Lecture 6 - Spermatogenesis and Fertilization

What are the ways sperm is transported?

1. Rapid sperm transfer

2. Formation of reservoir

3. Slow prolonged release

What is rapid sperm transfer?

-Immediately after mating the sperm reaches the oviduct

-Sperm is not viable because capacitation did not have time to occur

Why is the formation of reservoirs important for sperm transport?

Allow sperm to mature before they reach the oviduct

What is slow prolonged release?

-Over days the sperm reach the oviduct

-These sperm are viable since they have enough time for capacitation

What must spermatozoa do before they acquire maximum fertility?

They must reside in the female tract

What are the 3 steps of capacitation?

1. Epididymal

2. Ejaculated

3. Capacitated

What happens in the epididymal stage of capacitation?

In the epididymus, the sperm head gets coated with proteins that are important for binding to zona pellucida

What happens in the ejaculated stage of capacitation?

The proteins from seminal plasma coat the sperm head coatings to protect the proteins now on the sperm head from the female environment

What happens in the capacitated stage of capacitation?

In the female repro tract, seminal plasma proteins are stripped off and the sperm is competent for fertilization

Is capacitation reversible?

Yes

What is the function of ZP1 and ZP2 (zona pellucida proteins 1 and 2)?

Structural proteins providing the structural integrity of the zona

What is the function of ZP3 (zona pellucida protein 3)?

-Binds to proteins on the spermatozoa membrane

-Important for binding of sperm to egg

What is the acrosomal reaction?

-An orderly fusion of the spermatozoal membrane and the outer acrosomal membrane

-Pores are created to release acrosomal enzymes, which allows the sperm to digest its way through the zona pellucida

What are the enzymes found in the acrosomal reaction and what are their functions?

-Proacrosin: aids in binding sperm to the zona (after binding becomes acrosin)

-Acrosin: hydrolyzes zona proteins

What happens to the sperm after the acrosomal reaction?

The vesicles are sloughed and fusion proteins are exposed, which help the sperm and oocyte membrane fuse

What is the immediate effect of the sperm fusing with the oocyte?

Cortical reaction

What happens in the cortical reaction?

-Cortical granules under the oocyte membrane exocytose and cause a biochemical modification in the zona pellucida

-Prevents any other sperm from binding or traveling through the zona pellucida (polyspermy)

What is polyspermy?

Fertilization of an oocyte by more than one sperm, which results in embryo death

What is syngamy?

Fusion of the male and female pronuclei, formation of zygote

What are the 2 ways the cortical reaction prevents penetration by additional sperm?

1. Zona block: block traveling through zona pellucida

2. Vitelline block: sperm have traveled through zona but are stuck in the perivitelline space