The Development Of The Gametes Flashcards
(24 cards)
What are the two main reasons for meoisis to take place when producing gametes?
Reduce the chromosome number in the gamete to 23
Ensures that each gamete is genitcally unique
How does meosis produce genetic variation between the gametes?
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
Where do spermatozoa develop?
Within the seminiferous tubules in association with the sertoli cells
What is the importance of the blood testis barrier?
Sperm cells have different genetic material from the gather, and should appear as foreign and then have a different immune respose between them
What is the rete testis involved in?
Concentrating the spermatozoa
What is the raw material for spermatogenesis>
Spermatogonia
What are the two products of mitosis of spermatogonia?
Ad spermatogonium that act to maintain the stock
Ap spermatogonium that give rise to primary spermocytes
What happens to the primary spermacytes?
Divide by meosis giving rise to the secondary spermacytes and then spermatids
What is the proccess of spermiogensis?
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
What is the spermatogenic cycle?
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)
What are the contents of semen?
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
What is the route that the sperm takes before ejaculation?
Seminferous tubules- rete testis- ducti efferentes- epidiymis- vas deferens- urethra
What is sperm capication?
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
Why is sperm capication important?
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
How do female oocytes mature before birth?
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
What are the three stages oocytes go through assoicated with a menstural cycle?
Pre- antral
Antral
Preovulatory
What happens in the preantral stage?
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
What are some of the features of the antral stage?
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
What are some of the features of the preovulatory stage?
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
What are some of the features of ovuluation?
LH surge causes an increase in collagenase activitiy, prostagladins increase the response to LH and cause muscular contractions in the ovarian wall
What is the corpus leuteum?
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
How is the oocyte transported?
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
What happens to the corpus leuteum if feritlitsaiton does not occur?
The corpus leuteum degenerates, and forms fibrotic scar tissue, the corpus albicans, and the progesterone production decreases which cause menstural bleeding
What happens to the corpus leutem if fertilisation does occur?
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
