Control of ventilation Flashcards
what does ventilatory control require the stimulation of?
skeletal muscle of inspiration ie diaphragm, external intercostals (contract to elevate ribs)
what does ventilatory control physically occur by
phrenic nerve (to diaphragm) think DIAPHR-ENIC intercostal nerves (to external intercostal muscles)
what are the respiratory centres in the brain and what do they govern
pons and medulla
the rate and depth of respiration
is ventilatory control subconscious?
yes but it can be subject to voluntary modulation
what is breathing entirely dependent on
signalling from the brain
what crosses the blood brain barrier when PCO2 increases
CO2
what do central chemoreceptors monitor indirectly in the CSF
PCO2
common drugs that depress the respiratory centre
Barbiturates and opioids
examples of sitmuli that influence activity of respiratory centres
emotion
Voluntary over-ride (conscious decisions)
Mechano-sensory input from the thorax
chemoreceptor input
what is the most important stimuli
chemoreceptor input
what 2 types of chemoreceptors are there?
central and peripheral chemoreceptors
where are central chemoreceptors found and what do they respond to
in the medulla
respond directly to H+ (derived from CO2)
which are the primary ventilatory drive?
central chemoreceptors
where are peripheral chemoreceptors found and what do they respond to
carotid and aortic bodies
clusters of cells located on the common carotid artery and the aortic arch
respond primarily to plasma [H+] and PO2 (less so to PCO2)
which are the secondary ventilatory drive?
peripheral chemoreceptors
what parts of the body do the ventral respiratory group of neurons (VRG) supply?
Tongue, pharnyx, larynx, expiratory muscles
what parts of the body do the dorsal respiratory group of neurons (DRG) supply?
inspiratory muscles via the phrenic and intercostal nerves
what do central chemoreceptors detect around the brain
changes in H+ concentration in CSF
why do H+ levels rise in CSF
due to raised CO2 levels, so raised PCO2 when these rise H+ conc also rises
what is a raised PCO2 called
hypercapnea
how does hyperventilation occur? mention PCO2, H+ and chemoreceptors
ventilation is reflexly inhibited by a decrease in arterial PCO2
this reduces CSF H+ conc and as a result, switches off central chemoreceptors
True or false: central chemoreceptors don’t respond to direct changes in plasma [H+] because of the blood brain barrier
true
what happens when arterial PCO2 increases
CO2 moves across the blood brain barrier (gases can, not H+ as it is an ion)
what does PCO2 form in the CSF after passing through blood brain barrier
produces bicarbonate and H+
the receptors then respond to this increase in H+
what happens at the respiratory centres when PCO2 increases?
the respiratory centres increase ventilation rate
what change do peripheral chemoreceptors detect?
changes in arterial PO2 and H+ concentration
what happens when there is a significant fall in arterial PO2 or a rise in H+ conc?
Reflex stimularterialation of ventilation
if you have chronic lung disease how does your body detect changes in PO2
In people with chronic lung disease their PCO2 is chronically elevated so they become desensitised to PCO2 and instead rely on changes in PO2
where are peripheral chemoreceptors found
carotid and aortic bodies
if plasma pH falls ([H+] increases) what happens?
ventilation will be stimulated (acidosis)
if plasma pH rises ([H+] decreases) what happens?
e.g.vomiting (alkalosis), ventilation will be inhibited
CO2 to carbonate equation
CO2 + H20 –> H2CO3 –> HCO3- + H+
why can a person have a huge amount of voluntary control over breathing?
Descending neural pathways from cerebral cortex to respiratory motor neurons
True or false: Respiration is inhibited during swallowing to avoid aspiration of food or fluids into the airways.
True
what is the vagus nerve
the 10th cranial nerve and interfaces with parasympathetic control of the lungs
what follows swallowing?
Swallowing is followed by an expiration in order that any particles are dislodged outwards from the region of the glottis.
what will happen to resp rate in an anaemic patient with a blood oxygen content half the normal value
stay the same
What is anaemia
number of red blood cells or the amount of haemoglobin in red blood cells is less than normal- means less binding sites as less haemoglobin.
examples of other aspects of control of breathing
breath holding
hyperventilation
you cannot override involuntary stimuli such as PCO2 or H+ conc
decending neural pathways from cerebral cortex to respiratory motor neurons
What are accessory muscles of inspiration and when are they used?
sternocleidomastoid (contracts to elevate sternum)
pectoralis major and minor (push/pull ribs inwards/outwards)
serratus anterior (on side of rib cage)
latissimus dorsi (large muscle on the back)
serratus posterior superior.
typically only used under conditions of high metabolic demand (e.g. exercise) or respiratory dysfunction (e.g. an asthma attack).
