1b Disorders of Pregnancy Flashcards
What are the intervillous lacunae?
They are maternal blood spaces which are supplied by the maternal blood supply
Describe how the fetal demands on the placenta change through pregnancy?
They increase - The branching of the chorionic villi increases with progression through pregnancy to increase the surface area for exchange
What is the term given to describe early embryo nutrition?
Histiotrophic
What is histiotrophic nutrition?
Nutrition which is reliant on uterine gland secretions and breakdown of endometrial tissues
Describe the change which occurs in the type of nutrition at the start of the second trimester?
switches to haemotrophic support at the start of the second trimester
How is haemotrophic nutrition achieved?
Haemochorial type placenta where maternal blood is in direct contact with the fetal membranes = choronic villi
What are the chorionic Villi?
Finger-like extensions of the chorionic cytotrophoblasts, which then undergo branching
They provide substancial surface area or branching
What are the three stages of chorionic villi development?
Primary: Outgrowths of the cytotrophoblast and branching of these extensions
Secondary: growth of the fetal mesoderm into the primary villi
Tertiary: growth of the umbilical artery and umbilical vein into the villus mesoderm, providing vasculature
What cells are the chorionic villi formed from?
cytotrophoblast cells - they grown into the chorion, and then undergo vascularisation and branching
Describe the structure of the terminal villus microstructure?
Convoluted knot of vessels and vessel dilation - this slows blood flow enabling exchange between maternal and fetal blood
What is the whole terminal villus coated in?
Trophoblast cells
What happens to the terminal villus microstructure between early and late pregnancy?
Early pregnancy: 150-200µm diameter, approx. 10µm trophoblast thickness between capillaries and maternal blood.
Late pregnancy: villi thin to 40µm, vessels move within villi to leave only 1-2µm trophoblast separation from maternal blood.
What do the spiral arteries do?
They provide the maternal blood supply to the endometrium
What is the name given to the cells which coat the villi?
Extra-villus trophoblasts
What happens to the EVT’s during spiral artery remodelling?
Extra-villus trophoblast (EVT) cells coating the villi invade down into the maternal spiral arteries, forming endovascular EVT.
What happens to the endothelium and smooth muscle of the spiral arteries when they are remodelling?
Endothelium and smooth muscle is broken down – EVT coats inside of vessels
What is the process of conversion?
Conversion: turns the spiral artery into a low pressure, high capacity conduit for maternal blood flow.
What does EVT cell invasion trigger?
EVT cell invasion triggers endothelial cells to release chemokines, recruiting immune cells.
What happens when the EVT cells invade the spiral artery walls?
they break down the normal vessel and ECM, and replace it with a new matrix which is known as fibrinoid
What is meant by failed conversion?
Failed conversion: smooth muscle remains, immune cells become embedded in vessel wall and vessels occluded by RBCs, immune cells
When spiral arteries fail to remodel, what are the consequences of the retained smooth muscle?
Retained smooth muscle may allow residual contractile capacity -> perturb blood delivery to the intravillous space.
Restricts blood flow into the maternal blood spaces
What changes are unconverted spiral arteries vulnerable to?
- pathological change- intimal hyperplasia and atherosis
- can lead to:
pertubed flow and local hypoxia
free radical damage
inefficient delivery of substances into the intervillous spaces
Aside from spiral arteries, where can atherosis also occur as a result of failed spiral artery remodelling?
Atherosis can also occur in basal (non-spiral) arteries that would not normally be targeted by trophoblast.
What is pre-eclampsia?
New onset hypertension (in a previously normotensive woman) BP ≥140 mmHg systolic and/or ≥90 mmHg diastolic, occuring after 20 weeks gestation
What are the diagnostic features of PE?
reduced fetal movements / amniotic fluid volume
What are the associated symptoms of pre-eclampsia?
Oedema common but not discriminatory for PE
Headache (in around 40% of severe PE patients)
Abdominal pain (in around 15% of severe PE patients)
Visual disturbances, seizures and breathlessness associated with severe PE and risk of eclampsia (seizures)
What is the main risk of PE?
Can escalate to Eclampsia - severe neuronal seizures which can lead to maternal death
What are the two subtypes of Pre-Eclampsia?
Early onset <34 weeks
Late onset > 34 Weeks
What are the features of early onset Pre-Eclampsia?
Associated with fetal and maternal symptoms
Changes in placental structure
Reduced placental perfusion
What are the features of late onset Pre-Eclampsia?
Mostly maternal symptoms
Fetus generally OK
Less overt/no placental changes