Women's Health - Physiology of Pregnancy Flashcards
What is fertilisation?
Fusion of haploid sperm and oocyte
Where does fertilisation typically occur?
Ampulla of fallopian tube
What are the 6 stages of fertilisation?
- Capacitation
- Acrosome Reaction
- Adhesion + entry
- Cortical reaction
- Meiosis II
- Syngamy
What is capacitation?
Final stage of sperm maturation ; involves exposure of receptor sites involved in zona pellucida penetration.
What occurs during the acrosome reaction?
Loss of acrosome cap on the head of the sperm cell leads to release of lytic enzymes, which allows the sperm to penetrate the zona pellucida
What happens during adhesion and entry?
Fusion of sperm and egg membranes and the head of the sperm if phagocytosed - it then breaks down to release the sperm nucleus.
What happens during the cortical reaction?
modification of the zona pellucida, induced by
membrane fusion and mediated by cortical granules
What is the purpose of the cortical reaction?
Prevent polyspermy
What completes during meiosis II?
Oocyte completes meiosis II I (which until this point is arrested in
metaphase II) to give the second polar body.
What occurs during syngamy?
Pronuclei replicate DNA
the male and female pronuclei replicate DNA and shed their nuclear
membranes as they move toward one another, before aligning at a common metaphase
plate and undergoing mitosis.
When does implantation of blastocyst into the endometrium occur?
Day 6-7
What is formed during gastrulation?
Trilaminar disc from the primitive streak
What makes up the trilaminar disc?
endoderm
mesoderm
ectoderm
When do organ systems begin to develop?
Week 3-8
What is neurulation?
Development of the neural tube from the ectoderm
When does neurulation occur?
Week 4
At what week is the threshold of viability?
Week 23
What is the main purpose of placental exchange?
Gaseous and nutrition
How does oxygen move from mother to fetus?
Higher affinity of HbF
(oxygen moves readily from maternal to foetal haemoglobin (HbF) due
to HbF’s higher affinity)
How does CO2 move from fetus to mother?
Diffusion down concentration gradient
(CO2 diffuses from foetal to maternal blood down the concentration gradient).
How is glucose transferred to the fetus?
Facilitated diffusion (maternal to foetal circulation)
How do amino acids and free fatty acids cross from mother to foetus?
Active transport
Which hormones are produced/supplied by the placenta?
Human Chorionic Gonadotrophin (hCG)
Human Placental Lactogen (hPL)
Progesterone
Oestrogen
Which cells produced Human Chorionic Gonadotrophin (hCG) ?
Trophoblast cells
Purpose of hCG
maintains the corpus luteum to allow for sufficient progesterone production until
the placenta takes over
What hormone maintains the corpus luteum?
hCG
What does Human Placental Lactogen (hPL) increase?
Fatty acids, insulin
(increases maternal free fatty acid and insulin
levels, as well as inducing maternal insulin resistance.)
What is the effect of progesterone during pregnancy?
Inhibits uterine contractility
Thickens endometrium
Function of Oestrogen
stimulates myometrial growth
oxytocin receptor synthesis
pregnancy-related breast changes
What hormone stimulates myometrial growth?
Oestrogen
When does blastocyst implantation occur?
Day 6-7
What happens immediately after blastocyst implantation?
Trophoblastic invasion into the highly vascular uterine wall.
What invades the uterine wall during implantation?
Trophoblastic cells
What happens by mid-late week 2 (after the trophoblastic cells have invaded the uterine wall)?
trophoblastic cells invade endometrial capillaries and venules and form lacunae,
filled with maternal blood.
What fills the lacunae formed by trophoblastic invasion?
Maternal blood
What are the projections of invading cells called?
Primary villi
What forms within the villi of the placenta?
Foetal vessels
The projections of invading cells are referred to as primary villi - they form
branches which become secondary and tertiary villi.
What are the functional units of the placenta?
Cotyledons
What are cotyledons formed from?
stem villi and collections of their secondary/tertiary villi
What forms the exchange surface between maternal and foetal circulation?
Cotyledons
What forms the umbilical cord?
