Lungs

Lungs - how they work.

Breathing in. Intercostal muscles contract Diaphragm muscles contract Rib cage moves up and out Elastic tissue stretches Diaphragm moves down Volume in lungs increases Pressure in lungs decreases Air rushes into lunges to equal out pressure difference

Breathing out. Intercostal muscles relax Diaphragm muscles relax Rib cage moves down and in Elastic Tissue recoils Diaphragm moves up Volume in lungs decreases Pressure in lungs increases Air is pushed out to equal out pressure difference.

Gas Exchange in the Lungs.

Our lungs help us to exchange oxygen and carbon dioxide between the atmosphere and the blood

Oxygenated blood passes respiring cells and the oxygen diffuses out of the red blood cells to meet the cell's demand. CO2 then diffuses out of the cell and into the blood so it can be taken to the lungs to be removed.

Air is breathed in and travels down the trachea, through the bronchi and even smaller bronchioles until it reaches the bunches of alveoli which are the surface of gas exchange.

The oxygen reaches the epitheial cells of the alveolus wall and is diffused across, also diffuses across the endothelial cells of capillary wall, where it is then associated with deoxygenated blood to become oxygenated. The deoxygenated blood also diffuses CO2 into the alveolus to be removed.

Red blood cells have the same diameter as the lumen of the capillary for a short diffusion pathway and to allow more time for the O2 to travel. The cells of the alveolus walls are thin and flat (squamous) for short diffusion pathway. A steep concentration gradient for diffusion is maintained by the flow of blood carrying oxygenated blood away and ventilation to remove CO2

Rate of Exchange.

Rate of diffusion = Surface area x concentration gradient

Thickness of gas exchange surface.

Key Terms.

Tidal Volume = volume of air breathed in/out in one breath. Cm3 or Dm3. Breathing Rate = breaths in a minute. Pulmonary Ventilation = Tidal Volume x Breathing rate. Dm3 min-1 Vital Capacity = maximum volume of air breathed in/out. Residual Volume = left over air in alveoli Dead Space Air = air that doesn't reach alveoli, not used in gas exchange.

How we breathe

Gas exchange

Rate of exchange

Key Terms