IRM Flashcards
What does the DRG do?
Stimulates inspiration
What does the VRG do?
Also stimulates inspiration and passive expiration
What does the PRG do?
Influences the timing of breaths
What does the Botzinger complex do?
Inhibits inspiration and stimulates expiration
What is typical value for anatomical deadspace?
150mls
What is the equation for alveolar ventilation?
Va=(Vt-Vd) x f
What is a typical tidal volume value?
500mls
What is a typical Alveolar Ventilation value?
4.2L/min
What is the mechanism of action for opioids?
Attach to opioid receptors in the brainstem
Works via GPCR
Causes opening of pottasium channels causing hyperpolarisation
This decreases excitability and hence suppresses activity
How do benzodiazapines work?
They bind to GABA recpetors increasing their affinity
This causes GABA to bind and hyperpolarises neurones
Decreases excitation and causes respiratory depression
What is a typical Arterial blood 02 tension?
11-13Kpa
What is a typical Arterial C02 tension?
5-6Kpa
What is normal blood pH?
7.35-7.45
What is blood saturation?
Ratio of quantity of O2 combined with Hb in a given sample to O2 capacity of given sample
What is blood saturation for arterial and venous blood?
arterial: 98%
venous: 75%
What are the three ways that carbon dioxide is carried in the blood?
Dissolved in the Plasma
Bound in red blood cells as HB-CO2
As HCO3-
What are the two methods CO2 is made into HCO3-?
Slow method- combines with water in plasma and converted to HCO3- and H+
Fast method- moves into red blood cells and this reaction is catalysed by carbonic anhydrase
HCO3- then transported out of RBC against cl- moving in
What are the two peripheral chemoreceptors?
carotid bodies and aortic bodies
What do aortic bodies do?
group of cells on aortic arch that act as chemoreceptors
What do carotid bodies do?
Carotid bodies act as chemoreceptors and baroreceptors
High blodd flow so can react rapidly to changes in blood flow
What is the afferent nerve from the aortic bodies?
CN X Vagus Nerve
What is thee afferent nerve from the carotid bodies?
CN IX Glossopharangeal Nerve
What is the mechanism by which Carotid bodies detect a fall in O2?
Glomus cells of the carotid bodies are involved
Fall in O2 inhibits the K+ channels
this results in a rapid graded responce (depolarisation)
This increases the number of action potentials that are relayed to the DRG by CN IX
What is the afferent nerve for Baroreceptors?
CN IX Glossopharangeal nerve
Where do central chemoreceptors lie in the medulla?
Ventrally
What do central chemoreceptors do?
80% of responce to CO2
What happens during acclimatisation?
The constant increased breathing rate resulting from respiratory acidosis/alkalosis is gradually attenuated by the active transport of HCO3- from the blood to CSF or vice versa.
What are the three types of pulmonary stretch receptors?
Rapidly adapting irritant receptors
Slow adapting Stretch receptors
Juxtacapillary J-type receptors
What is the afferent nerve for all of the Pulmonary mechanical receptors?
CN X Vagus Nerve
What do rapidly adapting irritant receptors do?
1s immediate responce
Lie in between epithelial cells of the pulmonary tract
detect foreign paarticles and stimulate cough
What do slowly adapting stretch receptors do?
Firing rate sustained through stretch
Graded responce that is proportional
fires according to size of stretch
Inhibits inspiration and promotes expiration
What is the Hering-Breuer reflex?
Stop breathing when maximum stretch is achieved
involves the slowly adapting stretch receptors
As the afferent nerve is vagus a vagotomy results on long deep breaths as no reflex present
What are J-type receptors?
Juxtacapillary receptors detect interstitual fluid
result in rapid shallow breathing and bronchoconstriction
What is the normals PO2(A-a) mismatch? and why?
1Kpa
It is due to V/Q mismatch and R-L shunt
How does airflow vary from apex to base in the lung and why?
Airflow increases as you move down the lung
this is due to gravity pulling the lung downwards
This causes the apex to have a higher intrapleural pressure as it pulls away causing it to expand
This means that the apex has a lower compliance than the base as it is already inflated
With the same change in intrapleural pressure being applied to the apex and base it causes the base to expand the most and recieve the highest airflow
How does perfusion vary from apex to base in the lung and why?
Perfusion increases as you move down the lung
this is due to arterial pressure increasing as you move downwards
Alveolar pressure is constant throughout so at the top of the lung the arterial pressure cant overcome this hence no blood flow and vice versa at the bottom
What are the three zones of perfusion throughout the lungs?
Zone 1-no blood flow PA>Pa>Pv
Zone 2- some blood flow Pa>PA>Pv
Zone 3-distended vessels Pa>Pv>PA
What can be given to accelerate the maturation of lungs in RDS?
Glucocorticoids
How can the presence of surfactant be detected in prenatal screening?
The amount of surfactant in the amniotic fluid can be assessed through amniocentesis looking for phosphotidylcholines
What is haemoglobin made up of?
4 Haem groups
4 Globin chains
What effect does 2,3-DPG have on haemoglobin and why is this advantageous?
2,3-DPG binds to deoxyhaemoglobin causing a lowered affinity for oxygen
This is an advantage as it results in a shift of the Haemoglobin dissociation curve to the right
This means oxygen is unloaded more easily and is distributed to a wider body area
What does cooperative binding in terms of Haemoglobin mean?
Once the haemoglobin has bound one oxygen it undergoes a conformational shape change that means it binds other oxygens more easily
Why does no alpha chains in a foetus cause death but no beta chains can be survived?
Beta chains develop after birth so this would simply cause anaemia after birth which is survivable as there is effectively half the oxygen carrying capacity.
Alpha chains are present in the foetus so if these are damaged then it will cause an effective anaemia in the foetus
As there is lower partial pressure in foetal blood this is not survivable
