Respiratory System – Control Mechanisms
Control mechanisms – Local + CNS Higher CNS centers (cerebral cortex, limbic system, hypothalamus)-> brain stem -> spinal cord -> respiratory system To control respiration, what cells should you actually control? -control skeletal muscles involves in inhalation and exhalation These cells control respiratory minute volume – how do you control them? -respiratory minute volume involves the freq. and volume of a respiratory cycle -motor neurons control skeletal muscle -both voluntary and involuntary control – from several CNS control centers ow do we know when control is needed/where do the signals originate? -cognitive input via 5 senses (visual, auditory, olfactory, gustatory, touch) -sensory input stimulates changes in the CNS control centers -chemoreceptors -baroreceptors -others Control of respiration -peripheral and alveolar capillaries maintain balance during gas diffusion bu: -changes in depth and rate of respiration -changes in blood flow and O delivery -this requires excellent coordination between respiratory and cardiovascular systems *ventilation (air flow) -> perfusion (blood flow) coupling 1. lood flow toward alveolar capillaries directed toward lung lobules where PO2 levels are relatively high (CO2 levels are low) -alveolar capillaries constrict when PO2 is low -blood is directed to area to pick up O2 2. smooth muscle cells in walls of bronchioles are sensitive to PCO2 -increased PCO2 causes bronchiodilation -air flow directed toward lobules where PCO2 is high and CO2 is decreased (CO2 is bad) -these lobules contain CO2 obtained from blood (decreased PCO2 causes bronchioconstriction) Local controls – respiratory and cardiovascular systems scenario: cells in interstitum are very active, so O2 is being used and PO2 decreases CO2 is being produces (PCO2 increases) -O2 is good and CO2 is bad so you want to bring in O2 and remove CO2 -to bring in a gas, you open up the tube in which is flows/ you dilate that tube -dilate tube by relaxing muscles – vasodilate or bronchiodilate -to slow/restrict flow of a gas – you constrict the tube in which it flows -vasoconstrict or bronchioconstrict -PO2 ratio (95 mm blood vs 40 mm interstitum) gets steeper so more O2 goes to interstitium -PCO2 ratio changes (45 mm interstitium vs. 0 mm blood) so more CO2 goes to blood + increased CO2 causes smooth muscle relaxation in systemic BVs (vasodilation, blood flow increases and CO2 leaves) CNS control of respiration 1. voluntary centers – thinking about it -in cerebral cortex affect: -respiratory centers of pons and medulla oblongata -motor neurons that control respiratory muscles 2. involuntary centers – not thinking about it -brain stem -regulate respiratory muscles -in response to sensory information -resulting in changes in respiration patterns 5 sensory modifiers of respiratory center activities 1. hemoreceptors – are sensitive to PCO2, PO2, or pH of blood or cerebrospinal fluid 2. baroreceptors – in aortic or carotid sinuses are sensitive to changes in blood pressure 3. stretch receptors – respond to changes in lung volume 4. irritating physical or chemical stimuli – in nasal cavity, larynx, or bronchial tree – sneezing and coughing 5. other sensations – including pain, changes in body temp, abnormal visceral sensations chemoreceptor stimulation peripheral: -responses to changes in blood pH or PO2 -in carotid or aortic bodies (in carotid + aorta blood vessels) -leads to increased depth and rate of respiration subject to adaptation – decreased sensitivity due to chronic stimulation central: -receptors monitoring CSF by chemoreceptors -on ventrolateral surface of medulla oblongata -respond to increase PCO2 results in decrease in pH of CSF -chemoreceptors increase rate/depth of breathing -causes more air to move in and alveolar CO2 concentrations decrease *Same idea: if the pH is more acidic – correlates with more CO2 – then you want to breath more to get more oxygen in and decrease the CO2/O2 ratio = Ventilation-Perfusion Coupling baroreceptor reflexes measures BP -Carotid and aortic baroreceptor stimulation (common carotid artery – supplies head/neck with oxygenated blood) -affects BP and respiratory centers -when bp falls -respiration increases -when bp increases -respiration decreases respiratory centers – in brain stem -3 pairs of nuclei in the reticular formation of medulla oblongata and pons -respiratory rhythmicity centers of medulla oblongata -set the pace of respiration -can be divided into 2 groups -dorsal respiratory group (DRG) – inspiratory center, functions in quiet and forced breathing ventral respiratory group (VRG) – inspiratory and expiratory center, functions only in forced breathing Quiet breathing -activity in the DRG (dorsal respiratory group) -stimulates inspiratory muscles -DRG neurons become inactive -allowing passive exhalation Forced breathing -increased activity in DRG -stimulates VRG -which activates accessory inspiratory muscles -after inhalation -expiratory center neurons stimulate active exhalation Apneustic + Pneumotaxic centers of the pons -paired nuclei that adjust output of respiratory rhythmicity centers regulating respiratory rate and depth of respiration -Apneustic Center -provides continuous stimulation to its DRG center -Pneumotaxic Centers -inhibit the apneustic centers -promote passive or active exhalation -respiratory centers + reflex controls -interactions between VRG + DRG -establish basic pace and depth of respiration -the pneumotaxic center -modifies the pace SIDS (sudden infant death syndrome) -disrupts normal respiratory reflex pattern -may result from connection problems between pacemaker complex and respiratory centers Control of Respiration 1. Local controls 2. CNS controls
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