5. Gametogenesis

Question 1

What does genetic variation arise from in gametogenesis?

Answer 1

Crossing over.
Independent assortment.
Random segregation.

Question 2

What do spermatogonia divide by mitosis to produce?

Answer 2

Ad spermatogonium (reserve stock).
Ap spermatogonium (active, maintain stock and from puberty onwards produce type B spermatogonia which give rise to primary spermatocytes).

Question 3

From puberty onwards ap spermatogonium give rise to type B spermatogonia, which give rise to primary spermatocytes. What do these divide by and what does this produce?

Answer 3

By meiosis.

Produce secondary spermatocytes, then spermatids.

Question 4

By what process do spermatids form spermatozoa?

Answer 4

Spermiogensis (differentiation).

Question 5

What is the spermatic cycle?

Answer 5

Time taken for the reappearance of the same stage within a given segment of seminiferous tubule.

Question 6

What is the spermatogenic wave?

Answer 6

The distance in a seminiferous tubule between areas where the same stage of spermatogenesis is occurring.

Question 7

How do speratogenic waves move towards the inner part of the lumen of a seminiferous tubule?

Answer 7

In a corkscrew like spiral towards the centre. So different stages of spermatogenesis are ordered in space as well as time.

Question 8

What is spermiation?

Answer 8

The release of spermatids into the lumen of the seminiferous tubules.

Question 9

What happens as spermatids pass down the seminiferous tubule, through the rete testis and ductili efferentes into the epididymis?

Answer 9

Where spermiogensis occurs.

Remodel, finally form spermatozoa and become motile in the epididymis.

Question 10

In spermiogenesis, what assists the move the of non-motile spermatids until they reach the epididymis?

Answer 10

Sertoli cell secretions and peristaltic contractions.

Question 11

What are the 4 main components of semen? Which enter at the vas deferens and which enter at the urethra, and what percentage of semen does each make up?

Answer 11

Seminal vesicle secretions 70% - vas deferens.
Secretions of the prostate 25% - urethra.
Sperm 2-5% - vas deferens.
Bulbourethral gland secretions <1% - urethra.

Question 12

What happens in sperm capacitation?

Answer 12

Conditions in the female reproductive tract stimulate the removal of glycoproteins and cholesterol from the sperm membrane, and activation of sperm signalling pathways.

Question 13

What is sperm capacitation and what is its purpose of?

Answer 13

The final maturation step required for sperm to become fertile. Is to allow sperm to bind to the zona pellucida of the oocyte and initiate acrosome reaction.

Question 14

What do human sperm need to the incubated in before in vitro fertilisation?

Answer 14

Capacitation media.

Question 15

What happens in the first 3 months of embryology with regards to maturation of oocytes?

Answer 15

Germ cells (arise from yolk sac) colonise the gonadal cortex and differentiate into oogonia. These proliferate rapidly by mitosis and by the end of the 3rd month the oogonia have arranged in clusters surrounded by flat epithelial cells.

Question 16

What are primary oocytes?

Answer 16

Some oogonia that have entered meiosis and arrested in prophase of meiosis I. (Most continue to divide by mitosis to produce more oogonia).

Question 17

When are the maximum number of germ cells reached?

Answer 17

Mid gestation.

Question 18

What has happens to most oogonia and some primary oocytes in prophase of meiosis I by the 7th month of gestation?

Answer 18

Degenerated (atresia).
Surviving primary oocytes have now entered meiosis I and are individually surrounded by a layer of flat epithelial cells called follicular cells. Now called a primary follicle.

Question 19

When does maturation of oocytes continue after birth?

Answer 19

At puberty.

Question 20

What are the 3 stages of oocyte maturation each month?

Answer 20

Preantral.
Antral.
Preovulatory.

Question 21

What happens in the prenatal stage of oocyte maturation?

Answer 21

Primordial follicles begin to grow, surrounding follicular cels change from flat to cuboidal and proliferate to produce a stratified epithelium of granuloma cells. Granulosa cells secrete a layer of glycoproteins on the oocyte, forming the zona pellucida.

Question 22

What happens in the antral stage of oocyte maturation?

Answer 22

Fluid filled spaces appear between the granuloma cells, which coalesce to form the antrum. This is now a secondary follicle.

Question 23

What hormone is secreted by follicular cells?

Answer 23

Oestrogen.

Question 24

How many follicles usually reach maturity in each ovarian cycle, and what happens to the rest.

Answer 24

Usually only one reaches maturation, the rest become atretic.

Question 25

What happens in the preovulatory stage oocyte maturation?

Answer 25

Surge in LH induces preovulatory growth phase.
Meiosis I is now completed, resulting in 2 haploid daughter cells of unequal size. One receives most of the cytoplasm (secondary oocyte) and the other receives hardly any (first polar body).
The cell then enters meiosis II and arrests in metaphase about 3 hours before ovulation.
Meiosis II is only completed if the oocyte is fertilised, otherwise the cell degenerates 24 hours after ovulation.

Question 26

What happens in ovulation?

Answer 26

FHS and LH stimulate rapid growth of follicle several days before ovulation occurs, forming a Graafian follicle.
LH surge increases collagenase activity and prostaglandins increase in response to the LH, causing local muscular contractions in the ovarian wall.
The oocyte is extruded and breaks free from the ovary, piercing through the peritoneum.

Question 27

What forms the corpus luteum?

Answer 27

Remaining granulosa and theca interna cells from mature oocyte become vascularised. Develop a yellowing pigment and change into lutein cells, which form the corpus luteum.

Question 28

What hormones does the corpus luteum secrete? What do these stimulate?

Answer 28

Oestrogen and progesterone.

Stimulate the uterine mucosa to enter the secretory stage in preparation for embryo implantation.

Question 29

When does the corpus luteum die?

Answer 29

After 14 days if no fertilisation occurs.

Question 30

How is the oocyte transported after ovulation?

Answer 30

Before ovulation, fimbriae sweep over the surface of the ovary and the uterine tube begins to contract rhythmically. Oocyte carried into tube by sweeping movements of fimbriae and by motion of cilia on epithelial lining. Oocyte then propelled by peristaltic muscular contractions of the tube and by cilia in the mucosa.

Question 31

What is the corpus albicans?

Answer 31

The mass of fibrotic scar tissue formed by the corpus luteum degeneration if fertilisation has not occurred.

Question 32

What happens hormonally when the corpus albicans forms?

Answer 32

Progesterone production decreases, precipitating menstrual bleeding.

Question 33

What is the corpus luteum graviditatis?

Answer 33

Formed by the growth of the corpus luteum when fertilisation has occurred, as degeneration of the corpus lutetium is prevented by human chorionic gonadotrophin, secreted by the developing embryo.

Question 34

What hormone is secreted by the corpus luteum graviditatis and until when?

Answer 34

Progesterone.

Until 4th month, when secretion of progesterone by the placenta then becomes adequate.