Which of the following best describes the role of the hypothalamus in the hypothalamic-pituitary-adrenal (HPA) axis?
It directly releases cortisol into the bloodstream.
It secretes antidiuretic hormone (ADH) to control fluid balance.
It inhibits the release of aldosterone from the adrenal cortex.
It secretes corticotropin-releasing hormone (CRH) to stimulate ACTH release.
The Correct Answer is D
A. It directly releases cortisol into the bloodstream.: The hypothalamus does not release cortisol; cortisol is secreted by the adrenal cortex under pituitary control.
B. It secretes antidiuretic hormone (ADH) to control fluid balance.: ADH is synthesized in the hypothalamus but is stored and released from the posterior pituitary; secretion of ADH is one hypothalamic function but not the primary role in the HPA axis.
C. It inhibits the release of aldosterone from the adrenal cortex.: Aldosterone regulation is mainly via the renin–angiotensin system and potassium levels; the hypothalamus does not primarily inhibit aldosterone.
D. It secretes corticotropin-releasing hormone (CRH) to stimulate ACTH release.: The hypothalamus releases CRH, which stimulates the anterior pituitary to secrete ACTH, initiating the HPA axis cascade that leads to cortisol production.
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Related Questions
Correct Answer is C
Explanation
A. Negative feedback on the thyroid gland:Cushing's disease involves cortisol dysregulation and does not primarily disrupt negative feedback of the thyroid axis.
B. Positive feedback on the pituitary gland:Pituitary-driven Cushing's involves excess ACTH but the disrupted mechanism is not a physiological positive feedback loop on the pituitary.
C. Negative feedback on the hypothalamus and pituitary:Elevated cortisol should suppress CRH and ACTH via negative feedback; in Cushing's disease this feedback loop is impaired because a pituitary adenoma continues to produce ACTH despite high cortisol.
D. Positive feedback on the adrenal cortex:The adrenal cortex responds to ACTH but physiological regulation of cortisol does not operate via positive feedback on the cortex.
Correct Answer is A
Explanation
A. The endocrine system uses hormones for signaling, while the nervous system uses neurotransmitters.: The endocrine system releases chemical messengers (hormones) into the bloodstream that act on distant targets, while the nervous system transmits signals using neurons that release neurotransmitters at synapses for rapid, localized communication.
B. The endocrine system uses electrical signals, while the nervous system uses chemical signals.: The endocrine system relies on chemical hormones rather than electrical impulses; electrical signals are a primary feature of neuronal (nervous) communication.
C. The nervous system generates responses that take longer to occur compared to the endocrine system.: Nervous-system responses are typically rapid and short-lived because of fast electrical conduction and synaptic transmission, whereas endocrine responses are usually slower to start but longer-lasting.
D. Both systems use hormones for signaling but at different speeds.: While the endocrine system primarily uses hormones, the nervous system mainly uses electrical impulses and neurotransmitters; hormones can modulate neural function but the two systems do not both primarily use hormones.
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