Biology Week 10 - Respiratory System PDF

Respiratory System Florencia d. Munsayac, MD, MBA  Learning Outcomes – Describe the structures and functions of the parts of the respiratory system. – Explain how intrapleural and intrapulmonary pressures affects the process of breathing – Explain regulation of breathing – Expl...

Respiratory System Florencia d. Munsayac, MD, MBA  Learning Outcomes – Describe the structures and functions of the parts of the respiratory system. – Explain how intrapleural and intrapulmonary pressures affects the process of breathing – Explain regulation of breathing – Explain how blood gases and pH influence ventilation – Describe the conditions/factors that influence the oxyhemoglobin dissociation and oxygen transport – Explain the relationship between blood levels of CO2 and the blood pH – Describe the acid-base balance and its effects on respiration – Discuss some diseases associated with respiratory system  Organs and Structure of the Respiratory System – The respiratory system – is responsible for obtaining oxygen and getting rid of carbon dioxide, and aiding in speech production and in sensing odors – divided into two major areas: – conducting zone – respiratory zone  Organs and Structure of the Respiratory System – Conducting zone – Consists of all of the structures that provide passageways for air to travel into and out of the lungs: the nasal cavity, pharynx, trachea, bronchi, and most bronchioles – nasal passages contain the conchae and meatuses – helps to warm and humidify incoming air – removes debris and pathogens – pharynx is composed of three major sections: – nasopharynx, which is continuous with the nasal cavity – oropharynx, which borders the nasopharynx and the oral cavity – laryngopharynx, which borders the oropharynx, trachea, and esophagus  Organs and Structure of the Respiratory System – Respiratory zone – includes the structures of the lung that are directly involved in gas exchange – terminal bronchioles – alveoli – two types of alveolar cells – type I alveolar cells  comprise 95% to 97% of the total surface area of the lung  gas exchange with the blood – type II alveolar cells  cells that secrete pulmonary surfactant (discussed later) and that reabsorb Na+ and H2O  preventing fluid buildup within the alveoli  Organs and Structure of the Respiratory System – Conducting zone – composed mostly of pseudostratified ciliated columnar epithelium with goblet cells – mucus traps pathogens and debris – beating cilia move the mucus superiorly toward the throat  it is swallowed. – bronchioles to nearer the alveoli  the epithelium thins – Alveoli is simple squamous epithelium – respiratory membrane is formed by endothelium of the surrounding capillaries together with the alveolar epithelium – This is a blood-air barrier through which gas exchange occurs by simple diffusion. The Lungs – the major organs of the respiratory system – are responsible for performing gas exchange – are paired and separated into lobes – left lung consists of two lobes – right lung consists of three lobes. – blood circulation is very important  required to transport oxygen from the lungs to other tissues throughout the body – function of the pulmonary circulation is to aid in gas exchange – pulmonary artery provides deoxygenated blood to the capillaries that form respiratory membranes with the alveoli – pulmonary veins return newly oxygenated blood to the heart for further transport throughout the body The Lungs – are innervated by the parasympathetic and sympathetic nervous systems  coordinate the bronchodilation and bronchoconstriction of the airways – are enclosed by the pleura  a membrane that is composed of visceral and parietal pleural layers – pleural cavity  space between visceral and parietal layers – mesothelial cells of the pleural membrane create pleural fluid – serves as a lubricant (to reduce friction during breathing) and – as an adhesive to adhere the lungs to the thoracic wall (to facilitate movement of the lungs during ventilation)  The Process of Breathing – Respiration – Ventilation (breathing) – mechanical process that moves air into and out of the lungs – Gas exchange – occurs between the air and blood in the lungs and between blood and other tissues of the body – Oxygen utilization – Air enters  nasal passages  pharynx  valve like opening (glottis) between the vocal folds (larynx)  trachea  primary bronchi  bronchioles  alveoli The Process of Breathing  The process of Breathing – Air enters the lungs because the atmospheric pressure is greater than the intrapulmonary pressure or intra-alveolar pressure (inspiration) – An increase in lung volume during inspiration decreases intrapulmonary pressure to sub- atmospheric levels  air goes in – Expiration occurs when the intrapulmonary pressure is greater than the atmospheric pressure – A decrease in lung volume, raises the intrapulmonary pressure above that of atmosphere  expelling air from the lungs Intrapulmonary and Intrapleural Pressure Relationships Intra- – “Boyle’s