Why does Cushing's syndrome, characterized by excessive cortisol, sometimes arise from pituitary tumors that secrete ACTH, rather than directly from adrenal gland malfunctions?

💡 Explanation

ACTH-secreting pituitary tumors cause Cushing's because the elevated ACTH levels override the normal negative feedback loop that would typically suppress ACTH production in response to high cortisol levels. Therefore, cortisol levels remain elevated, rather than being regulated by the pituitary-adrenal axis under normal conditions.

• Why does histamine release in localized inflammation increase capillary permeability rather than decrease it, given the immune system's goal of containing infection?
• Why does vitamin D deficiency increase the risk of osteoporosis?
• Why does the sensation of satiety diminish faster after consuming primarily liquid calories compared to solid foods?
• Which mechanism explains why some bacterial infections become untreatable despite initial antibiotic sensitivity?
• If a drug selectively inhibited retinaldehyde regeneration within the retinal pigment epithelium (RPE), which consequence follows regarding vision?
• If a patient with osteoporosis begins resistance training, which consequence follows regarding bone remodeling?