NURS1108 Lecture 15 - Respiratory System.pptx

NURS1108: Introduction to Anatomy & Physiology Dr. Jermaine H. Whyte FMS- UWI [email protected] Respiratory System Objectives • Explain the physiology of ventilation, arterialisation, alveolar exchange, and gas transport; • Name the instruments used to measure lung volumes; • Relate...

NURS1108: Introduction to Anatomy & Physiology Dr. Jermaine H. Whyte FMS- UWI [email protected] Respiratory System Objectives • Explain the physiology of ventilation, arterialisation, alveolar exchange, and gas transport; • Name the instruments used to measure lung volumes; • Relate one law concerning gas to the internal respiratory process; • Outline the role of the respiratory system in the maintenance of acid-base balance; • Describe the physiological factors which regulate respiration; • Discuss the physiology of speech. Content 4. Functions of the respiratory system • • • • Ventiltion of the lungs Extraction of oxygen from the air & transfer to bloodstream Excretion of carbon dioxide & water vapour Maintenance of acid base of the blood 5. Physiology of respiration • • • • • • Pulmonary ventilation External respiration Transport of respiratory gases Internal respiration Types of breathing • • • Dalton’s law Boyle’s law Gaseous exchange in lungs 7. Diagnostic instrument (s) used in measuring lung volume 8. Regulation of respiration 9. Role of respiratory system in maintaining acid-base balance • • • • pH of blood Oxygen Carbon dioxide Haemoglobin Breathing Mechanism • Breathing or ventilation is the movement of air from outside of the body into the bronchial tree and the alveoli • The actions responsible for these air movements are inspiration, or inhalation, and expiration, or exhalation 5 Pulmonary Ventilation • First step in chain of events that takes oxygen from air into the interior of cells o Called inspiration • Last step in ridding body of carbon dioxide generated by metabolic processes of life o Called expiration • Air moves down pressure gradients from a region of higher pressure to a region of lower pressure Boyle’s Law • States that the pressure and volume of gas are inversely proportional o If volume decreases, pressure increases proportionally and vice versa • The product of pressure and volume is constant for a given number of gas molecules in an enclosed space (k): o pV = k • Intrapulmonary pressure is the pressure of air in the lungs Boyle’s Law and Air Flow Inspiration • Atmospheric pressure due to the weight of the air is the force that moves air into the lungs • At sea level, atmospheric pressure is 760 millimeters of mercury (mm Hg) • Moving the plunger of a syringe causes air to move in or out • Air movements in and out of the lungs occur in much the same way Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Air passageway Atmospheric pressure of 760 mm Hg on the outside Atmospheric pressure of 760 mm Hg on the inside Diaphragm Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 9 (a) (b) Inspiration • Intra-alveolar pressure decreases to about 758mm Hg as the thoracic cavity enlarges due to diaphragm downward movement caused by impulses carried by the phrenic nerves • Atmospheric pressure then forces air into the airways Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Atmospheric pressure (760 mm Hg) Intra-alveolar pressure (760 mm Hg) Intra-alveolar pressure (758 mm Hg) Diaphragm (a) (b) 10 Inspiration Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sternocleidomastoid elevates sternum Sternum moves Up and out Pectoralis minor elevates ribs External intercostal muscles pull ribs up and out Diaphragm contracts (a) Diaphragm contracts more (b) 11 12 Expiration • The forces responsible for normal resting expiration come from elastic recoil of lung tissues and from surface tension • These factors increase the intra-alveolar pressure about 1 mm Hg above atmospheric pressure forcing air out of the lungs 13 Expiration Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Posterior internal intercostal muscles pull ribs down and inward Diaphragm Diaphragm Abdominal organs recoil and press diaphragm upward Abdominal organs force diaphragm higher Abdominal wall muscles contract and compress abdominal organs (a) (b) 14 15 The Respiratory Cycle Muscles • Skeletal muscles of the diaphragm, chest wall, neck, and/or abdominal wall contract to enlarge or reduce the volume of the chest cavity and, with it, the volume of the lungs. • Scalene and sternocleidomastoid muscles of the neck suspend the sternum and first ribs from the skull o They elevate rib cage when they