Assessment Statements: 6.4.1 Distinguish between ventilation, respiration and gas exchange. 6.4.2 Explain the need for a ventilation system. 6.4.3 Describe the features of alveoli that adapt them to gas exchange. 6.4.4 Draw and label a diagram of the ventilation system, including trachea, lungs, bronchi, bronchioles and alveoli. 6.4.5 Explain the mechanism of ventilation of the lungs, in terms of volume and pressure changes caused by the internal and external intercostal muscles, the diaphragm and abdominal muscles.
Ventilation The flow of air in and out of the alveoli Two stages: inhalation and exhalation Lungs are not muscular and cannot ventilate themselves The thorax moves and changes size, due to the action of two sets of muscles: the intercostal muscles and the diaphragm.
Gas Exchange The diffusion of gases (oxygen and carbon dioxide) Two sites for gas exchange: • Alveoli: Oxygen diffuses into the blood from the alveoli and carbon dioxide diffuses from the blood into the alveoli • Tissues: Oxygen diffuses from blood into the cells and carbon dioxide diffuses from cells to the blood
Cell Respiration • Aerobic respiration uses oxygen in the mitochondria and produces carbon dioxide • Anaerobic respiration does not use oxygen but still produces carbon dioxide
Why do we need a ventilation system? To maintain a concentration gradient for diffusion Air is constantly being refreshed in the lungs keeping the concentration of oxygen high and carbon dioxide low At the same time bllood is constantly carrying away oxygen and bringing new carbon dioxide Both gases diffuse down their concentration gradient from high to low concentration
Features of alveoli for gas exchange Large numbers of alveoli gives large surface area for gas exchange Single layer of flattened cells in wall of alveoli Short distance for diffusion of gases Oxygen dissolves in thin film of moisture on inside of alveoli - this aids diffusion Surrounded by dense network of capillaries
The Ventilation System intercostal muscles bronchi ribs heart bronchioles diaphragm alveolus