Physiology

• Respiration


  O2/CO2 exchange; regulates pH

  
• Ventilation


  1. Inspiration

  2. Expiration
• External respiration


  Within alveoli
• Internal respiration


  Gas exchange in tissues

  
• Respiratory system anatomy


  • Nasal cavity
  • Naso-, oro-, laryngopharynx
  • Larynx
  • Trachea
  • Bronchi (1°,2°,3°)
  • Bronchioles
  • Alveoli
• Mucus


  • Trap particulates in airstream
• Cilia


  • Beat, produce directed movement
  • Within nasal cavity - beat downward
  • Within trachea - beat upward
  • Sneeze (CN V) & cough (CN X) - aid in this process
• Air must be warmed & humidified on its way down to the lungs
• Nasal mucosa is well-vascularized & performs this function
• Pleural cavity


  • Pleural fluid - lubricant, ↓ friction as membranes slide past one another
  • Holds visceral/parietal pleura together - ∴lungs stretch when thorax expands
• Trachea


  • Lined with pseudostratified ciliated columnar epithelium (mucociliary escalator)
  • Reinforced by C-shaped cartilage rings (open except when swallowing)
• Bronchioles


  • Lined with ciliated epithelium that becomes simple squamous epithelium
  • No cartilage support, smooth muscle present (constricts during asthma attack)
• Alveoli


  • Simple squamous epithelium, performs diffusion function
  • Secretory cells - produce surfactants
  • Dust cells - macrophages, defensive function
• Diaphragm


  • 1° muscle of ventilation
  • When contracted, pulled downward (flattens) ! ↑ volume/↓ pressure of thorax ! inspiration
  • When relaxed, returns to dome-shaped position ! ↓ volume/↑ pressure of thorax ! expiration

  
• Ventilation


  1. Requires a pressure gradient

  2. Air flows from high P ! low P area

  3. Compare intrapulmonary P vs. atmospheric P

  4. Boyle's Law - P & V are inversely proportional to one another

  
• At end of respiration cycle

  Pintrapulmonary = Patm, ∴ no air movement
• During inspiration


  Pintrapulmonary < Patm, ∴ air moves into lungs
• During expiration


  Pintrapulmonary > Patm, ∴air moves out of lungs
• Lungs contain elastic tissue ! stretch/recoil with changing thoracic volume
• Inspiration


  Inspiratory muscles contract ! ↑ Vthorax ! ↑ Vlungs ! ↓ Pintrapulmonary (stretch)

  
• Expiration


  Diaphragm relaxes ! ↓ Vthorax ! ↓ Vlungs ! ↑ Pintrapulmonary (recoil)
• Factors preventing lung collapse

  • Surfactants - reduce surface tension within alveoli
  • Negative intrapleural P - P within pleural cavity ~ 2mmHg below Patm
  • Residual volume - air that remains in the lungs after expiration
• Pneumothorax - air introduced into the pleural cavity ! lungs collapse
• Pulmonary volumes


  • TV (tidal volume) = 500 ml
  • IRV = 3000 ml
  • ERV = 1100 ml
  • RV = 1200 ml
  • Inspiratory capacity (IC) = 3500 ml
  • Functional residual capacity = 2300 ml
  • Vital capacity (VC) = 4600 ml
  • Total lung capacity (TLC) = 5800 ml
  • Minute respiratory volume (MRV) = 6 L/min
  • Anatomical/physiological dead space = 150 ml
  • Alveolar ventilation rate = 4.2 L/min
• Quiet vs. forced respiration - inspiration & forced expiration = active processes, ATP, quiet expiration = passive process, no ATP
• Compliance


  Measure of expansibility of lungs and thorax
• Respiratory membrane


  • Thin, large surface area; facilitates gas exchange
  • Components: surfactant/fluid layer, alveolar simple squamous epithelium, basement membrane, thin interstitial space, blood capillary basement membrane, blood capillary endothelium (simple squamous epithelium), RBC membrane
• Factors influencing rate of gas exchange across respiratory membrane

  • Thickness - ↑ thickness ! ↓ rate of diffusion
  • Surface area - ↓ surface area ! ↓ rate of diffusion
  • Partial pressure difference - as ↑ P1 - P2 ! ↑ rate of diffusion
  • Diffusion coefficient - depends upon the size/solubility of O2/CO2 in H2O

  
• O2 transport in blood

  97% bound to hemoglobin, 3% dissolved in plasma

  
• CO2 transport in blood

  8% dissolved in plasma, 20% bound to hemoglobin (carbaminohemoglobin), 72% in plasma as HCO3-

  
• Cl- shift


  Movement of Cl- into (tissue)/out of (lungs) RBC in exchange for HCO3-
• H+ binds to Hb


  Forms HHb, reduced Hb; prevents O2 binding, helps prevent drop in pH
• O2-Hb dissociation curve


  • Describes the percent of Hb saturation w/O2 at any pO2
  • Sigmoidal curve = cooperativity
  • Influenced by pH, CO2 & T

  
• In systemic arterial blood, ~100% saturation (each Hb has 4 O2)
• In tissues (at rest), ~75% saturation (each Hb loses 1 O2 during internal respiration)
• In tissues (exercise), ~25% saturation (3 O2 ! tissues; 1 O2 remains bound to Hb)
• BPG


  2,3 bisphosphoglycerate, produced by RBC, ↓ O2 binding affinity of Hb

  
• Nervous control of respiration

  1. Medulla - contains respiratory centers

  2. Pons - reinforce breathing rhythm with pontile centers

  3. Stretch receptors - in lungs; inflated lungs send inhibitory signal to I neurons causing exhalation

  4. Conscious control of ventilation - willfulness, pain, touch, T alter ventilation
• Chemical control of respiration

  1. CO2/pH - CO2 is primary regulator of respiration

  2. O2 - has less influence - must experience ~∆50% before signals received

  
• Functions of the urinary system


  • Removal of waste products from blood
  • Controls blood volume and BP
  • Regulation of ion concentration (Na+, K+, HCO3-)
  • Regulation of blood pH
  • Controls RBC production (erythropoeitin)
  • Controls vitamin D synthesis (skin, UV light)