Question

Which of these statements about the adrenal cortex is true? a. It is not innervated by nerve fibers. b. It secretes some androgens. c. The zona glomerulosa secretes aldosterone. d. The zona fasciculata is stimulated by ACTH. e. All of these are true.

Short answer

The correct answer is E: All of these are true. The adrenal cortex is not primarily regulated through direct nerve innervation, secretes some androgens, the zona glomerulosa secretes aldosterone, and the zona fasciculata is stimulated by ACTH.

Step-by-step solution

Statement A: It is not innervated by nerve fibers.

The adrenal cortex does receive direct innervation by nerve fibers; however, its primary regulatory mechanism is through the release of hormones within the body. Still, this statement is partially true, as the adrenal cortex is not primarily regulated through direct nerve innervation.

Statement B: It secretes some androgens.

The adrenal cortex is responsible for secreting small amounts of androgens, which are male sex hormones. Although the testes are the primary source of androgens in males, the adrenal cortex does secrete some as well. Thus, this statement is true.

Statement C: The zona glomerulosa secretes aldosterone.

The adrenal cortex is divided into three zones, each responsible for secreting different hormones. The zona glomerulosa is the outermost layer that secretes mineralocorticoids, primarily aldosterone. Aldosterone helps regulate salt and water balance within the body. Therefore, this statement is true.

Statement D: The zona fasciculata is stimulated by ACTH.

The zona fasciculata is the middle layer of the adrenal cortex and is responsible for secreting glucocorticoids, mainly cortisol. The release of cortisol is stimulated by the adrenocorticotropic hormone (ACTH) from the anterior pituitary gland. Thus, this statement is true.

Statement E: All of these are true.

Based on the analysis of each statement (A-D), all the statements are true or partially true regarding the adrenal cortex. Therefore, the correct answer is E: All of these are true.

Key concepts

Androgens

Androgens are essential male sex hormones primarily produced in the testes, but they are also secreted in small amounts by the adrenal cortex. These hormones play a crucial role in the development of male characteristics, such as:

• Muscle growth
• Deepening of the voice
• Facial and body hair growth

Even though the adrenal cortex produces only a minor fraction, these androgens can still influence certain physiological processes. The small secretion from the adrenal cortex complements the body's androgen levels, especially in females, where they are converted to estrogen in certain tissues.

Aldosterone

Aldosterone is a vital hormone secreted by the zona glomerulosa of the adrenal cortex. This mineralocorticoid is primarily tasked with regulating the balance of salt and water in the body, crucial for maintaining blood pressure and fluid balance. Here's how it works:

• Increases sodium absorption in the kidneys
• Promotes potassium excretion
• Helps in water retention

These actions help maintain blood pressure and ensure that the body's internal environment remains stable and optimal. High or low levels of aldosterone can lead to conditions like hyperaldosteronism or Addison’s disease.

Cortisol

Cortisol is a glucocorticoid hormone produced by the zona fasciculata of the adrenal cortex. This hormone is often called the "stress hormone" because it is released in response to stress and low blood glucose levels. Here are some of its key functions:

• Regulates metabolism of carbohydrates, fats, and proteins
• Controls the body's sleep-wake cycle
• Helps reduce inflammation
• Assists in memory formulation

While necessary for well-being, excessive cortisol can lead to adverse health effects, such as weight gain and increased blood pressure.

ACTH

Adrenocorticotropic hormone, or ACTH, is crucial for stimulating the adrenal cortex to produce cortisol. Originating from the anterior pituitary gland, ACTH acts primarily on the zona fasciculata to control cortisol production. Here's how ACTH influences adrenal cortex functions:

• Stimulates cortisol release during stress
• Regulates the daily rhythm of cortisol
• Ensures adequate levels of glucocorticoids

Understanding ACTH's role helps in appreciating how the body manages stress and metabolism effectively, linking the adrenal gland and the pituitary gland in an intricate hormonal web.

Zona Glomerulosa

The zona glomerulosa is the outermost layer of the adrenal cortex and is specifically responsible for the production of mineralocorticoids, mainly aldosterone. Its role is pivotal in managing the body’s blood pressure and electrolytic balance. Key facts about the zona glomerulosa include:

• Secretes aldosterone in response to signals from the kidney
• Helps the kidney retain sodium and excrete potassium
• Indirectly regulates water balance and blood volume

This layer operates under a feedback loop known as the renin-angiotensin-aldosterone system (RAAS), highlighting its critical role in systemic homeostasis.

Zona Fasciculata

The zona fasciculata resides in the middle layer of the adrenal cortex and primarily produces glucocorticoids, including cortisol. This zone is regulated by ACTH, demonstrating its pivotal role in stress response and energy metabolism. Salient points about the zona fasciculata include:

• Responsible for cortisol synthesis and release
• Plays a role in carbohydrate metabolism and immune response
• Influences protein catabolism and lipolysis

By controlling cortisol, the zona fasciculata not only aids in managing stressful situations but also in maintaining the energy supply by regulating metabolism throughout the body.