Fetal And Neonatal Physiology Flashcards
What are the vessels involved in foetal circulation
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
How does exchange occur between maternal blood flow and foetal capillaries
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
What is the supply to the intervillous space
Supplied by uterine arteries and drained by uterine veins
Is the PCO2 in foetal blood higher or maternal blood
Higher in the foetal blood will allow passage down a concentration gradient
How is the PCO2 concentration gradient established to allow transfer from foetus to the mother
Pregnancy causes ann increase in circulating progesterone and physiological hyperventilation blows off more co2 creating an effective concentration gradient
In order to facilitate transfer of oxygen to the foetus we must establish a state of _______ in the foetus
Hypoxia (relative)
Must establish a small diffusion gradient
What is the po2 in the umbilical vein
4.7pKA which is significantly lower than usual of 13kPa
Which factors promote gaseous exchange
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)
What is the Bohr effect
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
What is the haldane effect
What are the adaptations in place to prevent a further hypoxic state in the foetus
Redistribution of flow to protect the supply to the heart and brain by reducing supply to the GIT, kidney and limbs
What happens to foetal heart rate in response to hypoxia
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
What are effects of chronic hypoxia
Affects growth development and behavioural changes in the foetus
What is route of flow in foetal circulation
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
Why must blood still go to the right ventricle
Muscle requires nutrients to survive and prevent atrophy
Why is the ductus venosus shunt important
To avoid the liver
To ensure maximum saturated blood reaches the heart
As liver is highly vascular ( will use a lot of O2 consumption)
In the left atrium what is the % saturation of blood
60%
Why is blood able to transfer from right atrium into left atrium via shunt
Because pressure is greater in the right atrium
What is the crista dividens
Crest which is formed by the free border of the septum secondum
What does the crista dividens create
Two streams of flow of which the majority is to the left atrium and smaller to the left ventricle
How does the foramen ovale become the fossa ovalis
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
How does the ductus arteriosus close
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
Closing of the ductus arteriosus impacts what
The course of the left recurrent laryngeal nerve
How does the ductus venosus close
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
When does the bronchopulmonary tree begin to form
In the embryonic period (first 8 weeks)
What is functional specialisation and when does it occur
The ability to make a membrane that will functionally allow exchange of gas
What happens in the pseudoglandular stage (week 8-16)
Duct system begins to form within the bronchopumonary segments created during the embryonic period
Bronchioles develop during the foetal stage of development
What occurs in the canalicular stage of development (week 16-26)
Formation of respiratory bronchioles with budding from the initial bronchioles formed from the previous stage
What happens in the terminal stage of development
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
Function of T1 pneumocytes
Gas exchange
Function of T2 pneumocytes
Surfactant production
What happens to the lungs during T2 and T3
Only go through developmental programme during T2 and T3 of gestation
Alveoli are continuing to created to full term
What happens if you fail to activate muscles of diaphragm and intercostals
Atrophy
What will breathing movements cause
Inhalation of amniotic fluid which contains mediators that promote normal lung development and differentiation of terminal sacs
What happens if terminal sac differentiation has not occurred
No capacity for gas exchange and can’t support life
Why do preterm babies often experience respiratory distress syndrome
There is insufficient differentiation of cells into T2 pneumocytes and insufficient surfactant production
Causes stiff lungs
In the case of pre-eclampsia what cna be given to the mother to increase surfactant production
Glucocorticoids
What causes severe lung disease
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
What is teratology of fallot
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
What happens if RVOTO is severe
Pulmonary circulation remains dependent on ductus arteriosus after birth
What is the incidence of congenital heart defects in the world
Is the most common birth defect
1% incidence
90% survive to adulthood as opposed to only 20% in 1950
What is transposition of the great arteries
Aorta arises from the right ventricle
Pulmonary trunk arises from the left ventricle
Leads to cyanosis
What kinds of septal defects are there
- excessive resorption of the septum primum
- septum primum is too short
- absent septum secundum
- septum secundum is too small
- absent septum primum and secundum
