7. gametogenesis, fertilisation Flashcards
The ovarian cycle: 1+2
the primary oocyte is surrounded by a single layer of follicular cells and together is the PRIMARY FOLLICLE
The ovarian cycle: 3+4
- at the beginning of each monthly cycle following puberty, 5-12 follicles begin to develop and become GROWING FOLLICLES.
the follicular cells multiple and become several-layered.
they become separated from the oocyte by an acellular mucopolysaccharide layer- septum pellucidum - usually all but one of the growing follicles degenerate to form CORPUS ATRETICUM (scar) (replaced by connective tissue)
The ovarian cycle: 5
The follicular cells of the growing follicle secrete a fluid- producing fluid-filled antrum.
The ovarian (non-gamete) cells surrounding follicle form thecal layer- divided into vascular theca interna (produces oestrogen) and avascular inactive theca interna
The ovarian cycle: 6
MATURE OR GRAAFIAN FOLLICLE: most of cells form stratum granulosum (produces progesteron)
remainder surround oocyte as cumulus oophorus
it is now a SECONDARY OOCYTE
The ovarian cycle: 7 + 8
- mature follicle ruptures to release the ovum. this retains the covering follicle cells which form corona radiata
septum pellucium has expanded to form zona pellucida - cells of theca interna and stratum granulosum enlarge
turn yellow and form CORPUS LUTEUM
secretes large amounts of progesterone -prepare uterus to receive discharged ovum (and oestrogen)
prior to ovulation mainly oestrogen
The ovarian cycle: 9+ 10
- if fertilisation does not occur- corpus luteum has life of 12 days.
degenerates into CORPUS ALBICANS
cessation of hormones leads to menstruation - fertilisation: corpus luteum sustained by HCG produced by conceptus and forms large corpus luteum of pregnancy.
eventually forms large corpus albicans
continues producing progesterone
what happens to the discharged ovum
shed into abdominal cavity
must be caught by fallopian tube
it is outside the reproductive system for a moment
- infundibulum
- fallopian tube, ampulla
why is the female abdominal cavity a route for infection
it communicates with the exterior
vagina-> fallopian tube-> abdominal cavity
issues during discharge of ovum
it may not be caught into tube and can end up in abdominal cavity or inside the tube
spermatogenesis
mitosis to form stem cells spermatogonium -> primary spermatocyte
during first meiosis: one primary spermatocyte is retained as stem cell then the other undergoes 2nd meiosis to form spermatids to
mature to spermatocytes
fertilisation
1% sperm deposited penetrates cervix
reach isthmus- becomes less motile
chemoattractants from cumulus cells on ovulation makes them motile- swim to ampulla- fertilisation
capacitation of sperm cells make them fertile- acromial region loses glycoprotein coat
spermatozoon
head: nucleus with large cytoplasmic covering
acrosomal cap derived from golgi- enzymes to penetrate ovum
middle piece: mitochondria helically wound surround central axial bundle of fibrils
axial bundle contains arrangement of 9+2 fibrils continues throughout to tail piece
spermatogenesis vs oogenesis
spermatogenesis
mitosis then meiosis in testes haploid spermatozoa continuous from puberty takes 9 weeks motile low cytoplasmic: nuclear ratio fluid from other glands added prior to ejaculation
spermatogenesis vs oogenesis
oogenesis
meiosis in ovaries
haploid ova
discontinuous: all primary oocytes are present at birth, no stem cells retained, held suspended in diplotene stage
5-12 primary oocytes continue with meiosis each monthly cycle, does not complete until fertilisation
non motile
very high cytoplasmic: nuclear ratio
fertilisation: 1. shed secondary oocyte
halted through 2nd meiotic division
can see polar body
cells of corona radiata
fertilisation 2. mature ovum
penetration by spermatozoon prompts completion of 2nd meiotic division
acrosomal enzymes help disperse corona radiata and aid penetration of zona pellucida
plasma membranes of gametes fuse and nucleus is injected
fertilisation: 3. fertilised ovum
diploid again
permeability of zona pellcuda altered to prevent further penetration- zona reaction
3 polar bodies: correct no. of chromosomes can be assumed
ovum shrinks
perivitelline space
cytoplasm of ovum is all from mother
mitochondria has different DNA- from mother
fertilisation 4. cleavage
30h post fertilisation
2 daughter blastomeres formed by normal mitosis
fertilisation 5. further cleavage
cells continue to cleave to form ball of cells
progressively smaller blastomeres
DNA synth ++ but not much protein made
fertilisation 6. Morula
cytoplasmic: nuclear ratio fallen to near normal
cytoplasm differentially packaged
zone pellucida persists- prevent implantation
can take a cell away and no difference
16 cells solid ball
Blastocyst formation
second week
Morula cells undergo compaction- establish tight junctions between cell surface, zp starts to split
5 days post fertilisation- cavity develops and BLASTOCYST is formed
zp breaks down- hatching
beginnings of differentiation of inner cell mass (embryoblast) and trophoblast (cells of outer layer)
fluid filled cavity of blastocyst
polar cells
