6.4 Gas Exchange

Ventilation, Gas Exchange & Cellular Respiration Ventilation: movement of air into and out of the lungs Maintain concentration gradient between oxygen and carbon dioxide in the alveoli and blood capillary Allows for simple diffusion of gases

Gas Exchange: exchange of carbon dioxide for oxygen that occurs in the alveoli of the lungs Oxygen passes from the alveoli into the capillaries surrounding the alveoli Carbon dioxide passes from the capillaries into the alveoli The body needs oxygen to carry out cellular respiration

Cellular respiration: the controlled release of energy from organic molecules coupled with the production of ATP Uses oxygen provided by ventilation to create energy Also produces carbon dioxide that must be removed from the body

Concentration Gradient Ventilation system must maintain a high concentration gradient across the alveoli to allow for sufficient gas exchange Maintained by the amount of oxygen and carbon dioxide in the alveoli High concentration of oxygen allows for the movement of the oxygen form the alveoli into the blood stream Maintaining a low concentration of carbon dioxide allows for the movement of carbon dioxide from the capillaries into the alveoli

Pneumocytes (2 types) Type I pneumocytes: elongated with very thin cells. their shape helps with gas exchange Type II pneumocytes: are thick and have short cells They secrete a solution that has surfactant to ensure the membranes of the alveoli remain moist Moisture ensures they don’t stick together Helps facilitate a high rate of diffusion of respiratory gases

Pneumocytes

Features of Alveoli Feature Significance Many alveoli present Increase surface are for more efficient gas exchange Capillaries surround alveoli Close association with capillaries allows for efficient gas exchange between capillaries and alveoli (gas needs to diffuse a short distance) Alveoli are only one cell thick Allows ease of diffusion across a small distance Alveoli are moist Moisture increases the rate of diffusion by dissolving the gases and also prevents alveoli from sticking together Alveoli are flexible Single cell layer can stretch and become thinner to facilitate rapid gas exchange

The Ventilation System Includes the following parts: Mouth Nasal cavity Epiglottis trachea Lungs Bronchi Bronchioles Alveoli diaphragm

Gas Exchange Inhale & Exhale Based on pressure changes Air moves from an area of high pressure to low pressure Muscle Inhalation Exhalation Diaphragm Contracted (pulls downward) Relaxed (bends upward) Internal intercostals Relaxed Contracted (pulls ribs down & inward) External intercostals Contracted (pulls ribs up & outward) Abdominal muscles Relaxed and pushed out Contracted & pull inwards

Lung Cancer and Emphysema Causes Consequences Lung cancer Cigarette smoke Asbestos exposure Radon gas Exposure to air pollutants Genetics Persistent cough Coughing up blood Fatigue Weight loss Shortness of breath Emphysema Wheezing Coughing

Lung cancer Develops from cells that divide uncontrollably and destroy health lung tissue Most prevalent & deadliest cancer among men & women Number one cause cigarette smoke

Emphysema Chronic respiratory disorder caused by damage to alveoli