First Week Embryology Lecture Notes PDF

 1st week Fertilization  Definition: Meeting then union of male & female gametes wy  Site: Ampulla of uter...

 1st week Fertilization  Definition: Meeting then union of male & female gametes wy  Site: Ampulla of uterine tube  Steps: 1. 200-600 ×106 sperms are deposited in posterior fornix of vagina da 2. Capacitation Definition: Removal of seminal plasma proteins overlying head of sperm Aim: making the sperm more active and able to fertilize ovum Site: in female genital tract starting at cervix en Last: 5- 7 hours 3. Acrosomal reaction Release of enzymes from acrosome of sperm:  Hyaluourinidase: help in corona radiate penetration H  Zona lysin "acrosin" & Trypsin- like substance: pierce zona pellucida 4. Fusion of plasma membranes of oocyte & sperms: allowing head & tail to enter oocyte R. 5. Zona “cortical” reaction: Making zona pellucida impermeable in any other sperm to prevent poly-spermy 6. 2nd oocyte resume the 2nd meiosis: forming ♀ pro-nucleus D 7. ♂ pro-nucleus formation: after tail is lost & nucleus enlarge 8. Union of ♂& ♀ pro-nuclei: forming the zygote with 46S chromosome Anatomist “first week” 1  Results: 1. Sex determination of embryo : if sperm carries Y chromosome it wy gives male & if it carries X chromosome it gives female 2. Determining health state of embryo 3. Resuming 2nd meiosis da 4. Restoring normal diploid number of chromosomes “46S chromosomes” en 5. Initiating zygote cell division  Anomalies: H 1. Parthenogenesis: to be pregnant without fertilization. All offspring are female 2. Dispermy triploidy: 2 sperms penetrate one ovum forming zygote R. 3. Superfecundation: fertilization of ≥ 2 ova released during the same menstrual cycle by sperms from separate act of coitus D Anatomist “first week” 2  Cleavage “segmentation”  Definition: repeated mitosis of blastomers of zygote leading to rapid increase in number of cells during its passage in uterine tube wy  Steps:  (2) then (4) then (8) cell stage Blastomers undergo repeated mitosis during its passage in uterine da  Morula: It is formed of (16 - 32) cells within zona pellucida It is formed 3 days after fertilization en It is the satge that enter uterine cavity  Blastocyst stage “blastula”: Time: 4th day after fertilization Formation: H R. 1. Blastocele: cavity filled with fluid 2. Trophablast: outer flat cells which gives raise to fetal part of placenta D 3. Inner cell mass “embryoblast”: cellular mass at one pole which gives raise to the embryo Anatomist “first week” 3