BSC2086 A&P II Final Exam Study Guide – Lesson 14 1 Lesson 14: The Respiratory System Part II Introduction to Gas Exchange • Respiration = two integrated processes o External Respiration: Includes all processes involved in exchanging O2 & CO2 with the environment o Internal Respiration: Involves the uptake of O2 & production of CO2 within individual cells Result of cellular respiration Mitochondria use O2 & generate CO2 • Three (3) Processes of External Respiration: o Pulmonary Ventilation – breathing o Gas Diffusion – across membranes & capillaries o Transport of O2 & CO2 Between alveolar capillaries Between capillary beds in other tissues • Abnormal external respiration is dangerous o Hypoxia: Low tissue oxygen levels o Anoxia: Complete lack of oxygen that quickly kills cells o Some tissues require a steady flow of O2 more than others Pulmonary Ventilation • Pulmonary Ventilation: Physical movement of air in & out of the respiratory tract o Provides alveolar ventilation – air movement into & out of alveoli • Atmospheric Pressure: The weight of air o Compresses our bodies & everything around us o Has several important physiological effects • Gas Pressure & Volume o Boyle’s Law: Defines the relationship between gas pressure & volume P = 1/V In a contained gas… • External pressure forces molecules closer together • Movement of gas molecules exerts pressure on containerBSC2086 A&P II Final Exam Study Guide – Lesson 14 2 • Pressure Airflow to the Lungs o Air flows from area of higher pressure to area of lower pressure Concept similar to diffusion o Pulmonary ventilation causes volume changes that create changes in pressure Volume of thoracic cavity changes with expansion or contraction of diaphragm or rib cage o A respiratory cycle consists of: An inspiration – inhalation An expiration – exhalationBSC2086 A&P II Final Exam Study Guide – Lesson 14 3 • Pressure changes during inhalation & exhalation… o Can be measured inside or outside the lungs o Normal atmospheric pressure: 1 atm = 760 mmHg • Intrapulmonary Pressure (Intra-alveolar Pressure) o Relative to atmospheric pressure o During relaxed breathing, the difference between atmospheric pressure and intrapulmonary pressure is small About -1 mmHg on inhalation or +1 mmHg on exhalation o Maximum Intrapulmonary Pressure: Maximum straining, a dangerous activity, can increase range from -30 mmHg to +100 mmHg If too high, can cause alveolar rupture or hernia • Intrapleural Pressure: Pressure in space between parietal and visceral pleura o Averages -4 mmHg o Maximum = -18 mmHg (during powerful inhalation) o Usually negative o Positive = problem (will cause lungs to collapse) o Remains below atmospheric pressure throughout respiratory cycle o Caused by elastic recoil of lung tissue pulling on chest wall Two areas linked by pleural fluid Pulls on the chest wall as it recoils As you inhale, walls expand & pull on the lungs • Pneumothorax: Allows air into pleural cavity o Breaks fluid bond between the pleurae o Can be caused by: Ruptured alveoli through visceral pleura Injury that punctures parietal pleura • Atelectasis: Collapsed lung; result of pneumothoraxBSC2086 A&P II Final Exam Study Guide – Lesson 14 4 • Respiratory Muscles o Diaphragm – used during normal breathing o External intercostal muscles of the ribs – used during normal breathing o Accessory respiratory muscles – used during fast breathing Activated when respiration increases significantly • Inhalation is ALWAYS active o Muscles used during inhalation: Diaphragm: Contraction draws air into lungs • 75% of normal air movement External Intercostal Muscles: Assist inhalation • 25% of normal air movement Accessory muscles assist in elevating ribs during fast breathing • Sternocleidomastoid • Serratus anterior • Pectoralis minor • Scalene muscles • Exhalation can be passive OR active o Passive exhalation – relies on relaxation of inhalation muscles, recoil of lungs and thoracic cavity (elastic rebound) o Active exhalation – uses muscles during forceful exhalation o Muscles used in active exhalation: Internal intercostal muscles & transversus thoracis muscles • Depress the ribs Abdominal muscles • Compress the abdomen • Force diaphragm upward • Compliance: An indicator of expandability o Low compliance greater force needed to fill lungs o High compliance less force needed to fill lungsBSC2086 A&P II Final Exam Study Guide – Lesson 14 5 o Factors that affect compliance: Connective tissue structure of the lungs • Emphysema – alveolar tissue damage causes high compliance o Lungs fill to easily, but transfer of O2 & CO2 less efficient due to damage to respiratory surface Level of surfactant production • Low surfactant low compliance • Respiratory distress syndrome low compliance Mobility of the thoracic cage • Arthritis & skeletal disorders reduced compliance Gas Exchange • Gas exchange occurs… o Between blood & alveolar air o Across the respiratory membrane • Gas exchange depends on…BSC2086 A&P II Final Exam Study Guide – Lesson 14 6 o Partial pressures of the gases o Diffusion of molecules between gas & liquid Diffusion occurs in response to concentration gradients • Dalton’s Law: Each gas contributes to the total pressure in proportion to its number of molecules o Composition of air: Nitrogen (N2): ~79.6% – very low solubility in body Oxygen (O2): ~20.9% – very soluble in body Water vapor (H2O): ~0.5% Carbon dioxide (CO2): ~0.04% – less soluble in body o Atmospheric pressure (760 mmHg) – produced by air molecules bumping into each other • Partial Pressure: The pressure contributed by each gas in the atmosphere o All partial pressures together add up to about 760 mmHg o Difference due to contribution of water vapor • Henry’s Law o When gas under pressure comes in contact with liquid, gas dissolves in liquid until equilibrium is reached o At a given temperature, amount of gas in a solution is proportional to the partial pressure of that gas o The actual amount of a gas in solution (at given partial pressure & temperature) depends on the solubility of that gas in that particular
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