Fertilization to birth — A/L Biology

What must I remember about Fertilization to birth?

• Fertilization begins with capacitation of sperm in female tract, followed by Acrosome reaction releasing enzymes (hyaluronidase, acrosin) to penetrate corona radiata and zona pellucida of the secondary oocyte.
• Polyspermy blocks: Fast block (instant membrane depolarization) and Slow block (cortical reaction releasing granules that harden zona pellucida into fertilization envelope) ensure strictly monospermic fertilization.
• Cleavage and Blastocyst formation: Zygote undergoes rapid mitotic divisions without growth, progressing from 2-cell to morula (solid ball of 16-32 cells) to blastocyst (fluid-filled cavity / blastocoel, outer Trophoblast destined to form placenta, and Inner Cell Mass destined to form embryo proper).
• Implantation: Occurs ~day 6-7 post-fertilization when blastocyst trophoblast burrows into endometrium; trophoblast secretes Human Chorionic Gonadotropin (hCG) to maintain corpus luteum production of progesterone.
• Placentation and Parturition: Placenta allows nutrient, oxygen, and waste exchange between maternal and fetal blood without direct mixing, functioning as an endocrine organ (progesterone, estrogen, hPL); Parturition (labor) is triggered by fetal cortisol and maternal oxytocin/prostaglandins via positive feedback.

Test yourself (1 minute)

1. Three germ layers formed during Gastrulation

   Ectoderm (nervous system, epidermis, sensory organs), Mesoderm (skeletal system, muscles, circulatory/lymphatic systems, kidneys), and Endoderm (epithelial lining of digestive, respiratory tracts, liver, pancreas).

2. hCG diagnostic indicator

   Presence of hCG in maternal urine/blood within 10-14 days forms the biochemical basis for standard home pregnancy tests.

3. Three stages of Labor

   1) Dilation stage (cervix dilates to 10 cm, amnion ruptures), 2) Expulsion stage (strong uterine and abdominal contractions deliver baby), 3) Placental stage (delivery of placenta / afterbirth within 15-30 min).

Practise Fertilization to birth questions today

Source: NIE G.C.E. (A/L) Biology Syllabus & Resource Book, Unit 5

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Where does Fertilization to birth fit in the syllabus?

Year 2 · Term 1