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Scientific Basis of Midwifery > Foetal Circulation > Flashcards

Flashcards in Foetal Circulation Deck (43)
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How is the cardiac output distributed?

- Heart - 5%
- Skeleton - 5%
- Brain - 15%
- Muscle - 15%
- Kidneys - 20%
- Body to Heart - 64%
- Lungs - 100%


What is required for effective CVS function?

- Cardiogenesis
- Blood volume and BP
- Non-severed blood vessels
- RBC mass and fluidity
- Myocardial contractions
- Vascular resistance
- Tissue metabolism


What is the paediatrician circulating blood volume?

- Neonate = 85ml/kg
- Infant = 80ml/kg
- Child = 70ml/kg


Give an overview of cardiogenesis

Day 15-16 = cardiogenic mesoderm receives signal
Day 17 = Induction of angiogenesis in yolk sac
Day 18-19 = endocardial tubes
Day 21 = single cardiac tube
Day 22 = heart beats
Day 24 = cardiac looping
Day 26 - week 8 = atrial separation
Day 35 - week 8 = ventricular separation
Weeks 4-7 = great vessels and vascular network
Week 16 = conduction pathway complete


What is angiogenesis?

Formation of blood vessels


Describe foetal circulation

- Systemic only (no pulmonary circuit)
- Depends on placenta for oxygen, nutrients and excretion
- In utero, pulmonary vascular resistance > systemic VR causes blood from right side of heart to bypass the lung through ductus arteriosus and foramen ovale


Why does foetal Hb have a higher affinity for oxygen?

They do not breathe so all of their oxygen is supplied in the blood from the placenta


Give 5 characteristics of foetal circulation

1. Single parallel circulation
2. Communications between right and left side
3. Pulmonary circulation is redundant
4. Well-oxygenated blood delivered to the brain, myocardium and upper body
5. Less-oxygenated blood delivered to lower parts of body and then back to placental site


What is a foetal shunt and what are the 3 main ones?

A structure that allows blood to bypass the lungs
1. Foramen ovale
2. Ductus arteriosus
3. Ductus venosus


Describe the foramen ovale

- Opening between left and right atria
- Closes when there is an increased volume of blood in left atrium
- Closes shortly after birth because there is a back-flow of blood when the cord is clamped, so the hole closes due to an increase in blood volume in the left atrium


Describe the ductus arteriosus

Right to left shunting of blood from pulmonary artery to the aorta, bypassing the lungs


Describe the first stage of the foetal circulation route

- Oxygenated blood travels from the umbilical vein to the inferior vena cava
- This vein divides into 2 branches; some blood flows into branch which joins the hepatic portal vein and enters the liver, but most flows in second branch called ductus venosus which drains into the inferior vena cava


Describe the second stage of the foetal circulation route

- Deoxygenated blood returning from lower limbs to the right atrium mixes with oxygenated blood from ductus venosus in inferior vena cava
- Deoxygenated blood returning from upper body enters right atrium via superior vena cava


Describe the third stage of the foetal circulation route

- Most mixed blood in right atrium enter left atrium through the foramen ovale
- Minimal blood enters right ventricle which flows through the pulmonary artery
- Small amount trickles into foetal lungs
- The rest crosses the ductus arteriosus to join the blood in the ascending aorta; this travels to the upper body


Describe the fourth stage of the foetal circulation route

- Blood in left atrium flows into left ventricle to flow into ascending aorta
- Joins blood coming through ductus arteriosus and subsequently into descending aorta and to lower limbs


Describe the fifth stage of the foetal circulation route

- Deoxygenated blood returns from the lower limbs of the foetus via the internal iliac arteries
- Drains into hypogastric arteries and finally into umbilical arteries back to placenta for re-oxygenation


Give some of the main postnatal adaptations

- Changes in blood flow and pressure
- Closure of foramen ovale and ductus arteriosus
- Establishment of neonatal circulation
- Right ventricular output = left ventricular output


What do BB and AB stand for?

BB = before birth
AB = after birth


How does the umbilical vein change?

BB - brings oxygenated arterial blood to liver and heart
AB - obliterates; becomes round ligament of liver


How do the umbilical arteries change?

BB - bring deoxygenated arteriovenous blood to placenta
AB - obliterated; become vesicle ligaments on anterior abdominal wall


How does the ductus venosus change?

BB - shunts arterial blood into inferior vena cava
AB - obliterated; becomes ligamentum venosum


How does the ductus arteriosus change?

BB - shunts arterial and some venous blood from pulmonary artery to aorta
AB - obliterated; becomes ligamentum arteriosum


How does the foramen ovale change?

BB - connects right and left atria
AB - obliterated (usually); if it stays open = heart defect


How do the lungs change?

BB - contain no air and very little blood
AB - filled with air and well supplied with blood


How does the aorta change?

BB - receives blood from both ventricles
AB - receives blood from left ventricle only


How does the inferior vena cava change?

BB - brings venous blood from body and arterial blood from placenta
AB - brings venous blood only to right atrium


Give 3 other things that change in foetal circulation when baby is born

1. Loss of placenta
2. Opening of pulmonary arteries
3. Reduced myocardial mass


Name some things that may stimulate the baby to take its first breath

Effects of:
- Lung fluid elimination
- Hypercapnia (high levels of carbon dioxide)
- Hypoxia
- Cold air
- Noise
- Tactile stimuli


Describe the process of the first breath

- Central neuronal response
- Deep pulmonary ventilation
- Surfactant prevents surface tension in lungs
- First alveolar expansion
- Lowering of surface tension
- Alveolar ventilation and perfusion


What are the effects of the initial breathing?

- Decrease in PVR (pulmonary ventilation rate)
- Increase in oxygen concentration
- Dilates patent blood vessels
- Opens unused blood vessels
- Neonate must establish and maintain extra-uterine life