Control of Respiration Flashcards
name and state the location of the respiratory centres (Nuceli) ; indicate briefly what their function is thought to be
medulla is major rhythm generator
pons - fairly normal ventilation retained if section above medulla
spinal cord - ventilation ceases if section below medulla
explain how rhythmic breathing is thought to be established
rhythm - inspiration followed by expiration
breathing rhythm generated by network of neurones called Pre-Botzinger complex
these neurones display pacemaker activity
located near upper end of medullary respiratory centre
rhythm is generated by Pre-Botzinger complex
this excites dorsal respiratory group neurones (inspiratory)
fire in bursts
firing leads to contraction of inspiratory muscles - inspiration
firing stops - passive expiration
describe involuntary modifications of breathing - joint receptors
impulses from moving limbs reflexively increase breathing
contributes to increased ventilation during exercise
describe factors that increase ventilation during exercise
reflexes originating from body movement adrenaline relsease impulses from cerebral cortex increase in body temperature accumulation of carbon dioxide and H+ generated by active muscles
describe involuntary modifications of breathing - cough reflex
vital part of body defence mechanism
helps clears airways of dust, dirt or excessive secretion
activated by irritation of airways or tight airways (e.g. asthma)
centre in the medulla
afferent discharge stimulates;
short intake of breath, followed by closure of larynx, the contraction of abdominal muscles (increases intra-alveolar pressure_ , and finally opening of the larynx and expulsion of air at high speed
describe the chemical control of respiration
negative feedback control system
controlled variables are the blood gas tensions, especially carbon dioxide
chemoreceptors sense the values of gas tensions;
situated near the surface of the medulla of the brainstem
repsond to the {H+] of the cerebrospinal fluid (CSF)
CSF is separated from blood by the blood-brain barrier - relatively impermeable to H+ and HCO3-, CO2 diffuses readily
CSF contains less protein than blood and hence is less buffered than blood
CO2 + H2O H2CO3 H+ + HCO3-
peripheral chemoreceptors sense tensions oxygen and carbon dioxide; and [H+] in blood
describe hypercapnia and ventilation
hypercapnia is a build up of CO2 in the blood as a result of hypoventilation (holding your breath)
system is very response to PCO2 - CO2 generated H+ through the central chemoreceptors
describe hypoxic drive of respiration
effect is all via peripheral chemoreceptors
stimulated only when arterial PO2 falls to low levels (<8.0 kPa)
not important in normal respiration
may become important in patients with chronic CO2 retention (e.g. COPD)
important in high altitudes
describe the chemical control of respiration
negative feedback control system
controlled variables are the blood gas tensions, especially carbon dioxide
chemoreceptors sense the values of gas tensions (strong stimulation - dominant control of ventilation);
situated near the surface of the medulla of the brainstem
repsond to the {H+] of the cerebrospinal fluid (CSF)
CSF is separated from blood by the blood-brain barrier - relatively impermeable to H+ and HCO3-, CO2 diffuses readily
CSF contains less protein than blood and hence is less buffered than blood
CO2 + H2O H2CO3 H+ + HCO3-
peripheral chemoreceptors sense tensions oxygen and carbon dioxide; and [H+] in blood
describe hypoxia and ventilation
hypoxia is when a region of the body is deprived of adequate oxygen supply at tissue level
the central chemoreceptors depress the reparatory centre in severe hypoxia
neuron depressed when hypoxia so severe
peripheral chemoreceptors stimulated
describe the H+ drive in respiration
central chemoreceptors - H+ does not readily cross blood brain barrier (CO2 does)
effect is via peripheral chemoreceptors
peripheral chemoreceptors play a major role in adjusting for acidosis caused by addition of non-carbonic acid H+ to the blood )e.g. lactic acid dying exercise; and diabetic ketoacidosis)
their stimulation by H+ causes hyperventilation and increases elimination of CO2 from the body (CO2 can generate H+, its increased elimination can help reduce the load of H+ in the body)
important in acid-base balance
describe active expiration during hyperventilation
increased firing of dorsal neurones exciting a second group
ventral respiratory group neurones
excite internal intercostals, abdominals -> forecul expiration
describe how the rhythm generated in the medulla can be modified
modified via neurones in pons - pneumotaxic centre
stimulation terminates inspiration
PC stimulated when dorsal respiratory neurones fire
inspiration inhibited
without PC breathing is prolonged inspiratory gasps with brief expiration - apeneusis
describe the apneustic centre
impulses from these neurones excite inspiratory area of medulla
prolonged inspiration
describe how the respiratory centres can be influenced by stimuli
receive stimuli from;
higher brain centres (cerebral cortex, limbic system, hypothalamus)
stretch receptors in walls of bronchi and bronchioles - the inflation of Hering-Breur reflex - guard abasing hyperinflation
J receptors - stimulated via pulmonary capillary congestion and pulmonary oedema and pulmonary emboli –> rapid shallow breathing
joint receptors
baroreceptors - increased ventilatory rate in response to decreased blood pressure
