Here is part 2 of my college notes In order for lactation to occur estrogen and progesterone hormone levels decrease while prolactin, growth hormone and adrenal corticoids increase. Cow, goats and sheep all have one streak canal per gland In the picture the thing that looks like grapes are called Alveoli. The clusters that contain the alveoli are called lobules. Alveoli is kind of like the brain of this whole thing The streak canal is made up of smooth muscle fibers that are formed into a sphincter The medial suspensory ligament is so important when supporting the udder. The process of milk let down starts Epithelial cells line the alveoli which synthesize milk. Milk is then collected into the alveolus lumen which then travels down the ducts, collects in the cistern and is forced into the teat cistern which is then expressed thru the teat canal. Did you know it takes 500 liters of blood to produce one liter of milk. Crazy!