Coition fertilisation and blastocyst development Flashcards
describe the EPOR model
Desire
Excitement: response to psychogenic or somatogenic stimuli resulting in increasing arousal
Plateau: arousal is maintained and intensified causing increased pelvic haemodynamics
Orgasm: a few seconds of involuntary climax that relieves sexual tension by wave of intense pleasure. Associated with ejaculation in men.
Resolution: arousal dissipated and pelvic haemodynamics resolved to unstimulated state.
describe the variations in sexual responses between men and women
MEN:
- Entire response 2-4 min
- Absolute refractory period
WOMEN:
- Longer arousal period
- Entire response ~ 25 min
- No absolute refractory period (multiple orgasms possible)
- Many women do not reach orgasm during vaginal intercourse
The corpora cavernosa (trabeculated sinus space surrounded by a thick fibrous capsule called the ____ _______) is the main erectile tissue of the penis.
The corpora cavernosa (trabeculated sinus space surrounded by a thick fibrous capsule called the tunica albuginea) is the main erectile tissue of the penis.
why is the pressure of the corpus spoingiosum relatively low?
to prevent compression of the urethra to allow ejaculation
describe a flaccid penis
- sympathetic outflow of hypogastric nerve maintains myogenic tone of cavernous trabeculae.
- contraction of smooth muscle mounds at arterial input limits inflow
- low volume + low pressure of intercavernous space
describe tumescence in the penis
- Psymp stim of pelvic nerve decreases tone in arterial smooth muscle and the trabelulae muscle = increased flow into cavernosum
- venous outflow is reduced by compression of the sub-tunical venous plexus
- large volume - high pressure
describe the erection phase of the penis
Penis is in a fully rigid state such that in- and out-flow of blood are nearly absent.
Priapism – what is it?
Priapism – prolonged erection leading to ischemia; resolved pharmacologically.
describe Detumescence
Pressure reduction caused by the contraction of arterial smooth muscle causes arterial flow to decrease and increase venous outflow;
penis returns to flaccid state.
describe how NO is involved in penile erection
NOS produces NO.
actives GC - produces cGMP from GTP.
initiation of erection: neuronal NOS (nNOS) causes relaxation
maintaining erection: endothelial NOS (eNOS) in intracavernous space
describe how PDE5 is involved in detumescence
cGMP levels are converted to 5’-GMP by phosphodiesterase 5 (PDE5) causing vasoconstriction of smooth muscle in the intracavernous space thus reducing blood volume and penile rigidity.
what other muscles are involved in maintaining an erection?
To further increase penile rigidity and stabilize the erection, the ischiocavernous muscle (at crus of penis) and bulbospongiosus muscle (surrounds bulb of penis) contract to compress the proximal part of the corpus cavernosum.
This reflex is mediated via the pudendal nerve (S2, 3, 4).
describe the Bulbosponiosus reflex
This reflex is used to test the state of a spinal cord injury.
By squeezing the glans of the penis (or clitoris in women), the contraction of the anal sphincter can be assessed to determine the level of spinal cord injury.
define erectile dysfunctino
Erectile dysfunction is defined as the consistent and recurrent inability to attain and/or maintain a penile erection sufficient for sexual activity.
give some causes of erectile dysfunction
- Psychogenic factors
- Organic factors:
- Neurogenic – physical nerve damage, multiple sclerosis, diabetes (impairs release of nNOS), pelvic surgery, disc lesion
- Arteriogenic – hypertension, diabetes (impairs eNOS release), hyperlipidemia, tears in fibrous capsule of corpora cavernosa, vessel obstruction supplying the penis
- Endocrine – low testosterone, high prolactin
- Use or abuse of drugs – anti-hypertensives, anti-depressants, smoking, alcohol, drugs that antagonize neurotransmitters that mediate tumescence
treatments for erectile dysfunction?
- Sex therapy
- Intercavernosal injection or intraurethral injection of smooth muscle relaxants (such as synthetic prostanoid prostaglandin E1)
- Viagra – a pharmacological agent that maintains cGMP levels by way of inhibiting PDE5 to preserve intracavernous smooth muscle relaxation and to promote erection. Note that Viagra can cause damage through prolonged exposure (ischemic priaprism).
