Flashcards in Repro 8.1 Placental Function and Dysfunction Deck (58)
What is the placenta?
The interface between mother and baby through which nutrients are supplied from the mother and waste is removed from the embryo. A selective barrier.
When does development of the placenta begin and from what?
Soon after fertilisation at compaction from cells of the outer cell mass
What surounds the embryo?
Amnion and chorion membranes in a protective sac. The placenta develops as a specialisation of the chorion
When does specialisation of the chorion occur?
At implantation - fingerlike projections called chorionic villi develop
What are chorionic villi?
Functional units of the placenta that represent the point of exchange between the maternal and foetal circulations. Consist of a vascularised core covered by two epithelial layers
By what means does maternofoetal exchange occur?
Receptor mediated endocytosis
What does a counter current achieve in the placenta?
Combined maternal and foetal circulations create a counter current supply that ensures maternofoetal exchange is efficient and simply regulated
How does the placenta protect the foetus?
Selective barrier regulates access to the foetal circulation and affords considerable protection from harmful agents. However it can be breached
How might infectious agents breach the placental barrier?
Use of existing transport systems (HIV)
Actively penetrate (Treponema)
Opportunistically exploit gaps in the epithelium (Toxoplasma)
Other than nutrient supply and waste removal, what other functions does the placenta have?
Endocrine support of pregnancy
Provision of passive immunity that affords immune protection in the neonatal period
How does the placenta adapt as the foetus grows?
Matures to meet the increasing demand by decreasing the interhaemal distance by thinning of the trophoblast layer(s), margination of the foetal capillaries of the core of the villi and increasing the surface area for exchange through increased branching of the villus tree
What differences in placenta will be seen in women that smoke and why?
Reduced interhaemal distances. This occurs when there is a deficit of the demand for transported materials or restriction on the maternal side. Reduced placental blood flow and growth. Poor foetal nutrition -> reduced birth weight by on average 200g
If foetal demand is not met e.g. the interhaemal distance cannot compensate enough, what happens?
Major risk factor for intrauterine growth restriction and impaired foetal growth which has been linked to long-term adult health problems (Barker hypothesis - foetal origin of adult disease)
What should happen to the placenta during labour?
Sheds during parturition and the massive blood supply to the implantation site is shut down
What happens if the placenta fragments during labour?
Retained placenta which impairs shut-down of the utero-placental circulation and consequently can cause serious postpartum haemorrhage
During the first trimester, what tissue constitutes the placental barrier?
During the third trimester, what tissue constitutes the placental barrier?
Syncytiotrophoblast and foetal capillary endothelium
What molecules pass the placenta barrier by simple diffusion?
Urea and uric acid
What molecules pass the placenta barrier by facilitated diffusion?
What molecules pass the placenta barrier by active transport?
What substances pass the placenta barrier by receptor mediated transport?
Passive-immunity - Ig class specific (IgG only)
What hormones are produced by the placenta?
Human chorionic gonadotrophin
Human chorionic somatomammotrophin
Human chorionic thyrotrophin
Human chorionic corticotrophin
Describe the arrangement of the blood vessels in the umbilical cord.
2 umbilical arteries carry deoxygenated blood from foetus to placenta
1 umbilical vein carries oxygenated blood from placenta to foetus
How does alcohol cross the placenta?
Diffusion as it is lipid soluble
What implications does the ability of alcohol to diffuse across the placenta have on the baby of a mother who drinks significantly during pregnancy?
Foetal alcohol syndrome
Low birth weight
Growth retarded (potentially with mental retardation)
Head and facial abnormalities
Why might cytomegalovirus be a significant health hazard in pregnancy?
Can cross placenta and cause congenital defect (teratogenic). Normally only causes mild flu-like illness in infected adults
When would anti-D therapy be given and why?
Prophylactically to a Rh- pregnant mother or following birth if the baby is rhesus+ and the mother is rhesus-
If the foetal cells contain antigens which the mothers cells lack then the mother could raise antibodies against the antigens. Mother may therefore have antibodies to foetal rhesus antigens if blood has entered the maternal circulation. Anti-D antibody neutralises these antigens. The presence of anti-Rh antibodies in the foetal circulation causes rapid haemolysis when they bind to the foetal blood.
What are 2 complications that pregnant women may complain of due to increased progesterone levels?
(due to smooth muscle relaxation)
What type of oestrogen level in maternal serum/urine would best indicate foetal progress?
Oestriol as it is produced as a result of foetal liver function and adrenals as well as placental function. Low levels can indicate foetal distress such that early delivery may be desirable