Respiratory System

1. Respiratory System Chapter 42

2. Respiration • Respiration: the exchange of gases (O2 and CO2) between the external environment and the cell or body of an organism • Occurs mainly by diffusion (due to concentration gradients) • Thus, requires large surface areas and thin, moist membranes

3. Mechanisms of Gas Exchange • Invertebrates exchange gases in various ways • Hydras and sponges - directly across the moist surface of the organism • Earthworms and flatworms- diffusion of O2 and CO2 over the moist skin (large surface area) • Insects- Have spiracles (holes in skin surface) that connect to tracheae to carry O2and CO2 through the body – diffusion occurs across the moist endings of the tracheae

4. Vertebrate Gas Exchange • Fish • Gills– moist, thin-walled respiratory organs that create large surface area over which gas exchange can occur • Blood vessels flow under gills against water flow – exchange of CO2 and O2 occurs here – Countercurrent Exchange

5. Countercurrent Exchange in Fish

6. Vertebrate Gas Exchange • Amphibians, some fish, birds, mammals • Paired lungs act as an internal cavity for gas exchange • Oxygen transport molecules – have an “affinity” for oxygen molecules • Hemoglobin proteins – lower affinity for oxygen than myoglobin; transport up to 4 oxygen molecules • Myoglobin proteins – has a greater affinity for oxygen; takes oxygen from the blood to the muscle for use or storage

7. Partial Pressure of Oxygen (Po2) • Partial Pressure Po2) – pressure exerted by a gas (like O2) in a mixture of gases • Look at the relative amounts of O2 bound to hemoglobin at various partial pressures • The greater the partial pressure of O2, the more O2 there is, the higher the saturation of hemoglobin/myoglobin • Drop in pH (heavy exercise) moves graph to the right, so at a given Po2 (40mmHg), hemoglobin unloads more O2 at 7.2 than 7.4 (normal pH) soO2 saturation is lower

8. Gas exchange in humans • In through nose or mouth (oral or nasal cavity) • Through pharynx and larynx (voice box) • Air enters trachea (cartilage lined windpipe) – epiglottis covers trachea to prevent food/liquids from entering • 2 bronchi branch from trachea, each leading to a lung • Bronchi branch further into narrower tubes called bronchioles • Each bronchiole branch ends in an alveolus (alveoli – plural) which is surrounded by capillaries

9. Gas Exchange in Humans

10. Gas Exchange in Humans (cont) • Gas exchange occurs across moist membranes of the alveoli by diffusion • O2 moves from the alveoli, across moist membranes and into capillary with the red blood cells (RBCs) • CO2 (gaseous waste) goes in the opposite direction out • O2 is then carried by hemoglobin of the RBCs through the body (circulatory system) • O2 diffuses out of the RBCs, across capillary walls, into cells in the interstitial fluid • CO2 (gaseous waste) goes in the opposite direction out

11. Gas Exchange in Humans (cont) • CO2 is transported in blood as HCO3-(bicarbonate) • H2O + CO2 (uses carbonic anhydrase)  H2CO3  HCO3- + H+ • (Increases acidity, decreases pH) • The HCO3- ions are transported by the plasma (liquid part of the blood) • CO2 plays a role in controlling the rate of respiration. Chemoreceptors in the carotid arteries monitor blood pH. When blood pH decreases (due to more CO2), chemoreceptors send nerve impulses to the diaphragm and intercostal muscles (between ribs) to increase respiratory rate, returning the blood pH to normal • When the diaphragm contracts, it moves down during inhalation to allow lung volume to increase • When diaphragm relaxes, it moves up during exhalation to push air out and back up the trachea

12. Diaphragm movement

13. Animations • Lungs to blood • Blood to tissues • Tissues to blood • Blood to lungs