Hem acts as a buffer and binds hydrogen ions in the reaction that prevents large changes in the body’s pHIf H+ accumulates in plasma respiratory acidosis
Hemoglobin and CO223% of CO2 binds directly to hemoglobinForms carboaminohemoglobin Presence of CO2 and H+ facilitates formation of carboaminohemoglobin bc both these factors decrease hemoglobin’s binding affinity for oxygenCO2 Removal at the LungsDecrease in plasma PCO2 at lungs allows dissolved CO2 to diffuse out of the red blood cells produces more CO2 chloride shift reverses (Cl- goes back to plasma in exchange for HCO3- back into the red blood cells) HCO3- + H+ CO2 and H2O form CO2 diffuses out of red blood cell and intoalveoliRegulation of VentilationSkeletal muscle contraction must be initiated by somatic motor neurons controlled by the central nervous system1.Respiratory neurons in the medulla control inspiratory and expiratory muscles2.Neurons in the pons integrate sensory information and interact with medullary neurons to influence ventilation3.The rhythmic pattern of breathing arises from a neural network with spontaneously discharging neurons4.Ventilation is subject to continuous modulation by various chemoreceptor- and mechanoreceptor-linked reflexes and by higher brain centersNeurons in the Medulla Control BreathingNucleus tractus solitarius- contains dorsal respiratory group= control mostly muscles of inspirationOutput from DRG goes via the phrenic nerves to the diaphragm and via the intercostal nerves to the intercostal musclesPontine respiratory groups= provide tonic input to the medullary networks to help a smooth respiratory rhythm Ventral respiratory group= one area= pre-Botzinger complex= spontaneously firing neurons that act as basic pacemaker for respiratory rhythmNerve fibers from VRG inervate muscles of the larynx, pharynx, and tongue to keep the upper airways open during breathingMany neurons of the VRG remain inactive during quiet respirationActive expiration expiratory neurons from the VRG activate the internal intercostal and abdominal musclesCarbon Dioxide, Oxygen, and pH Influence VentilationPeripheral chemoreceptors= located in the carotid and aortic arteries. Sense changes in the PO2, pH, and PCO2 of the plasmaPeripheral ChemoreceptorsGlomus cells= in carotid and aortic bodies activated by a decrease in PO2 or pH or by an increase in PCO2 trigger a reflex increase in ventilationAny condition that reduces plasma pH or increases PCO2 will activate the carotid and aortic glomus cells and increase ventilation1.a stimulus inactivates K+ channels, causing receptor cell to depolarize2.voltage-gated Ca+ channels open 3.causes exocytosis of neurotransmitter onto the sensory neuron
4.neurotransmitters initiate action potentials in sensory neurons leading to the brain stem respiratory networks increase ventilationCentral ChemoreceptorsMost important chemical controller of ventilation= carbon dioxide
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- Spring '11
- Physiology, Hemoglobin