Session 8

Question 1

Describe the structure of the placenta and its adaptation for exchange of materials between fetal and maternal blood

Answer 1

1st trimester - relatively thick barrier (complete cytotrophoblast later beneath syncytiotrophoblast)
Term - increased SA, thin barrier, cytotrophoblast layer, beneath syncytiotrophoblast lost
Umbilical cord vessels:
Umbilical arteries (x2) - low O2 blood from fetus –> placenta
Umbilical vein (x1) - high O2 blood from placenta –> fetus

Question 2

Describe the condition pre-eclampsia and list its three main symptoms

Answer 2

Decreased maternal/fetal circulation establishment due to placental problem at around 20 weeks
Symptoms - hypertension, proteinuria, oedema

Question 3

Identify the major substances which are actively transported across the placenta

Answer 3

Amino acids
Iron
Vitamins

Question 4

Describe the role of the placenta as an endocrine organ supporting pregnancy

Answer 4

Protein - hCG, hCS, thryrotrophin, corticotrophin
Steroid - progesterone, oestrogen
hCG maintains corpus luteum, produced by syncytiotrophoblast, excreted in maternal urine
Steroids maintain a pregnant state, progesterone increases appetite to lay down fat stores, hCS/hPL increase glucose availability leading to insulin resistance

Question 5

Describe the hormonal basis of testing for pregnancy

Answer 5

hCG is produced by the syncytiotrophoblast so is therefore pregnancy specific

Question 6

Describe the function of the placenta as a provider of passive maternal immunity to the neonate

Answer 6

IgG is transported via RME

Question 7

Describe some of the complications that may occur due to placenta dysfunction

Answer 7

Teratogens e.g. thalidomide, alcohol, drugs, smoking 
Antibody transport (Rhesus) --> haemolytic disease of the newborn (therefore use anti D injection) 
Infectious agents e.g. varicella zoster, CMV, toxoplasma gondii, rubella --> microcephaly, PDA, cataracts

Question 8

Describe the metabolic function of the placenta

Answer 8

Synthesis of glycogen, cholesterol, fatty acids

Question 9

Define the term ‘cotyledon’

Answer 9

A group of chorionic villi bathed in maternal blood

Question 10

Describe the maternal physiological adaptations to pregnancy

Answer 10

CVS:
Displaced apex beat, increased blood volume, CO, SV, HR
Decreased systemic vascular resistance
Decreased blood pressure in 1st+2nd trimester, same in 3rd trimester
Progesterone, relaxin –> vasodilation
Urinary:
Increased GFR, renal plasma flow, creatinine clearance (low creatinine and urea)
Hydroureter –> hydronephrosis due to obstruction
Respiratory:
Diaphragm displaced –> decreased FVC, increased TV
Increased AP/transverse diameters
Physiological hyperventilation –> dyspnoea
Increased CO2 –> respiratory alkalosis compensated by renal bicarbonate
High PaO2, low PaCO2
GI:
Movement of viscera e,g, appendix –> RUQ
Smooth muscle relaxation
Delayed emptying
Biliary tract stasis
Increased pancreatitis risk

Question 11

Describe the mechanism and hallmark features of gestational diabetes

Answer 11

CHO metabolism:
Increased peripheral insulin resistance –> gluconeogenesis for the use of alternative fuels
Low fasting BG, high post-prandial BG
Achieved by human placental lactogen, prolactin, oestrogen/progesterone, cortisol
Increase in lipolysis –> high plasma FFA
Risks - macrosomic fetus, still birth, congenital defects

Question 12

Describe the metabolism of thyroid in pregnancy

Answer 12

Increased thyroid binding globulin production
High T3/T4
HCG has direct effect on TSH production (low)
Fetus is an allograft –> non-specific immune suppression
Hypo/hyperthyroidism

Question 13

Describe the hallmark features of anaemia in pregnancy

Answer 13

Increased blood volume 
Pro-thrombic state
Increased fibrin deposition at implantation site 
Increased fibrinogen, clotting factors
Decreased fibrinolysis 
--> thromboembolic disease

Question 14

List some procedures that may occur in antenatal screening

Answer 14

Risk factors
Blood tests - ABO, Rhesus
Urinalysis - proteinuria (pre-eclampsia)

Question 15

Describe the processes of implantation of the conceptus into the endometrium

Answer 15

Implantation is interstitial - conceptus implants within stroma
Placental membrane becomes progressively thinner as needs for the fetus increase
Placenta is haemomonochorial (single layer of trophoblast separates maternal and fetal blood)
To establish a basic unit of exchange:
1 - finger like projections of trophoblast
2 - invasion of mesenchyme into core
3 - invasion of core by Fetal vessels
Anchor placenta - outermost cytotrophoblast shell
Establish maternal blood flow - remodelling of spiral arteries (low resistance, high flow)