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Block 11 > Fetal And Neonatal Physiology > Flashcards

Fetal And Neonatal Physiology Flashcards

1
Q

What are the vessels involved in foetal circulation

A

A pair of umbilical arteries that - deoxygenated blood from foetus to maternal circulation

Single umbilical vein = contains blood with the highest PO2 and lowest pCO2

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2
Q

How does exchange occur between maternal blood flow and foetal capillaries

A

Foetal capillaries branch out within the chorionic villi - increases the surface area for exchange. Take up nutrients from intervillous space and give back any waste products

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3
Q

What is the supply to the intervillous space

A

Supplied by uterine arteries and drained by uterine veins

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4
Q

Is the PCO2 in foetal blood higher or maternal blood

A

Higher in the foetal blood will allow passage down a concentration gradient

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5
Q

How is the PCO2 concentration gradient established to allow transfer from foetus to the mother

A

Pregnancy causes ann increase in circulating progesterone and physiological hyperventilation blows off more co2 creating an effective concentration gradient

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6
Q

In order to facilitate transfer of oxygen to the foetus we must establish a state of _______ in the foetus

A

Hypoxia (relative)

Must establish a small diffusion gradient

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7
Q

What is the po2 in the umbilical vein

A

4.7pKA which is significantly lower than usual of 13kPa

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8
Q

Which factors promote gaseous exchange

A

HbF variant which acquires O2 at lower Pp

Increased foetal haematocrit

Increased maternal production of 2,3 DPG due to metabolic acidosis of pregnancy (biphosphoglycerate)

Double Bohr effect ( effect of pH on affinity of Hb)

Haldane effect (O2 concentration determines Hb affinity)

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9
Q

What is the Bohr effect

A

Decrease in the pH of the blood shifts the curve to the right meaning there is an increased faciliatation of delivery of oxygen. There is decreased affinity meaning more offloading occurs

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10
Q

What is the haldane effect

A
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11
Q

What are the adaptations in place to prevent a further hypoxic state in the foetus

A

Redistribution of flow to protect the supply to the heart and brain by reducing supply to the GIT, kidney and limbs

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12
Q

What happens to foetal heart rate in response to hypoxia

A

Heart rate decreases to reduce the demand for oxygen

Chemoreceptors function differently so that a decrease in PO2 or an increase in PCO2 would result in vagal stimulation and bradycardia

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13
Q

What are effects of chronic hypoxia

A

Affects growth development and behavioural changes in the foetus

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14
Q

What is route of flow in foetal circulation

A

Umbilical vein from the placenta brings oxygenated blood up towards the liver where it is shunted to the IVC via the ductus venosus. This now enters the right atrium. Most of the blood bypasses the right ventricle through blood flow from R atrium to L atrium via the foramen ovale.
This then goes into the L ventricle and out of the aorta to the rest of the body.

Some blood will still flow to the right ventricle and into the pulmonary trunk
But it will be shunted to the aorta via the ductus arteriosus

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15
Q

Why must blood still go to the right ventricle

A

Muscle requires nutrients to survive and prevent atrophy

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16
Q

Why is the ductus venosus shunt important

A

To avoid the liver

To ensure maximum saturated blood reaches the heart

As liver is highly vascular ( will use a lot of O2 consumption)

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17
Q

In the left atrium what is the % saturation of blood

A

60%

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18
Q

Why is blood able to transfer from right atrium into left atrium via shunt

A

Because pressure is greater in the right atrium

19
Q

What is the crista dividens

A

Crest which is formed by the free border of the septum secondum

20
Q

What does the crista dividens create

A

Two streams of flow of which the majority is to the left atrium and smaller to the left ventricle

21
Q

How does the foramen ovale become the fossa ovalis

A

As baby takes its first breath there is an increase in the flow of blood through the pulmonary vein

Pressure in l atrium > r atrium and septum primula is pushed against septum secodnum

22
Q

How does the ductus arteriosus close

A

Physiological closure; as any takes its first breath there is Ian increase in PO2 and undergoes vascular spasm
Over time there is knitting of the lining together and anatomical transformation into a fibrous cord

23
Q

Closing of the ductus arteriosus impacts what

A

The course of the left recurrent laryngeal nerve

24
Q

How does the ductus venosus close

A

There is no blood flow going through it so it becomes occluded as a fibrous cord

Ligamentum venosum wrapped around the liver in the adult

25
Q

When does the bronchopulmonary tree begin to form

A

In the embryonic period (first 8 weeks)

26
Q

What is functional specialisation and when does it occur

A

The ability to make a membrane that will functionally allow exchange of gas

27
Q

What happens in the pseudoglandular stage (week 8-16)

A

Duct system begins to form within the bronchopumonary segments created during the embryonic period

Bronchioles develop during the foetal stage of development

28
Q

What occurs in the canalicular stage of development (week 16-26)

A

Formation of respiratory bronchioles with budding from the initial bronchioles formed from the previous stage

29
Q

What happens in the terminal stage of development

A

26 weeks

Terminal sacs begin to bud from the respiratory bronchioles
These go on to develop the alveolar sacs

Cells will differentiate into type 1 and type 2 pneumocytes

30
Q

Function of T1 pneumocytes

A

Gas exchange

31
Q

Function of T2 pneumocytes

A

Surfactant production

32
Q

What happens to the lungs during T2 and T3

A

Only go through developmental programme during T2 and T3 of gestation

Alveoli are continuing to created to full term

33
Q

What happens if you fail to activate muscles of diaphragm and intercostals

A

Atrophy

34
Q

What will breathing movements cause

A

Inhalation of amniotic fluid which contains mediators that promote normal lung development and differentiation of terminal sacs

35
Q

What happens if terminal sac differentiation has not occurred

A

No capacity for gas exchange and can’t support life

36
Q

Why do preterm babies often experience respiratory distress syndrome

A

There is insufficient differentiation of cells into T2 pneumocytes and insufficient surfactant production
Causes stiff lungs

37
Q

In the case of pre-eclampsia what cna be given to the mother to increase surfactant production

A

Glucocorticoids

38
Q

What causes severe lung disease

A

When lungs fail to take over because there is not enough surfactant

If due to congenital heart abnormalities the body is dependent on the ductus arteriosus. Increases work heart has to do and may lead to pulmonary oedema that causes lung disease

39
Q

What is teratology of fallot

A

Is a heart defect made up of 4 different problems. Teratology of fallot describes 4 things that cause right ventricular outflow tract obstruction RVOTO

1) pulmonary stenosis (thickened and narrow pulmonary outflow tract)

2) thickened right ventricle wall

3) ventricular septal defect

4) aorta overrides septal defect ( septal defect is next to opening of aorta so deoxygenated blood mixes in with oxygenated blood

Important factor is neural crest cells

40
Q

What happens if RVOTO is severe

A

Pulmonary circulation remains dependent on ductus arteriosus after birth

41
Q

What is the incidence of congenital heart defects in the world

A

Is the most common birth defect

1% incidence

90% survive to adulthood as opposed to only 20% in 1950

42
Q

What is transposition of the great arteries

A

Aorta arises from the right ventricle

Pulmonary trunk arises from the left ventricle

Leads to cyanosis

43
Q

What kinds of septal defects are there

A
  • excessive resorption of the septum primum
  • septum primum is too short
  • absent septum secundum
  • septum secundum is too small
  • absent septum primum and secundum

Block 11 (13 decks)

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