Acid base in the Control of Respiration Flashcards
what receptors impact the respiratory control centre
- chemoreceptors
- mechanoreceptors
- peripheral chemoreceptors
- muscle propiroceptors
name the chemoreceptors
central chemoreceptors
name the mechanoreceptors
- Stretch
- J receptors
- irritant
name the peripheral chemoreceptors
- carotid
2. aortic
what do muscle proprioreceptors allow you to do
- they allow you to hold your breath for longer and they make you pretend to breath
what specialised tissues are in the ventricles of the brain
choroid plexus
what does the choroid plexus do
- it has capillaries in it that allow water and small ions to pass out
- fluid that escapes from this forms the cerebrospinal fluid, the cerebrospinal fluid fills the ventricles and this bathes the Brian in fluid
describe the structure of the choroid plexus
- endothelium is fenestrated
- ependyma - this regulates what an come out into the brain and what cannot for example water can come out but protein cannot
describe what chemoreceptors are and there job
- they are specialised neurones in the ventral surface of the medulla oblongata that are sensitive to the pH of the cerebrospinal fluid bathing them
How does carbon dioxide diffuse across to the CSF from the blood and what happens to it in the CSF
- diffuses freely through the blood brain barrier
- it then reacts with water to form carbonic acid, this is then converted to protons and bicarbonate by the enzyme carbonic anhydras
the concentration of protons in …
the CSF is directly proportional to carbon dioxide in the blood
what is on the ventral surface of the medulla
- there are chemoreceptors that are sensitive to pH
where are the chemoreceptors on the medulla
Ventral surface
what happens when acidity increases in the CSF
- increased acidity of the CSF increases the stimulation of chemoreceptors on the ventral surface of the medulla
- these stimulate neurones in the respiratory centres which are close to the chemoreceptors in the medulla
- this increases ventilation and depth and rate of breathing to expel more carbon dioxide from the lungs
- this reduces carbon dioxide in the blood
- therefore reduces acidity int he CSF as carbon dioxide in blood is directly proportional to hydrogen ions in the CSF
- this is a negative feedback system
what is the normal pH of the CSF
7.32
what does the choroid plexus not allow to diffuse through
- ## no plasma proteins are filtered through the choroid plexus thereof rehire CSF contains almost no protein
what does a lack of protein in the CSF mean
The lack of protein means it has a much lower pH buffering capacity than blood.
therefore the change in the CSF pH for a given change in Pco2 is greater than in blood
what happens to the chemoreceptors in chronic pulmonary disease
- there are chronically high levels of CO2 in the blood,
- the central chemoreceptors gradually become less sensitive (over a period of years) and the drive for ventilation from CO2 is reduced, therefore the blood and CSF is likely to become more acidic
what are the three lung based respiratory receptors
- pulmonary stretch receptors
- irritant receptors
- J receptors
describe what causes the activation of pulmonary stretch receptors
They respond when the lung is distended
- their activity is continued with lung inflation
- they show little adaptation.
describe what causes the activation of irritant receptors
- stimulated by noxious gases, cigarette smoke, inhaled dusts and cold air
describe what causes the activation of J receptors
- they respond to events such as pulmonary oedema, pulmonary emboli, pneumonia, congestive heart failure and barotrauma
where are irritant receptors found
they are found between epithelial cells in the trachea and large bronchi
what other types of receptors can influence respiration
proprioceptors - these are sensory endings in the joints and muscles
where are the pulmonary stretch receptors found
they are found in bronchioles and small bronchi
what do the pulmonary stretch receptors do
- they act as cut off switches that inhibit inspiration when lungs become fully inflated
- prevent damage to the delicate tissues of the lungs by overinflation
- prevent damage to the tissues of the lung by overinflation
They do this by .. - at the end of inspiration action potentials are sent through the afferents in the vagus nerve to the respiratory centres in the pons and medulla, this inhibits inspiration
- the inhibition of inspiration is known as the haring-breuer inflation reflex
what type of receptors are irritant receptors
mechanoreceptors
what do irritant receptors do
They detect the presence of objects in the airways too large to be carried away by mucus thus they activate cough reflexes.
what type of receptors are J receptors
chemoreceptors
what do J receptors do
- respond to events such as pulmonary edema, pulmonary emboli, pneumonia and barotrauma this causes a decrease in oxygenation
- thus they stimulate an increase in ventilation and respiration
- they detect fluid in alveoli and send afferent signals via vagus to stimulate the increased respiratory rate
ventilation response to arterial pressure of carbon dioxide is approximately ….
linear
why is the Ventilation Response to raised arterial partial pressure of CO2 is approximately linear
due to central chemoreceptors
what happens when you inhale carbon dioxide
- Each curve of total ventilation against alveolar PCO2 is for a different alveolar PO2.
- with the lower levels of oxygen the curve is steeper this shows that there is an increased sensitivity to carbon dioxide in hypoxia
describe the experimental response to 02
Responses to hypoxia at three different fixed levels of CO2.
