Gametogenesis

Question 1

What do germ cells do after colonising the gonad?

Answer 1

1. Proliferate by mitosis.
2. Genetically change by meiosis.
3. Cytodiffereniate to mature gametes.

Question 2

What are the 2 functions of meiosis.

Answer 2

1. Reduction of chromosome number to half.

2. Genetic variation.

Question 3

What are the 3 process of genetic variation called?

Answer 3

1. Crossing-over.
2. Independent assortment.
3. Random Segregation.

Question 4

Describe independent assortment.

Answer 4

Random orientation of each bivalent along the metaphase plate with respect to other bivalent.

Question 5

Describe Random Segregation.

Answer 5

Random distribution of alleles amongst the 4 gametes.

Question 6

Describe the movement of sperm.

Answer 6

Seminiferous tubule-> Rete Testis-> Ductili Efferentes-> Head of epididymis-> Tail of epididymis-> Vas deferens.

Question 7

Describe Spermatogenesis.

Answer 7

1. Spermatogonium (2n) undergoes mitosis.
2. Forms Ad spermatogoium and Ap spermatogonium.
3. Ap spermatogonium forms type B spermatogonium. This is a primary spermatocyte.
4. Primary spermatocyte undergo meiosis 1.
5. Form 2 1n secondary spermatocyte.
6. Secondary spermatocyte undergo meiosis 2.
7. Form Spermatid.
8. Spermatid is released into the seminiferous tubule by spermiation.
9. Remodel as they go through the seminiferous tubule by spermiogenesis.
10. This forms a spermatozoa.

Question 8

Define Spermatogenic Cycle.

Answer 8

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

Question 9

What is the typical spermatogenic cycle length in a human?

Answer 9

16 days.

Question 10

Define Spermatogenic Wave.

Answer 10

Distance between the same stage.

Question 11

Are Spermatid in spermiogenesis motile?

Answer 11

No, they are transported via Sertoli cell secretions assisted by peristaltic contraction until they reach the epididymis.

Question 12

Describe sperm capacitation.

Answer 12

The final maturation step in sperm, where glycoproteins and cholesterol are removed from the sperm membrane, activating the sperm signalling pathway (involving atypical soluble adenylyl cyclase and PKA).

Question 13

What does sperm capacitation allow the sperm to do?

Answer 13

Bind to the zona pellucida of the oocyte and initiate acrosome reaction.

Question 14

Describe the maturation of oocytes before birth.

Answer 14

1. Germ cells colonise in the gonadal cortex and differentiate into oogonia.
2. Oogonia proliferate rapidly by mitosis.
3. End of 3rd month oogonia are arranged in clusters surrounded by follicular cells (flat epithelial).
4. Most continue to divide by mitosis but some by meiosis.
5. Forms primary oocytes (arrest in prophase 1).
6. Cell death begins (atresia).
7. The remaining surviving primary oocytes are surrounded by follicular cells and called primordial follicles.

Question 15

Describe the Preantral Stage of Oogenesis (puberty).

Answer 15

1. Primordial follicles begin to grow, surrounding follicular cells become cuboidal and proliferate to produce stratified epithelium of granulosa cells.
2. Granulosa cells secrete glycoproteins to form the zona peullucida.

Question 16

Describe the Antral Stage of Oogenesis (puberty).

Answer 16

1. As development continues, fluid filled space appears between the granulosa cells-> Antrum. Outer fibrous layer is the theca externa and inner secretory layer is the theca interna.
2. Several follicles begin to develop with each ovarian cycle, only one reaches maturity.

Question 17

Describe the Preovulatory Stage of Oogenesis (puberty).

Answer 17

1. Surge in LH induces this stage.
2. Meiosis 1 completes-> n. 2 haploid, one with most of cytoplasm.
3. Enter meiosis 2, arrest at metaphase 2.

Question 18

What are granulosa cells surrounding the oocyte called?

Answer 18

Cumulus oophorus.

Question 19

Describe Ovulation.

Answer 19

FSH and LH stimulate rapid growth of the follicle several days before ovulation. The mature follicle is a Graafian follicle.
LH surge increases collagenase and prostraglandins causing muscular contractions in ovarian wall.
Oocyte extruded and break free from ovary.

Question 20

Describe the Corpus Luteum.

Answer 20

Remaining granulosa and theca interna cells become vascularised.
They develop a yellow ligament and change in lutein cells, forming the corpus luteum.
The corpus luteum secretes oestrogen and progesterone which stimulates the uterine mucosa to enter the secretory stage to prepare for implantation. If there is no fertilisation the corpus luteum dies in 14 days.

Question 21

How is the oocyte transported?

Answer 21

Fribimbriae sweep over the ovary and the Fallopian tube begins to contract rhythmically.
Cilia of Fallopian tubes help move it, as well as peristaltic muscular contractions.
If fertilised the oocyte will reach the uterine lumen in around 3 to 4 days.

Question 22

Describe the Corpus Albicans.

Answer 22

This mass of fibrotic scar tissue will develop if fertilisation occurs. Progesterone production decreases encouraging menstrual bleeding.

Question 23

What will happen to the corpus luteum is fertilisation does occur?

Answer 23

hCG will be secreted by the embryo, causing the corpus luteum to become the corpus luteum graviditatis, continuing to secrete progesterone till the 4th month, until the placenta can take over.

Question 24

Compare Spermatogenesis to Oogenesis.

Answer 24

200 million sperm are made a day compared to 1 ovum a month.
4 Spermatid are made of equal size compared to 1 ovum and 3 polar bodies (with less cytoplasm).
In men spermatogenesis occurs in puberty and in females in the fetus.
Men Spermatogenesis occurs throughout life whereas in women it ends at puberty.
Sperm are motile, ova are not.
All stages of spermatogenesis occur in the testes compared to meiosis 2 in the oviduct.