Chapter 9: Gas Exchange

Gas exchange Human gas exchange system links circulatory system w/ atmosphere Clean and warm entering air Maximize surface area for diffusion of oxygen and carbon dioxide Minimize distance for diffusion Maintain adequate gradients for diffusion

Gas exchange Need oxygen for respiration Multicellular organisms have gas exchange surface where external oxygen can diffuse into body, and carbon dioxide can diffuse out In humans: alveoli (found in lungs, total surface area over 70m sq)

Lungs Found in thoracic (chest) cavity surrounded by pleural membranes, which enclose an airtight pleural space (aka pleural cavity) pleural space contains small amount of fluid to reduce friction during ventilation

Trachea, bronchi, bronchioles Leading from the throat to the lungs is the trachea, and at the base are two bronchi (singular: bronchus) which then subdivide several times into even smaller bronchioles

Trachea, bronchi, bronchioles Cartilage in the trachea and bronchi keep airways open and air resistance low, and prevents them from collapsing or bursting as air pressure changes during breathing Trachea: regular C-shaped cartilage rings Bronchi: irregular blocks of cartilage

Bronchioles Surrounded by smooth muscle which contract/relax to adjust diameter of airways Relax= greater diameter, more air Possible b/c no cartilage

Warming and cleaning the air As air flows through nose and trachea, it is warmed and moistened by evaporation from the lining to protect lungs from drying out (desiccation) Small hairs inside nose and mucosal membranes trap suspended particles (dust, pollen, bacteria, viruses)

mucus In trachea and bronchi, goblet cells of the ciliated epithelium produce mucus, a slimy solution of mucin, which is composed of glycoproteins with many carbohydrate chains that make them sticky

mucus Also made by mucous glands beneath the epithelium Some chemical pollutants, like sulfur dioxide and nitrogen dioxide, can dissolve into mucus and irritate the airways

mucus Beneath goblet cells are ciliated cells that carry mucus upwards towards the larynx, where it is (usually) swallowed so pathogens can be destroyed by the acid in our stomachs

macrophages Phagocytic white blood cells patrol the surfaces of the airways scavenging small particles like bacteria and fine dust

alveoli Terminal end of bronchioles. Have very thin lining of epithelial tissues (single cell thick) and are surrounded by capillaries carrying deoxygenated blood Thinness of barriers ensures fast diffusion Walls contains elastic fibers which can stretch and recoil during breathing

alveoli Oxygen moves into bloods via partial pressure differences between alveoli (high) and capillaries (low) Carbon dioxide moves from high in capillaries to low in alveoli Blood is constantly moving so pressure gradient is maintained