Control of Ventilation Flashcards
Why is oxygen required?
To generate ATP through oxidative phosphorylation
If you eat lots of fats, how does this affect O2 intake?
Need to take in more O2
If you eat lots of carbohydrates, how does this affect O2 intake?
Need to take in less O2
What is the equation of minute ventilation?
Minute ventilation = breathing frequency x tidal volume 5L = 10 breaths per min x 500ml per breath (normal)
How much of breath is lost in dead space?
150ml of lung volume is dead space. Not all breath gets to lungs as last 150ml is lost (350ml gets to lungs)
How much can O2 consumption increase by during exercise?
10x
What can happen as a result of not getting rid of CO2 quick enough?
Acidosis
How can altitude affect breathing?
Less O2 in the air so need to work harder to maintain O2 supply
How is altitude sickness caused?
Hypoxic (due to lack of O2 in air) which generates reflex to respire more and breathe out more CO2. This causes CO2 levels to drop, causing you to stop breathing. (Alkalosis followed by acidosis)
How is altitude sickness treated?
Inhibit loss of bicarbonate ions in renal function which causes acidosis (so when you breathe harder to make up for hypoxia, you don’t generate alkalosis as a result)
How can sleep apnoea affect breathing?
Periodic cessation during sleep. Hypoxic effect in blood stimulates ventilation again and wakes patient up.
What are the 2 types of chemoreceptors?
Peripheral and central
Where are peripheral chemoreceptors?
Located in carotid body and aortic arch.
What are peripheral chemoreceptors sensitive to? What do they do?
Sensitive to hypoxia (low O2), hypercapnia (high CO2) and acidosis (high H+)
Detect large changes in pO2 as the arterial blood leaves the heart. Relatively insensitive but effects are almost instant.
What happens if peripheral chemoreceptors detect abnormally low pO2?
Afferent impulses travel to the respiratory centres in the brainstem and a number of response are coordinated which aim to increase pO2 again. 1. Increase respiratory rate and tidal volume –> allows more O2 to enter the lungs 2. Directing blood flow towards kidneys and brain (organs most sensitive to hypoxia) 3. Increasing cardiac output to maintain blood flow and O2 supply to body’s tissues
Where are central chemoreceptors?
Located in the medulla oblongata of the brainstem. Close to the medulla respiratory centres but also close to a rich blood supply
What do the central chemoreceptors do?
Sensitive to CO2 and H+
Receptors are more sensitive and detect smaller changes in arterial pO2. Constantly initiate negative feedback loops which act to control our respiratory system.
What happens if central chemoreceptors detect an increase in pCO2?
Leads to increase in ventilation, resulting in more CO2 being blown out so pCO2 returns to normal
What happens if central chemoreceptors detect a decrease in pO2?
Leads to a decrease in ventilation, resulting in more CO2 being retained in our lungs so pCO2 returns to normal.
Where is the respiratory centre? What does it control?
In the brain. Controls automatic breathing.
What receptors are in the lungs?
- Pulmonary stretch receptors (give reflex to stop lungs over expanding) 2. J receptors (C afferent fibres and sensitive to diseases that cause hypoxia) 3. Cough or lung irritant receptors
What are examples of input receptors?
Chemoreceptors, lung receptors, nasal and upper airway receptors, muscle stretch receptors, joint proprioceptors, arterial baroreceptors
What can override respiratory centre control?
Cortical control of voluntary breathing
What are the effector muscles of respiration?
- Diaphragm 2. Intercostal muscles 3. Abdominal muscles 4. Accessory muscles
What is medulla?
Core centre of respiratory control –> inspiratory and expiratory areas
What is the pons?
The largest part of the brainstem, located above the medulla and below the midbrain.
Has inputs which can influence respiratory centre (regulates medulla) Apneustic and pneumotaxic areas
What group must still function in the medulla for you to keep breathing?
Dorsal respiratory group in medulla. Responsible for inspiration.
What is ventral respiratory group (VRG) responsible for?
Mainly responsible for expiration
What are the reciprocal inhibitions of DRG and VRG?
DRG inhibits VRG and vice versa
What does the pneuomotaxic centre do?
Inhibits inspiratory neurones and activates inspiratory off switch
What does apneustic centre do?
Stimulates inspiratory neurones and prolongs inspiratory phase
What can inspiratory activity be depressed by?
Hypoxia, a wide variety of therapeutic drugs (opiates, anaesthetics), inhibition of blood supply
What are the 2 higher brain influences on respiratory?
- Cortical
- Hypothalamic
What does cortical control?
Voluntary hyperventilation
Voluntaru breath holding
What can voluntary hyperventilation lead to?
Hypocapnia (low CO2) –> alkalosis
What can voluntary breath holding lead to?
Hypoxia (low O2) –> unsustainable
What does hypothalamic control?