law” alveolar pressure changes during the different phases of the cycle. It equalizes at 760 mm Hg but does not remain at 760 mm Hg. The Process of Breathing – Factors that influence mechanism of ventilation: – Very distensible (stretchable), aka: compliance – can expand under pressure (with ease) – 100x distensible than a toy balloon – Lung compliance – defined as the change in lung volume per change in transpulmonary pressure = – Elasticity – refers to the tendency of a structure to return to its initial size after being distended – Surface tension of the fluid in the alveoli exerts a force directed inward, which acts to resist distension – pulmonary surfactant (a combination of phospholipid and protein) lowers the surface tension sufficiently  Diseases associated with Process of Breathing – Respiratory Distress Syndrome (RDS) or Hyaline membrane disease – the lungs of premature infants collapse because of a lack of surfactant – 60% occurs in babies born less than 28 weeks of gestation – 30% in 28 – 34 weeks of gestation – < 5% after 34 weeks of gestation – Acute Respiratory Distress Syndrome (ARDS) – occurs in people with lung injury caused by septic shock – Inflammation causes increased capillary permeability  producing protein-rich fluid in the lungs  reduces compliance and surfactant production  further reduces compliance. – Bronchial asthma  Diseases associated with Process of Breathing – Pneumothorax – Occurs when air enters the pleural space/cavity  raising intrapleural pressure  lung collapses – Chronic Obstructive Pulmonary Disease (COPD) – Emphysema and Chronic bronchitis – Sleep apnea – is a chronic disorder that can occur in children or adults – is characterized by the cessation of breathing during sleep – may last for several seconds or several minutes – leads to poor sleep: fatigue, evening napping, irritability, memory problems, morning headaches, dry throat upon waking up which may be due to excessive  Gas Exchange in the Lungs – According to Dalton’s law, the total pressure of a gas mixture is equal to the sum of the pressures that each gas in the mixture would exert independently. – The partial pressure of a gas in a dry gas mixture is thus equal to the total pressure times the percent composition of that gas in the mixture. – Because the total pressure of a gas mixture decreases with altitude above sea level, the partial pressures of the constituent gases likewise decrease with altitude. – When the partial pressure of a gas in a wet gas mixture is calculated, the water vapor pressure must be taken into account.  Gas Exchange in the Lungs – According to Henry’s law, the amount of gas that can be dissolved in a fluid is directly proportional to the partial pressure of that gas in contact with the fluid. – The concentrations of oxygen and carbon dioxide that are dissolved in plasma are proportional to an electric current generated by special electrodes that react with these gases. – Normal arterial blood has a pO2 of 100 mmHg, indicating a concentration of dissolved oxygen of 0.3 ml per 100 ml of blood; the oxygen contained in red blood cells (about 19.7 ml per 100 ml of blood) does not affect the pO2 measurement.  Gas Exchange in the Lungs – According to Henry’s law, the amount of gas that can be dissolved in a fluid is directly proportional to the partial pressure of that gas in contact with the fluid. – The pO2 and pCO2 measurements of arterial blood provide information about lung function. – In addition to proper ventilation of the lungs, blood flow (perfusion) in the lungs must be adequate and matched to air flow (ventilation) in order for adequate gas exchange to occur. – Abnormally high partial pressures of gases in blood can cause a variety of disorders, including oxygen toxicity, nitrogen narcosis, and decompression sickness. Gas Exchange in the Lungs  Regulation of Breathing – The rhythmicity center in the medulla oblongata directly controls the muscles of respiration. – Activity of the inspiratory and expiratory neurons varies in a reciprocal way to produce an automatic breathing cycle. – Activity in the medulla is influenced by the apneustic and pneumotaxic centers in the pons, as well as by sensory feedback information. – Conscious breathing involves direct control by the cerebral cortex via corticospinal tracts.  