Gas Exchange (Core)

Assessment StatementsObj Distinguish between ventilation, respiration and gas exchange Explain the need for a ventilation system Describe the features of alveoli that adapt them to gas exchange Draw and label a diagram of the ventilation system, including trachea, lungs, bronchi, bronchioles and alveoli Explain the mechanism of ventilation of the lungs, in terms of volume and pressure changes caused by the internal and external intercostal muscles, the diaphragm and abdominal muscles. 3 Assessment statements from: Online IB Biology Subject GuideOnline IB Biology Subject GuideCommand terms:

Concentration gradients Gases need moist surfaces (membranes) in order to diffuse. Our lungs are moist membranes, allowing oxygen to diffuse into the blood and carbon dioxide to diffuse out. The ventilation system maintains a large concentration gradient between the alveoli and the blood. The constant flow of blood past the alveoli brings blood with a high CO 2 concentration and low O 2 concentration. Breathing out keeps the CO 2 concentration in the alveoli low, so it diffuses out of the blood. Breathing in keeps O 2 concentration in the alveoli high, so it diffuses into the blood. Diagram from:

hill.com/sites/ /student_view0/chapter25/animation__gas _exchange_during_respiration.html

Type I & II Pneumocytes Type I Adapted to carry out gas exchange Large total surface area for diffusion Make up majority of epithelial cells lining the alveoli Flattened cells Adjacent cells also single cell layer thick Type II Secrete a solution containing a surfactant creating a moist surface preventing cell adherence Moisture allows oxygen to dissolve and diffuse into blood in capillaries and for CO2 to evaporated into air and be exhaled Rounded cells

Airways 1.Airways: nose, mouth  trachea  bronchi  bronchioles  alveoli. Trachea has rings of cartilage keeping open. Trachea divides into 2 bronchi, also strengthened with cartilage. In lungs bronchi divide to form narrower and narrower bronchioles w/ smooth muscle fibers in their walls. Alveoli at very end of bronchioles

Pressure changes When the same number of gas particles spread out, filling a larger volume, gas pressure decreases. When gas particles are compressed into a smaller space gas pressure increases. Gas always flows from high pressure to low pressure regions.

Inspiration Muscle contractions cause pressure inside thorax to drop below atmospheric pressure Result: INSPIRATION: air is drawn into lungs until pressure in lungs equals atmospheric pressure

Expiration Muscle contractions cause pressure in thorax to rise inside thorax above atmospheric pressure Result: EXPIRATION: air is forced out of the lungs

Antagonistic muscles Only move in one direction shorten when contracting lengthen when relaxing (pulled by contraction of another muscle) Only cause movement in one direction Inspiration and expiration involve opposite movements so different muscles are required working in antagonistic pairs

See chart on page in text book.

Lung cancer Causes Smoking 87% cases – tobacco contains mutagenic chemicals 2 nd hand smoking 3% cases Air pollution 5% - vehicle exhaust fumes, smoke Radon gas Asbestos, silica dust Consequences Difficulty breathing Persistent cough Coughing blood Chest pain Loss of appetite Weight loss Fatigue High mortality rates 15% 5-year survival Lung removal, chemo, radiation

Emphysema Causes Reduced number of alveoli with thicker cell walls Reduced gas exchange area Diffusion distance increased Lungs less elastic Phagocytes produce elastase enzyme to prevent lung infections Enzyme inhibitor alpha 1-antitrypsin prevents elastase from digesting lung tissue In smokers, # of phagocytes increases and additional elastase produced 30% smokers, elastase digests proteins in alveoli walls Consequences Chronic disease – irreversible Low O 2 saturation, high CO 2 concentrations Low energy Shortness of breath Labored and rapid breathing

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