Fertilization!

• “The elements that unite are single cells, each on the point of death; but by their union a rejuvenated individual is formed, which constitutes a link in the eternal process of Life.” ~ F. R. Lillie

Union of Sperm and Egg

Union of Egg and Sperm

• Oviduct• Can only

occur directly after egg ovulated

How many sperm fertilize egg?

• Survival of the fittest

• Polyspermy– nondisjunction????

• Blocks to polyspermy

http://www.molbiolcell.org/content/vol9/issue7/images/video/mk0780641001.mov

Slow Block to Polyspermy– formation of fertilization envelope

http://www.molbiolcell.org/content/vol9/issue7/images/video/mk0780641001.mov

Thought Question• What is the problem with 2+ sperm

fertilizing one egg?• How is this problem related to

nondisjunction?

Twins/IVF

TwinsZygote = fertilized egg

When fertilized egg splits partially

In Vitro Fertilization

In Vitro= in petri dish

Egg + sperm united outside body

Thought Question• What potential fertility problems (M

and F)may lead couples to engage in IVF?? Why??

• Think of at least 2!!!

IVF often leads to multiple births

• Multiple zygotes implanted

• Increased likelihood for complications

How Often Fertilization Works

How Often Fertilization Works

• “If you think it’s amazing that any one of us survives to be born, you are correct.”~ Gilbert, Developmental Biology

Thought Question

• Out of 20 hypothetical human eggs that come into contact with sperm, how many lead to:– Successful fertilization– Successful implantation– Successful development, 4th week– Successful development, 8th week– Fetuses coming to term

– OVERALL, what percentage of human conceptions successfully come to term?

½ to 2/3 of human conceptions don’t come to term

Implantation in Uterus/Nourishment for Baby

Implantation in Uterus

Ectopic Pregnancy

Umbilical Cord and Placenta

Amniotic Fluid

Contraception

Physical Barrier methods

Chemical Methods

Thought Question

• A woman taking birth control still receives her period. What must necessarily occur for this to happen?

• New birth control pills have been developed that allow women only to get their periods a few times a year. What must be different about these pills vs. normal birth control?

Figure 46.21 Mechanisms of some contraceptive methods