Respiratory III: Blood Transport of Gases/Regulation of Respiration PDF

Respiratory III: Blood Transport of Gases/ Regulation of Respiration ANSC 3080 G. Bedecarrats  Learning Objective  Explain the transport of oxygen in the blood  Explain the transport of carbon dioxide in the blood  Describe the mechanisms regulating the respiratory system ...

Respiratory III: Blood Transport of Gases/ Regulation of Respiration ANSC 3080 G. Bedecarrats  Learning Objective  Explain the transport of oxygen in the blood  Explain the transport of carbon dioxide in the blood  Describe the mechanisms regulating the respiratory system  Brief overview of the respiratory system in birds  Oxygen Transport in Blood  Most of the oxygen in blood (>97%) is reversibly bound to hemoglobin  Rest circulates dissolved in blood  Henry’s Law: amount of gas dissolved is directly proportional to partial pressure of that gas  However, solubility of O2 very low in aqueous solution  At a usual arterial pressure (PaO2=100mm Hg): 3 ml of O2 per L of blood is dissolved  In reality blood leaving the lungs contains ~200 ml O 2 per liter  197 ml/liter bound to hemoglobin  Significance  At rest, a greyhound (25 kg) consumes 125 ml O2 per min  During a race, O2 consumption jumps to 4500 ml per min  If O2 was carried only as dissolved in blood  What would be the necessary cardiac output to sustain the effort? 1500 liters of blood  Hemoglobin  Contains 4 heme groups, each with 1 iron atom that can bind 1 molecule of O2  1 hemoglobin binds 4 molecules of O2  Oxygen saturation is the amount of oxygen carried divided by the total oxygen capacity of blood  % saturation = amount O2 bound / max capacity of Hb for O2  When all 4 sites of all the blood Hb are bound: saturation = 100%  When half the potential binding sites are occupied: saturation = 50% FYI  Saturation Curve  Binding of O2 to Hb follows a mass action law  At equilibrium: Hb + O2  HbO2  If the concentration of 1 reagent changes, the equilibrium is displaced  pO2 is responsible for the amount of O2 dissolved in blood  Saturation directly linked to the pO2 (lungs, tissue)  Blood in lung capillaries = dissolved O2  = more HbO2  Blood passes through tissue capillaries = dissolved O2  = dissociation of HbO2 occurs  Oxygen saturation curve follows a sigmoid shape  Relation between Hb content and the pO2  Normal condition:  100% saturation out of lung  75% saturated out of tissue  Since is Hb completely saturated in the lungs. The main factor is the concentration of Hb  1g Hb caries 1.34 ml of O2  Normal concentration = 150g/l  200 ml of O2  Anemia: O2 transport reduced proportionally to amount of Hb  In high altitude, pO2 in air decrease  compensate by increasing the number of erythrocytes and Hb Saturation  Factors Affecting Hb Saturation  pH: increase in metabolism = increase in H+  Decreases affinity of Hb for O2  Curve shifted to the right: need higher pO2 for saturation, unloading occurs more rapidly  Temperature: increased metabolism = increased heat  Result similar to acidity  2,3DPG (diphosphoglycerate): result from glycolysis in erythrocytes. Binds to Hb  Similar effect  NOTE: the pO2 in the lung is generally sufficient to maintain 100% saturation in most situation. pH, T and DPG mainly affect the unloading (convenient during exercising)  Blood Transport of CO2 Carried in three forms:  Physical solution (5-10 %) = dissolved in blood  20 times more soluble in water than O2  Carbamino compounds (bound to proteins)  bind to –NH groups on proteins, especially hemoglobin  Stronger affinity for deoxyhemoglobin (no O2)  15%-20% of total carbon dioxide content  Bicarbonate (HCO3-), 70%-75%  CO2 + H2O  H2CO3  HCO3- + H+  Reaction in erythrocytes  HCO3- diffuse in plasma (much more soluble than CO2)  In the lung opposite reaction occurs (back to CO2 form) Ex. Cel Fluid  Regulation of Respiration  As the heart, respiratory muscles contract rhythmically  Contrary to the heart, no pace maker cells = skeletal muscle needs APs from motor neurons  Ventilation is automatic and is constantly adjusted to needs  Rhythmic nature originate in the Respiratory Center of the brain stem (medulla oblongata)  Respiratory Center  Network of synchronized neurons within the brain stem  Inspiratory neurons  stimulate motor neurons in the spinal cord  contraction of respiratory muscles  Inspiratory neurons controlled by another network in the brain stem: Central Pattern Generator (CPG)  Respiratory center under constant influence of pO2, pCO2 and H+ concentrations (chemicals)  Inspiratory neurons also under the influence of stretch receptor in the lung, bronchiole, and muscles  Reflex: stretch  sensory fiber  brain stem  in activity  Chemical Regulation  Chemoreceptors detect O2, CO2 and H+  Central chemoreceptors:  In brain stem  Indirectly detect changes in pCO2 in the blood to the brain  CO2 enters cerebrospinal fluid by diffusion from the blood across the blood-brain barrier, transformed into HCO3- + H+  H+ is the trigger  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 = problem with Hb Reduced blood flow to tissues Impaired cell metabolism (cyanide poisoning)  Remedy: inhalation pure O2  Respiration in Birds (FYI)  Gas exchange identical to mammals (diffusion)  Ventilation is different  Lungs relatively small and rigid; do not change in volume during inspiration/expiration  Air sacs (8): Thin-walled distensible Communicate with the lungs and the bronchi  Both inspiration and expiration are active processes  Possess unidirectional parabronchi that runs in the lung. Also involved in gas exchange Parabronchi Cycle 1:  Inspiration air enters airways goes to caudal air sacs and the lung  Expiration pushes air out the caudal air sac flows through the lungs  Air flows through the lung during both inspiration and expiration Cycle 2:  Inspiration air from the lung fills the cranial air sacs  Expiration air pushed out the cranial sac outside  Note that what happened in cycle 1 also happens in cycle 2