Respiratory System Physiology Dr. Vedat Evren
Respiration Processes involved in oxygen transport from the atmosphere to the body tissues and the release and transportation of carbon dioxide produced in the tissues to the atmosphere 3 systems must work in coordination Respiratory system Erythrocytes Circulatory system
Respiratory System Airways Lungs Thorax and the muscles of respiration Pulmonary circulation
Pulmonary Ventilation Boyle s Law: Gas pressure in closed container is inversely proportional to volume of container Air flow is a result of pressure differences
Ventilation Movement of air in and out of lungs Inspiration (inhalation): Breathing in Expiration (exhalation): Breathing out
Main Structure
Pleura
Pleura
Pleura
Importance of Pleura
Airway Structure
Alveoli
Alveoli
Respiratory Epithelium Epithelial and Goblet cells Lines entire airway passage Moisten and protect Mucociliary clearance (1-2 cm/hour upwards) Mucus: 100 ml/day
Respiratory Epithelium
Pressures Atmospheric pressure: 760 mmhg Intrapleural pressure: 756 mmhg Intrapulmonary pressure: Varies!!! Transpulmonary pressure: Pressure difference between intrapleural and intrapulmonary pressure!!!
Inspiration Intrapulmonary pressure must decrease in order to inhale! Thoracic cavity volume increases Lung volume increases IP pressure decreases... (~758 mmhg)
Expiration Intrapulmonary pressure must increase in order to exhale Thoracic cavity volume decreases Lung volume decreases (elastic recoiling mostly) IP pressure increases... (~763 mmhg)
Pulmonary Air Flow F = P / R Diameter of airways (especially bronchioles) Autonomic innervation Sympathetic Parasympathetic
Muscles
Intercostal Muscles
Respiratory Volumes and Capacities Tidal Volume (TV): 500 ml Inspiratory reserve volume (IRV): 3000 ml Expiratory reserve volume (ERV): 1100 ml Residual volume (RV): 1200 ml
Respiratory Volumes and Capacities Inspiratory Capacity: TV + IRV Functional Residual Capacity: ERV + RV Vital Capacity: IRV + TV + ERV Total Lung Capacity: IRV + TV + ERV + RV
Surface Tension Remember (!): Properties of water molecule... Surface tension tends to oppose alveoli expansion Pulmonary surfactant reduces surface tension
Surfactant Type II alveolar epithelial cells Detergent properties Reduces surface tension Prevents collapse
Surfactant
Matching Alveolar Air Flow with Blood Flow Pulmonary vessels Vessels can constrict in areas where oxygen flow is low Respiratory passageways Airways can dilate where carbon dioxide levels are high
Perfusion Lung blood circulation 5 25 L / minute 24 / 8 mmhg
Gas Exchange Partial Pressure Each gas in atmosphere contributes to the entire atmospheric pressure, denoted as P Gases in liquid Gas enters liquid and dissolves in proportion to its partial pressure O 2 and CO 2 Exchange by DIFFUSION PO 2 is 105 mmhg in alveoli and 40 in alveolar capillaries PCO 2 is 45 in alveolar capillaries and 40 in alveoli
Partial Pressures Oxygen is 21% of atmosphere 760 mmhg x.21 = 160 mmhg PO2 This mixes with old air already in alveolus to arrive at PO 2 of 105 mmhg
Partial Pressures Carbon dioxide is.04% of atmosphere 760 mmhg x.0004 =.3 mm Hg PCO 2 This mixes with high CO 2 levels from residual volume in the alveoli to arrive at PCO 2 of 40 mmhg
Partial Pressures
Partial Pressures
Gas Transport O 2 transport in blood Hemoglobin O 2 binds to the heme group on hemoglobin, with 4 oxygen / Hb PO 2 PO 2 is the most important factor determining whether O 2 and Hb combine or dissociate O 2 - Hb Dissociation curve
Oxygen Release
Influencing Factors ph CO 2 Temperature DPG
DPG 2,3-Bisphosphoglyceric acid Present in erythrocytes 5 mmol/l Binds and stabilizes deoxyhemoglobin (T state) Can t bind to oxyhemoglobin (R state) When there is need for oxygen for the tissues, 2,3DPG increases
Curve Shift
Curve Shift
Carbon Dioxide Transport 7% in plasma 23% in carbamino compounds (bound to globin part of Hb) 70% as Bicarbonate
Carbon Dioxide (CO 2 ) + (H 2 O) (H 2 CO 3 ) (H + ) + (HCO 3- ) Enzyme is Carbonic Anhydrase Chloride shift to compensate for bicarbonate moving in and out of RBC
Controls of Respiration Medullary Rhythmicity Area Medullary Inspiratory Neurons are main control of breathing Pons neurons influence inspiration, with Pneumotaxic area limiting inspiration and Apneustic area prolonging inspiration. Lung stretch receptors limit inspiration from being too deep
Controls Medullary Rhythmicity Area Medullary Expiratory Neurons Only active with exercise and forced expiration
Controls of rate and depth of respiration Arterial PO 2 When PO 2 is VERY low, ventilation increases Arterial PCO 2 The most important regulator of ventilation, small increases in PCO 2, greatly increases ventilation Arterial ph As hydrogen ions increase, alveolar ventilation increases, but hydrogen ions cannot diffuse into CSF as well as CO 2
EXERCISE Neural signals (rate & depth) PCO 2 (PO 2 and ph) Cardiac Output Maximal Hb saturation Dilate airways