Gas Exchange

Ventilation

Ventilation refers to the mechanical process by which air moves into and out of the lungs

Driven by pressure changes within the thoracic cavity

Boyle’s Law

At constant temperature, the process of a gas is inversely propotional to its volume

Gas pressure is produce by collisions of gas molecules with the walls of a container

• Volume increase, less pressure is exerted

• Volume decrease, more pressure is exerted

Pressure and air movement ( Ventilation )

Air flows down a pressure gradient

• Air moves from a areas of higher pressure to areas of lower pressure

• To ventulate the lungs, the body alters thoracic volume which changes pressure and drives airflow

Changing thoracic volume ( Ventilation )

Change by the action of repiratory muscles: Diaphragm and intercostal muscle

Inhalation/ Inspiration ( Ventilation )

External intercostal muscles contract ( Internal intercostal muscle relax) → Ribcage moves upwards and outwards → Diaphragm contracts anf flattens → Volume of the thoracic cavity increases → pressure in alveoli decreases → air move into the lungs

Exhalation / expiration (Ventilation )

External intercostal muscles relax → Ribcage moves downwards and inwards → Diaphragm relaxes and bulges up → Volume of the thoracic cavity decreases → Pressure in alveoli increases → air move out of the lungs

External respiration

Exchange of gases between the alveoli and the blood in pulmonary capillaries

Occurs by diffusion down partial pressure gradients ( partical pressure is the pressure exerted by an individual gas in a mixture which determines the direction off diffusion across a membrane )

External respiration in the lungs

O2 partical pressure is higher in alveoli than in blood → O2 diffuses into the blood

CO2 partial pressure is higher in blood than in alveoli → CO2 diffuses into the alveoli

Internal respiration

-exchange of gases between the blood and body tissues

support cellular respiration by supplying O2 to cells and removing CO2

Internal respiration in body tissues

O2 partial pressure is higher in blood in the cells → O2 diffuses into the cells

CO2 partial pressure is higher in cells than in blood → Co2 diffuses into the blood

N2 inspired air and expired air

79% ( not use/ produced by body process )

O2 inspired air

21% ( Used up in respiration )

O2 expired air

16% ( Used up in respiration )

Adaptations for efficient gas exchange - Large surface area

Milions of aveoli provide a surface area approximately to a tennis court

Adaptations for efficient gas exchange - Short diffusion pathway

alveolar anf cappilary walls are each one cells thick

Adaptations for efficient gas exchange - High concentration gradient: maontained by continous ventilation and blood flow

Adaptations for efficient gas exchange - Moist surface

The moist surface of the alveoli allow gases to dissolve and then diffuse through the cells

Adaptations for efficient gas exchange - The lungs are positioned deep within the body

prevent excessive evaporation of fluid