Origin Of The Gametes Flashcards
(22 cards)
What do germ cells become in the female?
They become oogonia ~ 7 million originally.
2 million survive to begin meiosis before birth.
How do germ cells proliferate?
By mitosis, they then reshuffle and reduce via meiosis
What stimulates the entry of oogonia into meiosis?
Mesonephric follicular cells surround the oogonia to creat a primordial follicle
What is the diplotene stage? What maintains this stage?
Diplotene stage is when primordial follicles are arrested after meiosis 1 of prophase.
Maintained by OMI- oocyte maturation inhibitor from follicular cells.
Can any more oocytes be produced after birth?
No! (Ticking time bomb of limited eggs REMEMBER?!)
What are the stages of follicular development?
Pre- antral, antral and pre-ovulatory
What occurs in the the pre antral stage?
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
What do the granulosa cells secrete?
Glycoprotein to surround oocyte in zona pellucida
What are the two layers of the theca?
Inner theca interna- vascular and endocrine secreted oestrogen
Outer theca externa- fibrous capsule
What occurs in the antral transisition?
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
What occurs in the pre-ovulatory phase?
LH receptors appear on granulosa cells
LH surge causes oocyte to restart meiosis
Asymmetric division
Follicle arrests in meiosis II
What occurs in ovulation?
LH stimulates collagenase activity and increased antral fluid leads to follicle rupture.
Ovum carried into Fallopian tube by fimbrae
What is the corpus luteum?
After ovulation the follicle reorganises into structure that secretes oestrogen and progesterone for 14 days.
In sync with menstrual cycle
What happens to the germ cells in males?
They colonise the seminiferous cords in the medulla of the primordial gonad.
They do not begin meiosis before puberty
What do the seminiferous cords become?
Seminiferous tubules that empty into the rete testis and then into the epididymis
Spermatozoa develop within the seminiferous tubules
What do leydig cells secrete?
Testosterone
What happens to the germ cells at puberty?
Germ cells form spermatagonia stem cells which undergo mitosis to create population of stem cells.
How do primary spermatocytes arise?
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
How are sperm made from spermatocytes?
Two meiosis divisions of primary spermatocytes gives 256 spermatids per A1 spermatogonium .
Cytoplasmic bridges break down and sperm are released into lumen
How long does spermatogenesis take?
70 days but 4 processes at a time as new starts every 16 days
What is emission?
When spermatozoa are mixed with components from the seminal vesicles and the prostate.
How many sperm in 3.5ml of ejaculate?
350 million sperm (fewer than 50 will reach fertilisation site)
