How the Lungs Work

Alveoli “Air Sacs” Resemble bunches of grapes Make up bulk of lungs

Respiratory Zone Includes respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli Only places where gas exchange occurs

Walls of Alveoli Made of single, thin layer of simple squamous epithelial cells Covered with a cobweb of pulmonary capillaries

Respiratory Membrane Made up of alveolar and capillary walls Has air flowing on one side, blood flowing on the other Gas exchange occurs through simple diffusion Oxygen from alveolar air to capillary blood Carbon dioxide leaving blood to air FUN FACT: total surface of alveoli walls is about 50-70 square meters - about the surface of a tennis court!

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Steps to Respiration 1. Pulmonary Ventilation (breathing) Air move in and out of lungs so alveoli air is refreshed 2. External Respiration Gas exchange between blood and alveoli air 3. Respiratory Gas Transport Gas transport between lungs and body by bloodstream 4. Internal Respiration (Cellular Respiration!) In body, at capillaries, gas exchange between blood and tissue cells

Respiration Inspiration Expiration Air flowing into lungs (breathe in!) Expiration Air leaving the lungs (breathe out.) Volume changes lead to pressure changes, which lead to the flow of gases to equalize the pressure!

Inspiration Diaphragm and external intercostals contract Diaphragm actually moves DOWN when contracts Thoracic cavity size increases Rib cage lifts Intrapulmonary volume increases Gas molecules spread out due to increased volume! This causes a decrease in pressure, which pulls in more gas.

Inspiration

Expiration Diaphragm and external intercostals relax Internal intercostals and abdominal muscles contract if expiration is forced Thoracic cavity size decrease Rib cage descends Intrapulmonary volume decreases Gas molecules get closer together due to the decrease in volume! This causes an increase in pressure, which forces gas out.

Expiration

Non-Respiratory Air Movements Cough Sneeze Crying – release of air in short breaths Laughing – release of air in short breaths Hiccups Yawn

Lung Development Fetus Birth All respiratory exchange made by placenta Lungs filled with fluid Birth Fluid drained, passageways fill with air Surfacant: fatty molecule that lines each alveolar sac to prevent from collapsing (don’t have enough of this until fetus is 30 weeks) Lungs do not fully inflate for 2 weeks after birth 20 to 40 respirations/min

Lung Development Teens Elderly 12 to 18 respirations/min (rates differ depending on source) Continue to develop alveoli (smoking stops this production!) Elderly Chest wall becomes rigid, lungs lose elasticity, cilia in trachea less effective Vital capacity decreases More at-risk for respiratory tract conditions 18 to 20 respirations/min