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79 Cards in this Set
- Front
- Back
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Why does respiratory failure happen?
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Respiratory system can't do its job
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What is responsible for respiratory failure (3)?
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Failure of:
1) Gas exhanging capabilities of the lungs 2) Neutral control of ventilation (the drive to breathe) 3) Neuromuscular breathing apparatus (the respiratory muscles and their innervation) |
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What is blood hypoxia?
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Deficient blood oxygenation
-> Low PaO2 and low %Hb saturation |
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What happens in hypoxic conditions if PaO2 decreases below 60mm Hg?
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O2 content in arterial and venous blood becomes lower than the normal values at sea level
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What are the 5 general cuases of hypoxia?
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1) Inhalation of low PO2
2) Hypoventilation 3) Ventilation/Perfusion imbalance in the lungs 4)Shunts of blood across the lungs 5) O2 diffusion impairment |
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When would you inhale low PO2?
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At high altitude
PO2 is lower cuz P atm is lower |
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What happens during hypoventilation?
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PaO2 decreases and PaCO2 increases
->alveolar ventilation is reduced, compared to metabolic CO2 production Hypoventilation occurs because of diseases in the CNS, neromuscular diseases, barbiturates, other drugs and narcotics |
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When is there a ventilation/perfusion imbalance in the lungs?
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Occurs when the amount of fresh gas reaching an alveolar region per breath is either too low or too much fo the blood flow through the caps of that region
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What happens when there are shunts of blood across the lungs?
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Venous blood bypasses the gas exchaniging region of the lungs and returns to systemic circulation, deoxygenated
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When do these types of shunts exist?
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Baby heart
foramen ovale: blood goes from right to left heart, bypasses the lungs |
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How can O2 diffusion be impaired?
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Thickening of the alveolar-capillary membrane or pulmonary edema
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What is automatic breathing?
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Involuntary activity that brings enough air into the pulmonary alveoli to maintain the O2 and CO2 tensions of alveoar gas or arterial blood at optimal levels in different conditions (sleep, rest or exercise)
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How does the CNS control gas exchange?
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By integrating all the info coming from the periphery
->get adequate depth and frequency of breathing (minute ventilation) |
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What is voluntary breathing?
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Voluntary Hyperventilation
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What controls voluntary breathing?
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The cerebral hemispheres
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What controls automatic/involuntary breathing?
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Brainstem
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Do the 2 systems of breathing interact?
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Yes
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Can voluntary breathing be effective if automatic control no longer fcts?
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Yes
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What happens if you voluntarily stop ventilation?
Why? |
Breathing will eventually start again
Arterial PCO2 has reached 50mm Hg and arterial PO2 has reached 70mm Hg -> Voluntary control is over-ridden at this point: Breaking point |
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What controls the over-riding of voluntary control by the automatic control?
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The info from the receptors sensitive to CO2 and O2 levels (in arterial blood and/or cerebro-spinal fluid)
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What are the components of the brain stem?
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Pons and medulla
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What are the 3 basic elements in the respiratory control system?
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Sensors
Controllers Effectors |
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What do the sensors do?
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Gather info about lung volume (pulmonary receptors) and O2 and CO2 content (chemoreceptors)
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What role do controllers play in the respiratory control system?
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Info from sensors are sent to the controller, in the pons and medulla, through te afferent neural fibers
When the info reaches the pons and medulla, the peripheral info and inputs from the higher structures of the CNS are integrated |
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What do the effectors do?
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Neuronal impulses are generated and sent by spinal motorneurons to the effectors after integration
Ventilation is adjusted to the person's metabolic needs |
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Describe the medulla.
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Contains pacemaker cells
Located mainly in 2 groups: -ventral respiratory group that generates the Basic Rhythm -dorsal respiratory group that receives several sensory inputs Ventral and dorsal groups connect to each other |
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What generates the basic respiratory rhytmicity?
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Respiratory neurons in the medulla
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What do cells in the rostral (upper) pons do?
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Turn Off inspiration
-> Get smaller tidal volume and increased breathing frequency |
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What happens if the pneumotaxic centers are cut?
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Breathing becomes deep and slow
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What else could be cut to produce the same result as cutting the pneumotaxic centers?
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Vagus nerve
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What happens if the influence of the vagus nerves and rostral pons are removed?
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Apneuses: tonic inspiratory activity interrupted by short expirations
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What is the apneustic center?
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Lower pons
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What do cells in the apneustic center do?
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Send excitatory impulses to the respiratory groups of the medulla
->promote inspiration |
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What happens if you cut off all parts of the brain except the pons and medulla?
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breathing will be fine
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What happens if you cut off the upper pons (the off switch)?
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Get deeper breaths
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What happens if you cut off all the pons?
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Get basic rhythm
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What happens if you cut off the vagi and upper pons?
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Defualt deeper breaths and lower frequency
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What happens if you cut off the vagi and the upper pons?
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Apneuses: tonic inspiratory activity interrupted by short expirations
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What do chemoreceptors do?