contract Muscles • Other ribs are suspended from those above by two sets of intercostal muscles • Transition point is the inward recoil of the lungs, perfectly balanced by the outward forces exerted by the chest wall • Inhalation expands chest volume away from the transition point, which requires the activity of three muscle groups Muscles Muscles • The muscles of forced expiration actively reduce the size of the thoracic cavity below its “resting size.” • Eupnea is quiet breathing o Exhalation during eupnea is passive Rate and Depth of Breathing • Normal person breathes about 12 times per minute at rest o Each breath moves about 500 mL of air into and out of conducting zone and respiratory zone • Referred to as tidal volume o Total amount of air moved into and out of lungs during one minute is called minute ventilation o About 70% reaches respiratory zone o About 30% remains in conducting zone • Constitutes anatomical dead space • No gas exchange Rate and Depth of Breathing • Alveolar ventilation rate (AVR) is calculated like minute ventilation (rate × volume) but uses fresh air in the calculation: o AVR = (tidal volume – dead space) × respiratory rate o For normal person: • AVR = (500 mL – 150 mL) × 12 = 4,200 mL (4.2 L) • Dead space is constant during deep breathing o Extra fresh air enters respiratory zone Ventilation • Physical factors can interfere with easy filling and emptying • Three important factors: 1. The ability of the diaphragm and the muscles of the torso to change the volume of the chest cavity 2. The ability of the lungs to respond to musculoskeletal forces 3. The ability of the airways to accommodate airflow • Muscle paralysis affects ventilation o Mechanical ventilatory assistance can be used • Compliance o Ease with which the lungs can be distended to accommodate increased volume Ventilation • Elastance o Ability of the lungs to return to their original dimension at the transition point • Air resistance affects ventilation o Asthma • Can be caused by inhaled irritants, allergens, cold air, an underlying viral infection, anxiety, or exercise • Bronchiolar muscle contraction and excessive mucus production which narrows and obstructs bronchioles • Spirometer o Instrument that quantifies the volume and rate of airflow into and out of the lungs Respiratory Air Volumes and Capacities • Different degrees of effort in breathing move different volumes of air in and out of the lungs • This measurement of volumes is called spirometry Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 6,000 Lung volume in milliliters (mL) 5,000 Inspiratory reserve volume Vital capacity 4,000 3,000 2,000 1,000 0 Tidal volume Residual volume Expiratory reserve volume Inspiratory capacity Total lung capacity Functional residual capacity 26 Ventilation • Spirogram o Recorded result of spirometer 28 Ventilation • Inspiratory capacity o Volume of air inhaled from the transition point • Inspiratory reserve volume o Extra amount of air inhaled above the tidal volume • Vital capacity o Total amount of air that can be moved in one breath with maximum inhalation and maximum exhalation • Total lung capacity o The entire volume of air that the lungs can hold Alveolar Ventilation • The volume of new atmospheric air moved into the respiratory passages each minute is minute ventilation • It equals the tidal volume multiplied by the breathing rate 30 Alveolar Ventilation • Much of the new air remains in the physiologic dead space • The tidal volume minus the physiologic dead space then multiplied by breathing rate is the alveolar ventilation rate • This is the volume of air that reaches the alveoli • This impacts the concentrations of oxygen and carbon dioxide in the alveoli 31 Nonrespiratory Air Movements • Air movements other than breathing are called nonrespiratory movements • They clear air passages, as in coughing and sneezing, or express emotions, as in laughing and crying 32 33 Control of Breathing • Normal breathing is a rhythmic, involuntary act that continues when a person is unconscious • Respiratory muscles can be controlled as well voluntarily 34 Respiratory Areas • Groups of neurons in the brainstem comprise the respiratory areas that control breathing • Impulses travel on cranial nerves and spinal nerves, causing inspiration and expiration • Respiratory areas also adjust the rate and depth of breathing • The respiratory areas include: • Respiratory center of the medulla • Respiratory group of the pons Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Midbrain Fourth ventricle Pontine respiratory group Pons Medulla oblongata