Respiratory Lecture 1 PDF

THE RESPIRATORY SYSTEM Lecture I I. OVERVIEW of FUNCTIONS II. INTRODUCTION to VENTILATION Bernard Leung [email protected] HSC1007, AY2023 Meeting ID: 958 3144 3025 Passcode: 728073  Learning O...

THE RESPIRATORY SYSTEM Lecture I I. OVERVIEW of FUNCTIONS II. INTRODUCTION to VENTILATION Bernard Leung [email protected] HSC1007, AY2023 Meeting ID: 958 3144 3025 Passcode: 728073  Learning Objectives Overview of the various components and functions in the respiratory system. How a pleural pressure is generated? How changes in alveolar pressure move air in & out of the lungs? A negative alveolar pressure is created during inspiration for airflow into the lungs. A positive alveolar pressure is created during expiration for airflow out of the lungs.  Respiration Cellular respiration is the intracellular metabolic reactions that use O2 and produce CO2 during ATP production. External respiration is the transfer of O2 and CO2 between the external environment and tissue cells. Respiratory and circulatory system function together to accomplish external respiration. Ch13, Introduction to Human Physiology, 9th Edition, L Sherwood  Functions of the respiratory system Metabolism & acid-base regulation Provides Oxygen to tissues for metabolism Removes Carbon Dioxide & regulates pH (H+ ions) (by-products of cellular metabolism) Clinical Requirements Ventilation in anaesthetised & intensive care patients, ie (paralysed by drugs etc.) Treatment of respiratory diseases eg. asthma, pneumonia, Covid-19. ‘Smokers’ lungs – Emphysema, destruction of alveolar surfaces, inadequate surface area for O2 & CO2 exchange. What else does the respiratory system do? Endocrine functions: activates hormone - Angiotensin II é Fluid retention, fluid intake é Blood pressure & volume Immunological functions: clearance of irritants/particles and potential pathogens (viruses & bacteria) Voice production by larynx (‘voice box’) Route for water loss and heat elimination Schematic diagram showing the circuitry of the cardiovascular system The arrows show the direction of blood flow, (%) of cardiac output Anatomical relationship with heart & major arteries Aorta: blood to rest of body Pulmonary (systemic circulation) trunk with L&R arteries: blood to lungs (pulmonary circulation) R L  Respiratory Airways The respiratory airways conduct air between the atmosphere and the alveoli. – nasal passages ANATOMY – pharynx Gross – Larynx Microscopic Lower Respiratory System FUNCTIONS – trachea Ventilation – right and left bronchi – bronchioles Gas exchange – alveoli Protective mechanisms For Upper/Lower Respiratory structures, please refer to Prof Karthik’s Anatomy notes* * Fundamentals of Anatomy & Physiology, 10th Edition, Martini, Pearson.  Lungs – Ventilation vs Perfusion Resin cast of the human airway tree shows the branching beginning at the trachea. Note the added pulmonary arteries (blue, deoxygenated blood) and veins (red, oxygenated blood) displayed in the left lung.  Functional relationship between Respiratory system & Circulatory system 2. Deoxgenated blood leaves heart via pulmonary arteries to lungs 1. Deoxgenated 5 blood from 3. Oxygenation 1 2 systemic of blood & 4 circulation enters 3R L release of CO2 heart in lungs (alveoli) 4. Oxygenated blood re-enters heart via pulmonary veins ® 5. Distributed to rest of body by aorta & branches  PLEURA: 2 layers Visceral pleura (lines lung) Parietal pleura (outer layer, lines chest wall and diaphragm) R Pleural space Potential space between 2 layers (layers usually in very close contact, glide over each other) Intrapleural fluid found in pleural cavity secreted by surfaces of the pleura lubricates pleural surfaces (5-15ml).  Lungs, Pleura, Diaphragm Visceral pleura: covers the 760 mm Hg lungs Parietal pleura: covers the inner thoracic wall Pleural cavity: filled with fluid Diaphragm: separates thorax from abdomen  Pressures Inter-relationships among pressures inside and outside the lungs are important in ventilation. Three pressure considerations: – atmospheric pressure (atm), 760 mmHg at sea level. – intra-alveolar pressure (intrapulmonary pressure), varies with ventilation. – intrapleural pressure, Think of a bicycle pump! 756 mmHg normally less than Atmospheric (-4 mmHg).  