Module 2
1. Module 2
1.26. Page 7
Module 2—The Endocrine System
Lesson Summary
The following focusing question was explored in this lessson:
- 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 the 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. Increased cellular metabolism releasing energy in the muscles then makes it possible to “fight or flight.” 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 can be 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 water in the tissues.
Watch and Listen
“The Adrenal Glands and the Gonads: Stress and Sexuality: Vital to Life” provides an excellent review of the concepts of this unit and includes many technologies and societal issues. You may choose to view the entire video at this point.
Lesson Glossary
Consult the glossary in the textbook for other definitions that you may need to complete your work.
adrenal cortex: the outer portion of the adrenal gland composed of three distinct layers of cells that respond to hormonal signals from the anterior pituitary by producing three groups of hormones, including the glucocorticoids, mineral corticoids, and gonadocorticoids; reacts to stress stimuli and affects salt and water balance
adrenal medulla: the central or middle part of the adrenal gland composed of modified nervous tissue that responds to sympathetic nerve signals by secreting the fight-or-flight hormones, epinephrine and norepinephrine, in reaction to stress
aldosterone: a hormone produced by the adrenal cortex in response to an increase in certain enzymes and high levels of ACTH; acts to increase sodium ion reabsorption
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 produced by the adrenal cortex in response to stimulation by ACTH.
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.
fight-or-flight response: a short-term stress response that ensures increased amounts of glucose and oxygen are available to muscle cells for cellular respiration, which results in increased available energy for use by muscles
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
mineralocorticoid: a hormone produced by the adrenal cortex that regulates salt and water homeostasis by influencing the reabsorption of sodium ions
norepinephrine: a second hormone produced by the adrenal medulla in response to stress, but in much smaller quantities than epinephrine
About 20% of adrenal medulla secretions are norepinephrine.