Control Of Lung Function Flashcards
What are the 4 distinct groups of nuclei in the pons and medulla that control breathing rate?
Dorsal respiratory group:
Inspiratory centre
Maincontroller of inspiration. Sets the rate
Ventral respiratory group:
Expirstory centre
Inactive during quiet breathing
Inhibits apneustic centre
Apneustic centre:
Stimulates activity in the dorsal respiratory group
Inhibited by pulmonary afferents
Pmeumotaxic centre:
The inspiratory off switch
Regulates depth as frequency
DIVE: dorsal inspire, ventral expire
What is the communication between the respiratory groups in the medulla oblongata?
Dorsal respiratory centre inhibits the ventral one
Ventral respiratory centre inhibits the dorsal one
Apneustic stimulates dorsal
Pneumotaxic inhibits dorsal
Ventral Anglos inhibits apneustic
What makes up the respiratory pacemaker?
Apneustic centre - stimulates activity in the dorsal respiratory group. It is inhibited by pulmonary afferents
The pneumotaxic centre - the insporatiry off switch. Regulates depth and frequency
Action potentials from the apneustic centre come in at a certain amplitude. Their frequency then increases increases increases increases. Until it reaches a threshold frequency and activates the pneumotaxic centre, creating a stop in the rythm, and inspiration ceases (the lung physics then leads to expiration). There is then a period of latency (around 3 seconds) after which the apneustic centre can kick in again
What is the innervation of the respiratory muscles?
Motor: C3 C4 and C5 make up the phrenic nerve (to the diaphragm) (3 4 and 5 keep the diaphragm alive)
T1-T11 go to the internal and external intercostal muscles (external= inspiration, internal=expiration)
What is chemo sensitivity in the medulla?
In the normal circulation the endothelial cells of the capillaries form a continuous layer, there are H20 filled gap junctions between the endothelial cells. But these are tiny
In the blood brain barrier, there are tight junctions between the capillary endothelial cells that hold the cells even closer together. This means there is heavy restriction on what can cross the BBB
Protons and bicarbonate (from CO2 in the blood) can’t cross the BBB due to lack of transporters or pores. Therefore dissolved carbon dioxide diffuses directly (as it is highly lipid soluble) from the capillaries into the CSF
In the CSF then: H2O + CO2 -> H+ + HCO3-
These protons then interact with the afferent fibres in the medulla which then take the signals to the dorsal respiratory group which determine what is done next
What are the pulmonary afferents that effect ventilation?
Irritant receptors:
afferent receptors embedded within and beneath airway epithelium
Leads to cough - which involves forceful expiration against a closed glottis with sudden glottal opening and high velocity expulsion of air
Stretch receptors:
Excessive inflation of lungs activates pulmonary stretch receptors
Afferent signals to respiratory centres inhibit dorsal respiratory group and apneustic centre and stimulate pneumotaxic and ventral centres
Inspiration is inhibited, and expiration is stimulated
J receptors:
Located juxtaalveolar, next to the gas exchange surfaces
Sensitive to oedema and pulmonary capillary engorgement (may be due to high BP)
Increases breathing frequency as these things may decrease the efficiency of gas exchange (thicker diffusion pathway)
What is volitional apnoea?
Holding the breath of your own will
During this the partial pressure of oxygen will decrease and the partial pressure of carbon dioxide will increase until it overtakes oxygen
As the CO2 increases, protons beyond the BBB will increase, stimulating the diaphragm to breath in
There is a CO2 threshold above which you struggle and need to breathe
There is an O2 threshold, below which you black out
What is an acid?
An acid: any molecule that has a loosely bound proton (H+ ion) it can donate
The higher the concentration of protons the lower the pH
Blood acidity must be tightly regulated as if it is not it may lead to a conformation change in proteins
H+A- -> H2CO3 <> H+ + HCO3-
What is a base?
An anionic molecule capable of reversibly binding protons
Who discovered the buffering capacity of the blood?
Pitt’s and swan
Blood has an anoous buffering capacity that can react almost immediately to Imbalances
What are the basics of pH?
H+ ions have a much lower concentration than ions like sodium and potassium
This measurement was made much more manageable by doing -log10[H] = pH
Inverse is 10^-pH
What are alkalaemia, acidaemia, alkalosis and acidosis?
Alkalaemia - higher than normal pH of blood
Acidaemia - Lowe than normal blood pH
Alkalosis - describes circumstances that will decrease [H+] and increase pH
Acidosis - circumstances that will increase [H+] and lower pH
How does acid base homeostasis work in relation to the lungs and kidneys?
Two main types of disturbance: metabolic (any changes in pH not die to breathing, fixed by the lungs) and ventilatory (changes in breathing that change the pH, corrected by the kidneys)
The ability of the lungs to respond is incredibly quick
The kidneys take days to respond
What are peripheral chemoreceptors?
Positioned near the carotid baroreceptors, at the biforcation of the carotid arteries, in specialised structures called the carotid bodies (and artic bodies in the aortic arch)
These contain pretty much all of the blood going to the brain
What are emotional hanged to ventilation?
Higher brain centres (limb i system (emotion)) and special senses —>
Emotional response —>
Respiratory control centre
