Control of ventilation Flashcards
Why do we need to breathe in oxygen and breathe out carbon dioxide?
To take in O2 – requirement for generating ATP through oxidative phosphorylation
To remove CO2 – a by-product of respiration
What is the volume of expiration equation?
VE = breathing frequency (f) X tidal volume (VT)
What affects the amount of breathing?
- Activity vs rest: O2 consumption can increase > 10-fold
- Altitude: Less O2 in the air so need to work harder to maintain O2 supply
- Disease: Compromising gas exchange or delivery
(pulmonary diseases e.g. emphysema)
(cardiovascular diseases; heart and vasculature)
Sleep apnoea – periodic cessation during sleep
Opioid depression of breathing
Conditions of chronic hypercapnia – require oxygen sensing
What are the 3 parts to respiration?
Factors/ sensors providing information to R centre- chemoreceptors, lung receptors and other receptors. Then the R centre- containing the medulla and pons. Then the output to the muscles; diaphragm, intercostal, abdominal and accessory muscles.
What is in the R centre
Medulla- lowest part of brain- primary centre.
Pons has inputs which can influence respiratory centre.
VRG and DRG responsible for respiratory neurones.
What does the VRG (ventral respiratory group) and the DRG (dorsal respiratory group) do?
VRG (ventral respiratory group) -contains mixed neurones
some fire during inspiration,
some during expiration
DRG (dorsal respiratory group)- contains neurones
which fire during inspiration
Do DRG and VRG inhibit each other?
Yes
What are the influence of Pons?
- Apneustic centre -Stimulates inspiratory neurones
* Pneumotaxic centre- Inhibits inspiratory neurones
How can inspiratory activity be depressed?
Inspiratory activity can be depressed by hypoxia, a wide variety of therapeutic drugs (opiates, barbiturates and anaesthetic agents) and inhibition of blood supply.
Factors / sensors providing information to the respiratory centre- higher brain influences- cortical and hypothalamic
• Cortical
-Voluntary hyperventilation – hypocapnia (low CO2) – alkalosis
-Voluntary breath holding – hypoxia (low O2) – unsustainable
• Hypothalamic
-Emotions – anger/anxiety = hyperventilation
-Sensory reflexes – pain, cold = hyperventilation/gasping
Factors / sensors providing information to the respiratory centre- pulmonary stretch receptors
- Afferent fibres from smooth muscle of bronchi and trachea
- Run in the vagus nerve to the respiratory centre (medulla)
- As inspiration progresses, impulses from stretch receptors increase
Hering-Breuer lung inflation reflex equation
=limits breathing frequency (f) X tidal volume (VT)
Factors / sensors providing information to the respiratory centre- irritant/ cough receptors
- Receptors throughout the airways which when stimulated initiate an explosive expiration – a cough
- Afferent fibres from these receptors run in the vagus to the respiratory centre.
- Others, also found in the upper airways and nose are irritant receptors. Stimulation leads to hyperpnoea (deep inhalation), and airway constriction which can lead on to coughing and also contribute to sneezing
- Local anaesthetics prevent these reflexes when passing endotracheal or nasogastric tubes into patients
Factors / sensors providing information to the respiratory centre- Muscle / joint stretch receptors and proprioreceptors- Muscle spindles
- Rich in intercostals, few in diaphragm
- Activated by stretch associated with contraction of breathing, but spindles in exercising muscles elsewhere can also stimulate breathing
Factors / sensors providing information to the respiratory centre- Muscle / joint stretch receptors and proprioreceptors- Proprioceptors
- In the joints
- Relay information about activity induced motion which can influence ventilation
What do baroreceptors do?
Baroreceptors, which sense blood pressure, can also influence ventilation
(blood pressure leads to decrease ventilation and vice versa)
What do J-receptors do?
J-receptors (juxtacapillary) lie close to (juxtaposed to) capillaries around the alveolar walls. They are activated by “traumas” such as pulmonary oedema (fluid in the alveoli), inflammatory agents, pneumonia. Their activation triggers increased ventilation.
Central chemoreceptors what do they do?
- Specialized regions close to medulla respiratory centres, but also close to a rich blood supply. Sensitive to CO2 and H+
- H+ cannot cross the blood-brain barrier, but CO2 can, which informs about H+ levels:
- A rise of CO2 or a rise of [H+] (= fall of pH, or acidosis) stimulates the central chemoreceptors and increases ventilation
Peripheral chemoreceptors- sensitive to what?
- Carotid and aortic bodies
- Sensitive to hypoxia (low O2), hypercapnia (high CO2) and acidosis (high [H+])
- CO2 goes up = ventilation rate increases until you become adapted
What is the neuronal process?
Hypoxia triggers Ca2+ influx into glomus cells via depolarization (like a nerve terminal). The Ca2+ triggers release of transmitters which initiate action potentials in the afferent nerve. Dopamine is one transmitter released, but the excitation is from ATP and acetylcholine.
What does the glomus body do?
Glomus body- sensor causing signal transduction in afferent nerve into the brain
Main organ regulating R function during hypoxia/ hyepercapnia.
