucose by converting amino acids, proteins, and fats into glucose. Cortisol also decreases the inflammatory response, so it is useful in treating allergic reactions and joint inflammations. High levels of cortisol are regulated by negative feedback on the hypothalamus and anterior pituitary, and their secretions of releasing hormone and ACTH respectively. Aldosterone, another hormone from the adrenal cortex, is concerned with regulation of sodium ions and subsequent homeostasis of tissue water.

Glossary

adrenal medulla: the central or middle part of the adrenal gland composed of modified nervous tissue which responds to sympathetic nerve signals by secreting the “fight or flight” hormones epinephrine and norepinephrine in reaction to stress

adrenal cortex: the outer portion of the adrenal gland composed of three distinct layers of cells which respond to hormonal signals from the anterior pituitary by producing three groups of hormones including the glucocorticoids and mineralocorticoids; reacts to stress stimuli and affects salt and water balance

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

mineralocorticoid: a hormone produced by the adrenal cortex that regulates salt and water homeostasis by influencing the reabsorption of sodium ions

fight or flight response: a collection of responses that prepare the body to combat an immediate stressful situation by increasing the availability of oxygen and glucose for aerobic cellular respiration which releases energy; short term stress responses that ensure increased amounts of glucose and oxygen available to muscle cells for cellular respiration, which results in increased available energy for use by muscles
 
cortisol: also called hydrocortisone or cortisone; cortisol is secreted in highest amounts in humans and is produced by the adrenal cortex in response to stimulation by ACTH; involved in enhancing short term stress responses and in stimulating conversion of protein and fat into glucose

aldosterone: hormone produced by adrenal cortex in response to an increase in certain enzymes and high levels of ACTH; acts to increase sodium ion reabsorption

epinephrine: a hormone produced by the adrenal medulla in response to stress; also called adrenaline; the adrenal gland produces about 80% epinephrine and 20% norepinephrine

norepinephrine: a second hormone produced by the adrenal medulla in response to stress but in much smaller quantities; about 20% of adrenal medulla secretions are norepinephrine

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