3.2 Gametogenesis Flashcards
Name the 3/4 things that germ cells do after colonising the gonad
Proliferate by mitosis
Reshuffle genetically
Reduce to haploid by meiosis
Cytodifferentiate
Compare oogenesis and spermatogenesis (simple)
Oogenesis
- Few gametes 400
- Intermittent production 1/month
Spermatogenesis
- Lots 200/day
- Continuous production
- Disposable
2 main functions of meiosis
Reduce chromosome number to 23
Genetically unique gametes
3 sources of genetic variation
Crossing over
Independent assortment
Random segregation
Which two types of spermatogonium are produced by mitosis in spermatogenesis?
Ad - resting
Ap - active
Ap produce type b spermatogonia which give rise to primary spermocytes which divide by meiosis to make secondary -> 4 haploid spermatids
Define spermiogenesis
Process by which the 4 haploid spermatids formed from each primary spermatocyte DIFFERENTIATE into spermatozoa
Define spermatogenic cycle
Time taken for reappearance of the same stage (of spermatogenesis) within a given segment of the tubule
About 16 days
Define Spermatogenic wave
Distance between the same stage of spermatogenesis
What is spermiation?
Spermatids released into lumen of seminiferous tubules
What 4 things make up semen?
Seminal vesicles secretions 70%
Secretions of prostate 25%
Sperm via vas deferens
Bulbourethral gland secretions
What is the other name for the bulbourethral gland?
What does the secretions do?
Cowper gland
Mucoproteins to lubricate and neutralise acidic urine in distal urethra
What happens in capacitation?
In female reproductive tract
- removal of glycoproteins and cholesterol from sperm membrane
- activation of signalling pathways
- allow sperm to bind to zone pellucida (acrosome reaction)
How many chromosomes and chromatids are there in an oogonium and in a primary oocyte?
Oogonium
- 46 chromosomes, 46 chromatids
Primary oocyte
- 46 chromosomes , 96 chromatids
What is a primordial follicle?
Primary oocyte in meiosis I surrounded by layer of flat epithelial cells called follicular cells
3 stages of maturation at puberty
1) Pre-Antral
2) Amtrak
3) Pre-ovulatory
Describe the preantral stage
Primordial follicle grows
Follicular cells change from flat to cuboidal
Follicular cells proliferate to form stratified epithelium of granulosa cells
What do granulosa cells do in the preantral stage?
Secrete layer of glycoproteins on oocyte to form zona pellucida
Describe Antral stage
Fluid filled spaces appear between granulosa cells
Spaces join to make antrum
What stimulates preovulatory stage?
LH surge
Describe preovulatory stage
One larger daughter cell enters meiosis II but arrests in metaphase
Only completed upon fertilisation
What is a mature follicle called?
Graafian follicle 2.5cm
Mature due to FSH and LH
What does LH surge cause during ovulation?
Increased collegenase activity
Increased prostaglandins which cause contractions in ovarian wall
Get ovulation
Promotes development of CL
How is corpus luteum formed?
Granulosa and theca interna cells become vascularises
Change into luteum cells
What does corpus luteum do?
Secrete oestrogen and progesterone
Cause uterine muscosa to enter secretory stage to prepare for implantation
Dies after 14 days
How is the oocyte transported?
Fimbriae
Cilia
Peristalsis
What happens if no fertilisation occurs?
CL degenerates into CA
Progesterone decreases
Menstruation
What happens if fertilisation occurs?
HCG from embryo maintains CL
Forms CL graviditatis
4th month, progesterone secretion taken over by placenta
