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Author: Aaron Mullally

- know which gland secretes prolactin

- know which cells synthesize and secrete prolactin

- know the target tissue for prolactin

- know what prolactin stimulates

This packet covers prolactin (functions and regulation). I will cover prolactin again when I discuss reproductive physiology.

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Prolactin Overview

Prolactin is another easy hormone to understand because it only has one major function, stimulating milk productin by the mammary glands. Remember that prolactin only stimulates the production of milk, not the secretion. The secretion of milk by the mammary glands is stimulated by oxytocing through a different mechanism.

Prolactin regulation is an interesting item to discuss. Thyroid-releasing hormone(TRH) is tonically (constantly) secreted from the hypothalamus to the anterior pituitary. TRH does also stimulate lactropes (prolactin secreting cells) to secrete prolactin. So after reading this you should be thinking we produce an abnormally  high amount of milk on a daily basis. This doesn't happy because of another regulatory signal, dopamine. The hypothalamus also secretes dopamine on a constant basis and this overrides the effects of TRH on lactoropes and prevents them from secreting prolactin.

Pregnancy is a situation that dramatically increases the production and secretion of prolactin. Also, parturition (birth) increases the activity of prolactin. In order for prolactin to remain high after the child is born the child must breast feed. Once the child stops breast feeding prolactin levels fall again and the mother stops producing milk.

Source: Mind of Aaron

Prolactin Overview

Source: Self made


Source: Self made