Physiology of the Respiratory System PDF

PHYSIOLOGY OF THE RESPIRATORY SYSTEM By Doaa Samy Professor of Physiology  1- FUNCTION, STRUCTURE OF RESPIRATORY SYSTEM * a- Function * supplies the cells of the body with O2 * removes CO2 produced by cellular activities. * b- Structure * it consis...

PHYSIOLOGY OF THE RESPIRATORY SYSTEM By Doaa Samy Professor of Physiology  1- FUNCTION, STRUCTURE OF RESPIRATORY SYSTEM * a- Function * supplies the cells of the body with O2 * removes CO2 produced by cellular activities. * b- Structure * it consists of respiratory passages which are the nose, pharynx, larynx, trachea, bronchi, bronchioles , and area of gas exchange which contains alveoli. b- Types of respiration: * 1- External respiration * 2- Internal respiration External respiration inhalation of O2 and removal of CO2  Internal respiration utilization of O2 and production of CO2 by cells (cellular respiration) 6  External respiration is divided into: 1- Pulmonary ventilation 2- Pulmonary perfusion 3- Diffusion of gases 4- Gas transport  EXTERNAL RESPIRATION 1-Ventilation 2-Diffusion 3-Perfusion The inflow and Exchange of (O2 Distribution of outflow of air and CO2) between blood through air in alveoli and the lungs blood  1- Pulmonary ventilation inflow and outflow of air between the atmosphere and the lung alveoli & distribution of air within the lung It occurs through breathing movements Regulated by respiratory centers in the brain stem  The Respiratory Airways Conducting zone Respiratory zone The airways consist of a series of branching tubes, which become narrower, shorter, and more numerous as they penetrate deeper into the lung  Functionally, the respiratory system consists of two zones: * a- The conducting zone includes all other respiratory passageways down to terminal bronchioles, which conduct air to reach the gas exchange sites * b- The respiratory zone. the actual site of gas exchange comprises the respiratory bronchioles, alveolar ducts, alveolar sacs and alveoli.  2- FUNCTIONS OF RESPIRATORY PASSAGES 1- 1- FUNCTIONS OF THE CONDUCTING ZONE * 1- Air conduction. * 2- Air conditioning (When the inspired air reaches the respiratory zone, its temperature is 37° C (body temperature) * 3- Humidification of air. (to protect delicate lung tissue from damage). * 4- Immunity (Secretion of Immunoglobulins)  2- FUNCTIONS OF RESPIRATORY PASSAGES FUNCTIONS OF THE CONDUCTING ZONE * 5- Filtration and cleaning of air. (Mucus secreted by cells of the conducting zone trap small particles in the inspired air ). * 6- Protective reflexes.(cough, sneezing) * 7- Phonation (sound protection). (The larynx produces sound When air passes across it, the vocal cords vibrate à producing sounds 2- Respiratory zone Respiratory bronchioles ➔alveolar ducts ➔ alveolar sacs ➔ alveoli Gas exchange occurs in this part. Mechanism of breathing  3- MECHANICS OF Breathing * a- Inspiration is an active process * 1- Downward movement of the diaphragm * 2- Elevation of the ribs by contraction of the external intercostal muscles * Expansion of the chest cavity ➔ rush of 500 ml (tidal volume) of air into the lungs.  3- MECHANICS OF BREATHING * b- Expiration: is a passive process * The thoracic cavity decreases in all dimensions, and elastic lungs recoil passively, causing 500 ml of air to flow out of the lungs. * N.B. * Forced expiration, as in muscular exercise, is an active process caused by the contraction of expiratory muscles, such as abdominal and internal intercostal muscles. 3- MECHANICS OF BREATHING  3- MECHANICS OF BREATHING Expansion of the chest cavity ➔ rush of 500 ml of air into the lungs Recoil of the lungs ➔ The 500 ml of air rush out of the lungs  Intra-pleural Pressure It is the pressure in the “potential space” between the lungs and chest wall (pleural space). It is a negative pressure (sub-atmospheric) Intra-pleural Pressure ØCauses of negative IPP: 1. Lack of air in the pleural cavity. 2. Elastic recoil of the lung which tends to collapse the lung. This is due to: a- the Elastic fibers of the lung tissue, which are continuously stretched and have recoil tendency. b-Surface tension of the fluid lining the alveoli. 3. Elastic properties of the chest wall, which tend to expand the thoracic cage, thus it pulls the parietal pleura outwards.  Intra-pleural Pressure ØImportance of negative IPP: 1. It helps the expansion of the lungs. 2. It is responsible for the negative intrathoracic pressure, which also helps the venous return to the heart. Ø In quiet breathing, a healthy man inspires about 500ml air/breath (tidal volume) Ø only 350ml of this volume reaches and ventilates normal alveoli. Ø The remainder 150ml fills the conducting air passage from the nose to respiratory bronchioles. Ø This volume does not take part in gas exchange with blood.  