Ejaculated spermatozoa are carried to the female tract in ……….?>………. (_____ and _______ together are called semen).
Ejaculated spermatozoa are carried to the female tract in seminal plasma
(spermatozoa and seminal plasma together are called semen).
how do sperm move from tubules to the vasa efferentia?
describe the sperm at this stage
After spermatogenesis in the testes, sperm move via passive, bulk flow from the
- testes
- to the rete testes
- and into the vasa efferentia
up to the vasa efferentia
describe the sperm
At this point, the sperm are non-fertile and immotile.
how do the sperm move in the epididymis
While in the epididymis, sperm move via epididymal muscle contractions into the vas deferens.
what happens to the sperm in the epididymis?
- Loss of the cytoplasmic droplet.
- Increased concentration of sperm due to fluid absorption in vas efferentia and epididymis
- Nuclear condensation (replacement of histones with protamines) and acrosomal remodeling
- Metabolic changes including the selective metabolism of cholesterol and phospholipids, and
- increased dependence on external fructose for glycolytic energy production
- Motility is achieved due to a rise in cAMP content in the tail flagellum, which becomes more rigid due to increased disuphide bonds.
- The membrane surface becomes coated with glycoproteins (aid in sperm-oocyte interactions).
why does the tail flagellum become more rigid?
and how is motility achieved?
Motility is achieved due to a rise in cAMP content in the tail flagellum, which becomes
more rigid due to increased disuphide bonds.
describe sperm in the cauda epididymis?
When they reach the cauda epididymis, sperm have the potential to be motile and fertilise oocytes.
what is a dtry orgasm
Dry orgasm – normal erection and orgasm but impaired emission
what do they red nad blue arrows show?
5 Key points of sperm maturation in the epididymis?
- eSpermatocrit (100x)
- Final morphological changes
- Capacity to move (but immotile): tail flagellumèrigid (écAMP)
• Metabolic changes
(fructose, cholesterol, phospholipids)
• Stabilising glycoproteins
Seminal fluid is derived from …..
Seminal fluid is derived from
major accessory sex glands (e.g., seminal vesicle, prostate gland, Cowper’s gland)
with only a small contribution of fluid from the epididymis.
The Cowper’s gland (bulbourethral gland) secretes …….
The Cowper’s gland (bulbourethral gland) secretes lubricant in the pre-ejaculate and the ejaculate
does the urethra run through the centre of the prostate?
yes
implications of the loss of prostate on fertility?
bad - no fertility
Activity of accessory glands depends on ……
Activity of accessory glands depends on androgens (e.g., 5-DHT)
since castration (removal of the testicles) and hypophysectomy (removal of the pituitary gland) inhibit normal function of the prostate and seminal vesicle (see practical notes).
is seminal plasma essential for sperm function?
Seminal plasma is not essential for sperm function but rather provides;
a vehicle for sperm transport,
nutritional factors (e.g., fructose),
a buffering agent to counteract the acid pH of the vaginal fluids,
and anti-oxidants (e.g., ascorbate, hypoteurine).
does seminal fluid contain prostaglandins?
It also contains prostaglandins, which might stimulate vaginal muscle contractions.
might seminal plasma be bad/
it may include potentially infectious agents (e.g., hepatitis B or C virus, HIV, HPV) and leucocytes. T
describe the levels of leukocytes in seminal plasma?
The presence of leucocytes is normal but high levels may indicate a urinary tract infection or infertility.
describe how sperm are propelled into the woman
With further stimulation, emission occurs when the prostate, vas deferens and seminal vesicle muscles contract and components of the seminal plasma with spermatozoa are expelled into the urethra.
With further stimulation, emission occurs when the prostate, vas deferens and seminal vesicle muscles contract and components of the seminal plasma with spermatozoa are expelled into the urethra.
which nerve fibres via the ________ plexus mediate this process?
With further stimulation, emission occurs when the prostate, vas deferens and seminal vesicle muscles contract and components of the seminal plasma with spermatozoa are expelled into the urethra.
