Session 3- Gametogenesis Flashcards
How does genetic variation occur i meiosis
Crossing-over
-exchange of regions of DNA betwee 2 homologous chromosomes
Independent assortment
-random orientation of each bovalent along the metaphase plate with expect to other bivalent
Random segregation
-random distribution of alleles among the four gamers
What is teh function f the blood testis barrier
Protect teh developing sperm from being recognised as non-self
Where do they spermatozoa develop
In the seminiferous tubules between the Sertoli cells they also differentiate
What are spermatogonium
Primordial germ cells - raw material for spermatogenesis
Spermatogenic cycle
Time take for reappearance of the same stage within a given segment of tubule
Spermatogenic wave
Different stages in spermatogeneis are also ordered in space as well as time
Each stage follows in an orderly sequence along the length of the tubule
The distance between the same stage is called teh spermatogenic wave
Spermiogeneis
Maturation and development of sperm
Spermation
Spermatids released into lumen of seminiferous tubules
Non-motile
Journey of sperm
Seminiferous tubules Rete testis Ductus efferentes Epididymis Vas deferens Urethra
What is sperm capacitation
Final maturation set required before sperm become fertile
Removal of glycoproteins and cholesterol from sperm membrane
Allow sperm t bind to zona pellucida do oocyte and initiate acrosome reaction
Maturation of oocyte
Germ cells (arise from yolk sac) colonise the gonadal cortex and differentiate into oogonia (single = oogonium). • Oogonia then proliferate rapidly by mitosis
• By end of 3rd month oogoniaarranged in clusters
surrounded by flat epithelial cells
• Majority continue to divide by mitosis but some enter meiosis (these arrest in prophase ofmeiosis I and are called primary oocytes)
WWhat is atresia
Cell death of oogonia majority dead by 7th month
What happens after atresia
All surviving primary oocytes have now entered meiosis 1 and are individually surrounded by layer of flair epithelial cells called follicular cells
Now called primordial follicle
What are the three stages of maturation of oocyes
Preantral
Antral
Preovulatory
Pre antral stage
As primordial follicles begin to grow the surrounding follicular cells change from flat to cuboidal and proliferation to produce a stratified epithelium of granulosa cells which secrete glycoprotein forming zona peullcida
Antral stage
As development continues, fluid filed spaces appear between granulosa cells which coalesce to form the antrum
Preovulatory stage
- surge in LH induces preovulatory growth stage
- Meosis 1 is now completed resulting in 2 haploid daughter cells of unequal size
- each cell has 23 chromosomes and 46 chromatids
- once cells receives most of cytoplasm and the other one received none and becomes a polar body
- cell then entrees meiosis 2 but arrests in metaphase
- meosis 2 is only completed if oocyte is fertilised otherwise cell degenerates
How is the oocyte extruded
FSH and Lh stimulate rapid growth of follicle several days before ovulation occurs
Mature follicle now called Graafian follicle
LH surge increase collagen are activity , prostaglandin increase reponse to LH and cause local muscular contractions in ovarian wall
Oocyte extrdes and breaks free
What is the corpus luteum
Remaining granulosa and theca interna cells become vascularised and develop a yellowish pigment and change into lutein cells which form the corpus luteum
What is the corpus albicans
Iffertilisation does not occur corpus luteum degenerates and forms a mass of fibrotic scar tissue
If fertilisation occurs what happens
• Degeneration of CL prevented by human chorionic gonadotropin, secreted
by developing embryo. • The corpus luteum continues to grow and forms the corpus luteum of
pregnancy (corpus luteum graviditatis). • Cells continue to secrete progesterone until ~ 4th month • Secretion of progesterone by placenta then becomes adequate
