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Module 10-Respiratory System.pdf

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Physiology 2130
Anita Woods

Module 10 - Respiratory System Functions • Transport of oxygen from air into blood • Removal of CO2 from blood into air • Control of the blood acidity (pH) • Temperature regulation • Defense to airborne particles Anatomy • Lungs located in thoracic cavity, surrounded by rib cage and diaphragm • Airways: nasal cavity and mouth, joining at pharynx. Pharynx leads to larynx (voice box) which becomes trachea. Trachea divides into two main bronchi (left and right), which continually divide into smaller and smaller bronchioles. These continually divide and end in alveoli. • Alveoli are site of gas exchange • Pulmonary artery (deoxygenated blood to lungs) branches to form dense network of capillaries around alveolus • Structure of capillary and blood flow characteristics maximize gas exchange • Characteristics: thin endothelial walls, large total cross-sectional area, and very low blood velocity • In capillaries, oxygen diffuses into blood and CO2 out • O2 rich blood flows to left side of the heart through pulmonary vein • ~300 million alveoli in human lung, diameter of ~0.3 mm • Walls of alveoli one cell thick and composed of alveolar epithelial cells (type I cells) • Type II cells secrete surfactant (fluid) that lines alveoli • Region between alveolar space and capillary lumen is respiratory membrane. Narrow as 0.3 microns • Cells of immune system, include microphages and lymphocytes, protecting from airborne particles going into alveoli • Fibers of elastin & collagen in walls of alveoli, around blood vessels and bronchi Intrapleural Pressure • Two thin pleural membranes: one lines and sticks to ribs (parietal pleura), other surrounds and sticks to lungs (visceral pleura) • Form intrapleural space containing pleural fluid (~10-15 mL) • Fluid reduces friction between pleural membranes during breathing Alveolar & Atmospheric Pressure • Pressure inside lungs is called alveolar (intrapulmonary) pressure. 760 mmHg • Pressure in between intrapleural space is called intrapleural pressure. 756 mmHg. Chest wall and lungs moving in opposite directions cause lower pressure. • Atmospheric pressure, outside body is 760 mmHg at sea level. Transpulmonary Pressure: difference between alveolar and intrapleural pressure Transpulmonary pressure = Alveolar pressure - Intrapleural pressure • Difference in pressure holds lungs open (+4 mmHg) • Healthy lungs, transpulmonary pressure is positive and keeps lungs and alveoli open Pneumothorax • If transpulmonary pressure = 0 mmHg, no pressure holding lungs open and they would collapse, producing pneumothorax • Occurs when intrapleural space punctured causing alveolar & intrapleural pressure to be 760 mmHg • Generally only one lung collapses because intrapleural space of each lung isolated form each other Boyle’s Law: volume of a container decreases, pressure inside increases (and vice- versa) Pressure α 1/Volume Ventilation - Inspiration and Expiration • Moving air into lungs requires pressure gradient, in lungs it’s air pressure gradient • Alveolar pressure is what changes • Inspiration: high pressure outside lungs - air moves in. Intrapulmonary = 757 mmHg Expiration: high pressure inside lungs - air moves out. Intrapulmonary = 763 mmHg • Mechanisms of Inspiration • Diaphragm contracts and moves down • External intercostal muscles of the rib contract lifting rib cage up and out • Causes lung volume to increase causing alveolar pressure to drop (759 mmHg) Results in air flowing into lungs • • Contraction of respiratory muscles is an active process from respiratory center of brainstem Mechanisms of Expiration At rest: Diaphragm and external intercostal muscles relax causing lungs to original size • • Volume decreases and alveolar pressure increases to 761 mmHg, air flows out • Passive process since no muscular contractions During exercise: • Air forced out by abdominal muscles and internal intercostal muscles When contracted, decrease volume of lungs and pressure increases to 763 mmHg • Pulmonary Compliance: stretchability of the lungs, volume change that occurs as a result of pressure change. Compliance = volume change/ pressure change • Determines the ease of breathing. Lower compliance, difficult to inflate. High compliance, easy to inflate but can be difficult to deflate. Major factors influencing compliance: • Amount of elastic tissue found in walls of alveoli, blood vessels and bronchi • Surface tension of the film of liquid that is lining all the alveoli • Both decrease compliance by tending to collapse lungs making breathing difficult • Pulmonary fibrosis is a disease that causes s decrease in compliance • Normal aging and pulmonary emphysema both increase compliance Pulmonary Compliance - Elastic Tissue Components • Elastin and collagen fibers in alveoli, blood vessels and bronchioles • Arranged (weave) where elastin fibers are easily stretched but collagen fibers aren’t • Arrangement contributes 1/3 of total compliance (elastic behavior) of healthy lung • More elastin, less compliant Pulmonary Compliance - Surface Tension • 2/3 of elastic behavior from surface tension of liquid film lining the alveoli • ST of thin film tends to collapse alveoli, decreasing compliance and making inflation difficult • Surface tension: force developed at surface of liquid due to attractive force between water molecules • Majority of forces between water molecules in drop of water are inward. No outward balancing force at surface of the water • Overall effect is to pull the water molecules into a tight ball Pulmonary Compliance - Pulmonary Surfactant • Lipoprotein substance produced by Type II (great) alveolar cells consisting of mainly phospholipids • Surfactant molecule has hydrophilic head and hydrophobic tail • When added to water, lies on the surface at air-water interface • Phospholipid head will be attracted to water water molecules and will balance inward force with an outward one • Water drop flattens out due to balanced force and decreased surface tension • Pulmonary surfactant released form Type II cells during deep breathing Infant Respiratory Distress Syndrome: • Premature babies before 36 weeks do not produce proper amounts of surfactant • Alveoli tend to collapse, making it very difficult to inhale • Expend incredible amounts of energy inflating their lungs and can die from exhaustion • To avoid this, premature babies receive a dose of surfactant directly into lungs at birth Lung Volume • Maximum amount of air our lungs can hold is ~5 L (not the amount every breath) • Device used to measure lung volume and capacities is a Spirometer • Spirometers also useful for diagnosing pulmonary diseases like asthma, bronchitis and emphysema Lung Capacities Four basic lung volumes and lung capacities. Capacity consists of two or more lung volumes. Volumes: 1. Tidal Volume: Volume of air entering or leaving the lungs during one breath at rest (500 mL) 2. Inspiratory reserve volume: Maximum amount of air that can enter the lungs in addition to tidal volume (2500 mL) 3. Expiratory reserve volume: Maximum amount of air that can be exhaled beyond the tidal volume (1000 mL) 4. Residual Volume: Remaining air in the lungs after a maximal expiration (1200 mL) Capacities 1. Inspiratory capacity: Maximum amount of air that can be inhaled after exhalation of tidal volume (tidal volume + inspiratory reserve volume) 2. Functional residual capacity: Amount of air still in the lungs after exhalation of tidal volume (expiratory reserve volume + residual volume) 3. Vital capacity: Maximum amount of air that can be exhaled after a maximal inhalation (inspiratory reserve volume + tidal volume + expiratory reserve volume) 4. Total lung capacity: Maximum amount of air that lungs can hold (vital capacity + residual volume) Pulmonary Ventilation (VE): Amount of air that enters all of the conducting and respiratory zones in one minute. Determines amount of air (and O2) available in the body. - Conducting zone (anatomical dead space) area of the lungs where no gas exchange takes place (no alveoli, i.e. trachea, primary bronchi, smaller bronchi and bronchioles) - Respiratory zone is region where alveoli are located VE = Tidal Volume (mL) x Respiratory Rate (breaths/min) • VE at rest is ~ 7500 mL/min. Alve
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