Lecture 2 - The control of respiration Flashcards
What is the normal control of respiration?
Cellular rate of CO2 production and O2 absorption at cells = 02 absorption and CO2 excretion at the lungs
Outline the local control of respiration at the tissues
Increased activity of peripheral tissue decreases PO2 and increases PCO2
Changes in gas exchange
Increased blood flow
Outline local control at the alveoli
Smooth muscle which relaxes allowing more air in
Outline the neural control of respiration
The respiratory centers in the brain
- O2 demand increases cardiac output and rate of respiration
Involuntary
- Regulates respiratory muscle activity
Frequency and depth
Responding to info from lungs and respiratory tract
Voluntary
- Reflects activity in the cerebral cortex
Affects output of respiratory centres
How is respiration controlled in the pons?
The apneustic and pneumotaxic centres
- Paired nuclei that adjust out of respiratory rhythmicity
- Pneumotaxic inhibits the apneustic and promote passive and active exhalation - increases pace of respiration and decreases duration of inhalation.
Apneustic - inhalation - stimulate DRG
What are the respiratory centres of the medulla oblongata?
DRG- Dorsal Respiratory Group
- Inspiratory center
Functions in quiet and forced breathing
VRG - Ventral Respiratory Group
- Inspiratory and expiratory center
- forced breathing
What are the respiratory reflexes?
Chemoreceptors - Sensitive to PCO2, PO2, or pH of blood or CSF
Baroreceptors (mechanoreceptors) - Sensitive to changes in blood pressure
Stretch receptors (mechanoreceptors) around the lungs - respond to changes in lung volume
What are the Hering-Breuer reflexes?
Forced breathing
Inflation reflex - Prevents overexpansion of lungs - as lung volume increases DRG is inhibited and VRG stimulated
Deflation Reflex - Inhibits expiratory centres
Stimulates inspiratory centres during lung deflation
Outline the chemoreceptor reflexes
From the glossopharyngeal nerve
(carotid bodies providing afferent feedback)
Vagus nerve
(Aortic bodies)
What happens to the respiratory rate when the PO2 drops to 40 mmHg?
Increases by 50 - 70%
What happens to the respiratory rate when there is a 10% rise in arterial PCO2?
Increases by 100%
How is chemoreceptor stimulation subjected to adaptation?
Decreased sensitivity due to the chronic stimulation
Increases in lactic acid affect respiration
How do chemoreceptors respond to an increase in PCO2?
Increased arterial PCO2 (hypercapnia)
Stimulates chemoreceptors
Stimulates respiratory muscles
Increased rate with increased elimination of CO2 at the alveoli
How do chemoreceptors respond to a decrease in PCO2?
Decreased arterial PCO2 (hypocapnia)
Inhibits chemoreceptors
Inhibits respiratory muscles
Decreased respiratory rate so decreased elimination of CO2 at the alveoli
Outline the control of respiration
Basic pace established by the interplay between respiratory centres in the pons and medulla oblongata
Pace modified by chemoreceptors etc
CO2 levels primary drivers
Can be interrupted by protective reflexes and conscious control
What are the respiratory changes at birth?
Before birth - Pulmonary vessels are collapsed, lungs contain no air
At birth - newborn overcomes force of surface tension to inflate bronchial tree and alveoli and take first breath
What are the respiratory changes in the elderly?
Deterioration in elastic tissue - compliance and VC
Arthritic changes and decreased flexibility
Emphysema - smoking (if they quit the rate of respiratory decline will decrease)
