The Respiratory Tract

RESPIRATION 1. The Respiratory Tract A. The upper respiratory tract • Nose  lined by ciliated columnar epithelium mucus secreting cells   dense vascular network in submucosa filtering air warming air humidifying air sneezing reflex     • • Pharynx  Epiglottis Larynx   vocal cords glottis B. The lower respiratory tract • • • • • Trachea Bronchi Bronchioles Respiratory bronchioles Alveolar ducts and alveoli • Conducting zone    to warm and humidify the air to distribute the gas to serve as part of body defense system • Respiratory zone • Respiratory tract defense system    Mucocilliary transport system: mucus escalator Cough reflex Macrophages 2. The Lung Mechanics A. Lung pressures and ventilation • The thorax and respiratory muscles  thoracic cage: ribs (12), sternum, diaphragm  pleural space  respiratory muscles during inspiration: - diaphragm - external intercostal muscles - accessory muscles  respiratory muscles during expiration: - Diaphragm - internal intercostal muscles - abdominal walls • Lung pressures  Air flows because of pressure gradients pleural pressure (Ppl)    alveolar pressure (PA) Pressure changes during respiratory cycle pneumothorax  • Lung volumes and capacities           Spirometry tidal volume (VT) inspiratory reserve volume (IRV) expiratory reserve volume (ERV) residual volume (RV) inspiratory capacity (IC) functional residual capacity (FRC) vital capacity (VC) total lung capacity (TLC) forced vital capacity (FVC)  FEV1: timed forced expiratory volume in one second FEV1/FVC = 80%: more useful for detecting obstructive vs restrictive lung diseases  • • • Minute respiratory volume (V, minute ventilation) V = VT * f (respiratory rate) Dead space volume (VD) Alveolar ventilation (VA): VA = (VT - VD) * f B. Mechanical Properties of the lung • Lung Distensibility • Pressure-volume curve • Compliance (CL= DV/DP) • Pulmonary surfactant  surface tension  Laplace Law: P = 2T/r  atelectasis • Work of breathing W = force X distance Factors that affect the amount of work:    lung compliance surface tension airway resistance - R  L  /r4 - diameter of the airways Bronchoconstriction: histamine Broncodilation: CO2, EP (2 receptors) 3. Pulmonary Circulation A. Vascular pressure and blood flow • Pulmonary circulation is a low-pressure system  pulmonary arterial systemic pressure: 25 mmHg pulmonary arterial diastolic pressure: 10 mmHg mean pulmonary arterial pressure: 15 mmHg effect of the special gravity of blood on distribution of blood flow in the lung: - poor perfusion in the upper lung (functional dead space volume)    • Hypoxic vasoconstriction balances blood flow with ventilation  regional hypoxia/hypoxemia hypoxic vasoconstriction a mechanism that balances the perfusion of blood with the availability of regional ventilation effect of hypoxic vasoconstriction at the high altitude   • Exercise recruits capillaries and decreases transit time 4. Gas Uptake and Transport A. Gases diffuse through respiratory membrane • Dalton’s law: PB = PO2 + PCO2 + PN2 + PH2O + PHe…  barometric pressure: PB at the sea level = 760 mmHg partial pressures PO2 = PB X F O2 = 760 X 0.21 = 160 mmHg vapor pressure of water PO2 in alveolar gas and venous blood: 100/40 mmHg     Gas exchange:alveoli and cells • Factors that affect the rate of gas diffusion through the respiratory membrane  thickness of respiratory membrane (alveolar-capillary membrane): normally 0.1 - 0.5 µm  pulmonary edema  fibrosis of the lung  surface area of the respiratory membrane: 70 m2 in the normal adult  emphysema (dissolution of alveolar walls) diffusion coefficient  solubility in water  molecular weight  carbon dioxide diffuses 20 times as rapidly as oxygen   pressure difference across the respiratory membrane Respiratory membrane • Pulmonary pathologies B. Transport of oxygen • • Transport of oxygen in the dissolved state  only 2% of oxygen transported in the dissolved state in the water of the plasma and cells Transport of oxygen by hemoglobin  98% oxygen is carried to the tissues by reversible combination with hemoglobin oxygen carrying capacity: 20 ml/100ml blood oxygen saturation: percent O2 saturation = O2 content/O2 capacity x 100 oxyhemoglobin dissociation curve factors that affect the oxyhemoglobin curve     Oxygen-hemoglobin dissociation "2,3-DPG and oxygen/Hb binding" • Factors that affect the oxyhemoglobin curve • Factors contributing to the total oxygen content of arterial blood C. Transport of carbon dioxide • • • Dissolved in plasma: (7-10%) Carbaminohemoglobin: (15-30%) As bicarbonate: (60-70%)  CO2 + H2O H2CO3 H+ + HCO3catalyzed carbonic anhydrase H+ + Hbchloride shift HHb   D. Control of Breathing • Neural mechanisms  Medullary respiratory centers inspiratory neurons: set the rhythm expiratory neurons  receive synaptic inputs from the cortex and pons  effects of pulmonary stretch receptors (proprioreceptors) failure of the respiratory center by physical damages (concussions, cerebral edema) by overdose of chemical substances (barbiturate, anesthetics)  • Reflex control of ventilation   Chemoreceptors monitor blood gases and pH Control centers in the brain stem regulate activity to respiratory muscles • Chemical mechanisms  chemoreceptors central chemoreceptors (in the medulla): monitor only H+ in CSF peripheral chemoreceptors (aortic bodies and carotid bodies)  control of the alveolar ventilation by the arterial CO2  control of the alveolar ventilation by the arterial H+: exclusively by peripheral chemoreceptors control of the alveolar ventilation by the hypoxia: relatively insensitive to hypoxia  Carotid body oxygen sensor Central chemoreceptor Chemoreceptor reflex