The first breath

Question 1

What are the stages of lung development

Answer 1

Embryonic 0-5 weeks
Pseudoglandular 5-17 weeks
Cannalicular 16-25 weeks
Alveolar 25 weeks-term

Question 2

Where do the lungs come from?

Answer 2

• The foregut (which are an anterior outpouching)
• This happens in the 0-5 weeks in the embryonic stage
• It is an outpouch of the oesophageal appendix

Question 3

What is the pseudo glandular stage of lung development?

Answer 3

Where thinks start to become glandular (5-17 weeks)
- Other components of the airway start to group
- Lungs are full of fluid pretty much until term. Lungs are not being used to oxygenate you - that is through the mother
- Angiogenesis (blood vessels start to form)

Question 4

What is the Cannalicular stage of lung development?

Answer 4

• Occurs at 16-25 weeks
• Distal architecture
• Vascularisation (formation of capillary bed)
• Respiratory bronchioles
• Alveolar ducts
• Terminal sacs

Question 5

What is the alveolar stage of lung development?

Answer 5

• Occurs at 25 weeks to term
• Alveolar sacs
• Type 1 + 2 cells
• alveoli simple with thick

Question 6

What happens to the alveolar membrane from birth to 3-5 years?

Answer 6

Thinning of alveolar membrane and interstitium

Question 7

What can go wrong in the embryonic stage?

Answer 7

• Laryngeal, Tracheal and oesophageal atresia (absence or abnormal narrowing of an opening or passage in the body)
• Tracheal and bronchial stenosis (narrowing of these structures)
• Pulmonary agenesis (failure of an organ to develop)

Question 8

What can go wrong in the Pseudoglandular phase?

Answer 8

Group of abnormalities
Bronchopulmonary sequestration
Cystic adenomatoid malformations (can occur at ant point in the this stage with any structure)
alveolar-capillary dysplasia

Question 9

What can go wrong with the Alveolar phase?

Answer 9

Acinar Dysplasia
Alveolar capillary dysplasia
Pulmonary hyoplasia

Question 10

What is the purpose of systemic vessels?

Answer 10

To deliver oxygen to hypoxic tissues

Question 11

Is hypoxia/ CO2 a vasodilator or vasoconstrictor?

Answer 11

Vasodilator in systemic vessels
Vasoconstrictor in pulmonary vessels

Question 12

Is oxygen a vasodilator or vasoconstrictor?

Answer 12

Vasoconstrictor in systemic vessels
Vasodilator in pulmonary vessels

Question 13

What is the purpose of the pulmonary vessels?

Answer 13

Pick up oxygen from oxygenated lung

Question 14

What are the lungs doing in the foetal?

Answer 14

• The lung is not a useful organ to the foetus
• PaO2 = 3.2kPa
• Shunting of blood right to left in heart
• High pulmonary vascular resistance (because you are hypoxic)
• Tissue resistance (fluid filled)
• Low systemic resistance (placenta)

Question 15

How do the lungs fill with fluid?

Answer 15

• Lungs are actively being filled with fluid by a chlorine/ potassium ion pump
• So they are ready for the first breath

Question 16

What does the Ductus venosus do?

Answer 16

• a proportion of nutrient filled blood will still pass through the liver as you need to filter it etc and then into the inferior vena cava
• BUT 1/3 diverted
• takes it directly from mother and straight into inferior vena cava

Question 17

What is the ductus arteriosus?

Answer 17

• Connection between the pulmonary trunk and aorta
• When blood into RA, RV straight into aorta, stopping blood go into the lungs and instead straight into the aorta
• One method of a right to left shunt
• this closes after birth

Question 18

What happens to the lungs as squeezed out at birth?

Answer 18

Lungs are given a physical squeeze as pushed out of the vagina which squeezes the fluid out of the lungs (like a sponge)

Question 19

What hormone is released during first breath?

Answer 19

Adrenaline stress leads to increased surfactant release
- Gas is inhaled which is rich in oxygen

Question 20

What happens after gas is first inhaled?

Answer 20

• Oxygen is a vasodilator in pulmonary vessels so pulmonary vascular resistance falls
• Right atrial pressure falls, closing the foramen ovale

Question 21

What happens to the arteries after first breath?

Answer 21

• Umbilical arteries constrict (as it is cut)
• Ductus arteriosus constricts (due to changes in O2 levels)

Question 22

What is Laplace’s Law?

Answer 22

P = 2T/R
T (surface area)
- Smaller alveoli may shut and bigger open when tension applied

Question 23

Why is surfactant important?

Answer 23

• Surface active phospholipid
• Produced by type 2 pneumocytes
• Keeps alveoli open to allow aeration and gets rid of surface tension
• So premature babies will be deficient in surfactant

Question 24

What diseases with a lack of surfactant?

Answer 24

Respiratory Distress Syndrome (HMD)
Loss of lung volume
Non-compliant lungs
Uneven aeration

Question 25

What can be done about a lack of surfactant?

Answer 25

Accelerated by
Distension of alveoli
Steroids
Adrenaline

Question 26

What can happen when we ventilate premature babies?

Answer 26

PIE (Pulmonary Interstitial Emphysema)
Lung cysts
Ruptured alveoli

Question 27

How do we treat Pulmonary Interstitial Emphysema?

Answer 27

• Warmth
• Surfactant replacement (if intubated)
• Oxygen and fluids
  -Continuous Positive Airway Pressure (maintain lung volumes, reduce work of breathing)
• Positive pressure ventilation if needed