Noradrenergic sympathetic fibres via the hypogastric plexus mediate this process.
Passage of semen back into the bladder is prevented by ,…..
Passage of semen back into the bladder is prevented by contraction of the vesicular urethral sphincter.
describe Retrograde ejaculation
Retrograde ejaculation – failure of the urethral sphincter causing ejaculate to enter the bladder.
Ejaculate is layered with highest proportion of content coming from:
Pre-ejaculate -
Early ejaculate –
Mid-ejaculate –
Late ejaculate –
Pre-ejaculate Cowper’s gland
Early ejaculate – prostate
Mid-ejaculate – vas deferens
Late ejaculate – seminal vesicle
ejaculate components:
The early fraction is rich in __________ from the ______
the mid-fraction is rich in __________ from the ________
and the late fraction is rich in _________ from the ___________
The early fraction is rich in acid phosphatase from the prostate,
the mid-fraction is rich in spermatozoa from the vas deferens,
and the late fraction is rich in fructose from the seminal vesicles
does ejaculate solidify?
Ejaculate coagulates when the components are mixed together in the vagina to ensure that sperm is retained, and liquefies again within 20-60 min.
describe how vaginal lubrication occurs
Vaginal lubrication occurs by transudation of fluid through the vaginal wall as the vagina expands and the labia majora become engorged with blood.
describe tenting
With increased stimulation, the width and length of the vagina increase further and the uterus elevates upwards into the false pelvis, lifting the cervical os to produce the so-called tenting effect.
Musclecontractionsinuterusand
vagina at orgasm
– are they important for sperm transport?
no
how do sperm enter the cervical os?
Successful sperm likely enter the cervix through their own propulsion and with the help of ciliated cells of the cervical os that waft the sperm towards the cervical canal
Vaginal and uterine muscle contractions during orgasm are/ are not required to propel sperm into the cervix.
Vaginal and uterine muscle contractions during orgasm are not required to propel sperm into the cervix.
describe how the cervic changes under hormonal influence?
Mostly closed to prevent infection
Oestrogen in follicular phase:
muscles relax = opening
epithelium secrete watery mucus allows easy entry for sperm
during progesterone / luteal phase:
cervix firmer
closed os
thick mucus - preventing spermies
how can we analyse cervial secretions ot monitor fertility?
First sperm in fallopian tube after ~_ min
First sperm in fallopian tube after ~5 min
Viable spermatozoa can survive between …. hours in the female genital tract.
Viable spermatozoa can survive between 28-48 hours in the female genital tract.
Mittelschmerz pain - what is it?
About 20% of women experience bleeding into the peritoneal cavity caused by ovulation leading to Mittelschmerz pain
T or F
At the isthmus where the oviduct meets the uterus, the sperm are briefly immobile and bind temporarily to the oviductal epithelial cells. Only at ovulation do sperm re-acquire motility to swim to the potential site of fertilization. Though not well understood, this might depend on the release of (unknown) chemoattractants by both the oocyte and the cumulus mass to cause hyperactive flagellar beating. The fittest sperm and oocyte come together in the ampullary region of the oviduct for fertilization.
T
describe sperm capacitation
The attainment of full fertilising capacity of sperm is achieved within the female reproductive tract and is called sperm capacitation.
Full capacitation of a spermatozoon is distinguished by two characteristics:
what are they
Hyperactivated motility defined by whiplash beats of the sperm tail (compared to wave-like beats). This is promoted by the opening of Ca2+ channels to activate PKA.
Changes in the surface membrane properties to allow the sperm to become sensitive to local signals sent out by the oocyte culminating in sperm activation. This increases the fusogenicity with the oocyte.
where? is optimal for sperm capacitation
The oestrogen-primed uterus or oviductal isthmus is optimal for sperm capacitation
capacitation involves the what key process?.
This is associated with a change in the surface charge and lipid structure of the sperm membrane, especially the loss of cholesterol.
In response to an influx of Ca2+, cAMP is generated and PKA is activated followed by the phosphorylation of tyrosines on a number of proteins.
capacitation involves the stripping of glycoproteins that coat the spermatozoal surface.