Amniotic membrane tube
(a tube of amniotic membrane which surrounds the connecting stalk
and vitelline duct)
Which vessels carry deoxygenated blood from the foetus to the mother?
the 2 Umbilical arteries
Which vessel carries oxygenated blood to the foetus?
The umbilical vein
What happens during systole in maternal blood flow?
Flows into intervillous space
(During systole, maternal blood flows out of flaccid invaded spiral arterioles into the intervillous space - it is here
that it contacts the foetal exchange surface of the chorionic plate, before rejoining the maternal circulation via
collecting venules. Maternal blood is supplied by the uterine arteries, branches of the internal iliac arteries.)
Where does maternal blood contact the fetal exchange surface?
Chorionic plate
What supplies maternal blood?
Uterine arteries, branches of the internal iliac arteries.
What decreases significantly in early pregnancy?
Total peripheral resistance
(Likely due to oestrogen and its effects on Nitric Oxide)
What hormone affects total peripheral resistance during early pregnancy?
Oestrogen
What causes the 45% increase in cardiac output during the first trimester?
Increased stroke volume
What contributes to increased cardiac preload?
Increased blood volume
What stimulates the increased blood volume?
Activation of RAAS stimulated by
the relative underfilling perceived by the kidneys as a result of the reduced
systemic vascular resistance.
What happens to red cell mass during pregnancy?
Increases
(this may be due to a combination of increased
erythropoietin and human placental lactogen)
What causes physiological anaemia in pregnancy?
Dilution from the even more increased plasma volume
What happens to total white cell count during pregnancy?
Increases
What is the effect on platelet count during pregnancy?
Decreased
What happens to Clotting Factors 7,8,9,10 in pregnancy?
All Increase
(Leading to a hypercoagulable state)
What increases in renal function during pregnancy?
Renal blood flow and GFR
How does the RAAS affect sodium during pregnancy?
Increases sodium reabsorption
(to facilitate increased blood volume)
What happens to serum urea and creatinine during pregnancy?
Lowered due to raised GFR
What stimulates increased minute ventilation?
Sensitisation of medulla to PaCO2
What helps remove fetal CO2?
Steeper fetal-maternal gradient
(Sensitisation of medulla to PaCO2 stimulates increased minute ventilation - this
drives a steeper foetal-maternal concentration gradient to remove more foetal
CO2)
How does the foetus avoid transplant rejection?
General maternal immunosuppression- mechanism unclear
AND
Trophoblast cells
What are Trophoblast cells?
the only direct interface with maternal circulation
Do Trophoblast cells express HLA Class I and II molecules?
Do not express
What is the immunological status of Trophoblast cells?
Immunologically inert
What is the uterus weight change during pregnancy?
approximately 40-100g to 800-1000g at term.
How much does uterine blood flow increase during pregnancy?
Tenfold
(The uterine arteries and their branches undergo hypertrophy and dilation)
What arteries supply blood to the gravid uterus?
Ovarian (gonadal) arteries
(this is not seen in non-pregnant women)
What changes occur in the cervix during the third trimester?
More vascular, loses collagen
when does the cervix lose collagen?
during the 3rd trimester
( it accumulates water and glycosaminoglycans to allow for stretching at
parturition)
(the vagina undergoes a similar process)
What forms to prevent infection during pregnancy?
Mucus plug
Cervical mucus becomes
thicker and eventually forms the operculum (mucus plug) to prevent infection.
What hormonal response leads to ductal proliferation in breasts?
High oestrogen levels
Which hormones influence the growth of alveoli (subunits of breast lobules) in breasts?
Progesterone and prolactin
What stimulates milk production from alveolar cells?
Prolactin
What happens to milk production levels immediately after delivery?
prolactin stimulates milk production which is inhibited during pregnancy but facilitated directly after delivery by the sudden drop in Oestrogen and Progesterone
How is the GI system impacted during pregnancy?
Gastric emptying is slowed and bowel motility is decreased, as progesterone acts
as a smooth muscle relaxant.
This can lead to gastric reflux and constipation.
What hormone slows gastric emptying?
Progesterone
What conditions can result from slowed gastric emptying?
