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Physiology - Respiration Notes.docx

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McGill University
NUR1 324

STRUCTURE OF LUNGS AND CHEST WALL Respiratory tract Trachea bronchi bronchioles terminal bronchi respiratory bronchi alveolar ducts alveolar sacs Nasal septum and nasal turbinates clean air in nose Pleura and pleural surfaces Parietal pleura against thoracic cage Visceral pleural against lung surface Pressure in pleural space is negative Conducting zone Mouth and nose openings terminal bronchioles Do not contribute to gas exchange Have anatomical dead space Functions o Defence against bacterial infections and foreign particles cilia and mucus o Warm and moisten air o Sound as air over vocal cords o Regulation of air flow via smooth muscles of airways Respiratory zone Site of gas exchange between air in alveoli and blood 300 million alveoli and each has 1000 capillaries associated with it Blood supply Pulmonary circulation bring mixed venous blood to lungs to get oxygenated left heart o Supplied via pulmonary artery from RV o Oxygenated back to heart via pulmonary veins Bronchial circulation supplying oxygenated blood from systemic circulation to airways o From aorta part of systemic circulation Alveolar cell types Epithelial cells o Line alveoli like a layer sealed by tight junctions o Type 1 dont know function o Type 2 produce surfactant decreases surface tension of alveoli Endothelial cells walls of pulmonary capillaries very thin Alveolar macrophages remove foreign particles which got through initially Respiratory muscles Inspiration o Diaphragm (main) innervated by phrenic nerves from cervical segments 3, 4, 5 contraction causes dome to descend and chest to expand o External intercoastals and parasternal intercartilaginous muscles (elevate ribs) o Accessory muscles scalenus, sternocleidomastoid during high levels of ventilation, asthma elevate and fix rib cage, and elevate sternum Expiration o Muscles only during high levels of ventilation or increased expiratory resistance (pathological) o Internal intercoastals, abdominal muscles force diaphragm upward o Essential for coughing, singing, vomiting, talking o Forced maximal contraction of expiratory muscles against closed glottis (Valsalvas maneuvre) enormous increase in pressure in thoracic cage and abdomen decrease in venous return to heart decrease in CO Inspiration Diaphragm and intercoastal muscles contract thoracic cage expands intrapleural pressure becomes more subatmospheric (negative) transpulmonary pressure increases lungs expand alveolar pressure becomes subatmospheric (negative) air flows into alveoli Expiration Diaphragm and external intercoastal muscles stop contracting chest wall moves towards preinspiratory value (more positive) transpulmonary pressure goes back towards preinspiratory value lung recoil towards preinspiratory volume air in lungs compressed alveolar pressure becomes greater than atmospheric pressure (more positive) air flows out of lungs *When Palv < Patm, driving force for air flow is negative air flows in (inspiration) *When Palv > Patm, driving force for air flow is positive air flows out (expiration Lung volumes Tidal volume regular breathing Inspiratory reserve volume extra you can breathe in (max) Expiratory reserve volume extra you can breathe out (max) Residual volume air left after you breathe out max amount Vital capacity total when you breathe in max and breathe out max Functional residual capacity total remaining to breathe out after you breathe in normal (expiratory reserve + residual) Inspiratory capacity total remaining to breathe in after you breathe out normal (inspiratory reserve + tidal v.) Total lung capacity max air in lungs VENTILATION Minute ventilation Minute ventilation (VE) = tidal volume (VT) x breaths/min (f) Alveolar ventilation Some air remains in conducting airways anatomical dead space Amount approximately 150mL (weight of person in lbs) Alveolar ventilation (VA) = (VT-dead space) x f Physiological dead-space Pathological: some air reaches respiratory zone but doesnt not take part in gas exchange Alveoli either receive decreased or no blood supply Physiological dead space (VD) = anatomical dead space + alveolar dead space Physiological dead space (VD) = tidal volume (VT) alveolar ventilation (VA) o Aka. How much you breathe in how much is actually used by alveoli = how much wasted in dead space Types of alveolar ventilation Blood going to blood from alveoli o PO2 = 100mHg PCO2 = 40mmHg Blood coming back to alveoli from body o PO2 = 40mmHg PCO2 = 46mmHg Alveolar hyperventilation o More O2 supplied and more CO2 removed than metabolic rate requires o VE exceeds needs of body o Alveolar partial pressure of O2 increases and of CO2 decreases o Ventilation has to be considered with respect to metabolism so ventilation during exercise is not hyperventilation Alveolar hypoventilation o Rate at which O2 is added to alveolar gas, and the rate at which CO2 is eliminated is lowered so that the alveolar partial pressure of O2 falls and of CO2 rises CO2 rises above normal level o COPD, damage to respiratory muscles, chest cage injured, central nervous system depressedGAS DIFFUSION Diffusion rate Diffusion rate proportional to: surface area and partial pressure gradient Diffusion rate inversely proportional to: thickness CO2 more soluble than O2 diffuses more 20 times more rapidly Edema fluid collects in interstitial space decreased diffusion Time required for equilibrium between alveolar air and capillary blood is approximately the same for O2 and CO2 Transit time Diffusion of O2 and CO2 accomplished within 1/3 of red blood cell transit time Resting person with impaired rate of diffusion PO2 and PCO2 may be normal and O2 may still be able to diffuse during transit time During exercise blood flow increases, so transit time shorter PO2 may decrease and PCO2 may increase PULMONARY BLOOD FLOW AND VENTILATION-PERFUSSION RATIO Pulmonary circulation and blood pressure BP in pulmonary circulation lower than in systemic circulation Walls of pulmonary capillaries thinner than in systemic circulation RV pressure of 25mmHg and pumps to pulmonary arteries then falls to 0mmHg pressure in pulmonary circulation lowers to a low of 8mmHg (mean of 15mmHg) RL pressure of 120mmHg blood to RA pressure falls to 3mmHg Vascular resistance Systemic circulation: flow same - high pressure, high resistance Pulmonary circulation: flow same low pressure, high resistance o Low resistance and high compliance allows lungs to accept whole cardiac output at all times Accommodation of pulmonary blood vessels Distension blood vessels already perfused, increase their cross-sectional area o Flow increases resistance dec
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