This is associated with a change in the surface charge and lipid structure of the sperm membrane, especially the loss of cholesterol. In response to an influx of Ca2+, cAMP is generated and PKA is activated followed by the phosphorylation of tyrosines on a number of proteins.
is capacitation reversible?
life span of capacitates sperm?
Remarkably, capacitation is experimentally reversible (decapacitation) by re-incubating the sperm in epididymal fluid or seminal plasma.
In a capacitated state, the sperm is unstable and will die if it does not find an oocyte fairly rapidly.
Hyper-activated motility (swim power)
how do sperm aquire this?
when does the temrinal phase of capacitation occur?
the terminal phase of capacitation and only occurs once the sperm comes into contact with the cumulus cells that surround the oocyte or the oocyte itself.
is the temrinal phase of capcitation reversible?
no
which is ejaculated?
which is capacitated?
describe sperm activation?
Activation is induced by binding directly to the zona pellucida (ZP) proteins on the oocyte.
The acrosome swells and its membrane fuses with the overlying plasma membrane, resulting in the exteriorization of the contents of the acrosomal vesicle (e.g., hyaluronidase that is required to digest the matrix between the cumulus cells to expose the zona pellucida) and the inner acrosomal membrane including acrosin (enzyme that digests zona pellucida).
how does sperm tail movement change upon sperm activation?
Sperm tail movement changes from wave motion to hyperactive whiplash promoted by the activation of PKC.
what are ZP proteins?
proteins on zona pellucida
induce acrosome reaction
4 ZPs in humans - esential for blocking corss species fertilisation
ZP3 is essential for sperm binding
describe the process of sperm penetration
- sperm binds zona pellucida
- penetrates zona pellucida
- can take 5-20 minutes
- At this point, the sperm enters the perivitelline space.
give 3 proteins essentail to sperm binding?
______ on the sperm surface binds to _______ on the oocyte allowing _______ to accumulate in the binding area to become a binding partner of _____
Izumo1 on the sperm surface binds to Juno on the oocyte allowing CD9 to accumulate in the binding area to become a binding partner of Juno
T or F
IZUMO1 binds to JUNO/CD9 complex
t
describe how calcium is involved in fertilisation of the oocyte?
- after fusion
- big rise in intracellular calcium
- last 2-3 minutes - occurs in waves - starting at where sperm entered
- critical for subsequent events
- egg called a zygote now
how is polyspermy prevented?
the elevated calcium levels resulting from oocyte activation lead to the cortical reaction:
- a release of the contents of subcortical granules into the perivitelline space, which prevent other sperm from binding the zona pellucida.
- The release of ovastatin allows for the cleavage of ZP3/4 and ZP2, thus removing the ZP sperm binding properties.
- ZPs also become cross-linked to make the zona pellucida impenetrable.
- Juno is also exocytosed off the oocyte membrane.
At ovulation, oocyte arrested in ….. which dividsion?
At ovulation, oocyte arrested in 2nd meiotic metaphase
The oocyte must also complete its second meiotic division.
Remember that the oocyte is ovulated while it is arrested in its second meiotic division and therefore, has …………. sets of chromosomes.
To transmit only one set to the next generation, it must complete its second meiotic division and extrude the ………
The failure to do this leads to what condition?
The oocyte must also complete its second meiotic division.
Remember that the oocyte is ovulated while it is arrested in its second meiotic division and therefore, has two haploid sets of chromosomes.
To transmit only one set to the next generation, it must complete its second meiotic division and extrude the second polar body.
The failure to do this leads to gynogenetic triploidy.
after penetration: The sperm nuclear membrane breaks down and the highly condensed chromatin starts unwind as _______ are replaces with _______.
The sperm nuclear membrane breaks down and the highly condensed chromatin starts unwind as protamines are replaces with histones.
describe the paternal and maternal pronuclei
The sperm nuclear membrane breaks down and the highly condensed chromatin starts unwind as protamines are replaces with histones.
This process is actively induced by oocyte factors.
The each set of haploid chromosomes becomes surrounded by distinct membranes to form the paternal and maternal pronuclei.
