Oxytocin and prolactin

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Oxytocin and prolactin


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Oxytocin and prolactin

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USMLE® Step 1 style questions USMLE

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A group of investigators are studying the hypothalamic-pituitary axis involved in the release of prolactin. Which of the following is true regarding the regulation of prolactin release?  

External References

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oxytocin p. 652

oxytocin for induction of p. 364

Lactation p. 654

oxytocin for p. 364


functions of p. 335

hypothalamic/pituitary drugs p. 364


hypothalamus production p. 511

lactation and p. 652

pituitary gland and p. 339

signaling pathways for p. 353


Oxytocin and prolactin are two hormones that are mostly involved in the production and release of milk from the breasts during the nursing period. Prolactin - pro meaning “for” and “lactin” referring to milk - it stimulates the production of milk.

Oxytocin, on the other hand, makes the smooth muscle cells around the glands in the breasts contract so that they release the milk.

Oxytocin also helps the muscle in the uterus contract during labor. Both of these hormones are synthesized all the way up in the brain, by two interconnected structures – the hypothalamus and the pituitary gland.

So, basically, the hypothalamus is a part of the brain made up of several nuclei – or clusters of neurons.

Two of these nuclei, the paraventricular and supraoptic nuclei, contain neurons that secrete oxytocin, as well as other hormones like vasopressin, or antidiuretic hormone, which is involved in regulating the amount of water in our body.

When oxytocin is produced, it travels down the axons of these neurons, and reaches the posterior lobe of the pituitary gland.

Down the length of these axons, there are small dilations called Herring bodies – which store the oxytocin until it’s released in the blood.

Outside of pregnancy, oxytocin levels are low, but production increases just a bit during an orgasm - so here’s the reason for that lovely “afterglow”.

Prolactin, on the other hand, is synthesized by special cells called lactotrophs, which are in the anterior lobe of the pituitary.

In women that are not pregnant or breastfeeding, and in men, prolactin levels are usually kept in check by the hypothalamus in two ways.


Oxytocin and prolactin are two hormones that are involved in a variety of physiological processes, including reproductive and lactation functions. During pregnancy, these hormones prepare the breasts for lactation, by stimulating the maturation of the milk-secreting alveoli.

Oxytocin is produced by the hypothalamus and released by the posterior pituitary gland. It plays a role in childbirth, lactation, and sexual behavior. It is also thought to have a role in social bonding and attachment. On the other hand, prolactin is produced by the anterior pituitary gland and plays a role in lactation and the production of breast milk. It is also involved in the regulation of the menstrual cycle and fertility.


  1. "Medical Physiology" Elsevier (2016)
  2. "Physiology" Elsevier (2017)
  3. "Human Anatomy & Physiology" Pearson (2018)
  4. "Principles of Anatomy and Physiology" Wiley (2014)
  5. "Biosynthesis of Human Growth Hormone and Prolactin" The Journal of Clinical Endocrinology & Metabolism (1970)
  6. "Dopamine: A Prolactin-Inhibiting Hormone*" Endocrine Reviews (1985)
  7. "Nonsocial functions of hypothalamic oxytocin" ISRN Neurosci (2013)
  8. "Oxytocin and Estrogen Receptor β in the Brain: An Overview" Front Endocrinol (Lausanne) (2015)
  9. "Prolactin: Structure, Function, and Regulation of Secretion" Physiological Reviews (2000)

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