Regulation of Lactation

by Thad Wilson, PhD

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    00:00 If we talk through the endocrine response that allows for the milk to be produced as well as let down to get to the right spot, we have four different classifications of endocrine hormones we need to discuss. The first are mammogenic. These promote alveolar and ductal cells so that you can produce more milk. Things that are involved in this manner are estrogens, growth hormones, cortisol, progestins, prolactin, and even relaxin. All of those help this proliferation of breast tissue in response to pregnancy and lactation. Then you have lactogenic-specific hormones and these help by initiating milk production. So if you initiate production, this is getting the process started of getting those secretions across so that you have milk collecting in those open areas of those alveolar cells. Prolactin is a great example of a hormone that does this. We also have hCS. Now hCS is not hCG that you measured to determine if someone is pregnant, this is a different hormone. We'll get to it in just a second. Cortisol, insulin, insulin-like growth factor, all are lactogenic and they promote milk production. Thyroid hormones can also have a small role as well. Interestingly if you start to change hormone levels, this can also stimulate this process. So if you start to remove estrogens and progestins, this will also allow for the initiation of milk production. There are galactokinetic hormones and this particular thing will be to help to get the milk out, which is milk ejection. This is contracting of mild epithelial cells to be able to get the milk to the right place, so when the infant suckles, it will be able to drink the milk. Oxytocin is the most important hormone at this regard and this is released from the posterior pituitary. Then you also have galactopoietic hormones and these help maintain milk production. So you have to initialize milk production but then you have to keep it going and to keep it going you need things like prolactin, cortisol as well as some other metabolic hormones but prolactin and cortisol are the most important. So you can see this is a very tightly regulated system with a lot of hormones involved. Each have a different step. Having different steps is good because you can transmit the different types of signals differently but that also means there's a lot of places for this to go wrong and sometimes it is difficult for one of these different steps to happen and the mother is not able to lactate her particular infant. So let's re-visit this hCS a little bit more. hCS is secreted by those specialized cells that synced up from that blastocyte and that was called a triple-blast layer.

    03:24 Those particular cells formed the pre-component of the placenta. This is very similar to growth hormone and this will increase in proportion to the size of the placenta. So as the placenta gets larger, you'll get more hCS being released. If it worked similar to growth hormone, it is going to stimulate growth both for the infant as well as for the mom and you remember it is also helpful for the development of the breast tissue. The suckling reflex is very important for delivering certain hormones at the right time. How this reflex responses is that first you need an event and that event is the infant suckling on the breast. This sense sensory afferents that then provide information back to the brain to change the release of two hormones. Those two hormones are prolactin and oxytocin. Prolactin is a hypothalamic anterior-released hormone and oxytocin is released from the posterior pituitary. Both of these are involved in the regulation of milk production as well as maintaining that myoepithelial tissue so that you can have milk let down. The decrease in GnRH also does one other thing. It served to suppress the menstrual cycle and in certain lactating females can cause amenorrhea. So the suckling reflex becomes very important in releasing two prominent hormones, prolactin and oxytocin.

    05:05 Therefore, if you don't have a suckling infant, there these two hormones will be lower.

    About the Lecture

    The lecture Regulation of Lactation by Thad Wilson, PhD is from the course Reproductive Physiology.

    Author of lecture Regulation of Lactation

     Thad Wilson, PhD

    Thad Wilson, PhD

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