gametogenesis

Question 1

where do gonocytes originate from

Answer 1

yolk endoderm

Question 2

what do the gonocytes do at the genital ridges

Answer 2

differnetiate to oogonia or spermatagonia

Question 3

what happens to cells surrounding the gonocytes

Answer 3

differentiates to follicle or sertoli cells

Question 4

what day does gonadal development occur

Answer 4

38-40th day of embryogenesis

Question 5

oogenesis vs spermatogenesis

Answer 5

> occurs mostly in ovaries * occurs all in testes
unequal div cytoplasm * Equal div cytoplasm
only 1 made, rest polar bods *4 made
begins in foetus * begins at puberty
monthly release after pub * continuous release
stops after menopause * lifetime

Question 6

primary oocytes start meiosis. what day are oogonia differnetiated to this

Answer 6

10-12th week of human embryogenesis

Question 7

where is meiotic division stopped at before puberty

Answer 7

diplotene

Question 8

at what stage is it considered oocyte maturation

Answer 8

completion of 1st meiotic div and progression to metaphase 2

Question 9

what develops during oocyte maturation

Answer 9

granulosa + theca cells
zona pellucida (glycoprotein covering)

Question 10

Explain follilce stages in ovary

Answer 10

1. primordial follicle (around primary oocyte)
2. primary follicle
3. gonatrophic hormones (FSH) stimulates follicle growth
4. secondary follicle ( multiple cell layers around oocyte)
5. tertiary follicle (with antrum)
6. Graafian follicle

Question 11

what stage is ovulated oocyte arrested at. and what happens after ovulation

Answer 11

metaphase 2, it has polar body and meiotic spindle.
after ovulation, follicle cells (cumulus cells) still connected to oocyte

Question 12

briefly explain CORTICAL reaction

Answer 12

1. signal sent to ER when sperm head penetrates ZP + touches oocyte membrane
2. Calcium ions relased from ER + triggers exocytosis of CGs
3. Cgs change Zona reaction? + doesnt allow other spermatozoa to pass

Question 13

what are Cgs?

Answer 13

cortical granules - oocyte specific secretory vesicles
released during fertilization to prevent polyspermy

Question 14

role of somatic cells in spermatogenesis

Answer 14

starts at puberty. spermatogonia close to basment mem of seminiferous tubules.
LH goes to LEYDIG cells.
SERTOLI cells support and nourish spermatogenic cells
leydig cells make testosterone

Question 15

how long is meiotic period of spermatogenesis and differentiation

Answer 15

24 days
differentiation spermatids to spermatozoa = 5 weeks more

Question 16

spermatozoa mature in synctium. why?

Answer 16

1. to compensate possible recessive mutations by gene products of normal allele
2. share sex chromosome products.

Question 17

Structure mature spermatozoa

Answer 17

head - acrosome, nucleus, receptors on membrane (for egg recognition + attachment)
neck - has centriole
midpiece/body - has mitochondria
tail - axial filament

Question 18

spermiogenesis = differentiation of spermatozoa from spermatids. explain 4 main stages of it

Answer 18

1. nuclear condensation
2. acrosome formation (contains hyaluronidase + acrosin that break down ovum membrane)
3. cytoplasmic reduction (cytoplasmic components not needed are phagocyted by Sertoli cells)
4. flagellum development

Question 19

Nuclear condensation

Answer 19

majority of histones replaced by protamine’s
sperm chromatin = nucleoprotamines coiled into toroids

Question 20

structure of sperm tail

Answer 20

axoneme = flexible axis of tail
9 double outer microtubules + 2 single in centre

Question 21

what are Nexin + Dynein

Answer 21

nexin = connects adjacent microtubule doublets
dynein = btw microtubules + responsible for movement

movement is when microtubules doublet slide one another, helped by dynein