Gastric reflux, constipation
What causes increased pigmentation during pregnancy?
Raised melanocyte-stimulating hormone
What are common pigmentation changes?
Chloasma, Melasma (face)
Areola
linea nigra
What is linea nigra?
Increased pigmentation of linea alba
What causes striae gravidarum?
Disruption of collagen fibres due to adrenocortical hormones and mechanical stress.
What hormones rise throughout pregnancy?
Oestrogen and progesterone
What hormone rises in the third trimester?
Corticotropin releasing hormone
(this may play a role in labour)
What happens in the first 4 days post-fertilisation?
Cleavage into blastomeres, via mitosis
Is there cell growth in the first 4 days post-fertilisation?
No cell growth occurs during this period, so the total volume e of the embryo (still contained within the zona pellucida) remains unchanged
What happens at the 8 cell stage (post fertilisation)?
At the 8-cell
stage, the blastomeres start to segregate into embryoblast and trophoblast precursors and flatten
against the wall of the zona pellucida in a process called compaction.
What is the process called when blastomeres segregate into embryoblast and trophoblast precursors?
Compaction
Why is the embryoblast also referred to as the inner cell mass?
Eventually, the entire inner wall is lined by trophoblast cells, after compaction.
What happens at day 3-4 post fertilisation?
Morula formation (16 cells)
What is the term for the conceptus when it has divided into 16 cells?
Morula
When does the blastocyst form?
Day 5
What forms the cavity called blastocoel during blastocyst formation?
Active transport of electrolytes
(: the morula forms a cavity called a blastocoel by actively transporting
electrolytes and taking on water via osmosis.)
What is the inner cell mass also referred to as?
Embryoblast
What happens on days 5-6 post fertilisation?
hatching - the blastocyst breaks out of the zona pellucida and hatches into the uterus
What do lytic enzymes do on Day 5-6?
Allow blastocyst hatching
What occurs on Day 6-7 during implantation?
Implantation: Blastocyst adheres to endometrium
What do endometrial stromal cells differentiate into during implantation?
Decidual cells
(to accommodate the blastocyst in a process called the decidual reaction)
The trophoblast cells divide into the
Cytotrophoblast and
syncytiotrophoblast (a membrane-less mass of cytoplasm and nuclei), and the latter begins to invade into the uterine wall.
What begins to invade the uterine wall?
Syncytiotrophoblast
What increases in the uterine wall during implantation?
Vascularisation
What invades deeper into the uterine wall on Day 8?
Syncytiotrophoblast
The entire embryo is drawn into the uterine wall.
What assists the syncytiotrophoblast in invading?
Proteolytic enzymes produced by the cytotrophoblast
What forms the bilaminar disc?
Embryoblast differentiation
(The cells of the embryoblast differentiate into epiblast and hypoblast cells to form the
bilaminar disc.)
What begins to form between the epiblast and cytotrophoblast?
Amniotic cavity
What forms the primary yolk sac (Heuser’s membrane)?
Hypoblast cells spread and line the former blastocoel
What surrounds the embryo on Day 9?
Syncytiotrophoblast
(the embryo is fully implanted within the wall, and is surrounded by syncytiotrophoblast)
What forms extraembryonic mesoderm cells?
Heuser’s membrane
(formed ~ day 10-11)
When do lacunae invade maternal capillaries?
Day 10-11
What happens on days 10-11?
extraembryonic mesoderm expands.
When does extraembryonic mesoderm split into two layers?
Day 12-13
What forms the chorionic cavity?
Split of extraembryonic mesoderm
What is the result of the increase in pregnancy?
hypercoagulable
What is the result of a hypercoagulable state in VII, VIII, IX and X?
pregnancy
How does the chorionic cavity develop?
This cavity grows rapidly to become the dominant constituent of the embryo by day 13 -
at this point, the bilaminar disc, amnion, and yolk sac (surrounded by extraembryonic mesoderm) are
suspended within the chorionic cavity by the connecting stalk.
Where are bilaminar disc, amnion, and yolk sac suspended?
chorionic
What type of mesoderm surrounds bilaminar disc, amnion, and yolk sac?
extraembryonic
