Foetal Circulation Flashcards
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
- Single parallel circulation
- Communications between right and left side
- Pulmonary circulation is redundant
- Well-oxygenated blood delivered to the brain, myocardium and upper body
- 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
- Foramen ovale
- Ductus arteriosus
- 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
- Loss of placenta
- Opening of pulmonary arteries
- 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
What is survival dependent on?
- Successful adaptation
- Safe, effective care
- Absence of gross congenital abnormalities
Give 4 reasons for increased risk of morbidity
- Traumatic delivery
- Birth asphyxia
- Major pathology (disease)
- Prematurity
What changes should occur in the 1st week of life?
- Stabilisation of body temperature
- Successful bottle/ breast feeding
- Bladder and bowel action
- Haematopoiesis (liver and spleen 6 wks to 6 mths, bone marrow 6 mths)
What changes should occur by the end of the 1st month of life?
- Immune response
- Neuroendocrine function
- Neonatal circulation
Describe glucoregulation
- Glycogen stores
- Gluconeogenesis
- Ketogenesis (formation of ketones)
- Calories from feeding
- Warmth
Describe the metabolic adaptations that occur
- Energy crunch
- Immediate life tasks
- Increase adrenaline, noradrenaline and glucagon
- Glycogen stores exhausted in 2-3 hours
Describe thermoregulation
- Immature hypothalamus
- Large SA:Vol ratio
- Thin body shell
- Brown fat thermogenesis
- Initially liable (easily changes) but gradually settles
How does the hepatobiliary system change?
- Breakdown of foetal Hb
- Physiological jaundice resolved by 10 days
- Vitamin K prophylaxis (treatment to prevent disease)
How is jaundice caused?
When there is too much bilirubin in the blood
How does the respiratory system change?
- Upper airways different
- Shorter, smaller airways
- Rib cage different; less ossified
- Reduced respiratory muscle mass
- Limited muscle endurance
- Smaller alveolar SA
How does the nervous system change?
- Glucose and oxygen requirement increases
- Less rigid cranium
- Delicate brain cells and blood vessels
- Immature cerebral cortex, vital centres, blood-brain barrier
How does the urinary system change?
- Pass urine within 24 hours
- Renal structure maturation
- Passage of dilute urine
- Adult shaped bladder at 6 yrs of age
- Endocrine maturity at 4 yrs of age
How does the immune system change?
- Maternal antibodies in infancy
- Skin and bowel colonisation in 1st week of life
- Integration of whole system at 1 year
- Full antibody complement for bacterial infection at 2 yrs of age
