Lecture 14 - Fetal Physiology

Question 1

Where does maternal blood end up at the placenta?

Answer 1

In the intervillous spaces (between the chorionic villi) of the placenta

Question 2

What blood vessel carries oxygenated blood from placenta to fetus?

What blood vessel carries deoxygenated blood away from fetus to placenta?

Answer 2

Ox = umbilical vein

Deoxygenated = umbilical artery

Question 3

What are the 3 factors that facilitate the transport of oxygen from maternal blood to fetal blood across the placenta?

Answer 3

High Partial pressure gradient of oxygen between fetal and maternal blood

Fetal Hb has higher affinity for Oxygen than maternal Hb

Double Bohr effect and double haldane effect

Question 4

How does HbF differ to Adult Hb?

Answer 4

Adult = 2a and 2b subunits
Fetal = 2a and 2gamma subunits

Question 5

Why does Fetal Hb have a higher affinity for oxygen than adult Hb?

Answer 5

The gamma subunits make it say 2,3-diphosphoglycerate cant bind as easily compared to HbA

Question 6

What is the double Bohr effect and how does it aid gas exchange?

Answer 6

When the Bohr effect is acting on both the maternal and fetal side of the placenta

Fetus gives up CO2 at placenta making maternal bloo more acidic asking the HbA have a decreased affinity for O2
This makes fetal blood more alkaline so HbF has a higher affinity for O2

Question 7

How does the Double Haldane effect assist with the gas exchange and fetal uptake of oxygen at the placenta?

Answer 7

As the material HbA gives up O2 it has an increased affinty for CO2 so fetus gives up more CO2 (decreased HbF affinty for CO2) this helps with Bohr effect by making the maternal blood more acidic

Question 8

What are the 2 main organs that blood is shunted to avoid in the fetus to maintain as high oxygen saturations as possible?

Answer 8

Lungs
Liver

Question 9

What are the 3 main fetal shunts?

Answer 9

Ductus venosus
Foramen ovale
Ductus Arteriosus

Question 10

What 2 blood vessels does the Ductus venosus connect?

What organ is shunted?

Answer 10

Umbilical vein and the inferior vena cava so oxygenated blood can be taken to the right atrium

Question 11

What does the Foramen ovale connect?

What is the purpose of it?

Answer 11

Shuts oxygenated blood from the right atrium to the left atrium so blood can be pumped through aorta to brain

Allows lungs to be bypassed since blood already oxygenated and lungs not functional

Question 12

What is the function of the ductus arteriosus?

Answer 12

Shunts blood from the pulmonary artery into the aorta to ensure any blood that made it into the pulmonary trunk can be shunted from the lungs

Question 13

What is the fetal response to hypoxia?

Answer 13

Decreased Heart rate (bradycardia) to decrease O2 demand

Detected by chemoreceptors (low pO2 or high pCO2)

Question 14

What negative effects occur as a result of chronic Hypoxaemia to the fetus?

Answer 14

Growth restriction

Reduced fetal movement

Question 15

What are the 2 main functions of amniotic fluid?

Answer 15

Protects fetus
Contributes to lung development

Question 16

What is the danger with babies being delivered late?

Answer 16

Amniotic fluid depletes so it means the baby has less protection in-utero

Question 17

When does fetal urine start being produced?

Answer 17

Week 9

Question 18

What organ produces the most amniotic fluid?

Answer 18

Fetal urinary tract (kidneys)

Question 19

How is amniotic fluid recycled to prevent polyhydramnios?

Answer 19

Fetal GI tract
Fetus swallows the amniotic fluid and the debris accumulates in its gut

Question 20

How can preeclampsia lead to Oligohydramnios?

Answer 20

Poor fetal-placental circulation may lead to poor fetal renal perfusion
Reduces kidney function (GFR)
Means reduced urine production so reduced amniotic fluid

Question 21

How can oesophageal atresia lead to polyhydramnios?

Answer 21

Cant swallow the fluid so it builds up since its not recycled

Question 22

What is Oligohydramnios?

What is polyhydramnios?

Answer 22

Oligohydramnios = too little amniotic fluid

Polyhydramnios = too much amniotic fluid

Question 23

What is contained in amniotic fluid?

Answer 23

Essentially fetal urine:

98% water
Fetal cells
Hormones
Electrolytes
Bile
Creatinine
Urea

Question 24

What is meconium?

Answer 24

The first shit a baby takes after birth which contains all the debris from fetal development

Question 25

Is passing meconium before birth normall?

Answer 25

No its often a sign of stress

Can tell if they have by the green bile staining seen in amniotic fluid

Question 26

What is amniocentesis?

Answer 26

When amniotic fluid is sampled

The fetal cells in the amniotic fluid can be used for fetal karyotypinngg/diagnostic testing

Question 27

What is a risk of amniocentesis?

Answer 27

Risk of miscarriage (1%)

Question 28

What are some Intra partum monitoring techniques?

Answer 28

Intermittent heart auscultation

Cardiotocograph (CTG) (only really used when theres concern)

Question 29

What type of ultrasounds are done early in the pregancy?

Answer 29

Transvaginal ultrasound

Question 30

Before fetal urine starts being produced, how is amniotic fluid produced?

Answer 30

Fetal sweating
Amnion cells

Question 31

How will a mother smoking affect oxygen flow to fetus?

Answer 31

Decreased

Mother breathing in more CO2 and CO decreasing Hb affinity for O2

Question 32

What 4 signs can suggest Fetal distress?

Answer 32

Meconium before birth

Bradycardia

No movements

No accelerations (no tachycardia with contractions/Fetal movements)

Question 33

What are normal accelerations?

Answer 33

When the baby moves it should be accompanied by tachycardia/increased heart rate