Question

Hormones from the hypothalamus affect the release of all of the following except

• A. Prolactin
• B. Oxytocin
• C. Thyroid stimulating hormone
• D. Growth hormone

Answer 1

The correct option is B Oxytocin

Oxytocin and vasopressin, two peptide hormones, are actually synthesized in the hypothalamus and then transported axonally to the posterior pituitary gland. Oxytocin is controlled by a positive feedback mechanism where a release of the hormone causes an action which stimulates more of its own release. There is also a positive feedback involved in the milk-ejection reflex. When a baby sucks at the breast of its mother, the stimulation leads to oxytocin secretion into the blood which then causes milk to be let down into the breast.

The anterior pituitary gland, unlike the posterior pituitary, is not derived from the brain and does not receive an axon tract from the hypothalamus. Nevertheless, the hypothalamus controls the production and secretion of the anterior pituitary hormones. This control is exerted hormonally rather than by means of nerve axons. Neurons in the hypothalamus secrete releasing hormones and inhibiting hormones which regulate the secretion of specific anterior pituitary hormones. Prolactin, TSH, and GH are all anterior pituitary hormones.