Fertilisation and implantation Flashcards
maturation of spermatozoA
100 fold concentration of sperm, oestrogen dependent
completion of sperm modelling
changes in metabolism
acquisiton of forward motion
changes in membrane surface proteins, charge and fluidity
coating of sperm plasma membrane with glycoproteins
dpeends on adequate stimulation of epididymis by androgen
what is coitus mediated by
sympatheti
parasympathetic
somatic
coitus sympathetic
hypogastric nerve
vascular tone in penile and clitoral arteries
emission of semen in the urethra
coitus parasympathetic
pelvic nerve
promotes vasodilation and erection of penile and clitoral tissues, lubrication
coitus somatic
pudenal nerve
sensations following stimulation of glans penis/clitoris emisison in internal urethra
reflex rhythmical contractions of muscles during ejaculation
where does fertilisation occur
in ampulla of fallopian tubes
issues sperm encounters in the vagina
physical loss of sperm form vagina
survival of sperm cells in the vagina
adaptations of sperm to prevent loss form vagina
semenogelin 1, 2 and fibronectin
aggregate to form coagulum
forced retention
broken down in 20 mins
via proteolytic cleavage of semenogelins by prostate specific antigen so sperm can regain motility and continue journey
vaginal environment
normal vaginal flora prevent colonisation of pathogenic bacteria as lactobacillus produce lactic acid from anaerobic digestion of glycogen
vagna secretes hydrogen perodixde and antimicrobial peptides to exhibit strong adhesion to vaginal epithelium
abundance of immune cells
how do the sperm neutralise and overwhelm vaginal defences
neutralisation of acidic vaginal environement by alkaline seminal fluid
attenuation of vaginal immune response by immunosuppressive compounds in the seminal fluid e.g. prostaglandins
large number of sperm ejaculated overwhelms innate immune
sperm deposited near cervical os allowing fast escape though cervix
penetrating the cervix
sperm migrate out of seminal plasma and into mucus immediately
characterisics of the cervical canal
cervical crypts
quality of the cervical mucus
mucins
glycoproteins: long and flexible
aligned by secretory flow in the mucosal grooves
muc5B and muc4: hydrophillic
penetrating cervix in follicular phase
oestrogen relxaes muscles of cervix
increases secretion and hydration of cervical mucus
facilitates sperm penetration into the uterus
penetrating cervic in the luteal phase
progesterone decreases cervical mucus secretion and hydration level
impermeable to sperm and pathogens
protecting potential fertilised embryo
travel through uterus
self propulsion
cilitated endothelial celsl of endometrium create fluid current
oestrogen driven contractions of myometrium towards fundus during follicular phase
sperm capacitation
loss of glycoprotein coat
reveals binding sites and receptors, epididymal protease inhibitor which facilitates acrosome reaction and increases sperm receptivity to chemo-attractants
change in the surface membrane properties
loss of membrane cholesterol destabilises the plasma membrane
facilitates the acrosome reaction
increase in intracellular Ca2+
activation of protein kinase A needed for acrosome reaction
how does the sperm enter the right fallopian tube
labelled microspheres show to be preferentially transported to fallopian tube in late follicular phase
dominant follicel secrete progesterone, disperses to ipsilateral fallopian tube, relaxation of musces at utero-tubual junction
ipsilateral to dominant follicle allows controlled sperm penetration
how do sperm find the oocyte in the fallopian tube
specific receptors on capacitated sperm responding to chemo attractive substances: ANP or progesterone from follicualr fluid or cumulus oophorus or odorant recpetors similar to those in the olfactory epithelium
activation of adenylate kinase, cAMP mediated rise in intracellular Ca2+ for chemotaxis and chemokinesis
ovulated oocyte pathway
moved from the surface of the ovary by fimbrated ostium
passes into the ampulla of fallopian tube adhering epithelium via cumulus cells
