Gametogenesis, Fertilisation and the Blastocyst Flashcards
Outline the parts of the female reproductive system
Ovaries- where ovum is produced
Fallopian tubes-finger-like projections (fimbriae) which catch egg after being released
Cilia- waft egg towards uterus
Uterus- thick muscular lining when unoccupied
Cervix (neck of uterus)
Linked to vagina
4 parts of the fallopian tube
1) Infundibulum
2) Ampulla
3) Isthmus
4) Interstitial/ Intramural
Steps of female gametogenesis
1) Prenatally- many oogonium
2) Prepubertal/ postpubertal- these mature into the primary fascicle: nuclear material surrounded by a single layer of follicular cells
3) At beginning of each monthly cycle 5-12 primary fascicles are released- develop and become growing follicles. Follicular cells become multi-layered and separated form ovum by acellular mucopolysaccharide layer- septum pellucidum
4) All but 1 growing fascicles become small corpus atreticum/scar
5) In remaining growing fascicle, follicular cells secrete fluid filled antrum within follicle. Surrounding follicle a thecal layer is formed. This is divided into 2 layers: theca interna (produces oestrogen- influence female reproductive tract) and avascular inactive theca externa
6) Mature/ Graafian follicle or secondary oocyte: fluid filled space expands. Egg moves over to the side. Follicular cells form 2 layers- Theca interna becomes stratum granulosum (produce progesterone)- uterine lining gets ready to receive egg. Theca externa becomes cumulus oophorus.
7) Mature follicle ruptures to release ovum into peritoneal cavity. Still retains layer of follicular cells which form corona radiata. Septum pellucidum becomes zona pellucidum (bigger).
8) Cells of theca interna and stratum granulosum (especially latter) enlarge forming corpus luteum (yellow body)- produces testosterone (prior to ovulation produced oestrogen)
9) If no fertilisation after 12 days degenerates into corpus albicans. Stop producing progesterone. We start menstrual period.
10) Site pf implantation at uterus produces hCG- sustains corpus luteum (becomes large corpus luteum of pregnancy) so keep producing progesterone and this will remain throughout pregnancy and. Eventually form large corpus albicans.
What idea are pregnancy pills based on?
When no longer progesterone produced- menstruation starts
Go through what different parts of the oocyte is called at different stages
- primary oocyte
- primary follicle
- growing follicle
- corpus atreticum
- Graafian follicle/ mature follicle and secondary oocyte
- corpus luteum
- If fertilisation occurs–> large corpus luteum of pregnancy
- If not- corpus albicans
Outline the structure of the male reproductive system
- bladder linking to the prostate and urethra running through this into penis
- various tubes running from testis up through epididymis and feeding into prostate where other components are added to seminal fluid and out through penis- released in ejaculation
- Mens’ testicles held in scrotum behind penis
Why is the testicles outside of the body
Sperm production has to occur in cooler environment- body too warm
Outline male gametogenesis
- Testes contains stem cells
- Divides to form spermatogonium (46XY)
- these divide by mitosis to create primary spermatocyte (46XY)
- Undergoes 1st meiosis to form secondary spermatocytes (23 X or Y with double chromatid)
- Undergoes 2nd meiosis to form spermatids (23 X or Y with single chromatid)
- Mature to form spermatozoa
Structure of spermatozoa
- head- mainly nucleus with little cytoplasm, contains acrosomal cap (derived largely from Golgi apparatus) with digestive enzymes for ovum penetration
- middle piece contains helically wound mitochondria surrounding central axial bundle of fibrils
- Tail- axial bundle with 9+2 arrangement of fibrils
What is Kartageners syndrome?
Lack of dianin arms (needed for cilia/ flagella)
- sperm tails don’t work
- fallopian tubes don’t work
Cant breathe properly as cilia in respiratory tract don’t work
Explain mitosis/ meiosis for females- when does this occur
- With egg cells al mitosis done prenatally- in first 7 months before born (we have all eggs we need throughout our life already made)
- Then meiosis 1 in ovaries occurs changing primary oocytes to secondary oocytes (prepuberty) and then fertilisation occurs causing meiosis 2 to take place
- At each part of meiosis we see a polar body being produced form the egg
Why are there more chromosomal defects in older/ younger women
In older and younger women syndromes with extra chromosomes- eggs more likely to mutate as older/premature
Compare male VS female spermatogenesis
Male: mitosis followed by meiosis I and II, continuous from puberty till old ages (70), each sperm takes about 9 weeks to mature, 300X10^6 per ejaculate, motile, low cytoplasmic: nuclear ratio, fluid added form other glands prior to ejection (seminal vesicle and prostate gland)
Female: meiosis in the ovaries producing haploid ova, discontinuous- all primary oocytes (2X10^6) are present at birth- no stem cells retained. Primary oocytes are partway through meiosis.
5-12 primary oocytes continue with meiosis with each monthly cycle following puberty- don’t complete meiosis until fertilisation, non-motile, very high cytoplasmic: nuclear ratio
Significance of egg having high cytoplasmic: nuclear ratio
- Lots of cytoplasm in egg- therefore all of this is inherited form mother
- Only maternal DNA seen in mitochondria
Useful for studies- as simple line and less DNA
Is the female/ male abdominal cavity closed or open?
Male abdominal cavity= closed
Female- reproductive system is open to the peritoneal cavity (vagina–> uterus–> fallopian tubes–> peritoneal cavity)
