Chapter 7: Endocrine Physiology
Which of the following hormones is produced in the hypothalamus?
(A) adrenocorticotropic hormone
(E) thyroid-stimulating hormone
The answer is C. Oxytocin and arginine vasopressin are both produced by magnocellular neurons in the hypothalamus. These neurons originate in the paraventricular and supraoptic nuclei of the hypothalamus and terminate in the posterior pituitary.
Parvicellular neurons of the hypothalamus release hypophysiotropic hormones that regulate the anterior pituitary. Hormones released include: corticotropin-releasing hormone (CRH), gonadotropin-releasing hormone (GnRH), thyrotropin-releasing hormone (TRH), growth hormone-releasing hormone (GHRH), and dopamine. The parvicellular neurons terminate in the median eminence of the hypothalamus, and the hypophysiotropic hormones travel via a plexus of capillaries and hypophysial portal veins to reach the anterior pituitary.
Ref: Molina PE. Endocrine Physiology. 4th ed. New York, NY: McGraw Hill; 2013.
Hormone secretion is regulated via a complex array of mechanisms including feedback regulation. The feedback substrate may be another hormone, nutrient, or ion. Which of the following hormones is paired correctly with its feedback substrate?
(C) aldosterone: plasma K+ levels
(D) insulin: plasma Ca2+ levels
The answer is C. Plasma K+ concentration plays a role in the feedback regulation of aldosterone secretion. Aldosterone release is stimulated by an increase in plasma K+ concentration and also by angiotensin II (as part of the renin-angiotensin-aldosterone system). Aldosterone then acts to increase K+ excretion via the kidney (and increase Na+ and water reabsorption).
The anterior pituitary produces three different families of hormones:
Glycoproteins: thyroid-stimulating hormone (TSH), follicle-stimulating hormone (FSH), and luteinizing hormone (LH)
Pro-opiomelanocortin (POMC): adrenocorticotropic hormone (ACTH), β-endorphin, and melanocyte-stimulating hormones (MSH)
Growth hormone and prolactin
Typically, hormones released by the anterior pituitary are under negative feedback control via the hormones released by their target organs. For example, TSH binds to receptors in the thyroid gland and stimulates release of thyroxine (T4) and triiodothyronine (T3). TSH secretion is then decreased via negative feedback inhibition by T3. Another example of negative feedback inhibition, glucocorticoids (cortisol) will inhibit the secretion of corticotropin-releasing hormone CRH and adrenocorticotropic hormone ACTH (part of the hypothalamic-pituitary-adrenal [HPA] axis). Similarly, GH release is inhibited by insulin-like growth factor-1 (IGF-1) and somatostatin.