contractions of smooth muscle and oviductal cilia move cumulus oocyte to ampullary isthmic junction
intersittial celsl of Cajal
fetilisation
Sperm hyaluronidases dissolve cumulus cell extracellular matrix
Sperm cell reaches the zona pellucida (ZP)
Short-lived binding of capacitated sperm to ZP3/ZP4 complex
Increased intracellular Ca2+ in sperm cell via activation GCPR
Exocytosis of acrosome enzymes (acrosome reaction)
“drill” into ZP
Acrosin
Hyaluronidases
Hexosaminidases
use other flashcards
for fertilisatipn and cleavage
what do the trophoblast outer rim form
trophectoderm
extra embryonic support tissue precursor
what does the uterus consist of
An outer serous peritoneal layer
A thick layer of smooth muscles (myometrium) with spontaneous peristaltic activity
An internal endometrium consisting of a stromal matrix overlaid by a simple columnar epithelium containing ciliated and glandular cells
changes during hormone cycles
maternal recognition of conceptus
trophoblasts secrete HCG
prevents luteal regresison by binding to LH receptors on luteal cells, stimulates estrogen and progesteron secretion
preventing endometrium shedding
prepares uterus
triggers deciduation of the endometrial lining
to make the endometrium receptive to implantation
deciduation
differentiation from elongated fibroblast like endometrial stromal cells
into more rounded and high specialised secretory epithelioid cell type
blastocyst in implantation
Oxygen and metabolic substrates from uterine secretions
Continued growth and survival
Trophoblast cells use specific transport mechanisms to accumulate ions and organic molecules
Oxygen and carbon dioxide exchange through diffusion
zona pellcuida in implantation
Zona Pellucida
Prevents cells of pre-compaction conceptus from separating (monozygous twins)
Prevents genetically distinct conceptuses from forming a chimera
Prevents the blastocyst from implanting in an inappropriate location in the uterus
mucins in implantation
Mucins (MUC-1) in the endometrial glycocalyx prevents binding of the conceptus and guides it to a receptive area
phases of implantation
hatching
apposition
adhesion
invasion
hatching phase
ZP breaks down by lytic enzymes in glandualar secretions
hatching of the conceptus by contraction/expansion of conceptus allowing rapid size increase
apposition phase
paracrine signalling controlled unstable interaction between blastocyst and uterine epithelium
tropholbasts express L-selectin to allow blastocyst to roll across surface of uterus until it finds receptive area of uterine epithelium that express sulphated oligosaccharide ligand
leukaemia inhibitory factor: oestrogen induced cytokine that promotes luminal endothelial receptivity and stromal cell decidualisation
adhesion
receptive areas of endometrium are the pinopodes
EGF receptors expressed by trophoblast
luminal cells express Hb-EGF which bnnds EGFR
signals from blastocyst upreg cell adesion such as integrins which mediate firm adhesion of blastocyst to endometrial linng
invasion
adhesion triggers local singlaling events: proliferate and differentiate into cytotrophoblast and syncytiotrophoblast
St secrete TNFa which reduces intracellular adesion to allow ST invasion
produce lytic enzymes to invade stromal celsl
stromal reaction: oedema, increased sprouting and capillary growth, decidualisation
then secondary decidualisation reaction and endometrial component of the placenta is prepared
breakdown of decidual cells prodive nutrition
ST projections will degrade maternal vessels
casuing maternal blood to floow ST lacunae allowing direct uptake of nutrients
cytotrophoblastic cells form finger like projections in the syncytiotrophoblast
form foetal blood vessels
endometrial epithelium reforms behind
implantation window
Days 1-7 luteal phase
Endometrium is prereceptive
Long apical microvilli
High surface charge
Thick glycocalyx
Days 7-10 receptive phase
Transition to receptivity
Pinopodes appear
Loss of surface negative charge
Shortening of microvilli
Thinning of mucin coat
If no implantation:
Refactory phase
Resist attachment
