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Download Respiratory Physiology Anatomy of the Respiratory System
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11/8/12 Respiratory Physiology Cellular Respiration Pulmonary ventilation (breathing) Gas exchange between lungs and blood Transportation of gases in blood Gas exchange between blood and body tissues Anatomy of the Respiratory System Conducting airways (Nasal passages, pharynx, trachea, bronchii, bronchioles) Inspired air is warmed and humidified in these tubes. Moistening of air is essential to prevent drying out of alveolar linings. Photomicrograph of Tracheal Epithelium 1 11/8/12 Defence mechanisms Respiratory system is largest area of the body in direct contact with the environment. Large particles filtered out in hairs in nasal passages Respiratory airways lined with mucus to trap foreign objects Cilia move mucus upwards towards throat to be swallowed Coughs and sneezes Alveolar macrophages scavenge within the alveoli Function of the alveoli Exchange of gases between air and blood by diffusion 2 11/8/12 Alveoli Site of gas exchange 300 million alveoli/lung (tennis court size) Rich blood supply- capillaries form sheet over alveoli Alveolar pores Type I alveolar cells – make up wall of alveoli Single layer epithelial cells Type II alveolar cells – secrete surfactant Alveolar macrophages Resin cast of pulmonary blood vessels Scanning electron micrograph of capillaries around alveoli Pulmonary Circulation is low-pressure, low-resistance Ventilation-perfusion matching: blood flow through the pulmonary circulation is matched to ventilation 3 11/8/12 Structures of the Thoracic Cavity Chest wall – air tight, protects lungs Skeleton: rib cage;sternum; thoracic vertebrae Muscles: internal/external intercostals; diaphragm Lungs are surrounded by pleural sac Role of Pressure in pulmonary ventilation Air moves in and out of lungs by bulk flow Pressure gradient drives flow (air moves from high to low pressure) Atmospheric pressure = Patm (760mmHg at sea level) Intra-alveolar pressure = Palv Pressure of air in alveoli During inspiration = negative (less than atmospheric) During expiration = positive (more than atmospheric) Difference between Palv and Patm drives ventilation 4 11/8/12 Atmospheric Pressure 760 mm Hg at sea level Decreases as altitude increases Increases under water Other lung pressures given relative to atmospheric (set Patm = 0 mm Hg) Intrapleural Pressure Pressure inside pleural sac Always negative under normal conditions Always less than Palv Varies with phase of respiration At rest, -4 mm Hg Negative pressure due to elasticity in lungs and chest wall Lungs recoil inward Chest wall recoils outward Opposing pulls on intrapleural space Surface tension of intrapleural fluid holds wall and lungs together Pneumothorax 5 11/8/12 Mechanics of Breathing Movement of air in and out of lungs due to pressure gradients Mechanics of breathing describes mechanisms for creating pressure gradients Boyle’s Law (pressure and volume are inversely related) The lungs follow the movement of the rib cage Forces for Air Flow Flow = Patm – Palv R Force for flow = pressure gradient Atmospheric pressure constant (during breathing cycle) Therefore, changes in alveolar pressure creates/changes gradients Muscles of Respiration Inspiratory muscles increase volume of thoracic cavity • Diaphragm & external intercostals Expiratory muscles decrease volume of thoracic cavity • Internal intercostals & abdominal muscles Expiration is generally passive (no muscles required): elastic recoil Active expiration requires expiratory muscles • Contraction of expiratory muscles creates greater and faster decrease in volume of thoracic cavity 6 11/8/12 Inspiration and Expiration Figure 17.11b Factors affecting ventilation Compliance Airway resistance Lung Compliance: Ease with which lungs can be stretched Larger lung compliance, easier to inspire Factors Affecting Lung Compliance: Elasticity Less elastic: less compliant Surface tension of lungs Greater tension: less compliant 7 11/8/12 Surface Tension in Lungs Thin layer of fluid lines alveoli Surface tension due to attractions between water molecules Force for alveoli to collapse or resist expansion To Overcome Surface Tension Surfactant secreted from type II cells Surfactant: detergent that decreases surface tension Surfactant increases lung compliance Makes inspiration easier Physiology Research Focus: the developing lung & ageing 8 11/8/12 Airway Resistance Like blood vessels, the resistance of the airways affects air flow Airway radius affects airway resistance Disease states: Asthma – caused by spasmic contractions of smooth muscle of bronchioles. Histamine is a bronchoconstrictor Chronic obstructive pulmonary diseases – COPD Extrinsic control Autonomic nervous system Sympathetic Relaxation of smooth muscle Bronchodilation Parasympathetic Contraction of smooth muscle Bronchoconstriction Hormonal Control Adrenaline Relaxation of smooth muscle Bronchodilation Physiology Research Focus: respiratory disease 9
