Questions and answers on respiratory physiology by dr Khaled Abulfadle

Admin عدد المساهمات : 9696 تاريخ التسجيل : 06/08/2009

Q: Describe gross structure of the lungs and relate it to function?

A: Trachea through terminal bronchioles (conductive) and respiratory bronchioles and alveoli (respiratory zones), function of lung is to bring air into contact with blood to permit rapid equilibration between gas in the alveoli and blood.

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Q: How does the structure of the alveolar-capillary membrane relate to function?

A: The alveolar-capillary membrane is 3 layers thick: Type I pneumocyte, basement membrane, and endothelial cell. Rate of diffusion of substance from higher to lower concentration is inversely proportional to diffusion distance size, and proportional to surface area.

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Q: Explain the changes that occur in the heart and pulmonary circulation at birth, following the first breath air?

A
:
During fetal life:
1. Lungs are not expanded.
2. Gas exchange occurs across placenta.
3. Pulmonary resistance is very high (ductus arteriosus shunts blood from pulmonary artery to aorta).
4. No flow of blood from lungs into left atrium.
5. Left atrial pressure is lower than right atrial pressure.
6. Venous blood returns to right atrium and flows through foramen oval (inter-atrial septum) into left atrium.
7. Venous blood fills both ventricles and is pumped by both ventricles into the aorta.

After birth:
1. Lungs inflate.
2. Pulmonary resistance drops.
3. Umbilical artery constricts.
4. Systemic resistance increases.
5. Left atrial pressure is more than right atrial pressure.
6. Foramen ovale closes.
7. Pulmonary artery pressure is lower than aortic pressure.
8. The flow of blood in ductus arteriosus is reduced and it closes over hours to days.

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Admin عدد المساهمات : 9696 تاريخ التسجيل : 06/08/2009

Q: Compare pulmonary circulation to systemic circulation?

A: Pulmonary circulation is characterized by:

1. Low pressure and low resistance.
2. Its blood flow is about 101% of cardiac output i.e. whole output of heart (blood from pulmonary artery to capillary bed and returned to left atrium via pulmonary veins) with additional blood from bronchial arteries.
3. Pulmonary artery pressure: 15mmHg. Left atrial pressure: 5mmHg. Thus, the driving pressure through pulmonary circulation: 10mmHg (15- 5).
4. Aortic pressure: 92mmHg. Right atrial pressure: 2mmHg. Thus, the driving pressure through systemic circulation: 90mmHg (92-2).

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Q: Describe pressures affecting fluid movement in the lungs and how this keeps the alveoli dry.

A:
1. Hydrostatic pressure in capillaries and surface tension in alveolus push fluid from capillary to alveolus.
2. Air pressure and colloid osmotic pressure pull fluid back into capillaries.
3. Extra fluid drains into the lymphatic system.

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Admin عدد المساهمات : 9696 تاريخ التسجيل : 06/08/2009

Q: Diagram the relationships between lung volumes and lung capacities?

A:
• Inspiratory reserve volume (IRV): volume of air entering lungs when going from end of normal inspiration to maximal inspiration.
• Tidal volume (TV): normal breath volume.

• Expiratory reserve volume (ERV): volume of air that can be expired with maximal effort beyond relaxed (end-expiratory) volume.
• Residual volume (RV): volume of air left in the lung after forced expiration.
• Vital capacity (VC)= IRV+TV+ERV.
• Inspiratory capacity (IC)=IRV+TV.
• Functional residual capacity (FRC)= ERV+RV.
• Total lung capacity (TLC)= IRV+TV+ERV+RV.

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