STD-12 UNIT-6 CHA-3
HUMAN REPRODUCTION
Pregnancy placenta, paruration and lactation
- Pregnancy is simply defined as a sequence of events that normally includes fertilization, cleavage, blastulation, implantation, gastrulation and total embryonic development up to child birth is called as pregnancy.
- Pregnancy starts in post ovulatory phase during ovulation ovum released from ovary on 14th day of menstrual cycle.
- Life span of ovum in female genital tract is 24 hours .
- If within 24 hours ovum received sperm ovum then gets fertilized and zygot is formed.
- Pregnancy period in human female is 280 days starts from first day of the last menstrual cycle which is stopped is also known as gestation .
- After fertilization zygote nucleus under goes continuous mitotic divisions in the process of cleavage within 3 days or 72 hours of fertilization many celled morula is formed .
- Morula gets converted into blastula within 6th or 7th day of fertilization.
- Blastula gets implanted in the endometrium of uterus on 7th and 8th day of fertilization .
- After implantation implanted blastula gets converted into three germ layered structure gastrula.
- Three germ layers are ectoderm endoderm and mesoderm.
- After gastrulation extra embryonic membranes are formed amnion, chorion, allantois and yolk sac.
- In organogenesis particular body organs and systems are formed from these germ layers.
- During pregnancy period health of uterus is maintained by progesterone secreted by corpus luteum.
- Embryo gets attached to the endometrium of uterus by placenta , through placenta nourishment given to embryo .
- There are three parts of Pregnancy period in human female each part of Pregnancy period is of 3 month
- It is the time of most radical change for both the mother and the embrys
- During first 2-4 weeks of development embryo obtains nutrients directly from the endometrial layer
- The first trimester period is the main period of the organogenesis and development of many body organs.
- In this first trimester period all major body structures of adult are rudimentary less developed up to 8 weeks of Pregnancy Embryo grows upto 5 cm in length .
- In first trimester period level of progesterone in blood becomes very high brings about main change reproductia organs ,uterus become larger ovulation and menstrual cycle stops temporarily .
- In second trimester the uterus grows enough for the maintenance of Pregnancy .
- In this phase foetus becomes very active and grows upto 30 cm in length.
- Due to decreased level of human chorionic gonadotropin, placenta secrets more and more progesterone to maintain Pregnancy.
- In this period foetal growth is very fast and weight increases upto 3- 4 kg and length upto 50 cm .
- As per foetal growth the size of uterus around foetus enlarges .
- In this stage internal organs of pregnant woman due to increase in the size of uterus get compressed may leading to frequent urination , digestive blockages, pains in back muscles .
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