Emotions (anger, anxiety)
Sensory reflexes (pain, cold)
What can emotions/sensory reflexes lead to/
Hyperventilation
Gasping/hyperventilation
What are pulmonary stretch receptors?
Afferent fibres from smooth muscle of bronchi and trachea.
Where do pulmonary stretch receptors run?
Run in vagus nerve to the respiratory centre (medulla)
What happens during inflation to pulmonary stretch receptors?
During inspiration, bronchioles and trachea stimulate these receptors that has a feedback effect of inhibiting inspiration (don’t over inflate lungs). As inspiration progresses, impulses from stretch receptors increase.
What is the Hering-Breuer lung inflation reflex?
Reflex triggered to prevent over-inflation of lung
Pulmonary stretch receptors present on the wall of bronchi and bronchioles of the airways respond to excessive stretching of the lung during large inspirations
What are the irritant/cough receptors? Where are they found?
Cough - Receptors throughout the airways which, when stimulated, initiate an explosive expiration (cough)
Irritant - Found in upper airways and nose
Afferent fibres from these receptors run in the vagus to the respiratory centre
What does stimulation of the cough/irritant receptors cause?
An explosive irritation (a cough)
Stimulation leds to hyperpnoea (deep inhalation) and airway constriction –> leads to coughing and contributes to sneezing
When would local anaesthetics be used to prevent the reflexes of the cough/irritant receptors?
When passing endotracheal or nasogastric tubes into patients
What are muscle joint/stretch receptors?
Tension receptors in the muscles (rich in intercostals, few in diaphragm) that feed into the brainstem. Designed to measure how much tension/stretch is in muscle and feed into brainstem
What are muscle stretch receptors stimulated by?
Activated by stretch associated with contraction of breathing, but spindles in exercising muscles elsewhere can also stimulate breathing
What are proprioreceptors?
In joints. Relay information about activity induced motion which can influence ventilation
What are baroreceptors?
Sense blood pressure, which can also influence ventilation (increased blood pressure leads to decreased ventilation and vice versa)
What are J-receptors?
Lie close to capillaries around the alveolar walls. C-afferent fibres.
What are J-receptors activated by?
Activated by ‘traumas’ such as pulmonary oedema (fluid in the alveoli), inflammatoru agents, pneumonia. Their activation triggers increased ventilation
What are C afferent fibres?
Class of nerve fibre found in the somatic sensory system. Convey input signals from the periphery to the CNS
How are chemoreceptors informed about H+ even though H+ cannot cross the blood-brain barrier?
CO2 can cross the barrier
What happens to CSF during respiratory acidosis?
CO2 diffuses across blood-brain barrier and reacts with water –> makes carbonic acid and then H+ ions to be released. –> causes acidic CSF
What does an acidic CSF stimulate?
Stimuates the central chemoreceptors and increases ventilation
What is a carotid body? Where is it located?
Small cluster of chemoreceptor cells and supporting sustenacular cells
Located in the bifurcation (fork) of the common carotid artery which runs along both sides of the neck
What is the primary sensor of hypoxia?
Carotid body
How does hypoxia trigger carotid body?
Hypoxia triggers Ca2+ influx into glomus cells via depolarisation (like a nerve terminal). Ca2+ triggers release of transmitters which iniate action potentials in the afferent nerve that fires up to the brain
Describe the basic route from input to output regarding respiratory
- Input (chemical regulation, higher brain ‘override’, neural regulation)
- Centra respiratory centre (pons and medulla)
- Output (diaphragm, intercostals and other muscles involved in breathing)
Give one example of a transmitter released by the glomus cell? What causes this excitation?
Dopamine
ATP and acetylcholine
What 2 respiratory groups are present the medulla?
Dorsal respiratory group
Ventral respiratory group
Which respiratory group has the most fundamental role in breathing?
Dorsal –> initiates inspiration, set and maintain rate of respiration
Where is the pneumotaxic centre?
Located in the upper part of the pons
What does the pneumotaxic centre do?
Controls both the rate and the pattern of breathing.
Sends inhibitory signals to the inspiratory center of the medulla, provides an inspiratory ‘off switch’. Decreases tidal volume and regulates respiratory rate.
Is considered an antagonist to the apneustic centre.
What does the apneustic centre do?
Stimulates the inspiratory neurons of the DRG and VRG –> promote inhalation
Over stimulation from the apneustic center results in apneustic breathing which is characterised by long gasping inspirations interrupted by occasional expirations.
How is rate of breathing controlled?
The apneustic (stimulating) and pnuemotaxic (limiting) centers of the pons work together to control rate of breathing.
What part of the brain controls voluntary breathing?
The cerebral cortex
What do baroreceptors respond to?
What do chemoreceptors detect?
Detect the presence of chemicals.
What do proprioreceptors detect?
Sense of position
