Origin Of The Gametes

Question 0

What do germ cells become in the female?

Answer 0

They become oogonia ~ 7 million originally.

2 million survive to begin meiosis before birth.

Question 1

How do germ cells proliferate?

Answer 1

By mitosis, they then reshuffle and reduce via meiosis

Question 2

What stimulates the entry of oogonia into meiosis?

Answer 2

Mesonephric follicular cells surround the oogonia to creat a primordial follicle

Question 3

What is the diplotene stage? What maintains this stage?

Answer 3

Diplotene stage is when primordial follicles are arrested after meiosis 1 of prophase.

Maintained by OMI- oocyte maturation inhibitor from follicular cells.

Question 4

Can any more oocytes be produced after birth?

Answer 4

No! (Ticking time bomb of limited eggs REMEMBER?!)

Question 5

What are the stages of follicular development?

Answer 5

Pre- antral, antral and pre-ovulatory

Question 6

What occurs in the the pre antral stage?

Answer 6

Dramatic growth of the primary oocyte.

Follicular cells change from flat to cuboidal creating multi layer epithelium - granulosa cells

Stromal connective tissue forms 2 layered theca

Question 7

What do the granulosa cells secrete?

Answer 7

Glycoprotein to surround oocyte in zona pellucida

Question 8

What are the two layers of the theca?

Answer 8

Inner theca interna- vascular and endocrine secreted oestrogen
Outer theca externa- fibrous capsule

Question 9

What occurs in the antral transisition?

Answer 9

Granulosa cells proliferate
Fluid filled Antrum arises- graaffian follicle up to 2mm

Then FSH and LH surge cause enlargement of one dominant follicle to 20mm

Question 10

What occurs in the pre-ovulatory phase?

Answer 10

LH receptors appear on granulosa cells
LH surge causes oocyte to restart meiosis
Asymmetric division
Follicle arrests in meiosis II

Question 11

What occurs in ovulation?

Answer 11

LH stimulates collagenase activity and increased antral fluid leads to follicle rupture.
Ovum carried into Fallopian tube by fimbrae

Question 12

What is the corpus luteum?

Answer 12

After ovulation the follicle reorganises into structure that secretes oestrogen and progesterone for 14 days.

In sync with menstrual cycle

Question 13

What happens to the germ cells in males?

Answer 13

They colonise the seminiferous cords in the medulla of the primordial gonad.
They do not begin meiosis before puberty

Question 14

What do the seminiferous cords become?

Answer 14

Seminiferous tubules that empty into the rete testis and then into the epididymis

Spermatozoa develop within the seminiferous tubules

Question 15

What do leydig cells secrete?

Answer 15

Testosterone

Question 16

What happens to the germ cells at puberty?

Answer 16

Germ cells form spermatagonia stem cells which undergo mitosis to create population of stem cells.

Question 17

How do primary spermatocytes arise?

Answer 17

A1 spermatagonia emerge and differentiate to give type A and B cells.

The type B cells then undergo 64 mitotic divisions to produce a clone of primary spermatocytes linked by cytoplasm bridges.

They then push towards the lumen if the tubule to being meiosis

Question 18

How are sperm made from spermatocytes?

Answer 18

Two meiosis divisions of primary spermatocytes gives 256 spermatids per A1 spermatogonium .

Cytoplasmic bridges break down and sperm are released into lumen

Question 19

How long does spermatogenesis take?

Answer 19

70 days but 4 processes at a time as new starts every 16 days

Question 20

What is emission?

Answer 20

When spermatozoa are mixed with components from the seminal vesicles and the prostate.

Question 21

How many sperm in 3.5ml of ejaculate?

Answer 21

350 million sperm (fewer than 50 will reach fertilisation site)