Question

does all the air the we breathed in reaches the exchange surfaces of the lungs during tidal volume? yes or no? and why?

Answer 1

No,all the air we breath in doesnot reach exchange surface of lungs during tidal volume.Respiratory system divided into 2 parts_conducting and exchange portions. Exchange part is alveolar sac and respiratory bronchioles.All other parts are conducting part.

The part of respiratory tract where gaseous exchange doesnot take place is called dead space,and the air present is called dead space air.

2 types_anatomical and physiological dead space.

Anatomical dead space_consist of nose to terminal bronchioles _nose,pharynx,trachea,bronchi,brochiolar branches upto terminal bronchiole.This is only for passage of air&gaseous exchamge doesnot take place (conducting part).

Physiological deadspace_ It is the anatomical dead space&2 additional volumes_that are_1.air in alveoli which are non functioning,In some respiratory diseases alveoli doesnot function because of dysfunction or destruction of alveolar membrane

2.Air in some alveoli,which doesnot receive adequate blood flow,bcoz gaseous exchange doesnot take place during inadequate blood supply.

Wasted ventillation--it is the volume of air that ventilates physiological dead space.Wasted air is which is not utilized for gaseous exchange =dead space air.

In normal condition physiological deadspace=anatomical deadspace.,as all alveoli are functioning &all alveoli receive adequate blood supply.physiological deadspace increases during respiratory diseases which affect blood flow to alveoli.

Value of normal dead space=150mL.

Dead space volume can be calculated by single breath nitrogen washout method.Here the subject respires normally for few minutes and then takes sudden inhalation of pure oxygen.,thus oxygen replaces the air in deadspace that is dead space air contains only oxygen & pushes othergases into alveoli.Now the subject exhales through a nitrogen meter,this shows the concentration of nitrogen in expired air continiously.(2nd part).