Control of breathing Flashcards
What are the methods of controlling breathing?
Neural control: Controlled by motor neurons in the brain which innervate respiratory muscles
Chemical control: Controlled by PO2, PCO2 and H+ concentrations
What are the respiratory centers of the brain?
Medulla oblongata: Comprised of the Dorsal Respiratory Group (DRG) and Ventral Respiratory Group (VRG)
Pons: Comprised of Pneumotaxic Center and Apneustic Center
Characteristics of medullary center
DRG and VRG are bilaterally located and bilaterally connected
Characteristics of the DRG
Lies in the dorsal part of the medulla
Functions:
Generation of basic rhythm of respiration initiated by pacemaker cells in the pre-Bötzinger complex (pre-BÖTC)
Stimulation of DRG emit signals → contraction of the diaphragm and external intercostal → INSPIRATION
Inhibition of DRG → relaxation of the diaphragm and external intercostal → EXPIRATION
Characteristics of VRG
Lies in the ventral part of the medulla.
Inactive during normal quiet breathing
Active during deep expiration
Function:
Stimulation of VRG → contraction of abdominal and internal intercostal muscles → DEEP EXPIRATION
Characteristics of Apneustic Center
Lies in the lower part of the pons
Function:
Stimulates DRG inspiratory neurons → prevents neurons from being switched off → PROLONGS DURATION OF INSPIRATION
Characteristics of Pneumotaxic Center
Lies in the upper pons
Functions:
Helps switch between inspiration and expiration
Inhibits the DRG inspiratory neurons → SHORTENS INSPIRATION DURATION thus INCREASING BREATHING RATE
What is the Hering-Breuer reflex?
Overstretching of lungs → Stimulation of stretch receptors in the wall of the bronchi and bronchioles → Inhibition of inspiratory center → Decrease the duration of inspiration and increase the rate
What are the sites of neural control of respiration?
Higher centers: Brain (voluntary control) and Hypothalamus (Pain, emotion)
Lungs: Hering-Breuer reflex
Air passages: Sneezing, Cough and Swallowing
Circulatory system: Increase venous return → stimulates respiratory system to increase ventilation of this venous return
Skeletal muscles and joints: Exercise increases respiration
Visceral reflex: Swallowing and Vomiting inhibit respiration
What chemical factors influence breathing?
Stimulated by: ↑ PCO2 in arterial blood, ↑H+ in arterial blood and ↓O2 in arterial blood
Inhibited by: ↓PCO2 in arterial blood, ↓H+ in arterial blood and ↑O2 in arterial blood
Where are changes in chemical factors detected?
Central and peripheral chemoreceptors
Central chemoreceptors exert a more powerful response than peripheral chemoreceptors
What are the sites of the central chemoreceptors?
Chemosensitive area (bilaterally located in the medulla)
Which stimuli affect the central chemoreceptors?
Highly sensitive to changes in blood PCO2 or H+ concentration
H+ concentration is the primary stimulus for central chemoreceptors
H+ cannot cross the blood brain barrier, so the source of H+ in the brain is from CO2 (whihc can cross the blood brain barrier)
CO2 + H2O → H2CO3 (catalysed by carbonic anhydrase enzyme)
H2CO3 → H+(which stimulates the central chemoreceptors) + HCO3-
What are the sites of the peripheral chemoreceptors?
Carotid bodies: Bifurcation of the common carotid → innervated by glossopharyngeal nerve → stimulates DRG
Aortic bodies: along the aortic arch → innervated by vagus nerve → stimulates DRG
Which stimuli affect the peripheral chemoreceptors?
Decreased arterial PO2 (Mainly)
Increased arterial PCO2
Increased arterial H+ concentration
Effect of decreased arterial PO2?
Stimulates peripheral chemoreceptors
Maximum potential increases in ventilation of 5-6 times
Effect of increased arterial PCO2?
Weaker stimulation of peripheral chemoreceptors but strong stimulation of central chemoreceptors
Maximum potential increase in ventilation rate of 11 times