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Respond to chemical signals
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What do chemoreceptors detect in arterial blood?
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PO2
PCO2 pH |
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What carries the info from the chemoreceptors?
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The respiratory neurons
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What happens if PaO2 is too low (less than 60 mmHg) or PaCO2 is too high (above 40 mm Hg)?
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Activity of the respiratory neurons will increase
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When will the activity of the respiratory neurons decrease?
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PaO2 is higher than 100 mmHG
PaCO2 is less than 40 mm Hg |
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Wat are the 2 types of chemoreceptors?
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Central and peripheral
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Wat are the 2 types of chemoreceptors?
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Central and peripheral
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Where are central chemoreceptors locted?
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Ventral surface of the medulla
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What do central chemoreceptors detect?
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pH of the CSF surrounding the them
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What influences the PCO2 and pH of the CSF?
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the PCO2 and pH of the arterial blood
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What gives rise to the main drive to breathe under normal circumstances?
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The central chemoreceptors
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What happens when the chemoreceptors are stimulated?
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Increase minute ventilation
->Hyperventilation, reduces PCO2 in the blood and .: the CSF |
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How can the sensitivity of the chemoreceptors be tested?
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CO2 rebreathing test
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What decides what will happen to the chemoreceptors?
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What happens in the CSF
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What effect does CO2 have on the CSF?
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CO2 decreases the pH of the CSF
->stimulates the chemoreceptor -> H+ and HCO3- can't easily cross the blood-brain barrier CO2 + H2O -> H2CO3 H2CO3 -> HO3- + H+ |
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What is hypercapnia?
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Elevated CO2 in the blood
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What are the ventilatory responses to hypercapnia?
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Small increases in PCO2 lead to:
Increase minute ventilation due to increase in respiratory rate and tidal volume |
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What are peripheral cemoreceptors mainly sensitive to?
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Changes in PO2
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What else are peripheral chemoreceptors sensitive to?
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Increased PCO2 and decreased pH
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Whre are the peripheral chemoreceptors located?
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carotid bodies (next to the ascending aorta)
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What makes up the carotid and aortic bodies?
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Blood vessels
Structural supporting tissues Nerves endings of sensory neurons of the glossophrayngeal and vagus nerves -> The afferent fibers of these receptors project to the dorsal group of respiratory neurons in the medulla) |
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What happens at increased PCO2?
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A decrease of PO2 to less than 100 mm Hg can already cause increase in minute ventilation
(under normal PCO2 conditions, alveolar PO2 can be reducaed to ~60mm Hg before major changes in minute ventilation occur) |
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How can an augmented ventilatory response be obtained?
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Increase in PCO2 and decrease in PO2 can interact
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What type of receptors are the pulmonary vagal receptors?
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Mechanical receptors
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What are the 3 type of receptors in the lungs that respond to mechanical stimuli?
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1) Pulmonary stretch receptors
2) Irritant receptors 3) Juxta-capillary or J-receptors (C-fibers) The afferent fibres from all these receptors travel up the vagus nerve |
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Where are the pulmonary stretch receptors located?
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Smooth muscles of the trachea down to the terminal bronchioles
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What innervates the pulmonary strech receptors? When do they discharge?
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Innervated by large, myelinated fibres
Discharge in response to distension of the lung ->Their activity is sustained as long as the lung is distended |
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How does activity of these receptors increase?
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Activity increases phasically as lung volume increases during each inspiration
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What is the Hering-Breuer Inflation reflex?
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Decrease in respiratory frequency due to prolongation of expiratory time
-> Increase in lung volume tends to inhibit the beginning of the next inspiratory effort (negative fdbk) |
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How is the Hering-Breur reflex in adults? Infants? Animals?
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Adults: weak
Infants/animals: noticeable |
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Is there a deflation reflex?
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Yes
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Where are the irritant receptors located?
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Between airway epithelial cells in the trachea dow to the respiratory bronchioles
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What stimulates the irritant receptors?
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Noxious gases, cigarette smoke, histamine, cold air, dust
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What innervates the irritant receptors?
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Myelinated fibers
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What happens when the irritant receptors are stimulated?
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Bronchoconstriction and hypernea (rapid breathing)
->might be important in the reflex bronchoconstriction triggered by histamine release during an allergic asthmatic attack |
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Where are the juxta-capillary receptors located?
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In the alveolar walls, near the capillaries
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What innervates the juxta-capillary receptors?
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Non-myelinated fibres
Have short bursts of activity Stimulated by an increase in pulmonary ISF (can happen in pulmonary congestion and edema) |
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What is te reflex effect of juxta-capillary receptors?
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Rapid and shallow respiration
->Intense stimulation can cause apnea |
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What is dyspnea?
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Sensation of difficulty breathing
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What is dyspnea associated with?
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Left heart failure and lung edema or congestion
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What controls ventilation during exercise?
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We don't know
->ventilation is increased, but arterial PO2 stays constant and arterial PCO2 is the same or even decreases So why does ventilation increase, if the main drive to breathe is CO2 crossing the barrier |
