ch7 gas exchange

• Hairs inside the nostrils filter dust particles from the inhaled air
• mucus-secreting cells in the lining of the nasal cavity secrete mucus which traps dust particles and microorganisms. Cilia of ciliated epithelial cells in the lining beat to sweep the mucus towards the pharynx. The mucus is coughed up or swallowed into the stomach where most microorganisms will be killed hydrochloric acid
• the mucus also moistens the inhaled air to prevent the surface inside the lungs from drying out
• lining of nasal cavity has a rich supply of blood vessels. the blood in the capillaries warm the inhaled air to avoid irritation of the lungs
• larynx is made of mainly cartilage which prevents it from collapsing due to pressure changes during breathing. there are two folds of tissues in the larynx called the vocal cords and sounds are produced when air passes the vocal cords, causing them to vibrate
• Trachea and bronchi

  -walls contain cartilage preventing it from collapsing, trachea cartilage is c-shaped to allow the oesophagus to expand when swallowing food.

  -contain smooth muscles which regulate diameter of airway ,and elastic fibres

  -lined with mucus-secreting cells and ciliated epithelial cells

  -rich supply of blood vessels
• bronchioles have no cartilage, and its walls are mostly made up of smooth muscles and elastic fibres. larger bronchioles have mucus-secreting cells and ciliated epithelial cells
• The wall of each air sac is made up of epithelium which is one-cell thick and secretes a watery fluid keeping the inner surface of the air sac warm
• air sacs are surrounded by a network of capillaries and receive deoxygenated blood from the heart via the pulmonary artery. after blood is oxygenated , it is carried away to the heart via the pulmonary vein
• lungs are protected by the rib cage , between ribs are intercostal muscles. below the lungs is the diaphragm. each lung is surrounded by two layers of pleural membranes. the space between them is the pleural cavity, containing a film of pleural fluid which acts as a lubricant to reduce friction between membranes during breathing.
• Uptake of oxygen

  -air flows into air sacs and the oxygen dissolves in the water film, increasing the oxygen concentration, making it higher than that of the deoxygenated blood. dissolved oxygen diffuses across the walls of air sacs and the capillaries into the blood
• removal of co2

  -carbon dioxide concentration of deoxygenated blood is higher than that of the water film, so carbon dioxide diffuses into the air in the air sacs, and is removed when we exhale
• after gas exchange, the oxygen content of blood increases and carbon dioxide content decreases. the blood is oxygenated. it is carried to the heart via the pulmonary veins
• adaptive features of air sacs

  -large number of air sacs to provide a large surface area for the diffusion of gases

  -thin walls of air sacs, one-celled thick to shorten the diffusion distance of gases

  -moist inner surface for oxygen to dissolve in before diffusion

  -rich supply of capillaries allow rapid transport of gases to ans away from air sacs, maintaining a steep concentration gradient of gases

  -walls of air sacs are in close contact with capillaries to reduce diffusion distance of gases
• composition of inhaled and exhaled air

  -nitrogen same

  -water vapour: variable to saturated as it is moistened by the water film

  -oxygen lowers as it diffuses into the blood

  -carbon dioxide: increases as it is produced by cells during respiration and diffuses into air sacs
• rbc

  packed with haemoglobin, an iron-containing protein and binds readily to oxygen. the binding is reversible. under high oxygen concentration, oxygen binds to haemoglobin to form oxyhaemoglobin. in low concentratio, oxyhaemoglobin breaks down into haemoglobin and oxygen
• haemoglobin increases the oxygen-carrying capacity of blood
• mature rbc have no nucleus, providing more space for haemoglobin
• the rbc have a concave shape to provide a large surface area to volume ratio and a short diffusion distance for oxygen, allowing oxygen to reach and leave haemoglobin rapidly
• oxygen concentration is low in body tissues as it is consumed continuously during respiration. oxyhaemoglobin in blood breaks down into haemoglobin and oxygen which diffuses into cells and the deoxygenated blood is carried to the heart then to the lungs via the pulmonary artery
• carbon dioxide diffuses into rbc and reacts with water to form hydrogencarbonate ions and hydrogen ions. the hydrogencarbonate ions diffuse out of the rbc and are carried by plasma to the air sacs
• co2 concentration is low as it is removed continuously when we exhale. hydrogencarbonate ions in plasma diffuse into rbc and react with hydrogen ions to form co2 and water. the co2 diffuses into plasma and then into the air sacs for removal
• Inhalation

  Intercostal muscles contract causing the rib cage to move upwards and outwards. the diaphragm muscles contract to cause the diaphragm to flatten. this increases the volume of the thoracic cavity, causing an increase in the volume of lungs. the air pressure in the lungs decreases and becomes lower than the atmospheric pressure. Air rushes into lungs
• exhalation

  Intercostal muscles relax causing the rib cage to move downwards and inwards. the diaphragm muscles contract to cause the diaphragm to return to its dome shape. this decreases the volume of the thoracic cavity, causing an decrease in the volume of lungs. the air pressure in the lungs increases and becomes higher than the atmospheric pressure. Air is forced out of lungs