Note that at normal level of CO2 (43.7) there is very little response of the respiratory system until you reach quite severe hypoxia (alveolar PO2 60 mm Hg)
what gas causes the main drive to breath
- carbon dioxide (hypercapnia)as it drives the central chemoreceptors which increase or decrease the ventilation rate
what does hypercapnia mean
this is an increase in carbon dioxide
hypoxia on its own…
does not stimulate breathing until the partial pressure of oxygen is less than 60mmHg
hypoxia increases the sensitivity….
of the respiratory centres to hypercapnia
where are the sensors for hypoxia
they are in the peripheral chemoreceptors
where are the peripheral chemoreceptors located
- they are located at the carotid bodies at the bifurcation of the common carotid arteries
- aortic bodies above and below the aortic arch
what does the carotid body contain
contains the most heavily vascularised tissue in the human body
what do the peripheral chemoreceptors respond to
- afferent nerves from these receptors respond mainly to
- reduced partial pressure of oxygen
- reduced plasma pH
- to raised partial pressure of carbon dioxide but not to strongly
where do the afferents from the chemoreceptors travel in
- mainly travel in the glossopharyngeal nerve
- some fibres may travel in the vagus
- they go to the brainstem
what two types of cells make up the carotid body
Gloms type I chief cells
Gloms Type II sustentacular cells
where are type I cells derived from
derived from neuroectoderm
what do type I cells do
They release neurotransmitters that stimulate the sensory endings of the vagus and glossopharyngeal afferent nerves that project to the medullary respiratory centres. When hypoxic
what do type II cells do
resemble glia and act as supporting cells.
How do type I cells detect hypoxia
- decrease in oxygen partial pressure or decrease in arterial pH causes the depolarisation of the glomus cell membrane
- hypoxia leads to inhibition of potassium channels, this causes potassium decay
- inward leak of sodium leads to depolarisation this opens the voltage sensitive calcium channels
- this triggers the release of acetylcholine and other transmitters
- these act on receptors on the afferent nerve fibres adjacent to the gloms cell and cause action potentials that travel up to the respiratory centres
how do the carotid body nerves react
- sensitively increases dramatically with low oxygen
- at normal arterial partial pressure of oxygen which is 100mmHg the carotid body nerves are nearly silent
- the response increases steeply below the P02 of 60mmHg
- shows that we are not sensitive to hypoxia to the level is less than 60mmHg
what receptors cause the urge to breathe
- comes from the central chemoreceptors
- less than 20% of the ventilatory response can be attributed to the peripheral chemoreceptors
- if there is arterial hypoxemia the peripheral chemoreceptors become active and their action is to potentiate the drive from hypercapnia
where are the medullary respiration receptors
reticular formation of the medulla beneath the floor of the fourth ventricle.
what is respiration controlled by
- controlled by a group of neurones that are located in the pons and medulla of the brain stem, these are the respiratory centres
- three main groups of neurones are recognised, the main one is the medulla
where does the medulla project down into
- reticulospinal tract
- this activates the diaphragm for inspiration
where does the reticulospinal tract arise and go
- it arises in the pons and medulla
- it then descends down the spinal cord around the margin of the ventral horn
what muscle does the phrenic nerve lie on
scalenus anterior muscle
where does the phrenic nerve enter the thorax
between the subclavian artery and subclavian vein
- the nerve then goes down the mediastinum lying anterior to the hilum of the lung and is squeezed between the pleura and pericardium
what is the only motor supply to the diaphragm
phrenic nerve
what are the motor and sensory fibres of the phrenic nerve
- The nerves supply motor fibres to the diaphragm,
- sensory fibres to the diaphragmatic pleura and peritoneum.
what part of the medulla is the NTS (nucleus of the solitary tract) on
- the dorsal surface of the medulla
what does the NTS do
- recieves input from the pH detectors, pulmonary stretch, cough, J receptors
- projects to the dorsal respiratory group which contain cells that fire during inspiration
when does forced expiration occur
- occurs when neurones in the ventral respiratory group int he ventral medulla becomes active
- axons project down into the reticulospinal tract and activate the internal intercostals
- this causes the internal intercostals to squeeze the lungs
what are the two other regions in the potion reticular formation
- apneustic centre
- prenumotaxic
what does the apneustic centre do
- prolongs inspiration
what is the pneumotaxic modulate
- the apnuestic centre therefore it decreases tidal volume and respiratory rate
what does the cerebral cortex do in regards to pneumotaxic and apneustic centres
The cerebral cortex acts via the pneumotaxic and apneustic centres to regulate breathing for vocalisation
- this enables us to talk and sing and hold our breath voluntary
what does the pneumataix centre do
the pneumotaxic center is responsible for limiting inspiration, providing an inspiratory off-switch
what do the dorsal groups of neurones do
drive inspiration
what do the ventral groups of neurones do
drive forced expiration
what happens if there is damage to the brain stem
- cheyne stokes breathing, this is when sensory input to the meudall is damaged, respiration continues but is abnormal
how would you characterise cheyne stokes breathing
- gradual increase in depth and rate of breathing followed by gradual decrease that results in temporary stop in breathing called an apnoea
where is cheyne stokes breathing seen
patients with.. - heart failure - strokes - brain tumours - hyponatremia - traumatic brain injuries - carbon monoxide poisoning - seen after morphine administration - damage to brainstem respiratory receptors happens in patients that effect blood supply to the brain