Pressures important in ventilation Atmospheric pressure Atmosphere The pressure exerted by the weight 760 mm Hg of the gas in the atmosphere on objects on Earth’s surface = 760 mm Hg at sea level Airways (represents all airways collectively) Intra-alveolar pressure Thoracic wall (represents The pressure within the alveoli entire thoracic cage) = 760 mm Hg when equilibrated with atmospheric pressure 760 mm Hg Pleural sac (space represents pleural cavity) Lungs (represents all alveoli Intrapleural pressure collectively) The pressure within the pleural sac 756 mm Hg The pressure exerted outside the lungs within the thoracic cavity, usually less than atmospheric pressure at 756 mm Hg Ch13, Introduction to Human Physiology, 9th Edition, L Sherwood  Air Movement – Into & Out of the Lungs No Flow Flow In Flow Out Atmospheric pressure (760 mmHg) Volume changes (lung) Pink = Intra-alveolar pressure Blue = Intrapleural pressure Pressure gradient (Patm- Palv) Air flow Ch13, Introduction to Human Physiology, 9th Edition, L Sherwood Intra-alveolar and intrapleural pressure changes throughout the respiratory cycle 1. During inspiration, intra-alveolar pressure is less than atm pressure. 2. During expiration, intra-alveolar pressure is greater than atm pressure. 3. At the end of both inspiration and expiration, intra-alveolar pressure is equal to atm pressure because the alveoli are in direct communication with the atmosphere, and air continues to flow down its pressure gradient until the two pressures equilibrate. 4. Throughout the respiratory cycle, intrapleural pressure is less than intra-alveolar pressure. 5.Thus, a transmural pressure gradient always exists, and the lung is always stretched to some degree, even during expiration. Ch13, Introduction to Human Physiology, 9th Edition, L Sherwood Intra-alveolar and intrapleural pressure changes throughout the respiratory cycle (Intrapleural pressure)* (Transmural pressure) (Intra-alveolar Pressure) The sequence during inspiration results in a fall in intra-alveolar pressure causing air to flow into the lungs. *Intrapleural/pleural; transmural/transpulmonary; Intra-alveolar/alveolar pressures.  PLEURA Pleural space Usually a potential space Can expand if filled with - excess fluid (pleural effusion) lung ie. fluid leaking from capillaries ↑ hydrostatic pressure - excess air (pneumothorax) eg. from puncture of lung (lung also collapses) Disrupts air movement into/out of lungs  Alveoli are sites of Gas exchange Physiologic, or also known as Anatomic Dead Space. Airway Generation Regarding physiological functions, the airway from the trachea to the terminal bronchioles (0-16th division) is called the conducting zone, and the area from the respiratory bronchioles to the alveolar sacs (17–23rd division) is called the transitional and respiratory zone. But this varies within normal healthy population, age & other factors. Transitional/Respiratory zone can start from 15th division onwards, ie, gas exchange!  Alveoli are sites of Gas exchange Alveolar sacs @ end of bronchioles, total of 300-500 million alveoli. Rich supply of vascular supply. Large surface area for gas exchange (≥80 X that of skin, 50-100m2). Alveolus and Surrounding Environment Elastin fiber Alveolar macrophage (Immunity/Foreign Particles) Interstitial fluid Monocyte Type II Alveolar cell (Produce Surfactant) Erythrocyte (RBC) 300 µm Alveolus Pulmonary capillary Type I Alveolar cell Alveolar fluid lining with Pulmonary surfactant 0.5 µm 0.5-µm barrier separating air and blood Ch13, Introduction to Human Physiology, 9th Edition, L Sherwood  RBC O2 Endothelial cell (capillary) 0.5 µm Basement membranes/ interstitial fluid Alveolar CO2 Epithelium Gas exchange occurs by diffusion across thin barrier (~ 0.5µm): from high ® low concentration Contact (travel) time between blood in capillary & alveolus ~ 0.75s: at rest, blood is fully oxygenated by 0.25s.  Innervation & musculature of airways Trachea & bronchi: mainly cartilage, little smooth muscle Bronchioles up to terminal bronchioles: mainly smooth muscle Bronchi & bronchioles can constrict & dilate: smooth muscles innervated by - autonomic nervous system (sympathetic - brochodilation & parasympathetic - bronchoconstriction) Asthma - excessive bronchoconstriction b2-adrenergic receptor agonist bronchodilator that relaxes the smooth muscle in the airways which allows air to flow in and out of the lungs more easily.  Protective mechanisms of airways Protection of respiratory epithelium (mucosa) Humidification of air in upper passages Mucous secretion Protection of lungs Mucociliary trapping of foreign matter Ciliary escalator Alveolar macrophages Airway reflexes eg. cough, sneeze, epiglottis closes glottis during swallowing  cilia epithelial cell globlet cell (secretes mucus) Mucus moves away from lungs Epithelium of upper airways to trachea, bronchi & bronchioles have cilia Epithelium is also covered by mucus Cilia beat to move particles away from lung (ciliary escalator) - macrophages ingest small particles which reach lung Defective ciliary movements may lead to lung infections  SUMMARY: FUNCTIONS of RESPIRATORY SYSTEM Gas exchange - Pulmonary circulation brings blood from rest of body to lungs for gas