The Development Of The Gametes

Question 1

What are the two main reasons for meoisis to take place when producing gametes?

Answer 1

Reduce the chromosome number in the gamete to 23

Ensures that each gamete is genitcally unique

Question 2

How does meosis produce genetic variation between the gametes?

Answer 2

Crossing over of genetic material that occurs in prophase 1
Random segregation- the dsitrubutin of chromosomes between 4 gametes
Independant assortment: the two homologus chromosomes must go into seperate gametes

Question 3

Where do spermatozoa develop?

Answer 3

Within the seminiferous tubules in association with the sertoli cells

Question 4

What is the importance of the blood testis barrier?

Answer 4

Sperm cells have different genetic material from the gather, and should appear as foreign and then have a different immune respose between them

Question 5

What is the rete testis involved in?

Answer 5

Concentrating the spermatozoa

Question 6

What is the raw material for spermatogenesis>

Answer 6

Spermatogonia

Question 7

What are the two products of mitosis of spermatogonia?

Answer 7

Ad spermatogonium that act to maintain the stock

Ap spermatogonium that give rise to primary spermocytes

Question 8

What happens to the primary spermacytes?

Answer 8

Divide by meosis giving rise to the secondary spermacytes and then spermatids

Question 9

What is the proccess of spermiogensis?

Answer 9

When spermatids are realeased into the seminiferous tubules, they are remodelled as they pass down, for example they are non motile until they reach the epidiymis

Question 10

What is the spermatogenic cycle?

Answer 10

This is the time taken for the reappearance of the same stage of spermatogenis within a given segement of seminiferous tubule, ( as the cells tend to group will the cells that have the same maturation stages)

Question 11

What are the contents of semen?

Answer 11

Seminal vessel secretions (70%)- eg amino acids, citrate, fructose and prostaglandins
Secretions of prostate (25%) including proteolytic enzymes
Sperm via vas deferens (2-5%)
Bulbourethral gland secretions

Question 12

What is the route that the sperm takes before ejaculation?

Answer 12

Seminferous tubules- rete testis- ducti efferentes- epidiymis- vas deferens- urethra

Question 13

What is sperm capication?

Answer 13

The final maturation step required before sperm can become fertile, stimulated by conditions in the female gential tract, the removal of glycoportiens and cholestrol from the sperm membrane

Question 14

Why is sperm capication important?

Answer 14

Allows the sperm to become fertile, and activates the sperm singnalling pathways and allows the sperm to bind to the zona pelludcia of the oocyte

Question 15

How do female oocytes mature before birth?

Answer 15

Germ cells colonise the cortex of the primary gonad before becoming oogonia, and then proliferate rapidly by mitosis however most will die in gestation, and will begin mesois before birth, arrested in prophase 1. Primary oocyte is surrounded by the follicular cells to help form the primary follicle

Question 16

What are the three stages oocytes go through assoicated with a menstural cycle?

Answer 16

Pre- antral
Antral
Preovulatory

Question 17

What happens in the preantral stage?

Answer 17

Primary oocyte grows rapidly but does not start meosis again, follicular cells go from flat to cubodial and proliferate to form a cubodial epithelium of granulosa cells, that secrete glycoprotein to surround the oocyte with a zona pellucida. There is also formation of a inner theca interna that is vasular and endocrine, and an outer theca externa that involves a fibrous capulse

Question 18

What are some of the features of the antral stage?

Answer 18

Granulosa cells proliferate and fluid filled spaces emerge to form a antrum, the follicles expand which is helped by follicle stimulating hormone, and osterogens are also secreted

Question 19

What are some of the features of the preovulatory stage?

Answer 19

Begins 37 hours before ovuluation, under the influence of LH, the oocyte completes mesosis I and produces two daughter cells of unequal size (one cell has most of the cytoplasm), the secondary follicle reenters mesois and then arrests again 3 hours before ovuluation, Lh stimualtes collagenase activity leading to follcile rupture, and ovum is carried out by the fluid

Question 20

What are some of the features of ovuluation?

Answer 20

LH surge causes an increase in collagenase activitiy, prostagladins increase the response to LH and cause muscular contractions in the ovarian wall

Question 21

What is the corpus leuteum?

Answer 21

Remaining granulosa and theca interna cells becuase vasucularised, develop a yellow pigament, and change into leutin cells, secretes osetrogen and progesterone and dies after 14 days if fertilisation does not occur

Question 22

How is the oocyte transported?

Answer 22

Shortly before ovulation the fimbrae sweep over the surface of the ovary, and the uterine tube begins to contract rheymically, and ovum is carried by the sweping movements of fimbra and propelled by peristalic muscular contractions and by fluid

Question 23

What happens to the corpus leuteum if feritlitsaiton does not occur?

Answer 23

The corpus leuteum degenerates, and forms fibrotic scar tissue, the corpus albicans, and the progesterone production decreases which cause menstural bleeding

Question 24

What happens to the corpus leutem if fertilisation does occur?

Answer 24

Degeneration is prevented by human chrononic gondotropin, and grows and forms the corpus leuteum of pregancy, and cells continue to secrete progrestone until the 4th month when the placenta is able to take over