Fetal Phsyiology

Question 1

Does fetal blood have a lower or higher pO2 than maternal blood?

Answer 1

Lower, to allow a gradient of transfer from mother to fetus

Question 2

Progesterone causes hyperventilation in mum-> maternal Respiratory alkalosis.

How is this counteracted?

Answer 2

Increased maternal 2,3 BPG production, reducing Hb’s O2 affinity and promoting release of O2 to fetus

(Hyperventilation maintains a CO2 gradient from fetus to mother)

Question 3

When is HbF predominant in the baby?

Describe its structure

Why does it have a greater O2 affinity than maternal Hb?

Answer 3

• By week 12
• 2 Alpha and 2 Gamma subunits
• Doesn’t bind 2,3 BPG as effectively as Maternal Hb

Question 4

Describe the Double Bohr effect on Fetal and Maternal Circulation

Answer 4

Maternal;

• CO2 passes into intervillous blood -> pH decrease
• Decreased O2 affinity in Maternal Hb

Fetal;

• Gives up CO2-> pH Increase
• Increased O2 affinity in HbF

Question 5

Describe the Double Haldane effect in maternal and Fetal circulation

Answer 5

Maternal;
- As maternal Hb gives up O2, accepts more CO2

Fetal;
- As O2 is accepted, more CO2 is given up

Question 6

Suggest a possible Fetal response to hypoxia

Answer 6

Bradycardia via vagal stimulation, to reduce O2 demand of heart

(Can be included in the term Fetal Distress)

Question 7

Smoking can cause chronic Hypoxaemia leading to what fetal condition?

Answer 7

Intrauterine growth restriction

Question 8

Are lungs function in utero?

Answer 8

No

Question 9

What veins are connected by the Ducts Venosus?

Answer 9

Umbilical vein to IVC

Carries oxygenated blood from Placenta, bypassing Liver

Question 10

Why is it important that the liver is bypassed by the Ductus Venosus?

Answer 10

Maintains high level of O2 saturation in blood

Question 11

What is the Crista Dividens?

What is its function?

Answer 11

A ‘Crest’ formed from the free border of the Septum Secundum

Creates 2 streams of blood flow;

• Majority goes to LA
• Remaining continues to RV

Question 12

In the Fetus, what 2 organs get the most O2?

Answer 12

Brain and Heart (Coronary arteries)

Question 13

What hormones are key to Fetal growth?

Answer 13

Insulin-like Growth Factors (IGF 1 and 2)

Question 14

Describe the normal growth pattern of the fetus during pregnancy

Answer 14

Trimester 1 (Weeks 0-20): Hyperplasia of cells

Trimester 2 (Weeks 20-28): Mix of Hyperplasia and Hypertrophy

Trimester 3 (Week 28 onwards): Mainly Hypertrophy

Question 15

What are 2 consequences of Maternal Malnutrition?

Nutritional and hormones status during fetal life can also affect health in later life

Answer 15

Symmetrical growth restriction: All parts of fetus are small

Asymmetrical growth restriction: ‘Head sparing’. Restriction on abdomen, but it is disproportionately smaller than head

Question 16

What are 2 functions of the Amniotic Fluid?

What is the volume proportional to?

Answer 16

• Mechanical protection
• Contains substances critical for lung development
• Fetus size

Question 17

Describe how Amniotic fluid can be used as an investigation technique

Answer 17

• Contains fetal cells, can be aspirated (Amniocentesis)

- Can be useful for Fetal Karyotyping (E.g Down’s)

Question 18

Suggest 2 disadvantages of Amniocentesis

Answer 18

• Invasive

- Carries risk of miscarriage

Question 19

Describe 1 sign of Fetal Distress

Answer 19

Meconium staining/ Meconium stained liquor :

• Mecoinium released prematurely from fetal GI tract
• Inhaled by fetus-> Meconium Aspiration

(Can also occur in pregnancies longer than 40 weeks, which can cause fetal distress)

Question 20

Describe the production of amniotic fluid

Answer 20

• Essentially composed of Fetal urine

- Production of urine begins around week 9

Question 21

Describe the composition of Amniotic Fluid

Answer 21

• Mainly water, electrolytes and other substances typically found in urine
• Also contains elements of fetal skin that have been lost during pregnancy

Question 22

List the 2 mechanisms of recycling amniotic fluid

Answer 22

• Inhalation of fluid by Fetus PRACTICING breathing movements
• Swallowing of Amniotic fluid by Fetus

Question 23

Inhalation of amniotic fluid by the Fetus contributes to production of what?

Answer 23

Production of lung, especially surfactant

Question 24

What is Meconium?

When is it first passed out of the GI tract and how?

Answer 24

• Accumulation of debris in the GI tract

- Passed out after delivery as the baby’s first stool

Question 25

Why is Physiological Jaundice common in newborns?

What if Jaundice appears within 24hrs after delivery?

Answer 25

• Delay in ability to conjugate and excrete Bilirubin, as Placenta handled this during Gestation
• Within 24 hours, often indicative of a more serious pathology