exchange - & back to heart to be distributed via the systemic circulation - Gas exchange occurs between blood in alveolar capillaries & air in alveoli Immunological & other protective functions Endocrine functions (ie angiotensin II) Voice production, water/heat lost  Break & Couple of MCQs Q1. When the diaphragm contracts, it moves inferiorly, causing _____. (a) a decrease in the volume of the thoracic cavity. (b) an increase in the volume of the thoracic cavity. (c) increased pressure in the thoracic cavity. (d) intra-pulmonary pressure remains the same. Q2. Respiratory zone of the airways where gas exchange first take place at which division? (a) 5 (b) 10 (c) 15 (d) 19  PART II: INTRODUCTION TO VENTILATION How does: Air (O2) get from the atmosphere into alveoli to reach capillary blood? Waste (CO2) get expelled from blood through lungs? Ventilation ALVEOLI Perfusion (air) Diffusion (blood) (membranes)  INTRODUCTION TO VENTILATION Ventilation Movement of air into & out of respiratory tract Does the ‘fresh air’ reach the alveoli? R L Does the ‘waste air’ leave the lungs effectively?  INTRODUCTION TO VENTILATION How do lungs move air in & out? Air is drawn in (inspired) & expelled (expired) by movements of the chest wall & lungs Chest wall: skeleton (ribs, sternum, clavicles) & muscles (diaphragm, intercostal muscles) clavicle ribs sternum intercostal muscles diaphragm  Respiratory Skeleton Muscle Activity During Inspiration and Expiration Before inspiration Inspiration External intercostal muscles (relaxed) Elevation of ribs causes sternum to move upward and outward, Sternum which increases front-to-back dimension of thoracic cavity Diaphragm Contraction of (relaxed) diaphragm Contraction of external intercostal Lowering of diaphragm on muscles causes elevation of ribs, contraction increases vertical which increases side-to-side dimension of thoracic cavity dimension of thoracic cavity  INTRODUCTION TO VENTILATION Lungs & chest wall are elastic structures Can expand ® form bigger volume ® pressure in lungs ↓ ® Intrapleural pressure? SIT Internal Can recoil ® form smaller volume PRINCIPAL MOVEMENTS FOR RESPIRATION IN ALL 3 DIMENSIONS ® pressure in lungs ↑ Increased A-P diameter Increased transverse diameter Prof Karthik’s Lecture lung Pump & Bucket handle movements Increased vertical diameter Picture courtesy: Gray’s Anatomy for students, 3rd Edition, Elsevier Ltd. Pleural Pleura cavity Diaphragm Inspiration: Quiet Expiration: Chest cavity expands: Chest cavity recoils: intrathoracic volume ↑ volume ↓ (diaphragm & inspiratory (diaphragm & inspiratory chest wall muscles contract) chest wall muscles relax) Pressures in thorax & Pressures in thorax & pleural cavity ↓ pleural cavity ↑ Lungs expand: air flows in Lungs recoil: air flows out ACTIVE PASSIVE When ventilation is stimulated eg.in exercise Other muscles are recruited (intercostals, abdominals) ® enhance movement of chest wall: Stronger inspiratory efforts Stronger expiratory efforts ► ↑ lung volumes further ► ↓ lung volumes further ► ↑ air drawn into lungs ► ↑ air expelled from lungs per unit time per unit time ACTIVE ACTIVE How do lungs move air in & out??? Ventilation: Not all inspired air undergoes gas exchange with blood - must reach alveoli! Volume of air that does not exchange with blood: Physiologic Dead Space (Anatomic Dead Space: airways up to respiratory bronchioles just short of R L alveoli) Vol. of air that reaches alveoli / min: Alveolar Ventilation Ventilation: Not all inspired air undergoes gas exchange with blood - must reach alveoli! Vol. of air that reaches alveoli / min: Alveolar Ventilation = (Tidal volume – Anatomic dead space) X Breaths per min R L  INTRODUCTION TO VENTILATION SUMMARY Ventilation is effected by changes in thoracic volumes & pressures Integrity of lungs & pleura, muscles & innervation, rib cage Alveolar ventilation is crucial Inspired air ► reach alveoli ► deliver O2 to blood Expired air (with CO2) ► expelled from alveoli  Learning Objectives Overview of the various components and functions in the respiratory system. How a pleural pressure is generated? How changes in alveolar pressure move air in & out of the lungs? A negative alveolar pressure is created during inspiration for airflow into the lungs. A positive alveolar pressure is created during expiration for airflow out of the lungs.  References The Respiratory System: Ch23, Fundamentals of Anatomy & Physiology, 10th Edition, Martini. Ch13, Introduction to Human Physiology, 9th Edition, L Sherwood. https://hstalks.com.singaporetech.remotexs.co/t/5068/introduction-to-the- respiratory-system/?biosci (approx. 32mins via SIT library). Visible Body – Launch A&P App Visible Body – Respiratory System, Ch34-37 Visible Body – Practice MCQs