Lecture 73: Repro Physio of the Male and Fertilization

Question 1

What are the two main cell types in the male testis? What hormones do they respond to and what do they secrete?

Answer 1

Leydig (intersititial) cells
- contain receptors for LH
- Produce T4
- Secrete inhibin

Sertoli cells
- Contain receptors for FSH
- Convert testosterone to estradiol
- secrete inhibin

Question 2

What are the three phases of spermatogenesis?

Answer 2

1) Proliferation: mitotic divisions
2) Meiotic phase: involves primary and second spermatocytes
- phase in which genetic diversity is guaranteed by DNA replication and crossing over
3) Differentiation phase: Spermiogenesis
- No further cell divisions
- Marked by transformation from spermatid to spermatozoa (from spherical shape to having a head, midpiece, and flagellum)

Question 3

Differentiation consists of 4 phases. What are they?

Answer 3

1) Golgi Phase: acrosomic vesicle formation
2) Cap phase: acrosomic vesicle spreading over the nucleus
3) Acrosomal phase: Nuclear and cytoplasmic elongation
4) Maturation phase: Final assembly that forms a spermatozon

Question 4

Describe the sperm pathway to fertilization

Answer 4

Sperm deposition (either in uterus or vagina)
Then capacitation
Then to oviducts
Binds to ZP
Acrosome reaction
Penetrates Zp
Bind to the oocyte plasma membrane
Enters the oocyte cytoplasm
Decondensation
Male pronucleus

Question 5

What is the oviductal reservoir? What does it do?

Answer 5

Spermatozoal reservoir in the oviductal isthmus

The estrus cycle probably regulates the number and motility of spermatozoa attached

Question 6

What is the result of capacitation of sperm?

Answer 6

Hyper-activated sperm in the oviduct (ampulla)
Unmasking of ZP binding sites

Question 7

What are the postcapacitation sequence of events leading to fertilization? List them in order

Answer 7

Hyperactive motility
Binding to zona pellucida
Acrosomal reaction
Penetration of zona pellucida
Sperm-oocyte fusion
Sperm engulfed
Decondensation of sperm nucleus
Formation of male pronucleus

Question 8

What is the cortical reaction? What are the results?

Answer 8

The sperm head attaches to the oocyte plasma membrane (vitelline membrane) and initiates the block to polyspermy

Results in ZP binding, vitelline membrane changes, prevents other sperm from binding to the ZP

Question 9

What is syngamy? What is the resulting structure called?

Answer 9

the fusion of the female and male pronuclei, the resulting organism is called a zygote

Question 10

What is the difference between a zygote and an embryo?

Answer 10

Zygote is unicellular
Embryo is multi-cellular