Control Of Breathing Flashcards
What are the two key tasks of breathing control?
- Establish automatic rhythm
- Adjust the rhythm to accommodate
- metabolic (arterial blood gases and pH)
- mechanical (postural changes)
- episodic non-ventilatory behaviours (speaking, sniffing, eating)
How is breathing controlled?
Changes in blood flow and oxygen delivery → local
Changes in depth and rate of respiration → central
This involves a complex interaction between local and central mechanisms.
What is the balance achieved between O2 and CO2 in normal conditions?
O2: rate of absorption is matched to delivery; CO2: rate of generation is matched to removal
This balance is crucial for maintaining homeostasis in the body.
What happens to P_O2 and P_CO2 in active tissue?
↓P_O2 —> increases O2 delivery and blood flow
↑P_CO2 —>↑CO_2 removal and ↑blood flow (vasodilation)
What effect does ↓P_O2 have on lung perfusion?
Vasoconstriction, ↓ blood flow
directs blood to areas of higher P_O2
What do central chemoreceptors respond to?
Located in medulla
- change in pH
- Hypercapnia (increased CO2)
- no effect of hypoxia
Which gas has no effect on central chemoreceptors?
P_O2
Central chemoreceptors do not respond directly to changes in oxygen levels.
What are peripheral chemoreceptors sensitive to?
Hypoxia, hypercapnia, and changes in pH
Located in the aortic and carotid bodies, they play a crucial role in ventilatory responses.
What is the Hering-Breuer reflex?
A defense mechanism that inhibits respiratory centers in response to over-inflation
Involves slowly adapting stretch receptors in the lungs.
What happens during respiratory acidosis?
Increased P_CO2 (>43 mmHg) leads to more H+ released and a drop in pH (pH < 7.35)
Equation shifts to the right
CO2 + H2O <—> H2CO3 <—> H+ + HCO3-
This condition can arise from limited gas exchange, such as in emphysema.
What is the response when P_O2 drops below 60 mmHg?
Ventilation is increased
This response is mediated by peripheral chemoreceptors.
What are the three types of mechanoreceptors in lung tissue?
Characterised by response to lung inflation
- Slowly adapting stretch receptors = Hering Breuer reflex
- Rapidly adapting stretch receptors = cough reflex
- C-fibre receptors = defence mechanism
What is the role of the rhythmicity center in the medulla?
Controls automatic breathing
It consists of interacting neurons that fire during inspiration and expiration.
What do the pneumotaxic and apneustic centers in the pons do?
Modify firing patterns of medullary centers to regulate respiratory rate and depth
(Adjust rate & depth at which we breathe)
How does the body respond to increased levels of CO2?
Increased ventilation rate and depth
CO2 and H+ are key regulators of breathing.
Fill in the blank: The equation for ventilation rate (VR) is VR = ______.
TV x f
Where TV is tidal volume and f is respiratory rate.
True or False: Central chemoreceptors mainly detect changes in O2 levels.
False
Central chemoreceptors primarily respond to CO2 levels.
What effect does high P_CO2 have on alveolar ventilation?
Bronchodilation = increases air flow
Directs airflow to areas of higher P_CO2
What factors influence the rate and depth of breathing?
- change in body demands eg. Exercise
- altitude - acute mountain sickness
- disease
- changing levels of CO2, H+ and O2
Only a problem when pO2 of alveolar gas and arterial blood falls below 60 mmHg
What are mechanoreceptors sensitive to?
Lung receptors
- respond to stretch
- rapidly adapting receptors
- slow adapting receptors
- C-fibres receptors
What is the role of central chemoreceptors?
- located just beneath the ventral surface of the medulla
- close entry of VII & XI (type of) cranial nerves
- stimulated by acidic or high pCO2 in the cerebral spinal fluid (CSF)
High pCO2 —> lowers pH —> increases ventilation to exhale more CO2 —> lowers pCO2
CO2 crosses the blood-brain barrier = lipid soluble (CSF is only weakly buffered)
What is the role of peripheral chemoreceptors?
- detect changes in pO2, pCO2 and pH
- located outside the brain in the carotid body at bifurcation (where it splits) of carotid arteries
- Innervated by carotid sinus nerve (CSN) which is a branch of the glossopharyngeal nerve
- aortic bodies above and below the aortic arch
- Innervated by the vagus
What happens in respiratory alkalosis?
Decreased pCO2 (<37 mmHg) means less H+ and an increase in pH (>7.45)
Equation shifts to the left
CO2 + H2O <—> H2CO3 <—> H+ + HCO3-
E.g. hyperventilation (during panic attacks)
What happens when pO2 changes?
pO2 goes up
- Generates free radicals leading to coma and death
- e.g. breathing oxygen-rich gas mixtures
pO2 goes down
- arterial pO2 must drop below 60 mmHg before ventilation is increased
- central chemoreceptors switch off (as don’t respond to pO2)
- Peripheral chemoreceptors increase breathing rate
What is the role of slow adapting stretch receptors?
Known as bronchopulmonary stretch receptors
Located in the visceral pleura, bronchioles and alveoli
Over inflation —> increase discharge of receptors —> inhibition of respiratory centres
Known as the Hering-Breuer reflex = forces exhalation
What is the role of rapidly adapting stretch receptors?
Known as irritant receptors
Located in airway epithelia (close to mucosa)
Irritating stimulants (i.e. noxious gases, smoke, dust or cold air) —> increases discharge of the irritant receptors —> bronchoconstriction = coughing reflex
Shape the ventilatory pattern and protecting the airway
Initially fire rapidly but then soon decrease their firing rate
What is the role of C-fibres receptors?
Known as J receptors
Located in alveoli wall (close to the capillaries) and conducting airways (bronchial mucosa)
Chemical/ mechanical stimuli —> increase discharge of the receptors —> bronchoconstriction = rapid shallow breathing and mucus secretion
E.g. mechanical
Left heart failure causes engorgement of the pulmonary capillaries (due to backflow of blood)
Innervates the C-fibres receptors causing rapid shallow breathing
What is the role of the rhythmicity centre?
Set pace for respiratory movements
- I neurons in DRG regulate activity of phrenic nerve = set rhythm and stimulate muscles of quiet inspiration
- E neurons in VRG is a passive process = activity of E neurons inhibit I neurons
- Pneumotaxic and Apneustic centres of the pons adjust the output of the rhythmicity centres
What is the Dorsal Respiratory Group (DRG)?
Location in the medulla where I neurons (inspiratory neurons) are = inspiratory centre
What is the Ventral Respiratory Group (VRG)?
Location in the medulla where E neurons (expiratory neurons) and I neurons (inspiratory neurons) are = Expiratory centre
What is the role of the Pneumotaxic and Apneustic centres?
Modify firing pattern of medullary centres
Regulate respiratory rate and depth of respiration
Apneustic centre
- promotes inspiration, stimulates the I neurons
- increases intensity of inhalation during respiration cycle
Pneumotaxic centre
- inhibits Apneustic centre
- stops inhalation and promotes exhalation
