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Year 2 > Foetal and neonatal physiology > Flashcards

Foetal and neonatal physiology Flashcards

1
Q

What are the components involved in foetal blood circulation from the placenta?

A

Umbilical cord which consists of:
Two umbilical arteries that transport deoxygenated blood containing waste from the foetal tissues to the placenta for oxygenation
One umbilical vein which transports oxygenated blood from the placenta to the foetal body

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2
Q

What is the role of the lungs in development?

A

In utero, the foetus derives oxygen from the maternal blood via the foetus; the lungs are full of amniotic fluid and non-functional until post-birth. Therefore it is important that blood is re-directed to bypass the lungs to provide oxygen and nutrients to the functional and developing organs.

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3
Q

What point of gestation are the lungs fully functional?

A

37 weeks

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4
Q

How does circulation occur in adults?

A

Deoxygenated blood from upper body in Superior vena cava and lower body in inferior vena cava enter the heart in the right atria. This travels to the right ventricle and enters the pulmonary artery to enter the lungs.

Oxygenated blood returns via the 4 pulmonary veins in the left atria and travels through left ventricle to aorta to pump to the body.

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5
Q

How does oxygenated blood enter foetal circulation?

A

Umbilical vein carries oxygenated blood from the placenta towards the liver which is re-directed by the ductus venosus to the inferior vena cava. Oxygenated blood enters the right atrium of the heart in the inferior vena cava. The foramen ovale allows blood to move directly from the right atria -> left atria and leave the left ventricle to the ascending aorta to supply oxygen to the foetal tissues.

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6
Q

How does oxygenated blood enter the heart?

A

Oxygenated blood carried by the umbilical vein -> inferior vena cava, entering the right atria.

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7
Q

How does deoxygenated blood travel to the placenta?

A

Deoxygenated blood travels via the superior vena cava to enter the heart in the right atria. This moves to enter the right ventricle and then-> pulmonary trunk. Instead of travelling to the lungs, the ductus arteriosus causes it to bypass the lungs and enter the aorta, mixing with oxygenated blood from the descending aorta. Desending aorta transports blood to the structures and becomes the umbilical artery to return to the placenta.

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8
Q

What are foetal structures involved in controlling the passage of blood flow?

A

Ductus venosus
Ductus arteriosus
Foramen ovale
-> These must be reversible and close after birth to prevent pathology

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9
Q

What is the role of the ductus venosus?

A

Vascular shunt in the foetal liver which directs 60% of oxygen-rich blood from the umbilical vein to bypass the liver and enter directly into the inferior vena cava. There is a drop in oxygenation from 70% to 65%. This is to prevent excess oxygen consumption by the liver.

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10
Q

What is the role of the foramen ovale?

A

Vascular shunt located in the upper right atria. In the foetus, pressure in the right atria is greater than the left, so blood from the inferior vena cava directly moves from the right atrium to the left atrium. This allows blood to enter the left ventricle and leave via ascending aorta to provide nutrient rich blood to the body.

-> Ensure blood bypasses the right ventricle to limit blood entering the pulmonary trunk. Some blood will enter the right ventricle and mix with deoxygenated blood from the superior vena cava.

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11
Q

Why is it important that the foramen ovale does not cause the complete bypassing of blood from the right ventricle?

A

To ensure the right ventricles receives nutrients to prevent muscle atrophy.

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12
Q

What is the valve for the foramen ovale?

A

Septum secundum which is the roof of the foramen ovale eventually fuses with the septum primum to close the foramen ovale post-birth. Septum secundum forms the crista dividens.

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13
Q

What is responsible for the two streams of flow in the right atria?

A

This is caused by the free border of the septum sucundum called the crista dividens. Majority of blood flow is through to the left atria via the fossa ovale. Minrotiy of blood enters the right atrium to mix with deoxygenated blood from the superior vena cava.

This results in a pan systolic murmur and absence of this in newborn indicates cardiac disease.

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14
Q

What is the role of the ductus arteriosus?

A

Fusion of the pulmonary artery and aorta which re-directs deoxygenated blood flow in the right ventricle away from the lungs instead to the descending aorta, containing oxygenated blood from left ventricle. This minimises drop in O2 saturation.

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15
Q

What causes oxygenated blood to become less oxygenated in foetal circulation?

A

Oxygenated blood in umbilical vein mixes with
1) Deoxygenated blood from liver in the inferior vena cava, not completely prevented by ductus venosus
2) Right atrium, there is mixing of deoxygenated blood from the superior vena cava and oxygenated blood from inferior vena cava
3) Delivery of blood to foetal tissues through descending aorta.

