Gametogenesis Flashcards
What does meiosis and cyto differentiation do
- reduce the number of chromosomes
- compete maturation
What are primordial germ cells , how formed and their functions
-cells that diff into gametes
- formed form epiblast during 2nd week of development
- move through primitive streak during gastrulation and migrate to wall of yolk sac towards gonads
How do PGC’s increase in number
-mitotic division during migration to gonads and in the gonads
What are linked genes
/genes on same chromosome which are inherited together
What is synapsis and cross over
- coming together and condensing of homologous chromosomes during meiosis
- interchange of homologous chromosome segments as they break up during meiosis
What is a chiasma
-X like structure formed during cross over of homologs as points of interchange attach
Effects of meiosis
- genetic variability due to synapsis
- random distribution of chromosomes into daughter cells
What are polar bodies , how formed and fate
- of the 4 daughter cells from 1• oocyte only 1 is mature oocyte and the other 3 are polar bodies ; less cyto and smaller
- degenerate during development
What is oogenesis and where does it occur and when does it begin
- formation of ooctyes from oogenia in the ovaries
- before birth
What happens to PGC when it arrives at gonad during oogenesis
And what happens to its product
- it divides ( mitosis )and differentiates into oogenia
- divides mitotically around end of 1st trimester and becomes 1• oocyte surrounded by cluster of epi cells. Have arrested division at prophase 1
Where are follicular cells derived from
And oogenia In a cluster
- surface of epi covering ovaries
- single cell ( PGC )
What happens during 5th and 7th month of prenatal oogenesis
- max number of oogenia reached and cell death begins as cells become atretric
- most cells have degenerated except for a few near surface. No more oogenia and surviving oocytes have entered prophase of meiosis 1 individually surrounded by single squamous ( primordial follicule )
What happens at birth of oogenesisi
-primordial follicules enter resting stage of prophase known as diplotene stage
What stimulates diplotene stage and where does it come from
What is primordial follicle
- oocyte maturation inhibitor , small peptide secreted by follicules
- 1• oocyte arrested at prophase and its simple squamous epi
What happens to pool of primordial follicules
- they are recruited ( 15-20 ) each month and simple is now cuboidal and they secrete glycoprotein zona pellucida
- also proliferate into stratified granulosa layer
-growing follicule
What happens to growing follicule
- epi secrete zona
- proliferate into stratified granulosa layer
- now a 1• follicule
- some die but other accumulate fluid in space called antrum
Describe the Antrum stage
- 1• follicule accumulate fluid in between cells and the fluid filled spaces join and form antrum
- longest stage
Describe graafian / mature follicule stage
- antrum increases in size from a small crescent shape
- has cumulus oorphus
- has theca externa and interna
What separates granulosa from theca CT
-granulosa originated from basement membrane
Function of processes from follicular into zona and how connection formed !?
-finger like processes from follicular interdiginate with plasm of oocyte
/transport materia between the 2
What is cumulus oorphus
-intact granulosa around oocyte
Describe the theca interna and externa structure and functions
-more fibrous , cells secrete steroid , rich in blood vessels
Outer layer
-cellular inner layer , more diffuse
How many oocytes mature during ovarian cycle and what happens to the rest
- usually 1
- degenerate and become atretic
What happens to graafian follicule
Where is polar body located
- undergoes 1st meiotic division to reduce chromosomes # and form 2• oocyte
- polar body present now between zona and membrane of cell
What happens to 2• oocyte
- undergoes 2nd meiotic division to form 4 daughter cells
- polar body may also undergo division
What influences 1st and 2nd meiotic Division
-LH hormone ( luteinizing hormone ) which induces preovulatory growth phase
What is spermatogenesis and when and where does it occur
- begins at puberty
- process by which spermatogonium are converted into spermatozoa in the testis
Appearance of germ cells in testis and where are the support cells derived from
- pale appearance
- surface epi of testis
- sertoli or sustentacular
Function of support cells in testis and what happens to sex cords after puberty
- assist in release of spermatozoa
- protect, support
- participate in nutrition
-acquire lumen and become seminiferous tubes
Describe process of spermatogenesis
-PGS diff into spermatogonium - diff into type A dark spermatogonium - few mitotic divisions give type A pale spermatogonium - last division gives type B - diff’s into 1• spermatocyte which goes into prolonged prophase - 1st meiotic to form 2• spermatocytes - 2nd meiosis to form spermatids
What are cells connected throughout spermatogenesis
And where are cells found throughout development
- incomplete cytokinesis
- in sertoli
Function and MOD of LH in spermatogenesis
-LH produced by pituitary binds to receptors on Leydig cells , stimulate testosterone production wc binds to Sertoli cells stimulating testicular fluid prod and synthesis of intercellular androgen receptor proteins
What is spermiogenesis
-series of changes resulting in transformation of spermatids into spermatozoa
Describe the process of spermiogenesis
1 Formation of acrosome from Golgi which covers half of nucleus
2 nucleus condenses
3 formation of neck, middle and tail piece
4 shedding of most of cyto which is phagocytized as residual body by sertoli
5 spermatozoa enter lumen of seminiferous tubes
How are spermatozoa pushed into lumen
-by contractile elements in wall of seminiferous tubes
