Human Embryonic and Fetal Development
Key Questions
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Answer:
In humans , the gestation period is usually of 9 months i.e 266 days /38 weeks (+,- 7 days --depending upon the amount of Progesterone).
Explanation:
It is divided into three trimesters ;
Trimester 1
First week -Implantation takes place ( at he 7th day of fertilisation )
Second week - Germ layers are formed
Third week - Suppressed menstrual cycle indicates pregnancy (not confirmatory)
Fourth week - Blood vessels are formed . Heart is formed and brain starts developing .Trimester 2
Fifth week - Heart starts pumping the blood . LUB- DUB sound could be heard during ultrasound .
Sixth week- Internal organs are formed . Mouth , face are formed . Gonads are formed.
Seventh week - External , internal ear is formed
Eighth week - Eyelids are formed , but closed .Trimester 3
Complete organ formation takes place .