Minute Respiratory Volume Minute Ventilation at rest= Tidal volume X breathing rate = 500 ml X 12 b/min = 6000 ml/min = 6 L/min N.B. respiratory rate in adults = 12-20 b/min It is higher in children  SURFACTANT * a- Definition: It is a surface tension-lowering agent, which decreases the surface tension of the alveolar fluid. * b- Site of release: Type II alveolar epithelial cells * c-Structure: it is composed of phospholipids, proteins and calcium ions. Each phospholipid molecule has a hydrophilic head and a hydrophobic tail. The hydrophilic head dissolves in water lining the alveoli, while the hydrophobic tail is facing the alveolar air and doesn't dissolve in the fluid  d- Functions of surfactant * 1- It lowers the surface tension of alveolar fluid. * 2- It prevents lung collapse during expiration. * 3- It decreases the work of breathing. * 4- It keeps the alveoli dry. Factors affecting the formation of surfactant Factors that stimulate its formation -Thyroid hormones. -Glucocorticoid hormones. Factors that decrease its formation -Smoking. -Insulin. -Long term inhalation of pure O2. -Stoppage of the Pulmonary circulation for a long time.  Effect of surfactant deficiency * i- In adults, this results in “increased work of breathing”. * ii- In preterm infants, this results in “respiratory distress syndrome” Infant respiratory distress syndrome Absence of surfactantà difficult lung expansion at birth The surface tension is high with areas of atelectasis (collapsed alveoli), the alveoli are filled with fluid.  EXTERNAL RESPIRATION 1-Ventilation 2-Diffusion 3-Perfusion The inflow and Exchange of (O2 Distribution of outflow of air and CO2) between blood through air in alveoli and the lungs blood  2- Perfusion of the lung : Distribution of blood through the lungs. The normal volume of blood perusing the lungs is 5 L/min. = cardiac output of the right ventricle.  3- DIFFUSION OF GASES (gas transfer at lung) * a- Definition: * it is the exchange of O2 and CO2 between air in the alveoli and blood in the pulmonary capillaries * it is a passive process as it occurs according to pressure gradient of gases across alveolo-capillary (respiratory) membrane. b- Factors affecting rate of gas diffusion across respiratory membrane: * 1- Thickness of respiratory membrane. inversely proportional * 2- Surface area of the respiratory membrane. directly proportional * 3- Pressure gradient of gases across the respiratory membrane. directly proportional * 4- Solubility of gases in the respiratory membrane directly proportional * 5-Molecular weight (MW) of gases. inversely proportional  4- GAS transport q blood transports O2 from the lungs to the tissues and CO2 from the tissues to the lungs. q Gas can move from one point to another by diffusion from high-pressure to low- pressure  GAS TRANSPORT A- O2 transport * O2 is transported in 2 forms: 1- Dissolved O2: (3%) Physically dissolved in plasma It is responsible for O2 tension in the blood In arterial blood: It causes PO2 = 100 mm Hg. In venous blood: It causes PO2 = 40 mm Hg. in arterial blood. in venous blood. PO2 =100mmHg. PO2 = 40mmHg.  GAS TRANSPORT A- O2 transport * 2- Chemically combined with hemoglobin (Hb) i- It is the main form of transport; each molecule of hemoglobin carries 4 molecules of O2. II- Each 100 ml arterial blood carries about 20 ml of O2, but the tissues take only 5 ml O2/min at rest. 20ml/100ml in 15ml/100ml in arterial blood. venous blood. O2 Transport from the blood to the cells capillary RBC HB-O2 Cell Dissolved O2 Dissolved O2 diffuses to the cells è decreased PaO2 è release of O2 from HB 5 ml O2 Cells Gas Exchange in Lungs & Tissues  GAS TRANSPORT B- CO2 transport * CO2 is transported in 2 forms: 1- Dissolved CO2: (5%) Physically dissolved in plasma It is responsible for CO2 tension in the blood In arterial blood: It causes PCO2 = 40 mm Hg. In venous blood: PCO2 = 46 mm Hg. in arterial blood. in venous blood. PCO2 = 40 PCO2 = 46 mmHg. mmHg.  GAS TRANSPORT B- CO2 transport 2. Chemically combined CO2: (95%) a. Carbamino compounds: (5%) It is formed by the combination of CO2 and Hb. b. Bicarbonate: (90%) It is the major form by which CO2 is transported in the blood. KHCO3 (in the RBCs) & NaHCO3 (in the plasma)  Tidal CO2 It is the volume of CO2 that is added to each 100 ml of arterial blood during its flow through the tissues at rest. = 4ml CO2 /100 ml 4 ml CO2 Hypoxia O2 deficiency at tissue level Hypoxemia O2 deficiency in the blood  Types of hypoxia 1- Hypoxic hypoxia (decreased arterial pressure of O2 (PO2). that is caused by: i- Decreased PO2 in the inspired air as in high attitude. iii- Pulmonary diseases (hypoventilation, defective diffusion & depression of respiration) 2- Anemic hypoxia (decreased O2 carrying capacity of Hb). As in cases of: i- anemia: with reduced total Hb concentration. ii- carbon-monoxide (CO) poisoning: CO has 200 times more affinity to Hb than O2 decreasing the available amount of Hb that can carry O2. Carbon-monoxide Hb (Hb-CO is cherry red in color). 3- Stagnant hypoxia (decreased O2 supply to the tissue due to slow circulation) as in cases of heart failure. 4- Histotoxic (cytotoxic) hypoxia (decreased O2 uptake and utilization by tissues) as in cyanide poisoning that inhibits cytochrome oxidase enzyme which is necessary for O2 utilization.  Cyanosis Definition:- bluish discoloration of the skin and mucous membrane due to an abnormal increase in the amount of reduced Hb in the blood more than 5 gm/100ml. Hypoxia with Cyanosis: in hypoxic & stagnant types. Hypoxia without Cyanosis : in anemic & histotoxic types.