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16
Q

How is gas exchange maximised in the foetal-placental circulation?

A

Chorionic villi contain the foetal capillaries to increase the surface area for gas exchange in the intervillous space. The intervillous space contains the spiral arteries, the pools of maternal blood in the lacunae.

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17
Q

How is the maternal body adapted for foetal oxygen supply?

A

Shortness of breath in pregnancy is induced by the effects of progesterone on chemoreceptors in the brain to CO2. This hyperventilation increases the concentration gradient for low CO2;higher O2 in mother for allow increased uptake of CO2 from the foetal blood to maternal blood and loss of oxygen.

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18
Q

What is the O2 gradient between the mother and the foetus?

A

Minimal increase in maternal pO2 during pregnancy means there must be a state of relative hypoxia in the foetus, by reducing pO2 conc in the umbilical vein.

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19
Q

How does the foetus maximise gas exchange?

A

Foetal haemoglobin has a higher affinity for oxygen and consists of two alpha and two Gamma subunits and causes the dissassociation curve to shift to the left.
-> Adult hameoglobin contains two alpha and two Beta subunits

Maternal erythrocytes produce more 2,3 DPG; adult haemoglobin has a higher affinity for than foetal haemoglobin

Higher foetal haematocrit

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20
Q

What is the Bohr effect?

A

Acidity causes oxygen disassociation curve to shift to the right; the higher 2,3 BPG in maternal blood increases O2 uptake in foetus

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21
Q

What is the Haldane effect?

A

Oxygenated haemoglobin has a reduced affinity for CO2 compared to deoxygenated Hb; this allows CO2 to be removed from foetal blood

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22
Q

Why do maternal erythrocytes produce more 2,3 DPG?

A

More 2,3 DPG from maternal erythrocytes causes the oxygen disassociation curve to shift to the right and reduce its oxygen affinity

23
Q

Why is foetal haematocrit higher?

A

Due to relative anaemia in maternal blood with increase in plasma volume. Therefore, foetal blood has more erythrocytes for oxygen uptake and these erythrocytes have more Hb.

24
Q

What is the foetal response to hypoxia?

A

Bradycardia which also occurs due to high pCO2. Bloodflow is prioritised to the vital organs of the heart and brain, away from the liver, limbs and GIT. Foetal heart rate slows to reduce oxygen demand. Chronic hypoxia will affect growth development and post-birth, behavioural development.

25
Q

What is the response of foetal chemoreceptors to low O2?

A

Stimulates vagus nerve and induces bradycardia.

26
Q

What does ostium mean?

A

Opening.

27
Q

What is atrial septation?

A

Separation of the left and right atria- begins as a wedge of tissue where the septum primum forms and grows downwards. The gap between the atria left behind after growth is the ostium primum. When the septum primum separates, it creates an ostium secundum in the centre. A new fold grows inferiorly called the septum secundum

28
Q

How does the fossa ovale close?

A

This occurs when the lungs are functional after birth. The oxygenation of blood flow returns to the heart in the left atria, increasing the pressure compared to the blood pressure in right atria, resulting in the septum primum and the septum secundum located in the atria to close permanently.

29
Q

How does the ductus venosus close?

A

After birth, the lack of placental support of blood flow via the umbilical vein causes a rapid drop in BP and blood flow, causing the ductus venosus to retract and narrow, becoming the fibrous cord called the ligamentum venosum on the liver.

30
Q

What is the importance of the ligamentum venosum?

A

Located attached to the left branch of the portal vein in the porta hepatis of the liver, connecting to the inferior vena cava,

31
Q

How does the ductus arteriosus close?

A

After birth, the lungs become functional and cause an increase in neonatal pO2 which the smooth muscle of the ductus arteriosus is highly responsible to. The first breath results in vasoconstriction of the smooth muscle and vascular spasm. This impacts the movement of the left laryngeal nerve.

32
Q

How do the lungs develop?

A

Occurs in 3 phases:
Embryonic period
Foetal period
Post-natal period

33
Q

What is the embryonic period of lung development?

A

Formation of the bronchopulmonary tree via budding from the endoderm. It begins as an outpocket on the yolk sac, which is continuous with the foregut and this bifurcates and buds to form the bronchi.

34
Q

What is the foetal period of lung development?

