ape of the uterus, but also because the head is the heaviest part of the body. By the end of the third trimester, the fetus weighs about 330 g and is about 51 cm long. All of its body systems have developed, and it can now survive independently outside the uterus.BirthBirth is the process by which a fetus is pushed out of the uterus and the others body into the outside world. Birth occurs in three stages. The dilation, expulsion, and the placental stage. The first stage of birth lasts from beginning of contractions to the full dilation of the cervix. Membranes of the amniotic fluid rupture, lubricating the vagina. The second stage occurs when the involuntary uterine contractions become forceful that they push the baby through the cervix into the birth canal. During the last stage the placenta and umbilical cord are expelled from the mothers body.Milk ProductionNursing mothers have their hormone levels and uterine size return to normal much faster than non-nursing mothers. Breasts develop the capability for milk secretion about the mid point of pregnancy. Secretion of milk does not occur until delivery, and the action of prolactin. Suckling by the infant causes production of oxytocin to promote release of milk into the ducts emptying into the nipple.Growth and AgingOnce a baby is born, growth continues and learning begins. Human growth does not continue in a steady, linear process. It varies with age and with the individual and is somewhat sex dependant.InfancyInfancy lasts from birth until age two. Infant reflexes concern finding the nipple: suckling can occur minutes after birth, and the rooting reflex is a tactile clue for the infant to turn its head toward a touch. During the first year the infant passes through a series of developmental stages. An infant will double its birth weight by five months and triple its weight in a year. By two years of age, the infant learns to control its limbs, roll over, sit, crawl, and...
