CHAPTER 9 GAS EXCHANGE GAS EXCHANGE Human gas

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 70 m 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, 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, 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