D: syngamy
Syngamy is the final phase of fertilisation involving the coming together of gametic chromosomes occurs.
Immediately, the first cell division occurs so that the one-cell zygote becomes a two-cell conceptus (embryo).
is there DNA synthesis in the zygote?
yes - in preparation for the first mitotic division
what does the sperm contribute to the zxygote?
the sperm contributes the centriole and pericentriolar material to make up the centrosome, which is important for cytokinesis at mitosis and without it cellular division fails. Recent research has shown that the sperm also contribute non-coding RNA to the zygote.
describe the non coding RNA the sperm provide the zygote
These RNAs are sensitive to environmental stressors (e.g., diet) and have the potential to influence gene expression in the early embryo and disease risk in the adult
Paternal proteins from the sperm are….. whats their fate?
Paternal proteins from the sperm are ubiquinated and broken down.
T or F
All mitochondria in the adult are maternally-derived. Whilst paternal mitochondria may enter the oocyte at fertilisation, they do not survive.
T
are the male and female pronucleus at opposite poles?
yes
in syngamy do the 2 nuclear membranes break down?
yes
_____ spindle retrieves _____ pronucleus and brings both pronuclei to equator
Male spindle retrieves female pronucleus and brings both pronuclei to equator
why are sperm mitochondrion degraded?
Sperm mitochondrial (mt) DNA is susceptible to mutation through oxidative stress (theory)
- Natural exposure to reactive oxygen species
- No histones in mtDNA for protection
- No efficient DNA repair mechanisms in sperm
Poor quality sperm: mutated mtDNA
whats a hydatidiform mole
Other aneuploidy conceptuses may develop as tumors, such as hydatidiform mole (benign trophoblastic tumor)
A hydatidiform mole is a growing mass of tissue inside your womb (uterus) that will not develop into a baby. It is the result of abnormal conception. It may cause bleeding in early pregnancy and is usually picked up in an early pregnancy ultrasound scan. It needs to be removed and most women can expect a full recovery
Disorders of ploidy are likely to result from …..
Disorders of ploidy are likely to result from
failure of polar body formation,
polyspermy,
or failure of one early cleavage division.
A parthenogenetic conceptus (parthenote) contains chromosomes from….
A parthenogenetic conceptus (parthenote) contains chromosomes from only one parent.
sperm and egg DNA are functionall non equiverlent?
true
Human parthenogenetic embryos (2 egg DNA) do not survive to birth because development fails during the first cleavage due to …..
In mice, gynogenetic conceptuses only form embryonic lineages but die early due to a lack of placental tissue.
Human parthenogenetic embryos do not survive to birth because development fails during the first cleavage due to a lack of centriole inherited from the sperm.
In mice, gynogenetic conceptuses only form embryonic lineages but die early due to a lack of placental tissue.
outline the transport of the embryo down the fallopian tube
down the fallopian tube into the uterus with the help of smooth muscle contractions and ciliated cells on the fallopian tube.
Embryo transport requires oestrogen and progesterone, and may be obstructed by infection or scarring of the fallopian tube
what IS pregnancy initiated wiht?
Therefore, pregnancy is not initiated with fertilisation, but only when the conceptus has signaled its presence to the mother.
where does the first cell fate decision of the conceptus occur?
in fallopian tube:
(ICM versus trophectoderm)
at the morula stage - the embry undergoes what?
compaction
describe compaction?
increased cell-cell adhesion that transforms cells from non-polar (radially symmetrical) to highly polarized
some cells become localized to the inside of the embryo and some remain on the outside. This polarization and positioning initiates the first differentiation event and lineage segregation.
During pre-implantation development, the embryo is surrounded by the …..
During pre-implantation development, the embryo is surrounded by the zona pellucida.
what does the zona pellucida do?
It protects the developing embryo by ensuring that the cells do not fall apart and to prevent premature implantation into the fallopian tube or uterus.
