Respiratory Figs and Kidney Function(5 pages)
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Respiratory Figs and Kidney Function
- Lecture number:
- Lecture Note
- University of Southern California
- Bisc 307l - General Physiology
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BISC 307L 2nd Edition Lecture 36 Current Lecture Regulation of Ventilation Within the erythrocyte, as the CO2 flows into the alveolar air, that creates a gradient for CO2 to leave the erythrocyte, and that shifts the equilibrium for the carbaminohemoglobin as the CO2 is removed by diffusing into the plasma and then the alveolus. So CO2 comes off the Hb, that was about 23%. We start with Oxyhemoglobin (Hb- H). When oxygenated, hemoglobin loses its affinity for protons. They dissociate, and that makes the inside of the red blood cell more positive, and that attracts bicarbonate in across the membrane in exchange for chloride. That is called the reverse chloride shift. So we have protons and bicarbonate in here, which combines to carbonic acid. There’s a lot of carbonic anhydrase, so it dissociates. And driven by the removal of CO2, this whole reaction moves to the right and bicarbonate in the plasma is taken out and becomes CO2 in the RBC’s that diffuses out. So its pretty much everything running in reverse – to make it all work though, it is important that deoxyhemoglobin binds protons and oxyhemoglobin doesn’t. Regulation of Ventilation Skeletal muscles control ventilation – diaphragm, intercostal muscles, external cleidomastoids. They are not spontaneously active, but rather they are innervated by alpha motor neurons. And these are brain stem motor neurons (seen to the right). In the brain stem, there are two groups of nerve cells that are functionally defined, called the ventral and dorsal respiratory groups – those are where the AP’s of the respiratory system will originate. There are neurons with unstable membrane potentials that generate rhythmic AP’s in bursts. And that descending excitation from those neurons goes to spinal and brain stem neurons that innervate the respiratory muscles. The control of this outflow of motor information is determined by the level of the respiratory gases. Oxygen does not play a major role in ordinary moment-to-moment, quiet breathing. CO2 is much more important. Hb carries a tremendous reserve of oxygen, so oxygen levels in the blood are not a sensitive indicatory of a need for respiration. On the other hand, CO2 is, because it is a direct waste product of metabolism. So we need gas sensitive nerves/chemoreceptors. These reflexes are going to start with chemoreceptors that will sense the level of respiratory gases in the blood and respond appropriately. There are 2 types of chemoreceptors – central and peripheral. The central chemoreceptors are the ones in the brainstem, they sense the respiratory gases. The central just refers to the central nervous system. These are sensitive to carbon dioxide. Peripheral chemoreceptors are located in the aortic body and the carotid body. These are good places to measure the oxygen level of systemic circulation. Don't confuse the aortic and carotid bodies with the aortic and carotid sinuses – those participate in the baroreceptor reflex. The carotid body is a group of cells that are sensitive to oxygen in the carotid artery and the aortic body is a group ...
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