Module 2 Lesson 5 - 3
Lesson 5 — The Adrenal Gland
The Adrenal Medulla
Read pages 397 and 452
The sympathetic nerve activities, called the "fight-or-flight" responses, prepare the body for immediate action.
The adrenal medulla is composed of modified neurons and essentially is an extension of the autonomic nervous system (ANS). Nerve impulses from the sympathetic nerve system of the autonomic nervous system (ANS), whose centres are located in the hypothalamus, stimulate the adrenal medulla to release epinephrine (adrenaline) and norepinephrine (noradrenaline). These hormones circulate in the bloodstream and enhance the activities of the sympathetic nervous system. Together, the sympathetic nervous system and the release of hormones from the adrenal medulla provide the resources (oxygen and blood glucose) for energy release by aerobic cellular respiration, and they allow the body to perform far beyond its capacity.
You may have heard stories of a mother fearlessly fighting off a bear that was mauling her child or of a man lifting a car to free an accident victim pinned. These incredible feats were performed because the sympathetic nervous system stimulated the adrenal medulla to release a burst of adrenaline that enabled a large amount of energy to be released by metabolism.
Short-Term Stress
The short-term responses to stress commonly are referred to as "fight-or-flight" responses. similar to nerve impulses of the sympathetic nervous system, the hormones of the adrenal medulla prepare the body by increasing the levels of oxygen and glucose and their distribution to the muscles and tissues.
To increase the level of oxygen in the blood, breathing rate must increase and bronchioles dilate to get more oxygen into the lungs for diffusion. To increase the level of glucose in the blood, the liver and muscles are stimulated to convert stored glycogen into glucose.
Heart rate, cardiac output, and blood pressure increase so that distribution of the blood to the tissues is greater and faster. Peripheral skin blood vessels, as well as those to the digestive system, constrict and redirect blood to the muscles and tissues that need more blood.
Cellular respiration is increased and it releases more energy to deal with the situation or to run away quickly. In addition, sweating increases to deal with the extra heat produced from increased metabolism (cellular respiration) and pupils dilate so more light enters the eyeball and increases visual acuity so the danger can be seen more clearly.
Watch and Listen
The following segment of Biologix 12 will reinforce your understanding of how the adrenal medulla works to combat the effects of what is sometimes called short-term stress (4 minutes).
Self-Check
To review the concepts on the short-term stress response, complete the following questions.
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Describe a "fight" response and a "flight" response and include the biological mechanism behind these responses.
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Identify three groups of stress stimuli (categories of things that cause stress).
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Explain how the hypothalamus is involved in the release of epinephrine and norepinephrine by the adrenal medulla. You may choose to use a flow chart to illustrate your response.
Self-Check Answers
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The short-term responses to stress commonly are referred to as the "fight-or-flight" responses. Similar to the nerve impulses of the sympathetic nervous system, the hormones of the adrenal medulla prepare the body by increasing the levels of oxygen and glucose and their distribution to the muscles and tissues. To increase the level of oxygen in the blood, breathing rate increases and bronchioles dilate to get more oxygen into the lungs for diffusion. To increase the level of glucose in the blood, the liver and muscles are stimulated to convert stored glycogen into glucose. Heart rate, cardiac output, and blood pressure increase so that distribution of the blood to the tissues is greater and faster. Peripheral or skin blood vessels, as well as those to the digestive system, constrict and redirect blood to the muscles and tissues that need more blood. Cellular respiration is increased and releases more energy to deal with the situation or to run away quickly. In addition, sweating increases to deal with the extra heat produced from increased metabolism (cellular respiration) and pupils dilate so more light enters the eyeball and increases visual acuity so that the danger can be seen more clearly.
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Three groups of stress stimuli may be infection, injury to the body, or emotional stimuli such as fear, anger, or extreme sadness.
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The adrenal medulla is composed of modified neurons. Neurons from the sympathetic nervous system of the ANS, whose centres are located in the hypothalamus, directly stimulate the cells of the adrenal medulla to produce epinephrine and norepinephrine.
OR
A flow chart may resemble the following: