Respiratory III

Oxygen Transport in Blood

• Most of the oxygen in blood (>97%) is bound to hemoglobin
• Oxygen dissolved in blood follows Henry’s Law: amount of gas dissolved is directly proportional to partial pressure of that gas
• Solubility of O2 very low in blood
• At a usual arterial pressure (PaO2=100mm Hg): 3 ml of O2 per L of blood is dissolved
• Blood leaving the lungs contains ~200 ml O2 per liter, 197 ml/liter is bound to hemoglobin
• Hemoglobin contains 4 heme groups, each with 1 iron atom that can bind 1 molecule of O2
• Oxygen saturation is the amount of oxygen carried divided by the total oxygen capacity of blood
• When all 4 binding sites of hemoglobin are occupied: 100% saturation
• When half the binding sites are occupied: 50% saturation

Factors Affecting Hb Saturation

• pH: increase in H+ decreases affinity of Hb for O2, curve shifts to the right, need higher pO2 for saturation, unloading occurs more rapidly
• Temperature: increase in metabolism = increase in heat, similar effect as pH
• 2,3DPG (diphosphoglycerate): binds to Hb, similar effect as pH
• The pO2 in the lung is generally sufficient to maintain 100% saturation, pH, T and DPG mainly affect the unloading of oxygen

Blood Transport of CO2

• Carbon dioxide in blood is carried in three forms: physical solution, carbamino compounds, and bicarbonate
• Physical solution (5-10%) = dissolved in blood
• Carbamino compounds (bound to proteins) bind to –NH groups on proteins, especially hemoglobin, stronger affinity for deoxyhemoglobin
• Bicarbonate (HCO3-), 70%-75% of total carbon dioxide content, CO2 + H2O  H2CO3  HCO3- + H+

Regulation of Respiration

• Respiratory muscles contract rhythmically
• Respiratory center in the brain stem (medulla oblongata) originates rhythmic nature of breathing
• Inspiratory neurons stimulate motor neurons in the spinal cord  contraction of respiratory muscles
• Inspiratory neurons are controlled by Central Pattern Generator (CPG)
• Respiratory center is influenced by pO2, pCO2 and H+ concentrations
• Stretch receptor in lung, bronchiole, and muscles influence Inspiratory neurons

Chemoreceptors

• Chemoreceptors detect O2, CO2 and H+
• Central chemoreceptors: in brain stem, indirectly detect changes in pCO2 in the blood
• Peripheral chemoreceptors: in carotid and the aorta, detect direct arterial changes in pO2, pCO2 and H+
• Information sent to the respiratory centers:  pCO2,  H+ or  pO2  increase ventilation
• pCO2 most important factor leads to increase in H+

Hypoxia

• Deficit in O2 supply to the cells
• Symptoms: confusion, hallucination, loss of consciousness
• Causes: low arterial pO2 from pulmonary diseases/failure, high altitude, reduced transport capacity, reduced blood flow to tissues, impaired cell metabolism
• Remedy: inhalation pure O2

Respiration in Birds

• Gas exchange identical to mammals
• Ventilation different
• Lungs relatively small and rigid; do not change in volume during inspiration/expiration
• Air sacs communicate with the lungs and the bronchi
• Inspiration and expiration are active processes
• Possess unidirectional parabronchi that runs in the lung.