Regulation of Breathing – Breathing is affected by chemoreceptors sensitive to the pO2 , pH, and pCO2 of the blood – pCO2 of the blood and consequent changes in pH are usually of greater importance than the blood pO2 in the regulation of breathing – Central chemoreceptors in the medulla oblongata are sensitive to changes in blood pCO2 because of the resultant changes in the pH of cerebrospinal fluid – Peripheral chemoreceptors in the aortic and carotid bodies are sensitive to changes in blood pCO2 indirectly, because of consequent changes in blood pH  Regulation of Breathing – Decreases in blood pO2 directly stimulate breathing only when the blood pO2 is lower than 50 mmHg. A drop in pO2 also stimulates breathing indirectly, by making the chemoreceptors more sensitive to changes in pCO2 and pH. – At tidal volumes of 1 L or more, inspiration is inhibited by stretch receptors in the lungs (the Hering-Breuer reflex)  Transport of Gases – Oxygen is primarily transported through the blood by erythrocytes  contain a metalloprotein called hemoglobin – Hemoglobin is composed of two alpha and two beta polypeptide chains and four heme groups each containing a central atom of iron – When the iron is in the reduced form and not attached to oxygen  hemoglobin is called deoxyhemoglobin – When iron is attached to oxygen  hemoglobin is called oxyhemoglobin  Transport of Gases – Oxygen is primarily transported through the blood by erythrocytes. These cells contain a metalloprotein called hemoglobin, which is composed of four subunits with a ring-like structure. – Hemoglobin is composed of two alpha and two beta polypeptide chains and four heme groups each containing a central atom of iron. – If the iron is attached to carbon monoxide  the hemoglobin is called carboxyhemoglobin – When the iron is in an oxidized state and unable to transport any gas  the hemoglobin is called methemoglobin  Transport of Gases – When all of the heme units in the blood are bound to oxygen  hemoglobin is considered to be saturated – Hemoglobin is partially saturated when only some heme units are bound to oxygen – An oxygen–hemoglobin saturation/dissociation curve is a common way to depict the relationship of how easily oxygen binds to or dissociates from hemoglobin as a function of the partial pressure of oxygen – As the partial pressure of oxygen increases  hemoglobin binds to oxygen more readily  Transport of Gases – During exercise, the venous pO2 and percent oxyhemoglobin saturation are decreased  indicating that a higher percentage of the oxyhemoglobin has unloaded its oxygen to the tissues – The pH and temperature of the blood influence the affinity of hemoglobin for oxygen – A fall in pH decreases the affinity of hemoglobin for oxygen and a rise in pH increases the affinity  called the Bohr effect – A rise in temperature decreases the affinity of hemoglobin for oxygen  indicates a greater unloading percentage of oxygen to the tissues – The affinity of hemoglobin for oxygen is also decreased by an organic molecule in the red blood cells called 2,3-diphosphoglyceric acid (2,3-DPG)  Transport of Gases – Red blood cells contain an enzyme called carbonic anhydrase that catalyzes the reversible reaction  carbon dioxide and water are used to form carbonic acid. – This reaction is favored by the high pO2 in the tissue capillaries  carbon dioxide produced by the tissues is converted into carbonic acid in the red blood cells – Carbonic acid then ionizes to form H+ and HCO3 (bicarbonate) – Low pCO2 favors the conversion of carbonic acid to carbon dioxide  exhaled  Transport of Gases – By adjusting the blood concentration of carbon dioxide, and thus of carbonic acid, the process of ventilation helps to maintain proper acid-base balance of the blood. – Normal arterial blood pH is 7.40. – pH below 7.35 is termed acidosis – pH above 7.45 is termed alkalosis – Hyperventilation causes respiratory alkalosis, and hypoventilation causes respiratory acidosis – Metabolic acidosis stimulates hyperventilation  cause a respiratory alkalosis as a partial compensation  Acid-Base Balance – The normal pH of arterial blood is 7.40, with a range of 7.35 to 7.45. – Carbon dioxide  contributes to the blood pH  referred to as a volatile acid because it can be eliminated in the exhaled breath – Nonvolatile acids  lactic acid and the ketone bodies  are buffered by bicarbonate – Blood pH is maintained by a proper ratio of carbon dioxide to bicarbonate. – Lungs maintain the correct carbon dioxide concentration – An increase in carbon dioxide due to inadequate ventilation  produces respiratory acidosis – Kidneys maintain the free-bicarbonate concentration – Abnormally low plasma bicarbonate concentration  metabolic acidosis  Acid-Base Balance – Ventilation regulates the respiratory component of acid-base balance – Hypoventilation  increases the blood pCO2  lowers the plasma pH  respiratory acidosis – Hyperventilation  decreases the plasma pCO2  decreases formation of carbonic acid  increases the plasma pH  respiratory alkalosis – Action of the chemoreceptors  breathing is regulated to maintain a proper blood pCO2 and thus a normal blood pH  Summary – Describe the structures and functions of the parts of the respiratory system. – Explain how intrapleural and intrapulmonary pressures affects the process of breathing – Explain regulation of breathing – Explain how blood gases and pH influence ventilation – Describe the conditions/factors that influence the oxyhemoglobin dissociation and oxygen transport – Explain the relationship between blood levels of CO2 and the blood pH – Describe the acid-base balance and its effects on respiration – Discuss some diseases associated with respiratory system  Thank you for listening! Stay safe everyone!