>>Dr. Ketchum: The alveoli, and here’s sort
of a zoomed in version of the alveoli, they look a lot like the alveoli of the lungs,
right? So prolactin actually stimulates milk synthesis from the alveoli. So you have these
secretory cells that secrete milk. So you end up with milk in the lumen here. But then
you’ve got to get the milk out of the lumen of the alveoli and eject it. So oxytocin stimulates
the milk ejection reflex by stimulating myoepithelial cells. “Myo” is muscle, so these are epithelial
cells associated with muscle. So that can cause ejection of the milk. Let’s take a
closer look. This is a really nice flowchart that shows you how both hormones are involved
in lactation. So we have— there’s a tactile response in the nipples.
This is the stimulus, and that's caused by the suckling of the infant, which stimulates
the hypothalamus. The hypothalamus then is going to synthesize and secrete prolactin-releasing
hormone, but it’s not going to synthesize and secrete prolactin-inhibiting hormone.
It’s also going to increase the activity of the neurosecretory neurons, which stimulate
the posterior pituitary to release oxytocin. So oxytocin causes targets the breast that
causes contraction of the myoepithelial cell so the milk can be ejected. Now prolactin-releasing hormone. When it’s synthesized and secreted by the hypothalamus, it’s going
to stimulate the anterior pituitary to release prolactin, PRL, right? Which then targets
the breasts as well, and causes secretion of the milk by the alveoli. So then that’s
secretion of milk by the alveoli plus the contraction of the myoepithelial cells are
what are responsible together for milk ejection. So that concludes the reproductive system.