When the blastocyst matures, it hatches out of the zona pellucida and is free to interact with the uterus.
describe the Formation of the blastocoel
- Tight junctions on outer cells create diffusional ion gradient
- Cause influx of water into embryo to form blastocoel cavity
in the formation of the blastocoel:
which ions create the ion gradient to draw in water?
describe the layers of cells in the blastocoel stage of blastocyst
1) an outer rim of trophoblast cells called the trophectoderm surrounding the blastocoelic cavity, and
2) an inner group of pluriopotent cells that form the inner cell mass.
is the trophoectoderm extraembryonic?
yes
Instead they will form the trophoblast cells of the placenta and are concerned with the nutrition and support of the embryo/fetus.
the genes ……..(3)……… are transcription factors whose expression is restricted to the inner cells of the compact morula and early blastocyst.
For example, the genes OCT4, NANOG, and GATA6 are transcription factors whose expression is restricted to the inner cells of the compact morula and early blastocyst.
the expression of transcription factors, such as ………(3)……….. is restricted to the outer cells and are required to specify the trophectoderm cell lineage.
the expression of transcription factors, such as CDX2, GATA3, and EOMES, is restricted to the outer cells and are required to specify the trophectoderm cell lineage.
how does CDX2 and OCT4 expression in the blastocyst change?
initally all cells of 8 cell embryo
This restriction is, in part, dependent upon the degree of cell-cell contact. For example, the kinase Hippo is regulated by degree of cell-cell contact.
In non-polarized cells, Hippo is active and phosphorylates Yap (a transcription factor) preventing it from entering the nucleus.
Since a main function of Yap is to activate Cdx2 gene expression, Cdx2 remains off in these cells (i.e., inner cell mass). In polarized cells (the trophectoderm), Hippo expression is suppressed and therefore, Yap can enter the nucleus to initiate Cdx2 expression and trophectoderm cell fate.
The pre-implantation embryo obtains nutrients from …..
The pre-implantation embryo obtains nutrients from secretions from the fallopian tubes and the endometrial glands of the uterus
By the 8-cell stage, just prior to compaction, the embryo depends on ………… for energy
By the 8-cell stage, just prior to compaction, the embryo depends on glucose and essential amino acids for energy.
in order to implant - what must the blastocyst do?
hatch from the zona pellucida
describe blasticyte hatching
Hatching requires proteolytic enzymes secreted from the trophectoderm and possibly from the uterine secretions to dissolve a hole in the zona pellucida for the blastocyst to squeeze out.
does the zona pellicuda prevent premature hatching?
yes
where does implantation usualy occur
near the fundus of the uterus
This can occur in a posterior (55% of pregnancies) or anterior (44% of pregnancies) position
Abnormal implantation occurs when the blastocyst implants on or very close to the cervix resulting in ….
Abnormal implantation occurs when the blastocyst implants on or very close to the cervix resulting in placenta praevia (0.5% of pregnancies).
Ectopic implantation occurs where?
Ectopic implantation occurs in regions other than in the uterine lumen including in the ovary, Fallopian tube, Caesarean scar, abdominally, or cervically. T
his is painful for the woman and results in embryonic lethality.
is the implantation window narrow?
yes
is the uterine uysually receptoive to a implantation?
no
The uterus is receptive during which phase of the menstrual cycle.
The uterus is receptive during the progesterone dominance phase (luteal phase) of the menstrual cycle.
what are required to prime the uterine lining for implantation
Progesterone (from corpus luteum) and oestrogen (from ovary) are required to prime the uterine lining for implantation
________ is also responsible for preparing the conceptus for implantation
Oestrogen is also responsible for preparing the conceptus for implantation
During the non-receptive phase, the epithelial cells of the uterine endometrium are resistant to embryo adhesion. describe why?
During the non-receptive phase, the epithelial cells of the uterine endometrium are resistant to embryo adhesion.
The cells have a thick mucin (MUC1) glycoprotein coat, long microvilli and a negative surface charge that prevent the blastocyst from adhering.
in the receptive window - how is the uterine lining altered?
However, during the receptive window, the blastocysts able to adhere due to a thinner mucin coat, a loss of negative charge, the expression of LIF acting as a ‘come hither’ signal, and shortened microvilli on the endometrial epithelial cell surface.
repulsion vs adhesion
how does the trophoblast interact with the uterine endothelium
L-selectin on the surface of the trophectoderm is important for this interaction. It binds to the L-selectin ligand on epithelium.