Ventral respiratory group Dorsal respiratory group Medullary respiratory center Internal (expiratory) intercostal muscles External (inspiratory) intercostal muscles Diaphragm 35 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Respiratory areas Pontine respiratory group Medullary respiratory center Ventral respiratory group Dorsal respiratory group Nerve impulses Nerve impulses Respiratory muscles Basic rhythm of breathing Forceful breathing 36 The Control of Respiration • Respiratory rhythm is controlled by the brainstem • Respiratory center o Collection of neurons in the brainstem that initiates the cycle and modulates it in response to chemical or physical factors • Ventral respiratory group (VRG) o Sets the basic respiratory rhythm • Unconscious ventilation is regulated by central chemoreceptors in the medulla and, to a lesser extent, the peripheral chemoreceptors in the aortic arch and carotid arteries Respiratory Control Centers Central Chemoreceptors Factors that Affect or Modulate Breathing • pH, PCO2, and PO2 • Other factors: o Limbic system: fear and other emotions o Proprioceptive receptors: exercise o Body temperature: fever/hypothermia o Pain: prolonged somatic pain stimulates respiration while visceral pain suppresses it o Irritants: inhaled irritants stimulate coughing o Inflation reflex Factors Affecting Breathing • A number of factors affect breathing rate and depth including: • Partial pressure of oxygen (Po2) • Partial pressure of carbon dioxide (Pco2) • Degree of stretch of lung tissue • Emotional state • Level of physical activity • Receptors involved include mechanoreceptors and central and peripheral chemoreceptors Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Medulla oblongata Sensory nerve (branch of glossopharyngeal nerve) Carotid bodies Sensory nerve (branch of vagus nerve) Common carotid artery Aorta Aortic bodies Heart 41 Factors Affecting Breathing • Changes in blood pH, O2 and CO2 concentration stimulates chemoreceptors • Motor impulses can travel from the respiratory center to the diaphragm and external intercostal muscles • Contraction of these muscles causes the lungs to expand stimulating mechanoreceptors in the lungs • Inhibitory impulses from the mechanoreceptors back to the respiratory center prevent overinflation of the lungs Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Respiratory center Spinal cord – Sensory pathway – Motor pathways Vagus nerve Phrenic nerve External intercostal muscles Intercostal nerve Stretch receptors Rib Lung Diaphragm 42 43 Gas Exchange and Transport • Involves partial pressure gradients • Partial pressure is the pressure for a specific gas o Depends on two elements: • Concentration • Solubility Gas Exchange and Transport • Gas diffusion across the pulmonary membrane depends on two main factors: o The partial pressure gradients between alveolar air and blood o The health of lung tissue • Larger pressure gradients increase gas exchange o Partial pressure of oxygen is higher in the alveolus than in blood arriving at the lungs o Oxygen diffuses down its partial pressure gradient from the alveolus to the blood Alveolar Gas Exchanges • The alveoli are the sites of the vital process of gas exchange between the air and the blood 46 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Type I (squamous epithelial) cell of alveolar wall Type II (surfactantsecreting) cell Fluid with surfactant Macrophage Alveolus Respiratory membrane Cell of capillary wall Capillary lumen Alveolar fluid (with surfactant) Alveolar epithelium Alveolus Basement membrane of alveolar epithelium Interstitial space Respiratory membrane Basement membrane of capillary endothelium Capillary endothelium Diffusion of O2 Diffusion of CO2 Red blood cell Capillary 47 Respiratory Membrane • Part of the wall of an alveolus is made up of cells (type II cells) that secrete pulmonary surfactant • The bulk of the wall of an alveolus consists of a layer of simple squamous epithelium (type I cells) • Both of these layers make up the respiratory 48 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. EP AS BM RBC AS IS © Imagingbody.com 49 Gas Exchange and Transport • Partial pressures in pulmonary veins and alveolar air are the same. