Resp Physiology Flashcards
what are the resp centres in the brain?
pons
medulla
resp rate generated in medulla and modified in the pons
resp centres are mainly influenced by stimuli received from where?
mainly central chemoreceptors and peripheral chemoreceptors
resp centres are also influenced by stimuli received from where?
higher brain centres (cerebral cortex, limbic system, hypothalamus) stretch receptors juxtapulmonary (J) receptors joint receptors baroreceptors
how do stretch receptors work?
found in the walls of bronchi and bronchioles
inflation triggers hering-breur reflex which guards against hyperinflation
how do J receptors work?
stimulated by pulmonary capillary congestion and pulmonary oedema (also pulmonary emboli) and cause rapid shallow breathing
baroreceptor function?
increased ventilatory rate in response to decreased BP
factors which stimulate the resp centres cause what?
increased awareness of breathing discomfort - shortness of breath
what factors can stimulate resp centres?
hypoxia hypercapnia acidosis central arousal (anxiety etc) increased body temp pain joint movement during exercise drugs (amphetamines etc)
what do peripheral chemoreceptors do?
sense tension of oxygen and carbon dioxide and H+ concentration in the blood
what do central chemoreceptors respond to?
concentration of H+ in CSF
where are central chemoreceptors found?
near the surface of the medulla
where are peripheral chemoreceptors found?
carotid bodies
aortic bodies
describe the BBB
separates CSF from blood
relatively impermeable to H+ and HCO3
CO2 diffuses readily
why is CSF less buffered than blood?
contains less protein
buffer equation
CO2 + H2O <> H2CO3 <> H+ + HCO3
how does hypercapnia influence ventilation?
CO2 generates H+ in CSF which stimulate central chemoreceptors
increased CO2 = increased ventilation
(most potent stimulation of respiration in normal people)
how does hypoxia influence respiration?
ventilation increases as oxygen levels drop
peripheral chemoreceptors are stimulated first as oxygen levels drop
once oxygen levels drop below a certain level neurons are depressed and ventilation decreases again
how does hypoxia drive respiration?
effect is all via peripheral chemoreceptors
- only stimulated when pO2 <8 kPa
not important in normal respiration but becomes important in chronic CO2 retention (COPD) and at high altitudes
how does H+ drives respiration?
effect is via peripheral chemoreceptors as H+ doesnât cross BBB
peripheral chemoreceptors help adjust for acidosis caused by addition of non-carbonic acid H+ to the blood (lactic acid from exercise, DKA etc)
their stimulation by H+ causes hyperventilation and increases elimination of CO2 from the body
(CO2 helps generate H+ so elimination of CO2 reduces load of H+)
effect of increased CO2 in arterial blood and increased H+ in CSF?
strongly stimulates central chemoreceptors
dominant control of ventilation
weakly stimulates peripheral chemoreceptors
effect of increased H+ in arterial blood?
stimulates peripheral chemoreceptors
important in acid base balance
doesnât affect central chemoreceptors as arterial H+ cant penetrate BBB
what does the ventilatory pump consist of?
resp muscles peripheral nerves chest wall pleura (transmural pressure gradient) airways
what factors affect the ventilatory pump?
neuromuscular weakness
decreased compliance of chest wall
loss of transmural pressure gradient across lungs (pneumothorax)
increased airway resistance
inspiration is active or passive?
active (depends on active process)
expiration is passive
how is the volume of the thorax increased?
increased vertically by contraction of diaphragm (major resp muscle)
external intercostal muscle contraction lifts ribs and moves out sternum (bucket handle mechanism)
accessory muscles of inspiration?
sternocleidomastoid scalenus (only contract during forceful inspiration)
muscles of active expiration?
internal intercostal muscles abdominal muscles (contract only during active expiration)
major muscles of inspiration?
diaphragm
external intercostal