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Flashcards in 9.2 Deck (27):
1

Describe the fetal circulation before birth.

Oxygenated blood enters fetus via umbilical vein from placenta.
Bypasses liver by ductus venous
IVC (mixed with desaturated)
From RA -> LA by foramen ovale (some to RV via crusta dividens)
LA--> LV
RV-->From pulmonary artery --> aorta via ductus arteriosus
Aorta --> Deoxygenated blood leaves via 2 umbilical arteries.

2

Why does blood not enter the lungs?

Resistance is very high due to hypoxic pulmonary vasoconstriction

3

What happens when an infant takes its first breath?

Hypoxic pulmonary vasoconstriction removed.
Resistance of lungs reduced.

Greater venous return to LA
Pressure in LA > RA
Closure of foramen ovale

Increased oxygen saturation of blood and removed prostaglandins (placenta removed) results in:
Constriction of ductus arterioles
Contraction of umbilical artery

Stasis of blood in umbilical vein and ductus venous leads to clotting of blood and closure due to fibrosis.

4

What is the function of amniotic fluid?

Surrounds fetus providing mechanical protection - shock absorption, and a moist environment so the fetus does not dehydrate.

5

How much amniotic fluid is there at 8 weeks, 38 weeks and 42 weeks

10 ml at 8 weeks
1 L at 38 weeks
Falls to 300 ml at 42 weeks

6

How much urine is produced at 25 weeks and at term? How much do adults?

25 weeks - 100 ml per day
Term 500 ml per day
Adults 1L per day

7

What does amniotic fluid contain?

98% water
Electrolytes
Creatinine
Cells from fetus/amnion --> amniocentesis and karyotyping
Urea
Bile pigments
Renin
Glucose
Hormones

8

What happens to swallowed amniotic fluid?

Fetus absorbs water and electrolytes.
Debris accumulates in fetal gut
Fluid washes this away forming meconium together.
This is debris from amniotic fluid plus intestinal secretions including bile

9

What happens to fetal bilirubin?

Fetus cannot conjugate bilirubin due to immaturity of the liver and intestinal processes for metabolism, conjugation and excretion
Bilirubin crosses the placenta after accumulating
Excreted by the mother.

10

After birth, what stimulates neonate liver to begin conjugation?
What if this does not establish quickly?

Light exposure (Phototherapy)
Jaundice

11

How long are fetal oxygen stores

Very low - 2 mins

12

What is the haemomonochorial

Thin barrier that oxygen diffuses across in the placenta from the maternal blood.

13

What is the driving factor for this diffusion

Gradient of partial pressure between maternal and umbilical blood.

14

Why is the placenta well adapted for exchange?

Lass SA and low resistance to diffusion

15

What is used to indicate fetal oxygen saturation

Fetal heart rate

16

What is fetal pO2 and normal adult pO2 in arteries

Fetal 4kPa
Adult arterial 13.3kPa

17

How is fetal Hb adapted to work better at low pO2

Different Hb without beta chains and with gamma chains.
Doesn't readily bind 2,3-BPG
Higher affinity for O2
70% saturated at 4kPa
Adult is 45% saturated at 4kPa
Means that fetal blood contains 7.5mM/L O2, simlar to adult blood.
More Hb (higher haematocrit)

18

What is the double Bohr effect

Increase in pCO2 or [H+] results in Hb losing affinity and releasing more O2. Happens in both mother and fetus

19

How does the mother blow off extra CO2 from the baby?

Hyperventilation stimulated by progesterone

20

Why ultrasound scan at 20 weeks?

Organs big enough to see but early enough to abort

21

Why should pregnant women take folic acid

Important for neural tube development

22

Fetal heart rate at term

140-160 bpm

23

What is fetal abdominal circumference assessing?

Growth of liver and amount of subcutaneous fat

24

What does meconium in the amniotic fluid indicate

Fetal distress

25

What determines O2 transport rate

Umbilical arter pO2

26

Significance of CO2 in fetus

Cannot tolerate higher pCO2 than mother --> acid base problems
Placental transfer of CO2 facilitated by lower maternal pCO2 through hyperventilation

27

How is amniotic fluid formed

Early in pregnancy - from maternal fluids and fetal extracellular fluid by diffusion across skin
Late - fetal turnover