Human embryonic development parturition and lactation12th Biology by Anshul sharma

Embryonic development- soon after implantation the embryo differentiate in to the outer ectoderm and inner endoderm. The mesoderm develop soon after. These 3 tissue layers/ germ layers give rise to the tissues of body.
Process of formation of 3 germ layers in embryo is called gastrulation and embryo with 4 germ layer said to be in gastrula stage.
The inner cell mass or 3 germ layers contain stem cells that have the ability to give rise all the tissue and organs in the body.
FOETAL DEVELOPMENT-
Human pregnancy last for 9 months/280-270days
Following are major developmental mile stone and there time period.
1month- heart is formed
2month- limbs and digits are formed
3months- most of the major organ system are formed
5month- appearance of hairs on the head and first movement of the Fortis.
6month- body is covered with fine hairs
- eyelids separate, eye lashes are formed.
9month- Fortis is fully developed and ready delivery/parturation.
Parturition and lactation- Gestation period- " the average duration of pregnancy is called as gestation period". In human the gestation period is of 9 months"
Parturition- the process of child birth by which the Fortis is expelled or delivered due to vigrous contractions of the myometrium of uterus.
A full developed Fortis and placenta induce parturition. This causes mild contaction in uterus called foetal ejection reflex.
Foetal ejection reflex trigger the release of oxytocin from the mothers pitutary.
[ Oxytocin- synthesize by the neurosecretory cells of hypothalamus ( supraoptic nucleus), striped and secreted by posterior pitutary. Cause the contractions in smooth muscles of body. Medically injected to a pregnant female to induce uterine contractions. It is also responsible for the milk ejection from mammary glands. It control the maternal behavior of mother towards child.]
Oxytocin stimulate stronger contaction which stimulate more production of oxytocin.
The stimulatory positive feedback reflex continue between the uterine contractions and oxytocin release. This leads to stronger and stronger contaction till the baby is expelled out of the uterus through the birth canal.
Soon after the foetus is delivered the placenta is also delivered.
Lactation- once the baby is born the mother pitutary release prolactin hormone which initiate the onset of lactation ie production of milk from the mammary gland of female. Lactation continue for more than 6 months during which baby feeds on it only
Before the milk is secreted after the child birth, the mammary glands secret a yellowish liquid which is rich in special nutrients and antibodies (IgA) and provide immunity to the infant. This is known as colostrum. Earlier it was not given to the babies but with the passage of time, it has turned out that it is of most importance to the new born infant and hence must be given.

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