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Physiology: In utero, the placenta delivers oxygenated blood to the fetus through the umbilical vein. Upon delivery, the umbilical cord is cut. The cardiovascular system must now adapt. Blood CO 2 rises because it is now not removed by the placenta. This is a powerful stimulus for the infant to start breathing.
This begins with contractions of the uterus and dilation of the cervix. The fetus then descends to the cervix, where it is pushed out into the vagina, and eventually out of the female. The newborn, which is called an infant in humans, should typically begin respiration on its own shortly after birth. Not long after, the placenta is passed as well.
The egg cell is generally asymmetric, having an animal pole (future ectoderm).It is covered with protective envelopes, with different layers. The first envelope – the one in contact with the membrane of the egg – is made of glycoproteins and is known as the vitelline membrane (zona pellucida in mammals).
There is a positive relationship between mass at birth and length of gestation in eutherian mammals. [17] Larger mammals are more likely to produce a well-developed neonate than small mammals. Large mammals develop at an absolute slower rate compared to small mammals.
Placental expulsion (also called afterbirth) occurs when the placenta comes out of the birth canal after childbirth.The period of time starting just after the baby is expelled until just after the placenta is expelled is called the third stage of labor.
Hippomanes arise from unconsumed and thickened nutrient fluid (histiotrophe) of the placenta, in concentric layers around the centre of allantoic calculi of tissue debris. [1] The chemical composition is different to amniotic fluid, which along with the insolubility suggests that it's not a result of a simple precipitation process, but a ...
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In live bearing mammals, the placenta forms after the embryo implants into the wall of the uterus. The developing fetus is connected to the placenta via an umbilical cord. Mammalian placentas can be classified based on the number of tissues separating the maternal from the fetal blood. These include: endotheliochorial placentation