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Alveolus Diffusion of CO2 Alveolar wall PCO = 40 mm Hg 2 PCO = 45 mm Hg 2 PO = 104 mm Hg 2 Diffusion of O2 PO = 40 mm Hg 2 Blood flow (from body tissues) Blood flow (to body tissues) Capillary PCO = 40 mm Hg PO = 104 mm Hg 2 2 51 Diffusion Through the Respiratory Membrane • Molecules diffuse from regions where they are in higher concentration toward regions where they are in lower concentration • It is important to know the concentration gradient • In respiration, think in terms of gas partial pressures • Gases diffuse from areas of higher partial 52 Diffusion Through the Respiratory Membrane • The respiratory membrane is normally thin and gas exchange is rapid • Increased diffusion is favored with more surface area, shorter distance, greater solubility of gases and a steeper partial pressure gradient • Decreased diffusion occurs from decreased surface area 53 Gas Transport • Blood transports O2 and CO2 between the lungs and the body cells • As the gases enter the blood, they dissolve in the plasma or chemically combine with other atoms or molecules 54 Oxygen Transport • Almost all oxygen carried in the blood is bound to the protein hemoglobin in the form of oxyhemoglobin • Chemical bonds between O2 and hemoglobin are relatively unstable • Oxyhemoglobin releases O2 into the body cells • About 75% of the O2 remains bound to hemoglobin in the venous blood ensuring safe CO2 levels and thereby pH 55 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Alveolus Capillary Hemoglobin molecules Oxygen molecules Blood flow (to lungs) Oxyhemoglobin molecule Diffusion of oxygen Hemoglobin molecules Blood PO = 40 mm Hg 2 2 Alveolar wall Blood flow (from body tissues) (a) Blood PO = 95 mm Hg Diffusion of oxygen Tissue cells Tissue PO = 40 mm Hg 2 (b) 56 Oxygen Transport and External Gas Exchange Oxygen loading happens in the lungs • • Unloading happens in body cells Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 100 % saturation of hemoglobin 90 80 70 60 50 40 30 20 10 0 10 20 30 40 50 60 70 80 PO2(mm Hg) 90 100 110 120 130 140 Oxyhemoglobin dissociation at 38°C 58 • The amount of oxygen released from oxyhemoglobin increases with: Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 100 90 70 PCO = 60 2 20 mm Hg 40 mm Hg 80 mm Hg 50 40 30 20 10 10 20 30 40 50 60 70 80 PO (mm Hg) 90 100 110 120 130 140 2 Oxyhemoglobin dissociation at 38°C Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 100 90 80 70 pH = 60 7.6 50 7.4 7.2 40 30 20 10 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 0 10 20 30 40 50 60 70 80 90 100 PO2 (mm Hg) Oxyhemoglobin dissociation at 38°C 1 10 120 130 140 100 C 0° 90 °C 10 80 % saturation of hemoglobin 0 % saturation of hemoglobin % saturation of hemoglobin 80 °C 20 30 70 60 °C °C 38 43 50 °C 40 30 20 10 0 10 5930 20 40 50 60 70 80 PO2 (mm Hg) 90 100 110 120 Oxyhemoglobin dissociation at various temperatures 130 140 59 Carbon Dioxide Transport • Blood flowing through capillaries gains CO2 because the tissues have a high Pco2 • The CO2 is transported to the lungs in one of three forms: • As CO2 dissolved in plasma • As part of a compound with hemoglobin • As part of a bicarbonate ion 60 Carbon Dioxide Transport • Loading happens in tissues and unloading in lungs Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Tissue cell Tissue PCO2 = 45 mm Hg Cellular CO2 CO2 dissolved in plasma PCO = 40 mm Hg 2 Blood flow from systemic arteriole CO2 + H2O CO2 combined with hemoglobin to form carbaminohemoglobin H2CO3 PCO = 45 mm Hg HCO + H 3 + 2 + H combines with hemoglobin HCO3- Plasma Red blood cell Blood flow to systemic venule Capillary wall 62 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Capillary wall Cl- Red blood cell HCO3- Plasma Cl- HCO3HCO3Cl- 63 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Alveolus PCO = 40 mm Hg 2 CO2 CO2dissolved in plasma CO2 + H2O PCO = 45 mm Hg 2 Blood flow from pulmonary arteriole 3 H2CO3 CO2 Carbaminohemoglobin + H+ released from hemoglobin Red blood cell PCO = 40 mm Hg 2 HCO + H HCO3- Plasma CO2 Alveolar wall CO2 + hemoglobin Blood flow to pulmonary venule Capillary wall 64 65 Lifespan Changes • Lifespan changes reflect an accumulation of environmental influences and the effects of aging in other organ systems, and may include: • The cilia become less active • Mucous thickening • Swallowing, gagging, and coughing reflexes slowing • Macrophages in the lungs lose efficiency • An increased susceptibility to respiratory infections • A “barrel chest” may develop • Bronchial walls thin and collapse • Dead space increasing 66 Clinical Application The Effects of Cigarette Smoking on the Respiratory System • cilia disappear • excess mucus produced • lung congestion increases lung infections • lining of bronchioles thicken • bronchioles lose elasticity • emphysema fifteen times more common • lung cancer more common • much damage repaired when smoking stops 67