Fertilization Video

What is fertilization?

A single sperm to fight incredible odds to unite with a human egg and form new human life

How many sperm enter the vagina during sexual intercourse?

300 million

What is the fate of the sperm soon after ejaculation in the vagina?

Millions of them will flow out, or die in its acidic environment

Why do some sperm survive in the vagina?

Because of the protective elements provided in the fluid surrounding them

Where will the sperm go after they have entered the vagina?

They must pass through the cervix (an opening into the uterus- usually it remains tightly closed but the cervix is open for a few days while the women ovulates)

How are the sperm able to travel past the cervix?

The sperm swim through the cervical mucus, which is thinned to a more watery consistency for easier passage

Once the sperm travel through the cervix, what will happen?

Millions will die trying to make it through the mucus- some sperm remain behind, caught in the folds of the cervix (but may later continue the journey as a backup to the first group)

What will happen inside the uterus?

Muscular uterine contractions assist the sperm on their journey toward the egg

What do resident cells from the woman’s immune system do when they detect sperm?

Mistaken the sperm for foreign invaders so they destroy thousands more

Where do the sperm go after they have reached the uterus?

Half will head towards the empty fallopian tube, the other half swim toward the tube containing the unfertilized egg (now only a few thousand remain)

What happens inside the fallopian tube?

Tiny cilia push the egg toward the uterus, to continue, the sperm must surge against this motion to reach the egg

What is the fate of the sperm if they get trapped in the cilia?

Death

When do they sperm become hyperactive, how?

Chemicals in the reproductive tract cause the membranes covering the heads of the sperm to change causing them to swim harder and faster towards their destination

What happen when the sperm reaches the egg?

The sperm must push through the corona radiata layer to reach the zona pellucida 

How many sperm survive when they are close to reaching the egg?

Only a few dozen of the original 300 million sperm remain

What covers the egg?

A layer of cells called the corona radiata

What happens when the sperm reach the zona pellucida?

They attach to specialized sperm receptors on the surface. This triggers their acrosomes to release digestive enzymes, enabling the sperm to burrow into the layer

What is inside the zona pellucida?

There is a narrow, fluid-filled space just outside the egg cell membrane

What will happen to the first sperm that makes contact with the egg?

It will fertilize it; a single sperm attaches to the egg cell membrane

What happens when the sperm makes contact with the egg?

Within a few minutes, the outer membranes fuse, and the egg pulls the sperm inside, which causes changes in the egg membrane that prevent other sperm from attaching to it

Once the sperm reaches the egg, how does the egg stop other sperm from entering?

It releases chemicals that push other sperm away from the egg and create an impenetrable fertilization membrane

After the creation of the impenetrable fertilization membrane, what does the zona pellucida do?

As the reaction spreads outward, the zona pellucida hardens and traps any sperm unlucky enough to be caught inside

What is happening outside the egg after the zona pellucida hardens?

The sperm are no longer able to attach to the zona pellucida

What is happening inside the egg while the zona pellucida is hardening on the outside?

Tightly packed male genetic material spreads out and a new membrane forms around the genetic material called the male pronucleus

What is happening inside the male pronucleus?

The genetic material reforms into 23 chromosomes

How does the female genetic material awaken?

Due to the fusion of the sperm with the egg finishes dividing, causing the formation of the female pronucleus (which also contains 23 chromosomes)

What is happening as the male and female pronuclei form?

Microtubules pull them toward each other and the two sets of chromosomes join together completing the process of fertilization. They combine to create a unique genetic code, instantly determining gender, hair color, eye color, and many other traits

What is the term for the single cell formed from the fusion of the male and female gametes?

A zygote- the beginning of a new human being.

Where does the zygote travel after fertilization?

The cilia in the fallopian tube gently sweep the zygote toward the uterus

What happens when the zygote reaches the uterus?

It implants into the rich uterine lining, where it will grow and mature for about 9 months until birth