Fertilisation, cleavage and implantationनिषेचन, विदलन और अंतर्रोपण

NCERT Fig 2.11 · Class 12 Biology · Chapter 2 · interactive diagram

Parts and their functions

• Ovary (अंडाशय) — The Graafian follicle ruptures and releases the secondary oocyte (ovum) — ovulation, induced by the LH surge (~day 14).
• Fimbriae (झालर (फिम्ब्री)) — Finger-like edges of the funnel-shaped infundibulum; they collect the ovum after ovulation.
• Ampulla (तुंबिका (एम्पुला)) — Wider part of the fallopian tube. Sperms and ovum both reach here — fertilisation takes place in the ampullary region.
• Isthmus (संकीर्ण पथ (इस्थमस)) — Last, narrow part of the oviduct that joins the uterus. Cleavage begins as the zygote moves through it.
• Uterus (गर्भाशय) — Inverted-pear-shaped womb; the embryo implants in its wall and develops here.
• Endometrium (गर्भाशय अंतःस्तर) — Inner glandular lining of the uterus, kept ready by progesterone from the corpus luteum; the blastocyst embeds in it.
• Ovum (secondary oocyte) (अंडाणु (द्वितीयक अंडक)) — Released by ovulation, surrounded by the zona pellucida, and carried to the ampulla.
• Fertilisation (निषेचन) — One sperm enters through the zona pellucida (helped by acrosome enzymes); the membrane changes and blocks other sperms. Meiosis II of the oocyte completes (second polar body), then sperm and ovum nuclei fuse → diploid zygote. An X or Y sperm decides the sex.
• Cleavage (विदलन) — Mitotic divisions of the zygote as it moves through the isthmus towards the uterus: 2, 4, 8, 16 cells called blastomeres.
• Morula (तूतक (मोरुला)) — The embryo with 8 to 16 blastomeres; it keeps dividing and becomes a blastocyst as it moves into the uterus.
• Trophoblast (पोषकोरक) — Outer layer of the blastocyst; it attaches to the endometrium. Later its chorionic villi help form the placenta.
• Inner cell mass (अंतर कोशिका समूह) — Inner group of cells attached to the trophoblast; it becomes the embryo. It contains stem cells that can form all tissues and organs.
• Implantation (अंतर्रोपण) — The blastocyst becomes embedded in the endometrium as uterine cells divide and cover it. This leads to pregnancy.

Steps

1. 1 · Ovulation: the ovum is released and caught by the fimbriae.
2. 2 · Fertilisation in the ampulla → diploid zygote.
3. 3 · Cleavage in the isthmus: 2, 4, 8 blastomeres.
4. 4 · Morula (8–16 blastomeres) reaches the uterus.
5. 5 · Blastocyst: trophoblast + inner cell mass.
6. 6 · Implantation in the endometrium → pregnancy.

Original diagram drawn by Simple Learning Hub, based on NCERT Fig 2.11. Report a mistake