Control of ventilation Flashcards
Two types of chemoreceptors that control ventilation Effects of PaCO2, PaO2 and pH on chemoreceptors and ventilation Relationship between the chemical control of ventilation and acid-base balance Describe the priority of responses to changes in PaCO2 and PaO2, and the role of CSF pH
What are the roles of chemoreceptors? (2)
Chemical control of ventilation
Detect changes in arterial pCO2, pO2 and [H+]
What are the 2 types of chemoreceptors, where are they located and what do they detect?
Central chemoreceptors: Medulla - [H+] and pCO2
Peripheral chemoreceptors: aortic arch and carotid arteries - pO2 and pH
Explain the what happens at the blood brain barrier: (5)
- Increase of pCO2 causes CO2 to diffuse out of the blood vessel
- CO2 + H2O H2CO3 HCO3- + H+
- Increase in H+ extracellular fluid and cerebrospinal fluid. Detected by CCRs and leads to hyperventilation
- Hypervewntilation decrease pCO2 in blood and CSF
- Decrease pCO2 = hypoventilation
What is the blood brain barrier impermeable and impermeable to?
Impermeable: H+ & HCO3- (ions)
Permeable: CO2
What do pCO2 levels indirectly cause?
Indirectly activates CCRs causing a response of hyper or hypoventilation
What does the aortic arch detect and what is the result of this?
Arterial O2, CO2 levels
Hyperventilation when O2 decreases below 13.3mmHg (kPa)
What does the carotid artery detect?
pH levels
What is the priority of responses from a ventilation stimulus?
- PCO2
- pH
- PO2
What chemoreceptors are most sensitive to PCO2?
CCRs - levels held within 0.3kPa
What chemoreceptors are quickest to detect rapid changes in PCO2?
PCRs - levels held within 1.3kPa
Why do we control PCO2?
Avoid acid-base problems
How can we increase ventilation? (3)
Decrease pH making it more acidic
Increase CO2
Increase ventilation to remove CO2
What chemoreceptors detect changes in PO2?
PCRs - stimulated when levels drop lower than 13.3kPa
Why control PO2?
Avoid hypoxia
What is neural regulation of ventilation? (2)
Sets the rhythm and pattern of ventilation
Controls respiratory muscles
What is chemical regulation?
Detects central and peripheral arterial PCO2 and pH and peripheral PO2
Why is neural regulation faster than chemical regulation? (2)
Neural control - dependent on fast acting impulses to and from the CNS
Chemical control - responds to changes in partial pressure of CO2/O2
What are the parts in the medulla? (2)
Dorsal respiratory group (above ventral)
Ventral respiratory group
What is the role of the dorsal respiratory group? (3)
- Fibres from DRG innervate the diaphragm and external intercostal muscles
- Diaphragm contraction and thoracic cavity expansion causes inspiration
- DRG neurone switch on for 2s and switch off for 3s causing a rhythmic pattern
What is the role of the ventral respiratory group? (2)
- Fibres from VRG innervate the abdominal muscles and internal intercostal muscles
- Activity enhanced during forced expiration
What is involved within the Pons section of the brain? (2)
Pneumotaxic centre (above the medulla) Apneustic center
What is the role of the pneumotaxic centre? (5)
- Transmit signals to the DRG
- Role is to limit inspiration
- Fine tunes breathing - inhibits DRG with impulses
- Limit the period of inspiration to 2s
- Prevents over-inflammation of the lungs
What is the role of the apneustic centre? (3)
- responsible for prolonged inspiratory gasps
- Prolong DRG stimulation
- Apneusis observed in severe brain injury
What is the role of the vagus nerve? (2)
Sends afferent information from lungs to DRG
Role is to prevent over inflation of the lungs by switching off inspiration
What are the higher brain centers involved in ventilation? (5)
Cerebral cortex - breathing rate and depth
Hypothalamus - homeostasis, endocrine, thirst
Pons
Medulla
Brainstem
What is the role of the cerebral cortex? (3)
- Stimulates motor neurones of the inspiratory muscles
- Bypasses the medullary centers when consciously holding breath
- Limited ability to holds breath - respiratory centers automatically reinitiate breathing when O2 conc in blood reaches critical levels (drowning)
What is the role of the hypothalamus?
- Strong emotions, pain and changes in temp can alter rate and rhythm
- Apnoea (suspension of breathing) can be induced by anger, pain or decrease in temp
- Tachypnoea (rapid breathing) can bee induced by excitation or increase in temp
What are stretch receptors and where are they located? (4)
- Respiratory reflexes
- located in smooth muscle of trachea and bronchi
- Sensitive to lung expansion
- Stops overinflation of the lungs by short, shallower breaths
What are juxtapulmonary receptors? (3)
- Lie in the alveolar wall between epithelium and endothelium
- Stimulated by congestion, oedema, histamine
- Activation results in responses such as apnoea or rapid shallow breathing, bronchoconstriction and mucus secretion
What are irritant receptors? (4)
- Respiratory reflexes
- Located between epithelia cells
- Sensitive to irritant gases, smoke and dust
- Activation results in rapid shallow breathing, cough, bronchoconstriction, mucus secretion, augmented breaths
