Lecture 10 (Respiratory I) PDF

Respiratory I: Structure and Function ANSC 3080 G. Bedecarrats Learning Objectives  Outline the key stages during respiration  Describe the anatomy and organization of the respiratory system  Relate the anatomy and histology of the respiratory zone t...

Respiratory I: Structure and Function ANSC 3080 G. Bedecarrats Learning Objectives  Outline the key stages during respiration  Describe the anatomy and organization of the respiratory system  Relate the anatomy and histology of the respiratory zone to gas exchange  Describe the factors influencing ventilation  Define the pulmonary volumes Function of the Respiratory System  Respiratory function: gas transport for metabolism  Move oxygen from the air into pulmonary blood  Clearance of carbon dioxide  Non-respiratory function:  Lungs receive 100% of the cardiac output from the right heart.  Filter blood, chemical processing, maintenance and defenses (part of the first line of defense)  Facilitate venous return (respiratory pump) 1  Definitions Respiration = interchanges of gases between the atmosphere and the cells of the body Ventilation (breathing) = transport of air to and from the lungs Gas exchange = O2/CO2 exchange between the air in the lungs and cells in the body Cellular respiration = oxidation of cellular molecules that produces CO2, water and ATP Overall Gas Transport 1. Ventilation: movement of bulk airflow, delivering air to the respiratory zone where gas exchange occurs 2. Gas exchange/Lung diffusion: gas exchange between respiratory zone and blood - O2 moves across to blood and red blood cells; reverse process for CO2 3. Circulation/Transport (Blood  tissues) - Requires adequate function of the pulmonary and systemic circulations 4. Tissue diffusion: Erythrocyte/plasma  tissue cells = Passive diffusion 5. Internal respiration: metabolism using O2 and producing CO2 Ventilation Air transported through the airways from the atmosphere to the respiratory zone of the lungs Airways = system of tubular structures Nasal and oral cavities Pharynx and larynx Trachea Bronchi Bronchioles Bronchioles connect to alveoli where gas exchange occurs 2  Airways Main functions:  Delivering gas to the respiratory zone (alveoli)  Conditioning of the inhaled air  Air warmed to core body temperature (prevents temperature choc in the alveoli)  Gas humidification: saturation with vapor to prevent dehydration of the respiratory epithelium in alveoli  Filtration, cleansing: prevents foreign objects and microorganisms to enter the lungs (reduces risks of injury and infection) Structure:  Nasal/Oral cavities:  Inner surface = mucous membrane that warms and humidifies air  Some species = hair in nostrils act as first filter  Epithelium contains ciliated cells and mucus cells (goblet): trap foreign objects, move the mucus towards the pharynx  Pharynx:  Connection between nasal/oral cavity and the larynx  Larynx:  Connects pharynx and the trachea: glottis and epiglottis = cartilage that prevents food to enter the trachea  Contains the vocal cords 3  Trachea:  Flexible tube kept open by cartilage rings  Inner surface lined with ciliated and mucus cells  Mucus traps particles, and coordinated cilia movements push the trash back toward the pharynx  Bronchi:  Possess cartilage plates to maintain the shape  Starts with 1 tube per lung = primary bronchi  Branches off to narrower tubes with less cartilage  Bronchioles:  Lack cartilage = depend upon lung recoil to maintain potency. Possess smooth muscle  Bronchi and bronchiole also possess ciliated and mucus producing epithelial cells 4  Muscle layers INFLAMMED AIRWAY In general 20-24 branching from trachea and the terminal alveoli Airway cross-sectional area:  Increases DRAMATICALLY moving from trachea to respiratory zone  Geometric increase in number of small airways  Reduces velocity of airflow to virtually ZERO  Movement of gas in respiratory zone by DIFFUSION only  Velocity (cm/sec) = flow (cm3/sec)/cross-section area (cm2) Airway clearance:  Cilia and globlet cells work to move thin sheet of mucus from lower parts of the lungs to the throat region  Defensins:  Airway “Lysol” – destroy bacteria; first line of defense (2nd line is immune system proper) Endoscopic View: Trachea Accumulation of mucus and pus in the trachea associated with inflammation of the lower airways Role of the environment 5  Alveoli = Respiratory Zone Clusters around terminal bronchioles Formed by a single layer of epithelial cells Adult human: covers 75-80 m2 Surrounded by a capillary network Air separated from blood by 2 layers of cells (epithelium and endothelium): best for gas exchange Some epithelial cells (type 2) produce fluid = surfactant which reduces surface tension If small