Fertilisation and luteal phase

Question 1

What is the state of ejaculated semen?

Answer 1

Ejaculated semen is coagulated

Question 2

What does seminal fluid comprise of?

Answer 2

Prostatic and seminal vesicle secretions comprise seminal fluid which coagulates-prevents loss, later liquefies

Question 3

What does movement through cervical mucus remove?

Answer 3

Movement through cervical mucus removes seminal fluid, abnormally morphological sperm and cellular debris

Question 4

When sperm passes into cervix What quality of cervical mucus allows it to pass and why?

Answer 4

Cervical mucus is less viscous in the absence of progesterone allowing sperm to pass

Question 5

What can sperm inhabit when they pass into the cervix?

Answer 5

Sperm can inhabit cervical crypts which may form a reservoir

Question 6

What may attract the sperm to the egg?

Answer 6

-Chemoattractants released from the oocyte cumulus complex may attract the sperm

Question 7

What can happen to the sperm during its journey to the egg?

Answer 7

Sperm can become hyperactivated with forceful tail beats with increased frequency and amplitude mediated by Ca2+ influx via catsper channels

Question 8

What is sperm capacitation?

Answer 8

It is the biochemical arrangement of the surface of glycoprotein and changes in membrane composition which must occur before the acrosome reaction takes place

Question 9

How can sperm capacitation be partly achieved?

Answer 9

Is partly achieved by removing the sperm from seminal fluid

Question 10

What may promote sperm capacitation?

Answer 10

Uterine or tubal fluid may may contain factors which promote capacitation

Question 11

Where does the acrosome reaction occur?

Answer 11

Occurs in contact with the zona cumulus complex

Question 12

What happens in the acrosome reaction?

Answer 12

• The acrosomal membrane on the sperm head fuses releasing enzymes that cut through the complex
• Acrosin bound to the inner acrosomal membrane digests the zona pellucida so the sperm can enter

Question 13

What does progesterone make during the luteal phase?

Answer 13

Makes the endometrium secretory and receptive to implantation

Question 14

What does progesterone suppress in the luteal phase?

Answer 14

Supressess cilia in uterine tubes once oocyte has already passed

Question 15

What does progesterone make viscous again in the luteal phase?

Answer 15

Makes cervical mucus viscous again to prevent further sperm penetration

Question 16

What does oestrogen help in the luteal phase?

Answer 16

Helps to maintain endometrium in luteal phase

Question 17

What does the cumulus oophorus do and what is it derived from?

Answer 17

Protects egg and is derived from granulosa cells

Question 18

What is the corona radiata and what is in contact with?

Answer 18

It is the innermost layer of cumulus cells in contact with the zona pellucida

Question 19

What is the corona radiata formed by?

Answer 19

Formed by granulosa cells

Question 20

What does the corona radiata adhere to before it leaves the ovarian follicle?

Answer 20

Adheres to the oocyte before it leaves the ovarian follicle

Question 21

What is the zona pellucida secreted by?

Answer 21

Secreted by the egg

Question 22

What happens to the zona pellucida after the cortical reaction?

Answer 22

Becomes impenetrable after the cortical reaction

Question 23

Where does fertilisation usually occur?

Answer 23

Usually occurs in the ampulla of the uterine tubes

Question 24

What are the steps involved in sperm binding and penetration?

Answer 24

1. The acrosome reaction occurs in contact with the zona cumulus complex. The sperm penetrate the cumulus and bind to the zona pellucida
2. Sperm enzymes cut through the zona pellucida and sperm fuses with plasma membrane
3. Sperm taken in by phagocytosis. Phosphate zeta activated by basal Ca2+ inside egg. PIP2 –> DAG + IP3 causes the release of intracellular Ca2+ leading to a large Ca2+ spike
4. Cortical reaction as wave of Ca2+ sweeps around egg; release of proteases, peroxides and hyaline prevents polyspermy

Question 25

What are the steps involved syngamy?

Answer 25

1. After the sperm enters, Ca2+ causes completion of meiosis 2 expelling the second polar body and initiates the cortical reaction
2. The sperm nuclear membrane breaks down, the chromatin decondenses and chromosomes separate
3. 4-7 hours after fusion, the 2 sets of haploid chromosomes become surrounded by distinct membranes forming pronuclei. These haploid structures synthesise DNA in preparation for the first mitotic division
4. The pronuclei fuse and the mitotic metaphase spindle forms with the chromosomes assuming their position at its equator
5. Mitosis is completed and the one cell zygote becomes a 2 cell embryo