Respiratory Control Centers Respiratory nuclei in medulla Dorsal respiratory group DRG Another network of neurons that extends for much of the length of the medulla It is an integrating center that receives input from several sources higher brain center respiratory center in the pons and internal sense receptors It processes more involuntary input from sense receptors than other respiratory control groups The DRG issues output via DRG inspiratory neurons to inspiratory spinal motor neurons and to the VRG I neurons DRG can cause ventilation rate to increase or decrease 22 1 Respiratory Control Centers Pons Pontine respiratory group PRG Modifies rhythm of the VRG Receives input from higher brain centers hypothalamus limbic system cerebral cortex The PRG receives and processes more higher brain center input than DRG PRG receives no input from internal sense receptors Issues output to both DRG PRG hastens or delays the transition from inspiration to expiration smooths the transition btw inspir and expir It adjusts breathing to special circumstances such as sleep exercise vocalization and emotional responses Higher brain output anxiety or anger into PRG PRG output to DRG which stimulates the VRG stimulates VRG I and E neurons as part of forced inspiration and forced expiration Increased freq of quiet breathing is not forced breathing 22 2 Respiratory Control Centers Copyright The McGraw Hill Companies Inc Permission required for reproduction or display Key Inputs to respiratory centers of medulla Outputs to spinal centers and respiratory muscles Output from hypothalamus limbic system and higher brain centers Pons Pontine respiratory group PRG Dorsal respiratory group DRG Ventral respiratory group VRG Spinal integrating centers Central chemoreceptors Glossopharyngeal n Vagus n Medulla oblongata Intercostal nn Phrenic n Diaphragm and intercostal muscles Accessory muscles of respiration 22 3 Sensory Output to DRG Central chemoreceptors in medulla primarily monitor pH of cerebrospinal fluid Peripheral chemoreceptors found in major blood vessels aortic bodies and carotid bodies monitor blood pH CO2 and O2 levels 22 4 Peripheral Chemoreceptor Paths 22 5 Output to DRG From airways and lungs stretch receptors in airways inflation reflex In smooth muscle of bronchi and bronchioles as well as in visceral pleura excessive inflation of airways triggers reflex stops inspiration Signal DRG via vagus nerve irritant receptors in respiratory mucosa Nerve endings amid the epithelial cells that respond to smoke dust pollen cold air and excess mucus Transmit signals to the DRG that in turn initiates protective reflexes breathing Stimulate bronchoconstriction coughing and shallow 22 6 Voluntary Control Important in singing speaking breath holding and other special circumstances Neural pathways motor cortex of frontal lobe of cerebrum sends impulses down corticospinal tracts to respiratory neurons in spinal cord bypassing brainstem centers Limitations on voluntary control Rising blood CO2 or lowering O2 causes automatic respiration 22 7 Respiratory System Blood Gases and Respiratory Rhythm 22 8 Blood Chemistry and Respiratory Rhythm The PO2 of systemic arterial blood is normally 95 mm Hg and the PCO2 is 40 mm Hg with a pH of 7 4 0 05 Rate and depth of breathing adjusted to maintain levels of pH PCO2 PO2 The chemoreceptors of the CNS and peripheral nervous system monitor blood composition and relay signals to the DRG potent stimulus for breathing is pH followed by CO2 the least significant is O2 22 9 Effects of Hydrogen Ions pH of CSF most powerful respiratory stimulus H ions do not cross the blood brain barrier easily CO2 easily crosses blood brain barrier in CSF the CO2 reacts with water and produces H Increases in PCO2 in blood and CSF lead to increases in H in blood and CSF stimulate chemoreceptors which stimulate DRG I neurons lead to increased ventilation of lungs until CO2 and H levels return to normal 22 10 Effects of Hydrogen Ions Pul ventilation is adjusted ultimately to maintain the pH brain A blood pH lower than 7 35 is called acidosis and pH greater than 7 45 is alkalosis A PCO2 below normal is hypocapnia and a PCO2 above normal is hypercapnia The result of both shifts in PCO2 or failure of pul ventilation to match the body s rate of CO2 production is pH imbalance and they are termed respiratory alkalosis and respiratory acidosis 22 11 Effects of Hydrogen Ions A slower breathing rate helps to correct alkalosis by allowing CO2 to build up in blood CO2 H2O H2CO3 HCO3 increased breathing rate helps to correct acidosis by H removing CO2 from the blood CO2 expired H2O H2CO3 HCO3 increases in arterial proton concentration while arterial blood carbon dioxide levels are normal also stimulate ventilation via chemoreceptors for example due to lactic acid from strenuous exercise or diabetes H Only peripheral chemoreceptors respond because if CO2 is about the same in blood then brain detects no immediate change in pH CO2 crosses blood brain barrier much more easily than protons which cross but very slowly 22 12 Effects of Exercise Increased ventilation during moderate exercise is not due primarily to changes in arterial blood pH or gas concentrations When the brain sends motor commands to the muscles it also sends info to the resp centers which then increase pul ventilation Exercise stimulates proprioceptors of muscles and joints and these transmit excitatory signals to the DRG Immediate increase in ventilation which will match the increase in CO2 production and O2 use in tissues due to increased muscle activity Also immediate rise in CO2 levels in active tissue immediately stimulate the peripheral chemoreceptors which triggers an immediate increase in ventilation before the central chemoreceptors detect any change in blood pH or CO2 change Arterial blood gas values are kept near normal in spite of the increased O2 consumption and CO2 generation in tissues 22 13 Effects of Oxygen the PO2 has little effect on respiration Hypoxia is a deficiency of oxygen in tissues At low elevations a low ambient PO2 seldom occurs and normal PO2 levels are maintained PO2 falls below normal in arterial blood high altitudes after several days lung disease e g emphysema pneumonia stimulating ventilation via chemoreceptors Long term hypoxemia low blood O2 can lead to a condition called hypoxic drive in which resp is driven more by low PO2 than by pH or CO2 levels 22 14 The Urinary System Functions of urinary system Anatomy of