BSC2086 A&P II Exam #4 Study Guide 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 Exam #4 Study Guide 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 Exam #4 Study Guide 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 pneumothorax • Respiratory Cycle o Cyclical changes in intrapleural pressure operate the respiratory pump Aids in venous return to heartBSC2086 A&P II Exam #4 Study Guide 4 o Tidal Volume (VT): Amount of air moved in & out of lungs in a single respiratory cycle ~ 500 mL • 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 upwardBSC2086 A&P II Exam #4 Study Guide 5 • Compliance: An indicator of expandability o Low compliance greater force needed to fill lungs o High compliance less force needed to fill lungs 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 • Respiratory system adapts to changing oxygen demands by varying: o Number of breaths per minute – respiratory rateBSC2086 A&P II Exam #4 Study Guide 6 o Volume of air moved per breath – tidal volume • Respiratory Minute Volume (VE): Amount of air moved per minute o Used to measure pulmonary ventilation o Calculated by: Respiratory rate x tidal volume 12 breaths x 500 mL = ~1.6 gallons (6 liters) • Alveolar Ventilation (VA): Amount of air reaching alveoli each minute o Only a part of respiratory minute volume reaches alveolar exchange surfaces Volume of air remaining in conducting passages is anatomic dead space (~150 mL) o Air entering alveoli contains less O2 & more CO2 than atmospheric air Inhaled air mixes with exhaled air o (tidal volume – anatomic dead space) x respiratory rate = alveolar ventilation • Relationships among VT, VE, & VA o Determined by respiratory rate & tidal volume o For a given respiratory rate: Increasing tidal volume (breathing deeper) increases alveolar ventilation rate o For a given tidal volume: Increasing respiratory rate (breathing faster) increases alveolar
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