4Mechanisms of breathing – inspiration When you breathe in:Intercostal muscles pull ribs up and outintercostal muscles between the ribs contract, pulling the chest walls up and outthe diaphragm muscle below the lungs contracts and flattens, increasing the size of the chestthe lungs increase in size, so the pressure inside them falls. This causes air to rush in through the nose or mouth.Diaphragm contracts and moves down
5Mechanisms of breathing – expiration When you breathe out:Ribs move in and downIntercostal muscles between the ribs relax so that the chest walls move in and down.The diaphragm muscle below the lungs relaxes and bulges up, reducing the size of the chest.The lungs decrease in size, so the pressure inside increases and air is pushed up the trachea and out through the nose or mouth.Diaphragm relaxes and bulges up
9Respiratory system – 3 main processes Pulmonary respirationThe breathing of air into and out of the lungsExternal respirationExchange of O2 and CO2 between the lungs and the bloodInternal respirationExchange of O2 and CO2 between the blood and muscle tissues
10Gaseous ExchangeGaseous exchange refers to the exchange of gases, namely O2 and CO2 and relies on a process called diffusion
11How does Diffusion happen? PP – partial pressure of a gas is the pressure it exerts within a mixture of gases.EXAMPLE:Air – Nitrogen (79%); Oxygen (21%); Carbon Dioxide (0.03%)Together they exert a pressure of 760mmHg but individually they exert pressures of:O2 – 160mmHgHow do you work it out? –Partial Pressure = Atmospheric pressure x fractional concentration760mmHg x 0.21 = 159.6mmHg* Gases always move from an area of high pressure to an area of low pressure
12DiffusionDiffusion is the movement of gases from an area of high pressure to an area of low pressure.The difference between the high and low pressure is called the diffusion gradient – the bigger the gradient, the greater the diffusion and gaseous exchange that takes place.
14External Respiration (Alveoli) – What makes it so efficient? Alveoli walls very thin – diffusion distance is very short.Huge amount of alveoli with massive surface area for diffusionVast supply of capillaries – huge surface area for diffusionDiameter of capillaries is slightly narrower than area of red blood cellsCauses red blood cells to distort to increase surface area for gas exchangeForces red blood cells to go through capillaries in single file to maximise exposure to oxygen
15Internal Respiration (muscles) – why is it so efficient? Big diffusion gradient (65mmHg)Myoglobin in muscles has a higher affinity for oxygen than haemoglobin sp attracts oxygen from bloodExtensive capillary network – huge surafce areaCapillary wall only one cell thick – very short distance for diffusion