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The image above is a cake that pictures the mammary gland and it’s associated lobules and milk ducts. To the right is a picture diagram of the positive feedback loops present in lactation.
S/MS = suckling/mechanical stimulation
D = dopamine
PL = prolactin
O = oxytocin
M = milk
E = milk ejaculation
Positves and negatives signify inducing/inhibiting, respectively.
Red and blue pathways indicate the two positive feedback loops.
Lactation occurs at the end of pregnancy and is an example of a positive feedback loop. It is influenced by both hormonal stimuli, such as dopamine, prolactin, and oxytocin, and mechanical stimuli, such as suckling. The first positive feedback loop describes how mechanical stimuli induce the secretion of oxytocin, which leads to milk release and, therefore, facilitates more mechanical stimuli. The other feedback loop shows how mechanical stimulation inhibits dopamine secretion, leading to prolactin secretion and milk production. The production of milk leads to more mechanical stimulation.