Lecture 14 -- ap2 fertilization

fertilization

• occurs when the nuclei of the sperm and egg fuse

  • produce zygote (diploid)

when is pregnancy detectable? duration?

• early as 3.5 weeks (few days before missing a period)

• 40 wks

requirements of pregnancy

• growth of new endocrine organ

• development of a baby

• increased metabolic/cardiovascular/renal/etc demands

gamete transport — the egg & estradiol role

• ovum is released into peritoneal cavity to be picked up by fallopian tubes

  • viable for 1 day

  • ampulla is the fertilization site

• increased ciliary movement

• increased smooth muscle contractions

• decrease cervical mucus viscosity

• increase vaginal pH

gamete transport — the sperm

• in ejaculate → hundreds of millions

• in fallopian tubes —> hundreds to thousands

gamete transport — what do the sperm succumb to and are helped by on the way to the fallopian tubes?

• succumb to

  • gravity/energy

  • pH

  • folds of vaginal wall

  • cervical mucus

  • WBCs in uterus

• helps them

  • slightly less acidic

  • cervical mucus slightly thinner

  • ejaculate (all components)

capacitation

• biochemical and physiological changes sperm undergo to acquire fertilizing capacity

  • happens mostly in the female reproductive tract

  • can be performed in vitro

capacitation and hyperactivity

• cytoplasmic changes

  • increased fluidity of plasma membrane → dec cholesterol

• hyperactivation — motility changes

  • separate from capacitation, but happens concurrently

corona radiata

• granuloi cells

transport big picture and seminal vesicles

• sperm travels through vagina → cervix → uterus → down fallopian tube to reach the ovum

• seminal vesicles:

  • fructose

  • coagulase

  • prostaglandins

phases of fertilization

1. corona radiata penetration

2. zona pellucida penetration

3. fusion of the oocyte and sperm plasma membranes

draw out what’s involved of fertilization

• granulosa

• binding protein (ZP3)

• zona pellucida

• cell mem of oocyte

• ion channels

• lysosomes

• smooth ER

Phases of fertilization + prevention of polyspermy — draw out

1. binding ZP3 and acrosome fuses

2. enzymes make hole in ZP

3. sperm + oocyte membrane opens Na+ channels

   1. depolarization! — fast block to polyspermy

4. alpha subunit binds

5. sperm nuclear material released

6. SER Ca2+ release

   1. activates lysosomes

7. lysosomal enzymes degrade ZP3 and harden zona pellucida — slow block to polyspermy

the zygote & where do twins come from?

• single-celled, diploid product of fertilization

  • 2 eggs → fraternal

  • zygote splits → identical