BSC 2086 1st Edition Lecture 17 Outline of Last Lecture I. Introduction to Respiratory SystemII. Components of Respiratory SystemIII. Upper Respiratory TractIV. Larynx V. TracheaVI. Lungs Outline of Current LectureI. Introduction to Gas ExchangeII. Pulmonary VentilationIII. Gas Exchange Current LectureI. Introduction to Gas Exchangea. External respiration: all processes needed to exchange O2 and CO2 with the environment i. Three processes1. Pulmonary ventilation (breathing)2. Gas diffusion across the membranes and capillaries3. Transport of oxygen and carbon dioxide between:a. Alveolar capillariesb. Capillary beds in other tissuesii. Abnormalities1. Hypoxia: low oxygen tissue levels 2. Anoxia: complete lack of oxygen which quickly kills cellsb. Internal respiration: result of cellular respirationi. Uptake of O2 and production of CO2 in each individual cell1. Mitochondria uses oxygen and makes waterII. Pulmonary Ventilationa. Physical movement of air in and out of respiratory tract b. Provides alveolar ventilation, which moves air in and out of alveoli c. Atmospheric pressure: weight of air that compresses our bodies i. Several physiological effects d. Gas pressure and volumei. Boyles law defines this relationshipii. P = 1/Viii. In a contained gas, the external pressure forces molecules closer together1. This movement of gas molecules exerts pressure on the containere. Pressure and airflow to the lungsi. Similar to diffusion, air flows from an area of high pressure to one with lower pressureii. Pulmonary ventilation volume changes cause a change in pressure1. Expansion or contraction of the diaphragm or rib cage will cause a volume change of the thoracic cavityiii. Respiratory cycle:1. Inspiration (inhalation)a. Thoracic cavity expands, diaphragm pushes down, volume increases in thoracic cavity allowing the lungs to expand b. When pressure drops lower than atmospheric pressure, airflows into lungs2. Expiration (exhalation)a. Usually doesn’t involve musclesb. Ribs compress back down into there normal shape. 3. Pressure changes during either of these can be measured either inside or outside of the lungs a. Normal atmospheric pressure i. 1 atm = 760 mm Hgiv. Intrapulmonary Pressure (aka. intraalveolar pressure)1. Air pressure inside alveolus2. Relative to atmospheric pressure3. Difference between atmospheric pressure and intrapulmonary pressure is small in relaxed breathinga. About +1 mm Hg on exhalationb. About -1 mm Hg on inhalation 4. Maximum intrapulmonary pressurea. Max straining is a dangerous activity and can increase in range from -30 mmHg to +100 mmHgb. If it becomes too high alveolar rupture or hernia can occurv. Intrapleural pressure1. Pressure between parietal and visceral pleura 2. Averages -4 mmHg with a maximum of -18 mmHg during powerfulinhalation3. Stays below the atmospheric pressure during the respiratory cycle 4. Cause by elastic recoil of lung tissue pulling on chest wall vi. Chest wall injuries1. Pneumothorax: fluid enters pleural cavity and breaks the fluid bond between the plurae 2. Atelectasis: result of pneumothoraxa. Collapsed lungf. Respiratory Cyclei. Respiratory pump operated by cyclic changes in intrapleural pressure1. This helps in venous return to the heartii. Tidal volume (Vt) = about 500 mL1. The amount of air that goes in and out of the lungs in a single respiratory cycle iii. In a normal lung, the intrapleural pressure is always negative compared tothe intrapulmonary pressure g. Respiratory Musclesi. Diaphragm – necessary for normal breathingii. External intercostal muscles of ribs –necessary for normal breathingiii. Accessory respiratory muscles – necessary for fast breathing and activated when respiration increases significantlyh. Breathing mechanicsi. Inhalation is always active1. Diaphragm its contraction draws air into the lungsa. 75% of normal air movement2. External intercostal muscles help inhalation and are responsible for 25% of air movement3. Accessory muscles used to elevate ribs in fast breathing a. Sternocleidomastoidb. Serratus anteriorc. Pectoralis minord. Scalene muscles ii. Exhalation can be passive or active1. Passive: relaxation of inhalation muscles and elastic rebound which involves the recoil of both the lungs and the thoracic cavity2. Active: uses respiratory muscles for forceful exhalationa. Internal intercostal and transversus thoracic muscles depress the ribsb. The abdominal muscles compress abdomen and push the diaphragm upiii. Compliance – indicates expandability1. Low compliance = greater force needed to fill lungs2. High compliance = less force to fill lungs3. Factors: a. Connective tissue structure of lungsi. Emphysema causes high compliance due to alveolar damageb. Amount of surfactant productioni. Respiratory distress syndrome causes low compliancec. Mobility of thoracic cagei. Compliance reduced by arthritis or skeletal disorders i. Respiratory rates and Volumesi. Adapts to changing oxygen demands by changing:1. Respiratory rate number of breaths per minute2. Tidal volume volume of air moved per breathii. Respiratory Minute Volume (VE): used to measure pulmonary ventilation by measuring amount of air moved per minute 1. Respiratory rate (12 breaths) x tidal volume (500 mL) = about 1.6 gallons (6 liters)iii. Alveolar Ventilation (VA) 1. (Tidal volume – anatomic dead space) x respiratory rate2. Amount of air reaching alveoli per minute3. Not all of respiratory minute volume reaches the alveolar exchange surfacesa. Anatomic dead space is the volume of air remaining in conducting passages (about 150 mL) 4. Compared to atmospheric air, air going into alveoli has less O2 and more CO2a. Due to mixture of inhaled and exhaled airiv. Relationships between VT, VE, VA1. For any given respiratory rate, increasing the tidal volume by breathing deeper will increase alveolar ventilation rate2. For any given tidal volume, increasing respiratory rate by breathing faster will increase alveolar ventilationj. Respiratory Performance and Volume Relationshipsi. Total lung volume is able to diagnose problems by being divided into a series of volumes and capacitiesii. Four pulmonary volumes:1. Resting tidal volume (Vt): normal respiratory cycle2. Expiratory reserve volume (ERV): after a normal exhalation3. Residual volume: after max exhalation4. Inspiratory reserve volume (IRV): after a normal inhalationiii. Four calculated respiratory capacities:1. Inspiratory capacity: = TV + IRV2. Functional
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