physio

• Briefly describe 3 functions of respiration
• Ventilation


  Breathing, mechanical process to move air in and out of lungs
• Internal respiration


  Exchange of O2 and CO2 between blood in pulmonary circulation and tissues
• External respiration


  Exchange of air between atmosphere and lungs
• The difference between internal and external respiration is that internal respiration is the exchange of O2 and CO2 between blood in pulmonary circulation and tissues, while external respiration is the exchange of air between atmosphere and lungs
• External respiration


  1. Ventilation, exchange of air between atmosphere and lungs

  2. Gas exchange by diffusion
• Internal respiration


  1. Exchange of O2 and CO2 between blood in pulmonary circulation and tissues

  2. Cellular respiration, utilization of O2 and production of CO2 from capillary blood and cells
• Conducting zone


  Includes all anatomical structures of the respiratory system
• Respiratory zone


  Region where gas exchange occurs, including respiratory bronchioles and alveoli
• The purpose of branching in the respiratory system is to increase the surface area for gas exchange
• We have many alveoli to provide a large surface area for diffusion and a short distance for gas exchange between cells
• Alveoli


  • Type I alveolar cells comprise 97% of alveolar surface area and are thin membranes that fuse with capillary membrane, providing a very short diffusion distance
  • Type II alveolar cells secrete surfactant, a substance that reduces surface tension and regulates fluid balance
• Pleura


  A wet two-layer membrane that lines the inside of the thoracic wall (parietal pleura) and covers the surface of the lungs (visceral pleura), with a pleural cavity filled with serous fluid in between
• Air flows directly proportional to pressure difference and inversely proportional to frictional resistance to flow
• Intrapulmonary pressure


  Pressure within the alveoli, changes during phases of breathing and equalizes with atmospheric pressure
• Intrapleural pressure


  Pressure within the pleural cavity, always negative and less than intrapulmonary and atmospheric pressure
• Transpulmonary pressure


  Difference between intrapulmonary and intrapleural pressures, keeps air spaces in lungs from collapsing
• During inspiration


  Transpulmonary pressure causes lungs to expand as the thoracic volume expands
• Compliance


  Distensibility or stretchability, inverse of stiffness, defined as change in lung volumes per change in transpulmonary pressure
• Elasticity


  Tendency of a structure to return to its initial size after being distended, lungs are normally very elastic due to elastin protein content
• Surface tension


  Lungs secrete and absorb fluid in two antagonistic processes, leaving a thin film of fluid on the alveolar surface
• Surfactant is important because it reduces cohesive forces between water molecules on the alveolar surface, therefore decreasing surface tension and increasing compliance so lungs expand easier
• Mechanics of breathing


  1. Inspiration: Alveolar pressure < atmospheric pressure, air flows in

  2. Expiration: Alveolar pressure > atmospheric pressure, air flows out
• Dalton's law of partial pressures


  In a mixture of gases, the total pressure is the sum of partial pressures exerted independently by each gas in the mixture
• Henry's law


  If a mixture of gases is in contact with a liquid, each gas will dissolve into the liquid in proportion to its partial pressure
• CO2 and O2 exchange at approximately the same rate across the respiratory membrane because CO2 is a lot more soluble than O2, so to move an amount of O2, CO2 can just diffuse across the membrane
• Pulmonary hypertension


  Leads to an increase in filtration pressure that enters alveoli and impedes ventilation and gas exchange, resulting in pulmonary edema (excess fluid in lungs)
• Ventilation and perfusion must be matched for efficient gas exchange, this is called ventilation-perfusion coupling
• Regulation of breathing

  1. Cerebral cortex input

  2. Pons modifies signal

  3. Apneustic area stimulates inspiratory neurons

  4. Pneumotaxic area inhibits inspiration

  5. Medulla controls respiration

  6. Rhythmicity center sets inspiratory rhythm
• Chemoreceptors


  Provide automatic control of breathing by relaying information on changes in pH, PO2 and PCO2 in the blood and brain interstitial fluid
• rhythmicitycentercontrolsautomatic breathing
• Respiratory neurons


  • Inspiratory neurons
  • Expiratory neurons
• pre Botzingercomplex clusterofcentralpattern generatingneuronsthatsetinspiratoryrhythm
• Chemoreceptors


  Provide automatic control of breathing by relaying information on change in pH of brain IF and OSF as well as blood Poz, pH and PCO2
• Chemoreceptors can be found in central cerebral cortex and peripheral carotid aortic arteries
• Chemoreceptors send sensory info to the medulla to modify rate and depth of breathing
• 9 9 99 7 released n'is
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• Ht Hoos
• Chemoreceptor sensitivity to PCO2

  Augmented by a low PO2 and decreased by high PO2