Session 3- Gametogenesis

Question 1

How does genetic variation occur i meiosis

Answer 1

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

Question 2

What is teh function f the blood testis barrier

Answer 2

Protect teh developing sperm from being recognised as non-self

Question 3

Where do they spermatozoa develop

Answer 3

In the seminiferous tubules between the Sertoli cells they also differentiate

Question 4

What are spermatogonium

Answer 4

Primordial germ cells - raw material for spermatogenesis

Question 5

Spermatogenic cycle

Answer 5

Time take for reappearance of the same stage within a given segment of tubule

Question 6

Spermatogenic wave

Answer 6

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

Question 7

Spermiogeneis

Answer 7

Maturation and development of sperm

Question 8

Spermation

Answer 8

Spermatids released into lumen of seminiferous tubules

Non-motile

Question 9

Journey of sperm

Answer 9

Seminiferous tubules
Rete testis 
Ductus efferentes 
Epididymis 
Vas deferens 
Urethra

Question 10

What is sperm capacitation

Answer 10

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

Question 11

Maturation of oocyte

Answer 11

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)

Question 12

WWhat is atresia

Answer 12

Cell death of oogonia majority dead by 7th month

Question 13

What happens after atresia

Answer 13

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

Question 14

What are the three stages of maturation of oocyes

Answer 14

Preantral
Antral
Preovulatory

Question 15

Pre antral stage

Answer 15

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

Question 16

Antral stage

Answer 16

As development continues, fluid filed spaces appear between granulosa cells which coalesce to form the antrum

Question 17

Preovulatory stage

Answer 17

• 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

Question 18

How is the oocyte extruded

Answer 18

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

Question 19

What is the corpus luteum

Answer 19

Remaining granulosa and theca interna cells become vascularised and develop a yellowish pigment and change into lutein cells which form the corpus luteum

Question 20

What is the corpus albicans

Answer 20

Iffertilisation does not occur corpus luteum degenerates and forms a mass of fibrotic scar tissue

Question 21

If fertilisation occurs what happens

Answer 21

• 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