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Regulation, High Altitude

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imissyou419's version from 2017-02-02 19:46

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Voluntary systemchange breathing pattern i.e. breath hold, speaking, hyperventilate or hypoventilate; signals from cerebral cortex through corticospinal tract to spinal neurons that drive respiratory muscles.
But limited, ultimately the autonomic system takes over
Autonomic systemresponsible for maintaining normal blood gas values under a variety of conditions, efficient
Central controllercoordinates the responds to the information provided by receptors (response to respiratory muscles). Neurons located in 4 areas (inspiratory area, pneumotaxic area, apneustic centre, expiratory area)
Receptorscollect info of the current status of blood gas and other factors (input signals to central controller). 4 types - central chemoreceptor, peripheral chemoreceptor, lung receptor, other receptor
Respiratory musclesreceive impulses from the controller to ultimately affect ventilation (negative feedback to receptor)
Inspiratory area locationdorsal group of neurons in the medulla
Inspiratory area propertiescritical in respiration, inherent RHYTHMIC excitability to inspiratory muscles, initiates inspiratory drive
Pneumotaxic area locationgroup of neurons in the pons
Pneumotaxic area propertiesfine-tuning of respiratory but not essential, limits duration of inspiratory drive "switch off" by transmiting impulses to inspiratory area, control of inspiratory volume and respiratory rate (inhibits apneustic centre so no prolong breathing)
What happens if pneumotaxia area is damaged?really deep breaths with occassional expiratory gasps because no fine tuning / no inhibition to apneustic centre (responsible for prolonged breathing)
Apneustic centre locationgroup of neurons in lower pons
Apneustic centre propertiesnot sure, opposite of pneumotaxic centre in that it can prolong inspiration by transmitting signals to inspiratory area to prevent termination of inspiratory drive, pneumotaxic centre overrides apneustic centre
Expiratory area locationventral group of neurons in the medulla
Expiratory area propertieswhen needed (when respiratory drive for increased pulmonary ventilation becomes greater, signals from inspiratory area spill over to expiratory area), these neurons send signals to expiratory muscle resulting in active expiration (expiration normally passive)
When does breathing stop?when spinal cord is transected above the origin of phrenic nerves because need discharge from motor neurons that innervate the respiratory muscles
chemoreceptora receptor that responds to a change in the chemical composition of the fluid around it
What receptors are the most important receptors in the control of ventilation?central chemoreceptors
Central chemoreceptor locationlocated in medulla where they are surrounded by brain extracellular fluid
Central chemoreceptor responds tochanges in blood PCO2, this is an indirect response: the receptor reacts to change in [H+] in the extracellular brain fluid from blood CO2 (H+ does not diffuse to extracellular brain fluid so not directly by H+ of the blood); CO2 diffuse into CSF and has reaction to form H+ ions (↑H+ ions due to ↑ blood PCO2 increase ventilation)
Peripheral chemoreceptor, which of 2 locations is it most responsive in humans?carotid bodies at the bifurcation of the common carotid arteries,
aortic bodies above and below aortic arch
(in humans, carotid bodies peripheral receptors are most responsive)
Peripheral chemoreceptor responds tochanges in blood PO2, when arterial PO2 < 60 mmHg (i.e. high altitude) -> increase ventilation, no effect from increases in PO2 above normal levels, minor response to PCO2 and pH
Lung receptors locationlung
Lung receptor 2 types and responsespulmonary stretch receptors: responds to overdistention of lung -> slow ventilation rate to avoid overstretching.
Irritant receptors: responds to inhaled dust particles or cigarette smoke
Other receptors examplesreceptors in nose and airways responding to chemical or mechanical strains,
joint and muscle receptors,
pain and temp receptors
What is the most important regulator of ventilation?PCO2 (under normal circumstances, PO2 has small impact on ventilation)
Give an example where response to PCO2 can be largePCO2 increase from 40-60 mmHg can results in a 9x fold increase in ventilation very rapidly (if you inhale your CO2, would result in increase in ventilation);
variations in this system is low b/c efficient
What is the response to high PCO2Increase PCO2 -> central chemoreceptors -> central controller -> respiratory muscles to increase ventilation to decrease PCO2 (exhale more CO2), blood pH normal
What happens to response to increased PCO2 under chronic conditions?Adaptation i.e. people with emphysema have chronic CO2 retention so not high response to their CO2 levels (their high CO2 levels do not trigger high ventilation but reduced ventilation)
When is response to PO2 important?high altitude or diseases (↓PO2 -> ↑ ventilation)
What is the response to low PO2Decrease PO2 -> peripheral chemoreceptors -> central controller -> respiratory muscles to increase ventilation to increase PO2
What is the response to blood pH?may effect ventilation through peripheral chemoreceptors but hard to determine specific effects
What is the response to exercise?1. joint and muscle receptors,
2. neurogenic factors: cerebral cortex simultaneous signals to muscles for exercise and respiratory centre to increase ventilation (NOT CHEMORECEPTORS SINCE PCO2, PO2, PH REMAIN CONSTANT)
What is the combined effects of PaCO2 and PO2combined effects exceed the sum of individual responses (PaO2 decrease and PaCO2 increase trigger ventilation 10 fold increase compared to 2 fold each)
What are the response to high altitudePO2 low (could lead to hyperventilation)
1.↓ PaO2 which will lead to stimulation of peripheral chemoreceptors -> ↑ ventilation.
2. ↑ ventilation -> ↓PCO2 -> central chemoreceptors -> ↓ ventilation.
3. 1 day at high altitude -> adaptation -> reduced PCO2 response.
4. ↑ production of RBC -> ↑ capacity to carry O2 (high altitude training)
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