Pregnancy

Sperm

Egg

Human Reproduction: Ovulation, Semen Production, and Fertilization

Sperm race to fertilize the egg

Ovulation: when an egg is released from the ovary

1. Egg release from ovary = ovulation

2. Egg travels through the fallopian tube in an attempt to meet with a sperm

Fertilization

The best time for sperm to meet the egg is soon after

ovulation

To Recap:

Ovulation

Egg

Ejaculation

Sperm

Fertilization

Implantation

Pregnancy

Anatomy of the ovumThe egg is surrounded

by a thick coat called the zona pellucida.

The zona is surrounded by the corona radiata,

which is many cell layers formed by

follicle cells adhering to the egg before it leaves the follicle in the ovary.

The sperm must burrow

its way through the

zona pellucida. (Only one

sperm can do this!) Once inside the

sperm’s DNA combines with the

egg’s DNA.

Once fertilized, the egg is now called a zygote. The zygote begins rapid cell division.

At the end of this cell division, the zygote becomes a blastocyst. https://www.youtube.com/watch?v=W4pVICcRtxQ

Implantation (when the blastocyst burrows into the endometrium) usually happens about 8 days after

ovulation.

Implantation into endometrium

 The syncytiotrophoblast

erodes the uterine wall during

implantation and the begins the production

of the placenta.

The syncytiotrophoblast also produces the HCG (human chorionic gonadotropin) hormone. This is the hormone that

pregnancy tests test for. The presence of the syncytiotrophoblast = pregnancy.

Placenta

The placenta provides oxygen and nutrients to the fetus, while removing carbon dioxide and other waste products.

Timeline Day 0 – Day 5: Zygote

Day 5 – Day 10: Blastocyst

Week 2 – week 7: Embryo

Week 8 – week 40: Fetus

Day 0 – Day 5: ZygoteA zygote immediately begins to divide and grow into a ball of cells called a blastocyst.

Day 5 – Day 10: BlastocystThe thin layer becomes the placenta, an organ that regulates fetal development. The thick section of the blastocyst will become the embryo itself.

Week 2 – week 7: EmbryoMajor internal organs and external body structures take on identifiable shapes. The heart forms and begins to pump blood. The brain and spinal cord can be identified. Arms and legs sprout and take shape.

Week 8 – week 40: FetusStructures that have already formed continue to grow and develop.

Sex differentiation – how reproductive organs develop in utero

Sperm determines the sex of the embryo/fetus

But no matter what the sex is, male and female embryos

begin with the same fetal reproductive system

All embryos begin with this structure

The PINK tract is called the Mullerian duct. It will become

the female reproductive system.

The BLUE tract is called the Wolffian duct. It will become

the male reproductive system.The circles are the

gonads and will eventually become the ovaries or the

testicles.

How does this happen?

SRY is a gene located on the Y chromosome and is ESSENTIAL for

the development of the testes.

Once the testes develop, the leydig cells make testosterone

Male sex hormones are XY and females are XX

The presence of testosterone retains the wolffian duct and

develops it into the male reproductive system

Meanwhile, sertoli cells produce a hormone

called MIS (mullerian inhibiting substance),

which disintegrates the mullerian duct

What about in the female?Male sex hormones are XY and females are XX

Female only has XX chromosome, no Y chromosome No SRY gene Testes do not develop No cells make testosterone Wolffian duct is NOT maintained without the presence of testosterone Wolffian duct disintegrate Mullerian duct remains and develops into the female reproductive system

So what does all of this mean?The male reproductive system REQUIRES activation in order to development. It needs the SRY gene and

testosterone.

The female system DOES NOT require activation. It will simply develop without the presence of

testosterone. The female reproductive system is the DEFAULT system.

It’s not that we all start as females in utero. We all start as the SAME- neither male nor female.

Symptoms of PregnancyMissed periodTender or swollen breastsNausea (with or without vomiting)Slight bleeding or “spotting”Increased urinationFatigueFood aversions or craving

The only way to REALLY determine pregnancy is to take a test.