The gestation is a particular functional state specific to the Femelles of Mammifère which carries its or its small in its Utérus, between the Nidation of the egg and the Parturition (Setting-low or Accouchement). A female in gestation is known as “pregnant”. In the mankind, one speaks rather about Grossesse; a woman in a state of pregnancy is known as enclosure.
The gestation period is very variable according to the Espèces:
- Rats, Mouse: 15 to 20 days,
lapine : 31 days,
ferrets: 42 days,
She-cat: 63 to 65 days,
Dog and guinea-pig: 65 days,
Sow: 115 days (3 months, 3 weeks and 3 days),
ewe and Goat: 150 days (5 months),
Cow: 280 days (9 months),
Woman: 280 days (9 months),
Mare: 336 days (11 months),
Blue whale: 336 days (11 months),
She-ass: 365 days (1 year),
cow elephant: 600 to 660 days (20 to 22 month).
In the livestock, one also notes variations according to the Races: thus at the Bovine S, it is generally longer at the races bouchères than at the dairy races. This duration can also vary according to various factors such as the number of small of the range, the season, the type of food or the age of the mother.
the embryonic appendices : the parts of the Blastocyte which do not belong to the Embryon constitute the appendices or fetal envelopes. They insulate the Fetus in the liquid medium, put it at the shelter variations of pressure, the insulator also perfectly of the external medium and nourishing it.
it chorion: it derives directly from the trophoblaste and it is the envelope most external, thin and transparent but solid.
it is the chorion which will establish histological relations with the uterus and it is him which takes part in the formation of the placenta.
- aminios: is the pocket in which the fetus bathes. It is a thin membrane, less resistant than the chorion. To the beginning, it is entirely stuck to the fetus and gradually, it will delimit a cavity: aminiotic cavity filled with liquid:
- aminiotic liquid (1 with 4l in the cow in the long term) = (water with 98%, plus salts, amino-acids and lipids). It comes from an active transfer of maternal plasma is renewed every three hours.
to ensure the hydration of the fetus,
- to provide to the fetus a medium in which it can be driven,
- protection: it deadened all the shocks,
- to provide to the fetus a medium where the temperature is constant because the fetus does not have an effective function of thermoregulation,
The amniotic liquid is not only one protective medium. Circulating slowly in the digestive tract of the fetus, it penetrates in the blood-vessels and lymphatic. In the passing, the intestine of the fetus retains all waste such as the died cells, hairs, mucuses, which will form méconium, this hard excrement which the new born one will reject.
- The allantoïde is a membrane which also delimits a cavity filled with liquid: bag allantoidien which is lengthened and intercalated incompletely between chorion and aminios. It comprises in the cow two compartments connected to each other, and which are distributed in the two uterine horns, under the chorion, from where the name of allonto-chorion. It contains the liquid allontoidien (3.5 to 12 liters in the cow in the long term) and communicates with the bladder of the fetus by the channel of the auraque one: the liquid allantoidien is thus used amongst other things to eliminate the urine from the fetus.
The aminiotic liquid and allantoidien play at time of the low setting a part of lubricant at the instant of the failure of the pocket of water. This fetal body which, at the Primates, remains during the first two months of gestation, but which, at the sauropsidés , is used as breathing apparatus for the embryo.
- Cord and umbilical blister: is consisted the prolongation of the aminios and the allantoide, and by the blood-vessels connecting the fetus to the cotyledons. The fabric of the cord is rich in water known as “cold” which during the rupture prevents the hemorrhage.
- when with the umbilical blister, it is the first appendix which is created and it is on the level of its wall that will organize the first blood circulation by which the fetus will receive the nutritive elements but also oxygen. It is in this wall of the vitelline bag that to place the formation of the blood elements of the fetus.
Vitelline circulation is gradually replaced by the placental circulation which will be adapted to the growth of the fetus.
Simple: Gestation .
|Random links:||Belgian highway A13 | Felt-tip pen | Homology of Morse | Steria | Niševac | Myopie|