3. Gametogenesis

Question 1

What happens to germ cells after colonising the gonad?

Answer 1

Proliferate by mitosis
Reshuffle genetically and reduce to haploid by meiosis
Cytodifferentiate into mature gametes

Question 2

What are the 2 main functions of meiosis?

Answer 2

Reduce the chromosome number in the gamete to 23

Ensures every gamete is genetically unique

Question 3

What happens to the 4 daughter cells from meiosis in females?

Answer 3

One develops into a mature oocyte, others form polar bodies

Question 4

What does genetic variation arise from?

Answer 4

Crossing over (recombination)
Independent assortment
Random segregation

Question 5

Where does spermatogenesis occur?

Answer 5

Walls of seminiferous tubules

Question 6

Where do seminiferous tubules coalesce?

Answer 6

Rete testis

Question 7

Where do sperm mature and are stored?

Answer 7

Head of epididymis

Question 8

What is the importance of the blood testis barrier?

Answer 8

Sperm may induce an immune response as they are recognised as non-self

Question 9

What is the raw material for spermatogenesis?

Answer 9

Spermatogonia

Question 10

What does mitosis of spermatogonia give rise to?

Answer 10

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

Question 11

What happens to primary spermatocytes?

Answer 11

Divide by meiosis giving rise to secondary spermatocytes then spermatids (4)

Question 12

What is the spermatogenic cycle defined as?

Answer 12

Time taken for reappearance of the same stage within a given segment of tubule (16 days)

Question 13

What is the distance between the same stage of spermatogenesis called?

Answer 13

Spermatogenic wave

Question 14

What is spermiation?

Answer 14

Spermatids released into lumen of seminiferous tubules

Question 15

Where are spermatozoa formed?

Answer 15

Epididymis

Question 16

How do spermatids move until they reach the epididymis?

Answer 16

Transport via Sertoli cell secretions assisted by peristaltic contraction

Question 17

What is the pathway that sperm take?

Answer 17

Seminiferous tubules
Rete testis
Ductuli efferentes
Epididymis
Vas deferens
Urethra

Question 18

What makes up semen?

Answer 18

Seminal vesicle secretions (70%) - amino acids, citrate, fructose, prostaglandins
Secretions of prostate (25%) - proteolytic enzymes, zinc
Sperm (2-5%)
Bulbourethral gland secretions (<1%) - mucoproteins help lubricate, neutralise acidic urine

Question 19

How much semen is produced?

Answer 19

2ml per ejaculate

Question 20

What is sperm capacitation?

Answer 20

Final maturation step required before sperm become fertile
Conditions in female genital tract stimulate removal of glycoproteins and cholesterol from sperm membrane, activation of sperm signalling pathways, allow sperm to bind to zona pellucida of oocyte and initiate acrosome reaction

Question 21

What do female germ cells colonise?

Answer 21

Gonadal cortex and differentiate into oogonia

Question 22

What happens to oogonia by then end of the 3rd month?

Answer 22

Arranged in clusters surrounded by flat epithelial cells

Question 23

How many chromosomes and chromatids do oogonium have?

Answer 23

46 chromosomes

46 chromatids

Question 24

How many chromosomes and chromatids to primary oocytes in prophase of meiosis I have?

Answer 24

46 chromosomes

92 chromatids

Question 25

What happens to the surviving primary oocytes?

Answer 25

Entered meiosis I and are individually surrounded by layer of flat epithelial cells called follicular cells
Now called primordial follicle

Question 26

What happens to oocytes from puberty onwards?

Answer 26

~15-20 oocytes start to mature each month passing through 3 stages:

1. Preantral
2. Antral
3. Preovulatory

Question 27

What happens in the preantral stage?

Answer 27

As primordial follicles begin to grow, the surrounding follicular cells change from flat to cuboidal and proliferate to produce a stratified epithelium of granulosa cells

Question 28

What happens in the antral stage?

Answer 28

As development continues, fluid filled spaces appear between granulosa cells, they coalesce to form the antrum
Several follicles begin to develop with each ovarian cycle, usually only one reaches maturity

Question 29

What happens in the preovulatory stage?

Answer 29

Surge in LH induces preovulatory growth phase
2 haploid daughter cells
One cell receives most cytoplasm the other receives practically none
Cell then enters meiosis II but arrests in metaphase (3 hrs before ovulation)
Meiosis II only completed if oocyte is fertilised

Question 30

What happens during ovulation?

Answer 30

FSH and LH stimulate rapid growth of follicle several days before ovulation occurs
Mature follicle now called Graafian follicle
LH surge increases collagenase activity, prostaglandins increase response to LH and cause local muscular contractions in ovarian wall
Oocyte extruded and breaks free from ovary

Question 31

Describe oocyte transport

Answer 31

Shortly before ovulation, fimbriae sweep over surface of ovary
Uterine tube begin 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 tube