The Pulmonary System Structure and Function
Lungs • Lung tissue weighs 1 kg and covers half a tennis court (50-100 square feet) • Lung tissue is 20-50 times larger than the body’s external surface • Hold 4-6 liters of air. • Unattached to ribs; suspended inside the pleural sacs.
Function • Ventilation. Breathing (air in and air out) • Conduction. • Movement of air through the pulmonary system • Respiration. • Gas exchange (O2 and CO2)
Conduction Zone (humidify, filter) • Nasal cavity and Pharynx • Nose moistens, warms, and filters air; mouth does not. • Larynx - voice box • Epiglottis • Valsalva maneuver
Conduction Zone (humidify, filter) • Trachea • conducting tube (transports air) • Bronchi • Branches • contains muscle, serves to dilate and constrict • Anatomic dead space
Respiration • Bronchioles • further branching • Alveolar sacs (300 million) • Each alveoli is surrounded by a network or covering of capillaries. • Almost forms a “sheet” of blood. • At rest, a single blood cell passes by 2 or 3 alveoli in about 0.5 to 1.0 seconds
Respiration (gas exchange) • Occurs through thin walls (0.3 micrometers) • Diffusion of gases from high to low concentration.
Types of Respiration • Pulmonary (external) • Transfer of O2 and CO2 at the lungs. • 250 mL of oxygen is exchanged per minute at rest • 200 mL of CO2 is exchanged per minute at rest • These numbers can increase up to 25 times during heavy exercise • Cellular (internal) respiration - transfer of O2 and CO2 in the tissues.
Pleura • Pair of membranes (inner and outer) surrounding the lungs • Fluid in between two sacs provides the only attachment of the lungs to the thorasic cavity (ribs).
Pressure • Inspiration • Air moves into the lungs due to a lower pressure inside the lungs • Expansion of the rib cage and the lowering of the diaphragm increase the volume • As the volume gets larger, the pressure becomes lower.
Pressure • Expiration • Air moves out of the lungs due to a higher pressure inside the lungs • Constriction of the rib cage and the raising of the diaphragm decrease the volume • As the volume gets smaller, the pressure becomes higher.
Muscles of Ventilation • Inspiration • Rest • diaphragm and E.IC muscles • Exercise • pectorals, scalenes, SCM • Expiration • Rest • no muscles • Exercise • abs, I.IC. muscles)
Lungs and Exercise • At rest, the blood is 97-98% saturated with oxygen • Exercise, the blood remains 97-98% saturated • Healthy lungs do not limit a person’s ability to exercise • However, respiratory muscles need to be trained like any other skeletal muscle