University:
Western Sydney University
Course:
MEDI 2003 | Clinical Sciences 2
Academic year:

2024
Views:

416

Pages:

3
Author:

Mariam A. A.

Week 1 Fertilisation and early cell division Fertilisation • • • • Occurs in the ampulla of the oviduct Sperm provides sex-determining chromosome (X or Y), egg provides mitochondria Egg is surrounded by glycoprotein layer – zona pellucida (ZP) – and cellular layer – corona radiata Sperm binding to ZP triggers chemical reactions (acrosome and cortical reactions) to allow only one sperm to penetrate through ZP and deposit nuclear contents Cleavage (d2-3) • • • • • Fertilised egg (zygote) undergoes progressive divisions Still encased within ZP Mass of cells = morula (L. mulberry) Individual cells known as blastomeres Although cell number increases, overall size of morula does not Blastulation (d4) • • • • • • Morula undergoes compaction -> blastocyst Some cells centrally, some peripherally Peripheral cells = trophoblasts (- -> placenta) Central cells = inner cell mass (ICM) (- -> embryo proper) Cavity formed by trophoblast cells creating a basolateral Na+ gradient; water follows Zygote reaches uterus Hatching (d5) • • • ZP is enzymatically digested Blastocyst hatches from ZP in preparation for implantation Nutrients absorbed from uterine secretions Overview so far Implantation (d6-10) • • • • Embryo makes contact with uterine wall (apposition) ICM aligns closest to the wall Embryo penetrates uterine wall (adhesion) Trophoblast cells and ICM undergo differentiation End of Week 1 Key concepts in Week 1 • • • • • • Fertilization occurs Zygote undergoes - Cleavage (cellular division) -> morula - Compaction -> blastocyst Encased within ZP and travelling down oviduct to uterus Upon reaching uterus, zygote hatches out of ZP Begins implantation Begins specialized differentiation Clinical considerations • • • • Ectopic pregnancy - Embryo implantation outside of uterus (usually in oviduct) - Unilateral lower abdominal/pelvic pain (DDx appendicitis), cramping, vaginal bleeding Chemical pregnancy - Very early miscarriage: fertilized egg that has failed to develop - Late period, cramping, tissue loss Blighted ovum - Fertilized egg in which embryo proper has not developed - Diagnosis by U/S; induce miscarriage/wait for natural Miscarriages - Up to 50% of fertilized embryos miscarry - Most occur in the first 12 weeks of pregnancy - Cramping, vaginal bleeding, tissue loss