This promotes the secretion of human chorionic gonadotropin by the trophoblast cells, which signals to the epithelium to secrete trophinin and breakdown the MUC1 glycocalyx.
blastocyst to more easily interact with molecules on the surface of the uterine epithelial cells (e.g., integrins) required for adhesion.
T or F
LIF signaling acts both on the trophoectoderm and the uterine epithelium.
T
LIf signalling upregulated what?
It causes an up-regulation of HB-EGF (heparin binding epidermal growth factor-like growth factor) on the uterine epithelium, which binds to HSPG (heparine sulfate proteoglycan) on the trophectoderm.
LIF also induces the expression of adhesion molecules, such as integrins on the uterine epithelium and the trophectoderm.
as the trophoectodermal cells invade between eipthelial cells, what 2 types of messege exhcanges occur?
1) containment and control to keep the trophoblastic invasion in check (TIMPs); and
2) incitement and encouragement to promote the invasive events (MMPs). There is no evidence of epithelial cell death caused by trophoblastic invasion.
describe the stromal or decidual reaction.
This causes the endometrium to become a nutrient packed, highly vascular tissue called the decidua.
This is similar to a ‘proinflammatory endometrial reaction’ because prostaglandins are involved.
Maternal stromal cells of the endometrium, which are spindly, are converted to maternal decidual cells that are large and round due to the accumulation of lipids and glycogen.
Decidual cells secrete cytokines including IGF binding proteins and prolactin that aid the growth of the conceptus.
An important feature of the decidual response is the increased vascular permeability and angiogenesis.
Some decidualisation occurs in the absence of an implanted embryo in the secretory phase of the menstrual cycle.
By day ___, the conceptus has completely embedded itself into the uterine wall, which allows….
By day 11, the conceptus has completely embedded itself into the uterine wall, which allows it access to uterine glands and uterine spiral arteries as the placenta begins to grow
During development of the conceptus, the decidua becomes divided into three regions: t
what are they?
the decidua basalis (‘beneath the conceptus’; closest to the myometrium, and becomes the maternal face of the mature placenta),
the decidua capsularis (‘over the conceptus’; covers the protruding side of the conceptus and will disintegrate over time),
and the decidua parietalis (the remainder of the maternal decidua).
At the end of a normal menstrual cycle, progesterone levels drop allowing for the shedding of the endometrial lining.
This is because ……
At the end of a normal menstrual cycle, progesterone levels drop allowing for the shedding of the endometrial lining.
This is because decidual cells cannot de-differentiate back into stromal cells, and as a result, the endometrial lining is newly developed with each menstrual cycle.
The conceptus must prevent the shedding of the endometrial lining by signaling to the mother to let her know that she is pregnant (maternal recognition of pregnancy).
how does it do this?
During implantation in humans, the trophoblast cells secrete a hormone called human chorionic gonadotropin (hCG). This maintains the corpus luteum and therefore, progesterone levels remain suitably high enough to prevent a new menstrual cycle.
progesterone wise - what special about week 10?
By 10 weeks of pregnancy, the placenta secretes sufficient progesterone and the ovarian progesterone is no longer required. Of note, hCG is the chemical detected by most pregnancy tests since it is secreted in the urine and is only present during early pregnancy.
how is pregancy defined?
Pregnancy can be defined biochemically (based on the detection of hCG levels in urine or blood)
or clinically after the first missed menstrual period and ultrasound evidence of a conceptus.
give some Reasons for early pregnancy loss
While the reason behind pre-clinical and clinical miscarriage is not completely understood, some explanations might be:
- chromosomal abnormalities,
- physical factors,
- atypical uterine environment,
- and fertilization errors that might be due to separation of coitus from ovulation (old oocytes or sperm).
1-2% of couples experience recurrent pregnancy loss (three or more consecutive miscarriages) likely due to an endometrial defect since the incidence of genetic abnormalities is much lower in these conceptuses.
fat
mamba
well done
