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Read the given Assertion (A) and Reason (R) and select the most appropriate option:
Assertion (A): A woman has normal ovulation and fertilisation, but the zygote is expelled without attaching to the uterine wall because implantation has failed.
Reason (R): Implantation is the process by which the blastocyst embeds in the endometrium to establish pregnancy.
Choose the correct answer from the options given below:
A is true, but R is false
Both A and R are true, but R is not the correct explanation of A
A is false, but R is true
Both A and R are true, and R is the correct explanation of A
Both A and R are true, and R is the correct explanation of A
Implantation is the crucial biological process where the blastocyst adheres to and embeds itself within the uterine endometrium to form a connection for nutrient exchange. The failure of this process prevents the establishment of pregnancy, leading to the expulsion of the zygote/blastocyst.
Implantation is the crucial biological process where the blastocyst adheres to and embeds itself within the uterine endometrium to form a connection for nutrient exchange. The failure of this process prevents the establishment of pregnancy, leading to the expulsion of the zygote/blastocyst.
Think of implantation like a seed needing to firmly take root in fertile soil; if the soil (endometrium) isn't prepared, the seed (blastocyst) cannot anchor and will simply be washed away.
B-I-P: Blastocyst Implants in Progesterone-primed endometrium.
ZygoteтЖТMorulaтЖТBlastocyst
ProgesteroneтЖТEndometrialthickening
After fertilisation, the zygote undergoes cleavage to form a blastocyst. This blastocyst secretes proteolytic enzymes and releases human chorionic gonadotropin (hCG) to signal its arrival. Successful implantation requires the synchronized development of the blastocyst and a receptive, progesterone-primed endometrium. If this synchronization fails, the blastocyst cannot embed and is subsequently lost.
Implantation usually occurs about 6-7 days after fertilisation.
The hormone progesterone is essential for maintaining the decidual cells of the endometrium for implantation.
Failed implantation is a common cause of early pregnancy loss.
Natural biological checkpoint to ensure pregnancy viability
Can lead to infertility or early pregnancy wastage if hormonal balance is disturbed
In vitro fertilization (IVF) embryo transfer success rates
Understanding causes of female infertility
The blastocyst consists of an inner cell mass and an outer trophoblast layer, the latter of which facilitates implantation.
Option D is correct because R logically defines the physiological mechanism necessary to prevent the outcome described in A.
D is correct тАФ Implantation is the biological prerequisite for the blastocyst to embed, and its failure explains why the zygote is expelled.
Always verify if the Reason (R) provides the mechanism that directly validates the observation in the Assertion (A) before selecting 'correct explanation'.
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