Flashcards in Repro 1.2 Deck (50):
In the female, where are primordial germ cells?
Colonise the cortex of the primordial gonad and become oogonia which proliferate rapidly by mitosis
How many oogonia do female foetus have and what do they become?
At 12 week 20 of gestation, over 7million
Most die during gestation leaving about 2million
These all begin meiosis after birth to become primary oocytes
How are primary oocytes stimulated to enter meiosis 1 and what do they become?
By mesonephric cells (flattened epithelia - follicular cells) which surround the primary oocytes to form primordial follicles.
When is meiosis 1 of primary oocytes arrested? What causes this?
The diplotene stage (a resting stage) of prophase
Oocyte maturation inhibitor (OMI) from follicular cells stimulates the arrest.
What does the primordial follicle consist of?
Primary oocyte surrounded by follicular cells
Why is there increased risk of foetal chromosomal abnormalities in pregnancies of older women?
All oocytes are produced before birth and remain as primordial follicles until stimulated to develop further. Remaining in this arrested stage for many years increases the chance of cell damage
What are the stages of development to form a mature gamete?
Pre-antral (primordial follicle)
Antral follicle (Graafin or vesicular follicle)
What changes occur in the transition of a primordial follicle to pre-antral?
Follicular cells change from flat to cuboidal and proliferate to form multiple layered epithelium - granulosa cells
Zona pellucida forms around the primary oocyte from glycoprotein secreted by the granulosa cells
Surrounding stromal cells (connective tissue) form a theca folliculi of 2 parts
What are the 2 Thecal layers?
Internal theca - vascular and endocrine
External theca - fibrous capsule
How is oestrogen formed in the follicle?
Androgens secreted by the internal theca, stimulated by the binding of LH, which are then converted to oestrogen in the granulosa cells under the influence of FSH
Describe the antral transition of the pre-antral follicle.
Granulosa cells continue to proliferate and a fluid appears between them, eventually forming an antrum. As more fluid forms the graafian follicle expands dramatically. They grow to 2mm without hormones but continued development depends on FSH binding to granulosa cells and LH binding to thecal cells
How many follicles develop per cycle?
Only one tends to dominate and develop to further although many can begin to develop.
When does the pre-ovulatory follicle begin to develop?
37 hours before ovulation
What stimulates the formation of the pre-ovulatory follicle?
LH surge - receptors for LH appear on the on the outer granulosa cells under the influence of oestrogen
When is the first meiotic division of the oocyte completed?
Within 3 hrs of the LH surge.
What is formed after the meiotic division of the oocyte?
1 functional oocyte and 2/3 condensed polar bodies (no function, lack cytoplasm)
When does the the development of the secondary follicle arrest?
3 hours before ovulation
How does the secondary follicle size increase and what effect does this have on the follicle?
Increase in antral fluid volume (full size 25mm). Structure weakens
What causes the secondary follicle to rupture?
LH stimulates collagenase activity leading to follicle rupture
How does the ovum get into the fallopian tube?
Carried out in the fluid and gathered up by the fimbria
When is meiosis completed?
When fertilised (meiosis is not completed unless fertilised - degenerates 24 hours after ovulation)
What is the corpus luteum?
The re-organised remains of the follicle
What does the corpus luteum do?
secretes progesterone and oestrogen under the influence of LH
How long does the corpus luteum last?
after 14 days it spontaneously regresses unless fertilisation has occurred in which case hCG maintains it.
What is a menstrual bleed?
Shedding of the lining of the uterus at the end of every cycle when the corpus luteum regresses and progesterone and oestrogen are no longer present to stimulate the maintenance of the endometrium
When does antral development and ovulation begin?
towards the end of menstruation, culminating in ovulation about 10 days later (12-14 days after the onset of the mentrual bleed)
What is the ovarian cycle?
The pattern of ovarian changes during the menstrual cycle
What are the male germ cells and where are they?
Spermatogonia. Colonise the seminiferous cords in the medulla of the primordial gonad
From what and when do the seminiferous cords form?
At puberty from hollowing of the seminiferous cords
How many tubules does each testis have?
Where do spermatozoa develop?
Within seminiferous tubules in association with Sertoli cells
What does the blood testes barrier do?
separates tubules from surrounding interstitial tissue
What do Leydig cells secrete?
Up to what age are sperm available in men?
What are the different types of spermatogonia?
A type and B
What do type A spermatogonia do?
Stem cells - maintain pool to differentiate to form more spermatogonia
What do type B spermatogonia do?
Committed to differentiation to spermatozoa. Undergoes a fixed number of mitotic divisions to produce a clone (typically 64) primary spermatocytes all linked together by cytoplasm bridges
Where do primary spermatocytes lie?
Push their way to the lump on the tubule and begin meiosis
How are sperm formed?
Primary spermatocytes divide to form haploid secondary spermatocytes
Secondary spermatocytes divide again to form spermatids
Spermatids are the re-modelled to form sperm by spermatogenesis
What happens to the spermatozoa?
Once the spermatozoa are produced, the cytoplasmic bridges break down and the sperm are released into the lumen to be washed down to the rate testis by fluid secreted from Sertoli cells
How long does spermatogenesis take?
Approx. 70 days
How many spermatogenic processes occur simultaneously?
4 - New groups of A1 spermatogonia arise every 16 days
Why is it necessary for there to be multiple stages of spermatogenesis present at all times?
Different sections along the length of the tube begin the process at different times so some part is always releasing sperm in preparation for the rare time ovulation occurs in the female so fertilisation can occur
Spermatogenic "wave" of production
When do spermatozoa finally mature?
During progress through the epididymis
How are sperm moved through the vas deferens?
Copulation contraction moves sperm through the vas deferens to be mixed with other components of semen from the seminal vesicles and prostate (emission).
What part of the autonomic nervous system controls emission?
What is the typical volume of ejaculate?
How many sperm (approximately) are in ejaculate?
10million per ml
How many sperm reach the site of fertilisation?