particles reach alveoli = “phagocytized” by macrophages (immune defense) Thoracic Cavity Space within the thoracic cage between: Thoracic vertebras Ribs and intercostal muscles Sternum Diaphragm separate, thoracic and abdominal cavity Sheet of skeletal muscles and tendon Mediastinum Divide thoracic cage in 2 halves (from spine to sternum) Connective tissue containing vessels, nerves, trachea, esophagus and the heart Each lung fills 1 half 6  Visceral pleura Parietal pleura Thoracic Cavity Diaphragm Abdominal Cavity Abdominal Cavity Pleural membranes: wet epithelial surfaces, cover the lungs Intrapleural space filled with small amount of fluid = lubrication for friction free movements Ventilation Follows the laws of physic: flow from high to low pressure = depends on P Resistance to flow (R) due to friction of air particles with each others and with the ducts As for blood flow: F (flow) = P/R If R , P must  to maintain air flow If P , R must  to maintain air flow 7  Ventilation Pump (mechanics)  Compression/expansion of the lungs by respiratory muscles = controls P  Inspiration = active mechanism  Diaphragm contracts expands thoracic volume, creates negative pressure lung expands increase in alveolar volume negative pressure gradient facilitates flow down airways  Expiration = passive mechanism (at rest)  End of inspiration – inspiratory muscles relax, allows lung to spontaneously recoil increase pressure in alveoli create pressure gradient from alveoli to atmosphere  At rest diaphragm most important muscle  Boyle’s low of gases: for a gas at a set temperature, pressure and volume are linked: P1V1 = P2V2  If volume (V)  = pressure (P)   If volume (V)  = pressure (P)   Inspiration = P alveolar  P atmos = propels air through the airway until P alveolar = P atmos  Expiration (muscle relax, lungs recoil): P alveolar  P atmos = airflow outward until equilibrium reached Special Cases  Horses  End of expiration active beginning of inspiration passive (recoil)  Locomotion (walking running)  More than just the diaphragm and intercostal muscles involved  Muscles take active part in expiration (speeds it up)  Galloping: synchronization with breathing  Diving mammals  Voluntary apnea (up to 1 h)  Strong conducting airways  When under water, compressed gas pushed towards the air ways (no gas exchange) = prevents entry of gas in blood  Generally, do not dive with full lungs 8  Factors Influencing Ventilation  Air flow concept similar to blood flow (F = P/R)  Resistance in airways normally small  P major factor Air ways resistance:  Mostly in nasal cavity (diseases, obstruction)  During exercise, animals mainly use mouth to reduce resistance (except horses: flare nostrils)  Degree of turbulence: more turbulence = more resistance  Diameter: reduced with branching = increase resistance. Parallel branches results in increased cross/section (surface area) which compensates for increased resistance  Autonomic nervous system controls smooth muscle in bronchiole: Sympathetic relaxes cells = increased diameter Parasympathetic contracts cells = reduces diameter Lung compliance: Ability of the lung to distend followed by the ability to recoil Elastic fibers in the lung Muscle tissue in the intercostal muscles Depends on the elasticity of the tissues in the lung and the thoracic cage Depends on the surface tension in the alveoli Alveolar surface tension: Due to hydrogen bonds in water molecules when on contact with air (gives water drops their shape) Tends to reduce the surface area Since alveoli lined with moisture, it creates a surface tension against distension Reduced by the presence of SURFACTANT Mixture of phospholipids, Ca2+ and proteins Phopholipids reduce the surface tension between hydrogen molecules Barker syndrome in piglets: inadequate production of surfactant =  surface tension =  resistance to distension =  ventilation. 9  Pulmonary Volumes  Spirometer = measure volumes of air inhaled and exhaled (Spirogram = recording)  Volume flowing through airways = Tidal Volume (CVT)  Spirometer also used to monitor the respiratory frequency It is possible to further force more air during inspiration by maximum contraction of respiratory muscles = Inspiratory Reserve Volume (IRV) After normal expiration, it is possible to force more air out: Expiratory Reserve Volume (ERV) After ERV forced out, there always remains air in the lungs: Residual Volume (RV) Vital capacity (VT) is the maximum air that can be inhaled and exhaled Total lung capacity = RV + VT 10 Different Respiratory Patterns (FYI) Eupnea: normal breathing Hyperpnea: increased depth or frequency (exercise) Polypnea: increased frequency of shallow breathings (panting) Dyspnea: labored breathing Apnea: cessation of breathing 11