Question

Give a brief description for each of the following:

a) Describe the structures of the pulmonary system

b)Describe the pressures in the alveoli and pleural sac, and the flow of air during all the stages of an inhalation and exhalation

c)Describe the role of surfactants, and how they work.

d) Describe how flow of blood to regions of the lungs changes to match the flow of air

Answer 1

a) Pulmonary system consists of -

i) Upper Respiratory Airway - Nasal Cavity, Larynx and Pharynx

ii) Lower Respiratory airway - Trachea dvides into right and left primary bronchus --> secondary bronchus > Tertiary Bronchi > Bronchiole > Terminal Bronchiole > Respiratory Bronchiole > alveoli in Pulmonary lobule.

2) Intraalveolar pressure - It is the pressure inside the alveoli. It is equal to the atmospheric pressure at rest. It chages with phases of Respiration. During inspiration when the lung expands, alveoli also expand, leading to increased volume hence Decreased pressure inside alveoli, hence air is sucked into alveoli. During expiration alveoli decreses in volume hence has increased pressure than atmoshpheric pressure, hence airmove out of alveoli.

Pressure in pleural sac - It is pressure within the pleural cavity. It is a negative pressure created by contration of diaphragm and recoil of the lung parenchyma.

During inspiration the diaphragm contract, intra pleural pressure increases and becomes more negative. While during expiration it decreses.

C) Surfactant is a surface active molecule which helps in preventing collapse of the alveoli during expiration. It does so by lining itself on inner side of alveoli and hence increasing the surface tension. This prevents collapse of alveoli during expiration.

D) Flow of blood to region of lungs changes according to Euler-Liljestrand mechanism, which states that Pulmonary arteries constricts in response to alveolar hypoxia. Hence blood flow is less with area of lesser ventilation and more blood flow to the area of higher Ventilaton.