1. Gas Exchange IB objective 6.4 Pgs. 889-897 Campbell

2. Gaseous exchange in animals  Gaseous exchange is the exchange of gases between an organism and its surroundings Intake of oxygen and release of carbon dioxide  This exchange takes place by diffusion  Three factors determine the rate: 1. the size of the surface area 2. difference in concentration 3. length of the diffusion path  Therefore, thin surfaces

3. For many reasons …  Mammals have lungs Specialized organs for gas exchange Large, thin surface Protected by the thorax (chest) Must be ventilated  Ventilation system: Pumping mechanism that moves air into and out of the lungs Maintains concentration gradient for diffusion  Blood circulation system  Respiratory pigment (hemoglobin)

4. The working lungs  Lungs are housed in the thorax Airtight Lined by the pleural membrane  Secretes pleural fluid which protects the lungs from friction Formed by the rib cage and its muscles (intercostal muscles) and the diaphragm (floor)  Separates the abdomen from the thorax

5. The working lungs  The lungs connect with the pharynx at the rear of the mouth by the trachea  Air reaches the trachea from the mouth and nose, passes through the larynx Glottis Epiglottis  The trachea has incomplete rings of cartilage which prevent collapse under pressure from food

6. The working lungs  The trachea then divides into two bronchi (one to each lung) Smooth muscle and cartilage rings  The finest bronchioles end in air sacs (alveoli)

7. The structure of the thorax

8. Alveoli

10. Alveolar structure  Arranged in clusters  Served by tiny bronchiole  Elastic connective tissue in their walls  Capillary system wraps around the clusters  Each capillary is connected to a branch of the pulmonary artery and is drained by a branch of the pulmonary vein  Pulmonary circulation Supplied with deoxygenated blood from the right side of the heart Returns oxygenated blood to the left side of the heart to be pumped to the rest of the body

11. How we breath (ventilation)  Air is drawn into the alveoli when air pressure in the lungs is lower than atmospheric pressure  Air is forced out when pressure is higher than atmospheric pressure  Since the thorax is air tight, pressure changes in the lungs occurs when the volume of the thorax changes

12. Ventilation  The volume of the thorax is increased when: The ribs are moved up and out The diaphragm is lowered Contraction of diaphragm  The volume of the thorax is decreased when: Muscles relax Diaphragm is more dome-shaped Ribs move down and in

13. Inspiration vs. expiration Inspiration (inhalation) Structure/outcomeExpiration (exhalation) Muscles contract, flattening of diaphragm DiaphragmMuscles relax, pressure form abdomen pushes up Contract, rib cage up and out External intercostal muscle Relax Internal intercostal muscle Contract, moves rib cage down and in IncreasesVolume of thorax cavityDecreases Falls below atmospheric pressure Air pressure of thoraxRises above atmospheric pressure InAir flowOut

14. Ventilation

15. Why are lungs are so efficient FeatureEffects and consequences Surface area of alveoliHuge; 700 million alveoli in our lungs (70 m 2 ) Wall of alveoliVery thin, flattened epithelium; diffusion pathway is very short Capillary supply to alveoliNetwork of capillaries; maintains concentration gradient of O2 and CO2 Surface film of moistureO2 dissolves in water lining the alveoli; O2 diffuses into the blood

16. Exit Slip – 6 points  Outline two reasons why your lungs are so efficient for gas exchange.  What is happening to the pressure and volume of your thorax when you inhale?