are gestational sac and yolk sac the same
Gestational sac The yolk sac and embryo should be readily identifiable when the gestational sac reaches a certain size â€” a yolk sac should be seen when the gestational sac is 20mm and a fetal pole should be seen when the gestational sac reaches 25mm.
Mammary gland The basic components of a mature mammary gland are the alveoli (hollow cavities, a few millimeters large) lined with milk-secreting cuboidal cells and surrounded by myoepithelial cells. These alveoli join to form groups known as lobules. Each lobule has a lactiferous duct that drains into openings in the nipple. The myoepithelial cells contract under the stimulation of oxytocin, excreting the milk secreted by alveolar units into the lobule lumen toward the nipple. As the infant begins to suck, the oxytocin-mediated "let down reflex" ensues and the mother's milk is secreted — not sucked from the gland — into the baby's mouth.