Physiology Chapter 20: Adrenal Gland Endocrine System

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Questions and Answers

What percentage of the cells in the adrenal medulla are the epinephrine-secreting type in humans?

80%

70%

60%

90% (correct)

What is the main secretion of the adrenal medulla?

Glucocorticoids

Catecholamines (correct)

Aldosterone

Androgens

What is the function of the mineralocorticoid secreted by the adrenal cortex?

Regulation of carbohydrate metabolism

Regulation of protein metabolism

Maintenance of Na+ balance and extracellular fluid volume (correct)

Synthesis of sex hormones

What is the percentage of the adrenal gland that is made up of the adrenal medulla?

28% Signup and view all the answers

What type of hormones does the adrenal cortex secrete?

Steroid hormones Signup and view all the answers

What is another function of the adrenal cortex, aside from secreting glucocorticoids and mineralocorticoids?

Synthesis of sex hormones Signup and view all the answers

What happens to the cortisone formed in the liver?

It is promptly reduced and conjugated to form tetrahydrocortisone glucuronides Signup and view all the answers

What is the half-life of aldosterone?

About 20 min Signup and view all the answers

What is the major adrenal androgen?

Dehydroepiandrosterone Signup and view all the answers

What is the daily 17-ketosteroid excretion in normal adult men?

15 mg Signup and view all the answers

What is the effect of androgens on the body?

They promote protein anabolism and growth Signup and view all the answers

Where is androstenedione converted to a 17-ketosteroid?

In the liver Signup and view all the answers

What happens to plasma glucose levels in diabetics when glucocorticoids are present?

They increase Signup and view all the answers

What is the effect of glucocorticoids on ACTH secretion?

They inhibit ACTH secretion Signup and view all the answers

What is a characteristic of the nervous system in adrenal insufficiency?

Slowed electroencephalographic waves Signup and view all the answers

What happens to water metabolism in adrenal insufficiency?

The body is unable to excrete a water load Signup and view all the answers

What is the effect of glucocorticoids on circulating eosinophils?

They decrease the number of circulating eosinophils Signup and view all the answers

What is the effect of glucocorticoids on the number of neutrophils, platelets, and red blood cells?

They increase the number of neutrophils, platelets, and red blood cells Signup and view all the answers

What is necessary to restore normal adrenal responses to ACTH?

ACTH Signup and view all the answers

What is the approximate half-life of ACTH in human circulation?

10 min Signup and view all the answers

What happens to plasma cortisol levels in response to ACTH bursts?

They rise and fall Signup and view all the answers

What percentage of daily cortisol production occurs between 4:00 AM and 10:00 AM?

75% Signup and view all the answers

What is the effect of free glucocorticoids on ACTH secretion?

They inhibit ACTH secretion Signup and view all the answers

When are ACTH bursts most frequent?

Early morning Signup and view all the answers

What is the effect of a drop in resting corticoid levels on ACTH secretion?

It increases ACTH synthesis and secretion Signup and view all the answers

What is the primary effect of aldosterone on the ECF?

It increases the volume of the ECF Signup and view all the answers

What is the mechanism of aldosterone's action?

It binds to a cytoplasmic receptor and moves to the nucleus Signup and view all the answers

What is the result of the exchange of Na+ for K+ and H+ in the renal tubules under the influence of aldosterone?

An increase in urine acidity Signup and view all the answers

What is the effect of aldosterone-stimulated proteins on epithelial sodium channels?

It increases the activity of epithelial sodium channels Signup and view all the answers

What is the result of the increased reabsorption of Na+ from the urine, sweat, saliva, and the contents of the colon?

An increase in ECF volume Signup and view all the answers

Study Notes

Adrenal Gland Endocrine System

The adrenal gland has two endocrine organs: the inner adrenal medulla and the outer adrenal cortex.

Adrenal Medulla

The adrenal medulla constitutes 28% of the adrenal gland's mass and has two cell types: epinephrine-secreting (90%) and norepinephrine-secreting (10%).
The main secretions of the adrenal medulla are the catecholamines: epinephrine, norepinephrine, and dopamine.

Adrenal Cortex

The adrenal cortex secretes steroid hormones: glucocorticoids, mineralocorticoids, and androgens.
Glucocorticoids have widespread effects on carbohydrate and protein metabolism.
Mineralocorticoids are essential for maintaining Na+ balance and extracellular fluid (ECF) volume.
Androgens, such as testosterone, can exert effects on reproductive function.

Adrenocortical Hormones

Glucocorticoids:
- Cortisol is the primary glucocorticoid in humans.
- Cortisol is bound to protein to a significant extent and has a half-life of about 1-2 hours.
Mineralocorticoids:
- Aldosterone is the primary mineralocorticoid in humans.
- Aldosterone is bound to protein to only a slight extent and has a short half-life (about 20 minutes).

Physiologic Effects of Glucocorticoids

Glucocorticoids:
- Promote protein catabolism and gluconeogenesis.
- Increase plasma glucose levels, providing extra glucose to the brain and heart.
- Inhibit ACTH secretion, representing a negative feedback response on the pituitary.
- Have effects on the nervous system, including changes in electroencephalographic waves and personality changes.
- Affect water metabolism, preventing water intoxication.
- Decrease the number of circulating eosinophils and increase the number of neutrophils, platelets, and red blood cells.

Regulation of Glucocorticoid Secretion

Glucocorticoid secretion is regulated by ACTH from the anterior pituitary.
ACTH has a half-life in the circulation of about 10 minutes.
ACTH is necessary to restore normal adrenal responses to ACTH.
Circadian rhythm: ACTH is secreted in irregular bursts throughout the day, with the most frequent bursts in the early morning.
Glucocorticoid feedback: free glucocorticoids inhibit ACTH secretion, and the degree of pituitary inhibition is proportional to the circulating glucocorticoid level.

Regulation of Aldosterone Secretion

Aldosterone secretion is regulated by the renin-angiotensin system.
Aldosterone has a short half-life (about 20 minutes).

Physiologic Effects of Mineralocorticoids

Mineralocorticoids:
- Increase the reabsorption of Na+ from the urine, sweat, saliva, and the contents of the colon.
- Cause retention of Na+ in the ECF, expanding ECF volume.
- Increase the exchange of Na+ for K+ and H+ in the renal tubules, producing a K+ diuresis and an increase in urine acidity.
- Bind to a cytoplasmic receptor, altering the transcription of mRNAs.
- Stimulate the synthesis of proteins that increase the activity of epithelial sodium channels (ENaCs) and their synthesis.

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This quiz covers the adrenal gland endocrine system, including the adrenal medulla and adrenal cortex, glucocorticoids, and regulation of glucocorticoid and aldosterone secretion.