Lecture 20 - Control of breathing Flashcards
What are the two mechanisms used to achieve balance in breathing?
Local and Central
What does the local mechanism detect?
Changes in blood flow and oxygen delivery
What does the central mechanism detect?
Changes in depth and rate of respiration
How does the local mechanism use PO2 and PCO2 in active tissue to control gas transport?
A decrease in PO2 increases O2 delivery
An increase in PCO2 will increase PCO2 removal and causes vasodilation to increase blood flow
How does the local mechanism use lung perfusion to control gas transport?
A decrease in PO2 causes vasoconstriction and decrease blood flow
This allows blood to be directed to areas of higher PO2
How does the local mechanism use alveolar ventilation to control gas transport?
An increase in PCO2 causes bronchodilation which increases airflow
Airflow is directed to areas of higher PCO2
What is the overall process of the central mechanism?
Sensors in the body detect a change
The sensors activate the central controller
The central controller activates the effectors
What are the two types of receptors used in the central mechanism?
Chemoreceptors and Mechanoreceptors
What are the two types of chemoreceptor?
Central and peripheral
What and where are central chemoreceptors?
Underneath ventral surface of medulla
Close to entry of VIII and XI cranial nerves
They are stimulated by acidic or high PXO2 in the cerebrospinal fluid
What is the process of central chemoreceptors?
Increased PCO2 is detected
Central mechanism decreases pH
This increases ventilation
This then decreases PCO2
What and where are peripheral chemoreceptors?
They detect changes in PO2 PCO2 and pH
They are outside of the brain
Have a carotid body which is innervated by carotid sinus nerve
Have aortic bodies which are innervated by vagus
What occurs if CO2 increases?
Equation shifts right
There is increased H+ which decreases pH
This means its more acidic, causing respiratory acidosis
What happens if PCO2 decreases?
The equation shifts left
This decreases H+ which increases pH
It becomes more alkaline which causes respiratory alkalosis
What happens if PO2 increases?
It generates free radicals which leads to coma and death
What happens if PO2 decreases?
Central chemoreceptors switch off
Peripheral chemoreceptors increase breathing rate
What are the three types of mechanoreceptors?
Slowly adapting
Rapidly adapting
C-fibre endings
What are slowly adapting mechanoreceptors?
Also called bronchopulmonary stretch receptors
They are stretch receptors in the visceral pleura, bronchioles and alveoli
What is the Hering-Breuer reflex, the reflex that slowly adapting mechanoreceptors use?
There is overinflation
This increases discharge
This inhibits respiratory centres
What are rapidly adapting mechanoreceptors?
Irritant receptors
They are in airway epithelia close to the mucosa
Shape ventilatory pattern and protect airway
At first fire rapidly then decrease firing rate
What is bronchoconstriction, the reflex done by rapidly adapting mechanoreceptors?
There is a stimuli, eg noxious gases, smoke or cold air
This increases discharge
This causes bronchoconstriction, ie coughing
What are c-fibres receptors?
They initiate bronchoconstriction
In alveoli wall and conducting airways
What is bronchoconstriction as a reflex used by c-fibres receptors?
Theres mechanical or chemical stimuli
This increases discharge
This causes bronchoconstriction
What are the locations of the respiratory centres in the brain?
Medulla
Pons
What is the respiratory centre in the medulla?
The rhythmicity centre
What is the role of the rhythmicity centre in the medulla?
To control automatic breathing
To set pace for respiratory movements
What are the two respiratory groups in the rhythmicity centre?
Dorsal, which contains I neurons for inspiratory centre
Ventral, which contains E and I for expiratory centre
What are I neurons in the rhythmicity centre?
Regulate activity of phrenic nerve
Set rhythm and stimulate muscles of quiet inspiration
What are E neurons in the rhythmicity centre?
Passive process
Activity inhibits I neurons
What are the respiratory centres in the pons?
Pneumotaxic centre
Apneustic centre
What is the apneustic centre?
It promotes inspiration and stimulates I neurons
Increases intensity of exhalation
What is the pneumotaxic centre?
Inhibits apneustic centre
Stops inhalation and promotes exhalation
How do central neurons determine ventilation rate?
They regulate tidal volume and respiratory rate
VR = TV x f
