Question

2) What are ventilation and perfusion? Briefly explain how the process of ventilation-perfusion coupling is achieved 

3) Briefly describe the steps of normal quiet inspiration and expiration. 

Answer 1

Ventilation is the volume of air entering the respiratory system for gaseous exchange.

Types are- alveolar ventilation & dead space ventilation

Perfusion - blood flowing through the pulmonary artery and vein through the lungs for gaseous exchange.

Th major function of lung is to match ventilation with perfusion so that maximum amount of O2 carry to the tissue.

Ventilation & perfusion ratio is 0.8 in normal human.

Alveolar ventilation is 4.2 L per min. And pulmonary blood flow is 5.5L permin.

Due to effect of gravity perfusion is low at apex of lung, and ventilation is approximately equal at all zone of lung, so V/Q ratio is increased because of decrease in perfusion.

And at the base due to gravity their is high blood flow so perfusion is high so V/Q ratio is low.

So normally at physiological level ventilation and perfusion both are high at base of lung than the apex.

Q3- steps of normal respiration

During inspiration diaphragm contracts lead to decrease in intraalveolar pressure & intra pleural pressure. So due to negative pull inside alveoli air lows in to lung.

During expiration due to elastic recoil o lungs it expands passively lead to increased in intra alveolar pressure & intra pleural pressure. So positive pressure increased inside alveoli lead to air flows out of lung.