Fertilization

Question 1

What does seminal fluid consist of?

Answer 1

→ Prostatic and seminal vesicle secretions

Question 2

What is the function of seminal fluid?

Answer 2

→ It coagulates to prevent loss and later liquefies

Question 3

What is the function of the cervical mucus?

Answer 3

→ To remove seminal fluid

→ removing morphologically abnormal sperm and cellular debris

Question 4

When is cervical mucus less viscous and why?

Answer 4

→ in the absence of progesterone

→ allows sperm to pass

Question 5

What forms a reservoir of sperm in the female?

Answer 5

→ Cervical crypts

Question 6

When does fertilisation occur within?

Answer 6

→ 24-48 hours

→ sperm have been found alive after 5 days

Question 7

What attracts the sperm to the egg?

Answer 7

→ Chemoattractants released from the oocyte cumulus complex

→ Sperm become hyperactivated near the egg

Question 8

How do sperm become hyperactivated near the egg?

Answer 8

→ Forceful tail beats with increased frequency and amplitude
→ mediated by Ca2+ influx via CatSper channels

Question 9

How is capacitation achieved?

Answer 9

→ Removing the sperm from the seminal fluid

→ uterine or tubal fluid may contain factors which promote capacitation

Question 10

What must occur to the sperm before the acrosome reaction?

Answer 10

→ Biochemical rearrangement of the surface glycoprotein

→ changes in membrane composition

Question 11

What time does capacitation occur?

Answer 11

→ 4-16 hours

Question 12

Where does the acrosome reaction occur?

Answer 12

→ within the zona-cumulus complex

Question 13

How does the acrosome reaction occur?

Answer 13

→ Acrosomal membrane on the sperm fuses
→ releases enzymes that cut through the zona-cumulus complex
→ acrosin bound to the inner acrosomal membrane digests the zona pellucida so sperm can enter

Question 14

What causes the oocyte to undergo meiosis?

Answer 14

→ LH spike

Question 15

What does the LH spike make the oocyte change into?

Answer 15

→ Primary oocyte becomes seconday oocyte + 1st polar body

Question 16

What does the corpus luteum produce?

Answer 16

→ Progesterone

Question 17

What does progesterone do to the endometrium?

Answer 17

→ Makes it secretory and receptive to implantation

Question 18

What does progesterone do to the cilia?

Answer 18

→ Suppresses cilia in uterine tubes once the oocyte has passed

Question 19

What does progesterone do the the cervical mucus?

Answer 19

→ It makes it viscous to prevent further sperm penetration

Question 20

What is the function of estrogen in the luteal phase?

Answer 20

→ Maintains the endometrium

Question 21

What causes the LH spike?

Answer 21

→ sustained levels of estrogen produced by the dominant follicle

Question 22

After ovulation what happens to the follicle?

Answer 22

→ it becomes the corpus luteum

Question 23

What does progesterone do in the secretory phase?

Answer 23

→ Makes the stratum functionalis thicker

→ uterine glands become more secretory

Question 24

What causes the proliferative phase?

Answer 24

→ Estrogen from the follicular phase

Question 25

What is the life span of the CL?

Answer 25

→ 14 days

Question 26

What causes the inter cycle rise of FSH?

Answer 26

→ the fall in CL derived steroids

Question 27

What does the CL becomes when it dies?

Answer 27

→ Corpus albicans

Question 28

What happens to the CL in pregnancy?

Answer 28

→ It is rescued by the HcG from the embryo binding to the LH receptors
→ it continues to produce progesterone and maintain the endometrium

Question 29

What does the menstrual cycle achieve?

Answer 29

→ Selection of a single follicle and oocyte
→ Correct number of chromosomes in the oocyte
→ Changes in cervix and uterine tubes to enable egg transport and sperm access
→ Preparation of the endometrium
→ Support of the implanting embryo

Question 30

What are cumulus cells?

Answer 30

→ Remnants of the granulosa cells

Question 31

What is the corona radiata?

Answer 31

→ innermost granulosa cells

Question 32

What is the zona pellucida made from?

Answer 32

→ Matrix of proteins which are secreted from the egg

Question 33

What is a polar body?

Answer 33

→ The other half of cell division without the cytoplasm

Question 34

What does the first polar body mean?

Answer 34

→ That meiosis I has occurred

Question 35

When is meiosis triggered to finish?

Answer 35

→ By LH at ovulation

Question 36

Where does the acrosome reaction occur?

Answer 36

→ In contact with the zona-cumulus complex

Question 37

Describe sperm binding

Answer 37

1) Sperm penetrates the cumulus and bind to the ZP
2) Sperm enzymes cut through the ZP with ZP3 and the sperm fuses with the plasma membrane
3) Sperm are taken in by phagocytosis
4) Phospholipase Zeta is activated by basal Ca2+ inside the egg
PIP2 → DAG + IP3 which causes intracellular release of Ca2+ leading to a large Ca2+ spike
5) Cortical reaction as a wave of Ca2+ sweeps over the egg

Question 38

What is the cortical reaction?

Answer 38

→ Releases proteases, peroxides and hyaline which prevents polyspermy

Question 39

After meiosis I how many chromosomes does the oocyte have?

Answer 39

→ 23

→ 2 copies of each chromosomes are arranged as a sister chromatid

Question 40

What does entry of the sperm into the egg cause?

Answer 40

→ increase in Ca2+

Question 41

What does Ca2+ cause in the egg?

Answer 41

→ Completion of Meiosis II

Question 42

Describe syngamy

Answer 42

1) entry of sperm causes an increase in Ca2+ which causes the completion of meiosis II expelling the second polar body
2) Sperm nuclear membrane breaks down and chromatin decondenses and chromosomes separate
3) 4-7 hours after fusion the two sets of haploid chromosomes become surrounded by distinct membranes forming pro nuclei
4) the haploid structures synthesize DNA in preparation for the first mitotic division
5) pro nuclei fuse and mitotic metaphase spindle forms
6) mitosis occurs and one cell zygote becomes a two cell embryo