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
Birth of a Giant including "The Golden Age" (1959). Although available from the National Film Board either online or as a DVD, "Birth of a Giant" is now largely forgotten. A recent analysis emphasized the historical value of the film. "For those interested in the formative years of the Cold War and the Canadian aircraft that figured so prominently in it ..." Birth of a Giant Birth of a Giant (aka Naissance d'un géant for a French-language version) is a 29-minute 1957 Canadian documentary film, directed by Hugh O'Connor and produced by the National Film Board of Canada (NFB) for the Canadian Broadcasting Corporation