Mammary gland gestation, serum progesterone remains at a stably high concentration so signaling through its receptor is continuously activated. As one of the transcribed genes, Wnts secreted from mammary epithelial cells act paracrinely to induce more neighboring cells' branching. When the lactiferous duct tree is almost ready, "leaves" alveoli are differentiated from luminal epithelial cells and added at the end of each branch. In late pregnancy and for the first few days after giving birth, colostrum is secreted. Milk secretion (lactation) begins a few days later due to reduction in circulating progesterone and the presence of another important hormone prolactin, which mediates
Mammal tooth pairs of molars and between three or two premolars. For example, the tiger quoll ("Dasyurus maculatus") is a dasyurid marsupial native to Australia. The quoll possesses four upper incisors and three lower incisors per left and right-hand side [I = 14]. Along with two upper premolars [PM] and two lower premolars per side [PM = 8] and four upper and four lower molars per side [M = 16], giving the animal a complement of thirty-eight teeth. The Tiger quoll's dental formula is as follows: Rabbits and other lagomorphs usually shed their deciduous teeth before (or very shortly after) their birth,