Gametogenesis Flashcards
How is genetic variation produced by gametes
Recombination/crossing over
Independent assortment
Random segregation
Where does spermatogenesis occur
In the seminiferous tubules of the testes
Sertoli cells are responsible for spermatogenesis
What form the blood testis barrier and what is its function
Sertoli cells form the blood testis barrier due to tight junctions between cells
Barrier allows basal and adluminal compartments to exist side by side
Prevents immune response - sperm have large genetic diversity so are recoginsed as foreign by immune system
What do spermatogonia divide by mitosis into
Ad spermatogonium - reserve stock
Ap spermatogonium - maintains stock and produces type B spermatogonia which give rise to spermatocytes
What is the spermatogenic wave
Distance between groups of spermatids at the same level of maturation
What is the spermatogenic cycle
Time taken for reappearance of the same stage within a segment of tubule
What is spermiation
Release of sperm into the lumen of seminiferous tubules
What is spermiogenesis
Process by which spermatids become spermatozoa
How are non-motile spermatozoa transported to the epididymis and when do they become motile
They are transported via sertoli secretions, assisted by peristaltic contractions
Become motile when they reach the epididymis
What secretions form semen and what do the secretions contain. How many sperm per ejaculate
Seminal vesicle secretions - amino acids, citrate, fructose, prostaglandins
Prostate secretions - proteolytic enzymes, zinc
Sperm - from vas deferens. 200-500 million per ejaculate
Bulbourethral/cowper gland secretions - mucoproteins that lubricate and neutralise acidic urine
What is capacitation
Removal of the top layer of glycoproteins and cholesterol of the outer membranes of the spermatic head
Occurs in female reproductive tract and is final process in maturation of sperm
Describe the first part of oogenesis - before the preantral phase
Germ cells settle in ovary, form oogonia and rapidly divide
Oogonia are arranged into clusters surrounded by flat epithelial cells
Oogonia enter meiosis and arrest at prophase I - primary oocytes
Cell death occurs and many oogonia and primary oocytes degenerate to leave the best cells for reproduction
All surviving oocytes enter meiosis I and are surrouned by follicular cells - primordial follicles
What are the phases in oogenesis
Preantral phase
Antral phase
Pre-ovulatory phase
Ovulation
Oocyte transport
Describe the preantral phase
Primordial follicle grows and follicular cells change from flat to cubiodal
Proliferation occurs to form stratified epithelium of granulosa cells which secrete zona pellucida
Now primary follicle
Describe the antral phase
Fluid filled spaces appear between granulosa cells -> coalesce to form antrum - now secondary follicle
Outer fibrous layer develops into theca interna and externa
Describe the pre-ovulatory phase
Induced by LH surge
Follicle completes meiosis I
Graafian follicle is chosen to complete ovulation - it enters meiosis II but arrests in metaphase II
Describe ovulation
FSH and LH stimulate rapid growth of follicle several days before ovulation - pre-ovulatory phase
Mature follicle now 2.5cm in diameter - graafian follicle
LH surge increases collagenase acitivity while prostaglandins increase response to LH and cause local muscular contraction in ovarian wall
Oocyte extruded and breaks free from ovary
Following ovulation what happens to the granulosa and theca interna
They become vascularised and form the corpus luteum which secretes oestrogen and progesterone
This stimulates uterine mucosa to enter secretory stage in preparation for embryo implantation
Describe oocyte transport
At ovulation, oocyte is released when follicle ruptures and is caught by fimbriae which sweep over the surface of the ovary shortly before ovulation
Oocyte is carried into the tube and down it - cilia on epithelial lining waft and uterine tube contractions propel oocyte down the tube
What happens in the ovary if fertilisation occurs
Implanted embryo releases beta-hCG which maintains corpus luteum until placenta can take over production of progesterone
Corpus luteum continues to grow and forms corpus luteum graviditatis
What happens to the corpus luteum if fertilisation does not occur
Corpus luteum degenerates if fertilisation does not occur
It forms the corpus albicans - mass of scar tissue
Progesterone production decreases which precipitates menstral bleeding
