gametogenesis Flashcards
where does meiosis occur?
germ cells of the gonads
male vs. female meiosis
gives rise to 4 haploid cells in both
male all 4 gametes mature into spermatazoon
female 1 gamete - ovum - recieves almost all cytoplasm from mother cell - other 3 - polar bodies - degenerate
when do male spermatagonia proliiferate?
they’re present in small quantities before puberty, but undergo mitosis at puberty
when do oogonia proliferate?
during foetal development
production vs. development of male gamete
spermatogenesis + spermiogenesis
occur in medulla of testes - in seminiferous tubules
both processes take 64 days + are synchronised, so cross sections of seminiferous tubules look different at different parts
where does final maturation of spematozoa occur?
epididymis
process of spermatogenesis
- primordial germ cells migrate from yolk sac to indifferent gonad
- germ cells then migrate to medulla of testis
- undifferentiated diploid germ cells = spermatogonia A
- spermatagonia A undergo mitosis to produce more spermatogonia A - which maintain germ cell pool - and spermatagonia B - which undergo mitosis to produce primary spermatocytes
- primary spermatocytes undergo meiosis - process takes 3 weeks - daughter cells = secondary spermatocytes
- secondary spermatocytes undergo meiosis rapidly to becom spermatids - are rarely seen because of this
- spermatids undergo spermiogenesis to become spermatozoa
what are the endocrine cells in the testes relevant to spermatogenesis?
leydig cells - secrete testosterone - interstitial spaces between tubules
what cells support germ cells during spermatogenesis?
sertoli cells
- cytoplasmic barriers
- testis-blood barrier
- provide nutrients
- phagocytose
process of spermiogenesis
- acrosomal vesicle attaches to one pole of condensing nucleus of spermatid to form acrosomal head cap
- both centrioles migrate to opposite end of spermatid away from acrosome
- one centriole elongates to form the flagellum
- cytoplasm migrates to first part of flagellum - midpiece. - mitochondria thus gather in midpiece
- excess cytoplas is phagocytosed by surrouding sertoli cell
- spermatozoa is released into lumen - spermiation
spermiation
release of spermatozoa into lumen
maturation of spermatozoa
- in epididymis
- takes 1-21 days
- sperm gain fertilising capacity + high motility
passage of sperm
- seminiferous tubules
- tubuli recti
- rete testis
- efferent duct
- epididymis
- vas deferens
- urethra
santa told reese red turtles eat ducks every valentines day, understand?
glands which contribute to seminal fluid
seminal vesicles - 65%
prostate gland - 25%
bulbourethral gland - 10%
composition of ejaculate
- spermatazoa
- seminal plasma - comes from accessory glands - maintains PH - gives nutrients - transport medium
process of oogenesis
- primordial germ cells migrate from yolk sac to indifferent gonad
- migrate to cortex of ovary
- 4th month foetal development - oogania enlarge into primary oocytes
- primary oocytes begin firts meiotic division
- 7th month - layer of flalltened follicular cells surround oocyte - form primordial follicles = oocyte + follicle cells
- envelopment arrests meiosis until puberty
- at puberty folliculogenesis begins
degredation of female germ cells
atresia - can occur at any point of folliculogenesis
folliculogenesis stimulated by ____
FSH - follicle stimulating hormone
process of folliculogenesis
- primordial follicle enlarges to primary follicle - bigger oocyte + more follicular cells
- follicular cells now called granulosa cells
- follicular cells + oocyte secrete proteoglycans + glycoproteins - form thick homogenous layer called zona pellucida between granulosa + oocyte
- surrounding stromal cells form organised layer around follicle called theca folliculi
- granulosa proliferate to form several layers - zona granulosa
- fluid filled spaces develop between granulosa cells + coalesce to form follicular antrum
- now a secondary follicle
- in the secondary follicle primary oocyte is in thickened layer of granulosa called the cumulus oophorus
- theca folliculi has developed 2 layers - theca interna - round cells - theca externa - spindle cells
- first meiotic division completed just before ovulation - oocyte now secondary oocyte + follicle = GRAAF follicle
- cumulus oophorus diminishes - secondary oocyte surrounded by corona radiata now
- corona radiata attached to granulosa by thin bridges that break just before ovulation to leave oocyte floating freely
granulosa cells
what follicular cells becom after primordial follicle enlarges to primary follicle
- secrete glycoproteins + proteoglycans which form zona pellucida
stromal cells
connective tissue cells eg. fibroblasts which support perinchymal cells
theca folliculi
layer of stromal cells that surround primary follicle
follicular antrum
big fluid filled bubble in zona granulosa of SECONDARY follicle - develops when fluid filled spaces between granulosa cells coalesce
- changes primary follicle to secondary follicle
cumulus oophorus
thickened layer of granulosa in secondary follicle in which primary oocyte sits
2 layers of theca folliculi in secondary follicle
theca interna - round cells
theca externa - spinde cells
graaf follicle
when the primary oocyte in th esecondary follicle changes to secondary oocyte, the secondary follicle becomes graaf follicle
when does meiosis 1 end?
when does meiosis 2 end?
at ovulation
after fertilisation
corpus luteum periodicum
- after ovulation - ruptured follicle collapses + fills w/ a blood clot to become corpus hemorhagicum - endocrine gland that secretes progesterone
- progesterone secretion by corpus hemorhagicum dependent on lutenising hormone from pituitary - but LH inhibited by progesterone - after 12-14 days corpus regresses to become useless corpus albicans
- LH + progesterone stop after this + menstruation starts
- if implantation occurs - corpus luteum continues secreting progesterone + becomes vascularised so zygote can develop in it - now corpus graviditatis
when does menstraution start?
14 days after ovulation - when corpus albicans forms + LH and progesterone stop
granulosa lutein cells
after ovulation lutenising hormone from pituitary causes granulosa cells to enlarge + secrete progesterone - now granulosa lutein cells
theca lutein cells
LH causes theca interna cells to enlarge + secrete oestrogens - now theca lutein cells
when + where does fertilisation occur?
in the ampulla of fallopian tube 24-48 hours after ovulation
journey of the sperm
- after insemination sperm move against current - are moved by smooth muscle contraction to mid lumen
- sperm bind temporarily to epithelium of oviuct - compettion to bind is unique to humans
- when the oocyte binds to the medulla a signal cascade is sent which attracts the sperm to the oocyte
- in vitro, sperm move aimlessly - proves signal cascade gives direction
- only 3-4 sperm reach the oocyte
- only 1 spermatazoon enters oocyte - zona pellucida changes conformation - exocytosis of cortical granules - after sperm enters to prevent polysperm
prerequisite for sperm to fertilise
capacitation
- removal of glycoproteins + semial proteins from surface of sperm acrosome
- induced by glycosaminoglycans - heparin
- takes place in female genital tract
where does capacitation take place + what induces it
in female genital tract
glycosaminoglycans - heparin
how do sperm enter zona pellucida
- when sperm contact zona pellucida vesicles on plasma membrane of acrosome release proteolitic enzymes - acrosine - to digest zona pellucida
phases of fertilisation
- completion of meiosis 2 of oocyte
- penetration of corona radiata
- penetration of zona pellucida + exocytosis of cortical granules to change configuration
- formation of female - THEN male - pronuclei
- deterioration of pronuclear membranes + fusion - formation of gametes
corona radiata
cumulus oophorus cells rearrange themselves into corona radiata - layer of cells surrounding primary oocyte in secondary follicle
