BIOH122 Human Biological Science 2 Session 11 Respiratory System 2 Pulmonary Ventilation Bioscience Department Endeavour College of Natural Health endeavour.edu.au
Session plan o Pulmonary Ventilation Inspiration Expiration Factors affecting Pulmonary ventilation Breathing Patterns Modified Respiratory Movements o Lung volumes and capacities o Exchange of oxygen and carbon dioxide External respiration Internal respiration Endeavour College of Natural Health endeavour.edu.au 2
Pulmonary Ventilation Endeavour College of Natural Health endeavour.edu.au 3
Respiration o Respiration: the exchange of gases between the atmosphere, blood, and cells. o Three basic steps: Pulmonary ventilation (breathing) External (pulmonary) respiration Internal (tissue) respiration Endeavour College of Natural Health endeavour.edu.au 4
Pulmonary Ventilation o Pulmonary ventilation/breathing: The exchange of air between the atmosphere and the alveoli o is made possible by changes in the intrathoracic pressure/volume Two phase: Inhalation/inspiration: Air moves into lungs when pressure inside the lungs is less than atmospheric pressure Exhalation/expiration: Air moves out of the lungs when pressure inside the lungs is greater than atmospheric pressure o Atmospheric pressure = 1 atm or 760 mm Hg at sea level Endeavour College of Natural Health endeavour.edu.au 5
Boyle s Law o Differences in pressure caused by changes in lung volume force air in and out. o The movement of this air is in part determined by Boyle s law Endeavour College of Natural Health endeavour.edu.au 6
Dimensions of the Chest Cavity Changes in size of thoracic cavity during inhalation and exhalation During inhalation, the ribs move upward and outward like the handle on a bucket o Breathing requires muscular activity and chest size changes o Contraction of the diaphragm flattens the dome and increases the vertical dimension of the chest Endeavour College of Natural Health endeavour.edu.au 7
o Pressure changes: Created by contraction and relaxation of respiratory muscles. o During inhalation: The diaphragm contracts, the chest expands, the lungs are pulled outward, and alveolar pressure decreases. o During exhalation: The diaphragm relaxes, the lungs recoil inward, and alveolar pressure increases, forcing air out of the lungs. Pressure changes Endeavour College of Natural Health endeavour.edu.au 8
Summary of events of inhalation and exhalation Endeavour College of Natural Health endeavour.edu.au 9
o Involves Lung expansion: Inspiration Increase in lung volume decreases the pressure in the lungs to below atmospheric pressure. Contraction of the main muscles of inhalation, the diaphragm and external intercostals Increase in the size of the thorax, decreases the intrapleural (intrathoracic) pressure allows the lungs to expand. o Expansion of the lungs decreases alveolar pressure o Air moves along the pressure gradient from the atmosphere into the lungs The fall in intrathoracic pressure allows 500 ml air to be inhaled Endeavour College of Natural Health endeavour.edu.au 10
o Forced inhalation: Inspiration Also involves accessory muscles of inspiration: sternocleidomastoids, scalenes, and pectoralis minor lift chest upwards Endeavour College of Natural Health endeavour.edu.au 11
Expiration o Decrease in lung volume increases the alveolar pressure in the lungs above atmospheric pressure. o Normal/quiet expiration: A passive process because no muscular contractions are involved. starts when the inspiratory muscles relax o Elastic recoil of the chest wall and lungs: The recoil of elastic fibers that were stretched during inhalation The inward pull of surface tension due to the film of alveolar fluid. Endeavour College of Natural Health endeavour.edu.au 12
Forced/laboured expiration: o An active process Expiration o Also invlolves contraction of the internal intercostals and abdominal muscles: Abdominal muscles force diaphragm up Internal intercostals depress ribs o Increases pressure in the abdominal region and thorax.
Factors affecting pulmonary ventilation The rate of airflow and the amount of effort needed for breathing depends on: Pressure Changes Alveolar surface tension Compliance of the lungs Airway resistance. Endeavour College of Natural Health endeavour.edu.au 14
Alveolar Surface Tension o Surface tension: Inwardly directed force exerted by a thin layer of alveolar fluid that coats the luminal surface of alveoli Causes alveoli to remain as small as possible o During inhalation: The surfactant reduces alveolar surface tension below the surface tension of pure water. Allows alveoli to fill with air o During exhalation: The surface tension which accounts for two-thirds of lung elastic recoil, decreases the size of alveoli Prevents collapse of alveoli o Respiratory Distress Syndrome: A deficiency of surfactant in premature infants Endeavour College of Natural Health endeavour.edu.au 15
Compliance of the Lungs o Compliance: The effort required to stretch the lungs and chest wall. o depends on: Elasticity of lungs Surface tension o High compliance: Lungs and chest wall expand easily o Low compliance: Lungs resist expansion o Emphysema : Destruction of elastic fibers in alveolar walls Endeavour College of Natural Health endeavour.edu.au 16
Airway Resistance o Resistance to airflow depends upon airway size o Larger-diameter airways: Have decreased resistance, and greater airflow o During exhalation: Diameter of bronchioles decreases and Airway resistance increases o Regulated by: the degree of contraction or relaxation of smooth muscle in the walls of the airways o Asthma: A disease that constricts the bronchioles and increases airway resistance Endeavour College of Natural Health endeavour.edu.au 17
