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Lecture 27

Kinesiology 3222A/B Lecture 27: lecture 27: fertilization and pre embryotic

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Kinesiology 3222A/B
Dan Belliveau

Fertilization + Pre-embryonic Growth Learning Outcomes • Define pregnancy and the period of human development • Discuss the steps involved in fertilization • Describe implantation and pre-embryonic development • Identify the 3 primary germ layers derived from the process of gastrulation • Differentiate the various organ systems produced by the primary germ layers during embryogenesis Definitions • Pregnancy: events from time of fertilization (conception) until infant is born • Conceptus: developing offspring • Gestation period: period of development • From last menstrual period until birth • Typically 280 days o 38-42 weeks Egg to Embryo: Fertilization • Sperm must reach ovulated secondary oocyte • Ovum viable for 12-24 hours • Sperm capable of fertilizing egg for 24-72 hours • Happens once the egg is ovulated and sperm has reached it • This most often occurs in ampulla of uterine tubes Sperm Transport • Millions ejaculated • Millions leak from vagina after coitus • Millions destroyed by vaginal environment Cervical mucus MUST be fluidic • • The mucous transitions from fluid (proliferative) to viscous (secretory) • Progesterone = thick • Estrogen = thin • Uterine contractions disperse sperm • Hundreds-few thousands reach uterine tubes • Must undergo capacitation and acrosomal reaction Capacitation • Final maturation step • Confers ability to swim rapidly and to fertilize egg • Weakening of acrosomal membranes head • Necessary for appropriate release of enzymes Acrosomal Reaction • Penetrates corona radiata • Binds zona pellucida (yellow) • Release acrosomal enzymes • Release digest through glycoprotein to allow sperm to get to egg surface • Hyaluronidase • Acrosin • Proteases • Not done by 1 sperm, it’s a team effort Completing Meiosis Meiosis of oocyte done when it goes through meiosis II when sperm penetrates • 1. Sperm loses tail and midpiece 2. Migrates to centre 3. Nuclei swell 4. Becomes pronuclei 5. Membranes rupture releasing chromosomes 6. Combine forming zygote a. Pronuclei + chromosome = zygote 7. Chromosomes replicate and com
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