A

Includes Pseudoglandular stage, canalicular phase and terminal sac stage.

35
Q

What is the pseudoglandular stage?

A

Each bronchopulmonary segment forms the bronchioles and tertiary bronchus with bronchial and pulmonary artery. Duct system forms.

36
Q

What is the canalicular phase?

A

Budding from the terminal bronchioles creates the respiratory bronchioles and alveolar ducts.

37
Q

What is the terminal sac stage?

A

Budding from the respiratory bronchioles creates the terminal end sacs called the alveoli which differentiate into type 1 and type 2 and produce a surfactant. Surfactant production begins at 24 weeks but sufficient amounts to prevent atelactasis is at 32 week sgestation.

38
Q

What is type 1 alveoli?

A

Majority of alveoli formed of simple squamous epithelia for gas exchange.

39
Q

What is type 2 alveoli?

A

Cuboidal epithelia with microvilli which secrete a surfactant to prevent collapse of alveoli.

40
Q

What is the importance of trimester 2 and 3 for the lungs?

A

Lungs begin to develop in trimester 2 and 3 with alveoli continuing to develop even post birth

41
Q

What is the post-natal period of lung development?

A

Lungs must assume function over breathing from placenta; they are filled with fluid and foetus must use abdominal breathing to condition and strengthen the respiratory musculature to prevent atrophy.

42
Q

When is the stage where viability of life is possible, relative to lung development?

A

Once foetus enters the terminal sac stage of development with sufficent alveoli development and sufficient surfactant production to prevent atelactasis, around 32 weeks. Steroids such as cortisol are administered before and shortly after birth to induce further maturation of the lungs.

43
Q

What happens if pre-term baby does not develop type 2 pneumocytes?

A

Results in respiratory distress syndrome, where insufficient production of pulmonary surfactant prevents expansion and therefore inspiration occurring. Typical presentation is faster breathing rate, abdominal breathing. It is treated with corticosteroids to increase maturation.

44
Q

What is pulmonary hypoplasia?

A

Incomplete development of the lung tissue that means there is not enough tissue and blood flow to sustain functionality.

45
Q

What is patent ductus arteriosus?

A

Severe lung disease with failure of the closure of the ductus arteriosus, allowing the infiltration of oxygenated blood from the aorta to enter the pulmonary artery causing pulmonary artery vasoconstriciton. This increases blood flow to the lungs of oxygenated blood, resulting in right sided heart failure, pulmonary oedema which means greater cardiac output to compensate, decreasing blood flow to lower body resulting in renal failure.

46
Q

What is Tetrology of the Fallot?

A

Ventricular septal defect which allows oxygenated and deoxygenated blood between the left and right ventricle causing:

-> Right Ventricular hypertrophy: right ventricle is not adapted to deal with high pressure oxygenated blood from left ventricle

-> Stenosis of the pulmonary valve located between the right ventricle and pulmonary artery

-> Abnormal aortic position over the ventricular septal defect instead of the left ventricle. This is an over-riding aorta and causes the aorta to receive deoxygenated blood.

-> Ventricular septal defect

47
Q

What is transposition of the great arteries?

A

Pulmonary artery arises from the left ventricle and the arta rises from the right ventricle; switching of the great arteries f the heart leads to cyanosis and must be corrected with surgery. This is caused by rubella, infection or smoking/alcohol during pregnancy.

48
Q

What is the consequences of atrial septal defect?

A

Failure of the fossa ovale to close due to an issue with the septum primum being too short or resorbed or septum secundum being too short, leaving the ostium secundum behind and causing cyanosis, increasing high pressure blood flow to the lungs and causing damage to the vessels, leading to high blood pressure later in life. May go undetected because generally asymptomatic.

49
Q

Most common cause of indirect maternal death?

A

Cardiac disease

50
Q

How is the majority of CO2 transported in the body?

A

InN the blood as HC3- and H+.

51
Q

Where do umbilical arteries arise from in the foetus?

A

Branches of the internal iliac arteries.

52
Q

What is the embryonic origin of the pleura of lungs?

A

Mesoderm

53
Q

How does the interatrial septum form?

A

Septum primum grows downwards but stops, and leaves a gap called the foramen primum. The septum primum will undergoe apoptosis in the middle of its structure to create a foramen secundum.
Next to it, a septum secundum grows downwards and has a free border called the crista dividens where blood will flow through between the atria. High left atrial pressure causes the septum primum to fuse to the septum secundum and close the gap.

Year 2 (247 decks)

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