Breathing Patterns o Eupnoea: normal pattern of quiet breathing consists of shallow, deep, or combined shallow and deep breathing. o Costal breathing: A pattern of shallow chest breathing that requires contraction of external intercostal, usually during need for increased ventilation, as with exercise. o Diaphragmatic breathing: A pattern of deep abdominal breathing that involves contraction and descent of the diaphragm. o Apnoea: breath holding. o Dyspnoea: painful or difficult breathing. o Tachypnoea: rapid breathing rate. Endeavour College of Natural Health endeavour.edu.au 18
Lung Volumes and Capacities Endeavour College of Natural Health endeavour.edu.au 19
Lung Volumes o Lung Volumes: Air volumes exchanged during breathing and the rate of ventilation o Pulmonary air volumes exchanged in ventilation are: Tidal volume (500 ml), Inspiratory reserve volume (3100 ml), Expiratory reserve volume (1200 ml), Residual volume (1200 ml) o The Minute Ventilation(MV): The total volume of air inhaled and exhaled each minute MV = Respiratory rate X Tidal volume Endeavour College of Natural Health endeavour.edu.au 20
Lung Volumes o Only about 350 ml of the tidal volume actually reaches the alveoli, the other 150 ml remains in the airways in the anatomical dead space. o The alveolar ventilation rate: The volume of air per minute that actually reaches the respiratory zone. o Spirometer/Respirometer: The apparatus used to measure the volume of air exchanged during breathing and the respiratory rate. The record is called a spirogram. Endeavour College of Natural Health endeavour.edu.au 21
Lung Capacities o Lung capacities: The sum of two or more specific volumes Inspiratory capacity (3600 ml), Functional residual capacity (2400 ml), Vital capacity (4800 ml) Total lung capacities (6000 ml) o Measures of Lung Function: Vital Capacity or FVC FVC decreases with Chronic Obstructive Pulmonary Disease (COPD) and restrictive airway diseases FEV 1 : The proportion of air which can be forcibly exhaled from the lungs in the first second of a forced exhalation. FEV 1 in healthy lungs is >80% FEV1 / FVC ratio differentiates obstructive vs restrictive airway disease Endeavour College of Natural Health endeavour.edu.au 22
Lung Volumes and Capacities Spirogram of lung volumes and capacities: The average values for a healthy adult male and female are indicated, with the values for a female in parentheses. The spirogram is read from right (start of record) to left (end of record). Endeavour College of Natural Health endeavour.edu.au 23
Exchange of Oxygen and Carbon Dioxide Endeavour College of Natural Health endeavour.edu.au 24
Exchange of Oxygen and Carbon Dioxide o The exchange of oxygen and carbon dioxide between alveolar air and pulmonary blood occurs via passive diffusion. o Governed by two gas laws: Dalton s law: explains how gases move down their pressure differences by diffusion Henry s law: explains how the solubility of a gas relates to its diffusion Endeavour College of Natural Health endeavour.edu.au 25
Dalton s Law o Diffusion of Gases: From areas of higher partial pressure to areas of lower partial pressure. o The greater the difference in partial pressure, the faster the rate of diffusion. Endeavour College of Natural Health endeavour.edu.au 26
Henry s Law o The quantity of a gas that will dissolve in a liquid is proportional to the partial pressure of the gas and its solubility. o The higher the partial pressure of a gas over a liquid and the higher the solubility, the more gas will stay in solution. o Solubility of CO2 is 24 times greater than that of O2, more CO2 is dissolved in blood plasma. O2 has poor solubility hence out need for an oxygen carrying molecule (haemoglobin) o Breathing O2 under pressure dissolves more O2 in the blood Endeavour College of Natural Health endeavour.edu.au 27
Henry s Law o Hyperbaric oxygenation: A major clinical application of Henry s law use of pressure to dissolve more O2 in the blood treatment for patients with anaerobic bacterial infections (tetanus and gangrene) anaerobic bacteria die in the presence of O2 o Hyperbaric chamber pressure raised to 3 to 4 atmospheres so that tissues absorb more O2 o Used to treat heart disorders, carbon monoxide poisoning, cerebral oedema, bone infections, gas embolisms and crush injuries Endeavour College of Natural Health endeavour.edu.au 28
Henry s Law o Solubility of N2 is very low at sea level, very little of it dissolves in blood plasma even though higher concentration in atmospheric air. o Scuba divers: Dive deep and the increased pressure forces more N2 to dissolve in the blood (nitrogen narcosis) Decompression sickness (the bends) occurs if diver come back to surface too fast or stay deep too long Endeavour College of Natural Health endeavour.edu.au 29
Rate of Diffusion of Gases Factors affecting rate of diffusion: o Partial pressure difference of gases in air o Surface area available for gas exchange o Diffusion distance o Solubility and molecular weight of gases Endeavour College of Natural Health endeavour.edu.au 30
External Respiration o Pulmonary gas exchange: between alveoli of the lungs and pulmonary blood capillaries o Converts deoxygenated blood coming from the right side of the heart into oxygenated blood that returns to the left side of the heart Endeavour College of Natural Health endeavour.edu.au 31
Internal Respiration o Systemic gas exchange: The exchange of O2 and CO2 between systemic capillaries and tissue cells o Converts oxygenated blood of systemic circulation into deoxygenated blood Endeavour College of Natural Health endeavour.edu.au 32
Readings and Resources o Tortora, GJ & Derrickson, B 2014. Principles of Anatomy and Physiology, 14th edn, Wiley. o Harris, P, Nagy, S & Vardaxis, N 2010, Mosby s Dictionary of Medicine, Nursing and Health Professions, 2nd edn, Mosby Elsevier. o Guyton, AC & Hall, JE 2011, Textbook of Medical Physiology, 12th edn, Saunders Elsevier. o Marieb, EN & Hoehn, K 2010, Human Anatomy and Physiology, 8th edn, Benjamin Cummings Pearson. o Moore, KL, Dalley, AF & Agur, AMR 2010, Clinically Orientated Anatomy, 6th edn, Lippincott, Williams & Wilkins. Endeavour College of Natural Health endeavour.edu.au 33
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