Week 11 - Blood Gas Transport & Control Of Breathing Flashcards
What factors affect rate of diffusion at the alveoli
- diffusion surface area
- diffusion distance
- concentration gradient
- solubility of gases
- coordinated blood flow and airflow
What is Dalton’s law of partial pressure?
“The total pressure exerted by a mixture of gases is the sum of the pressures exerted independently by each gas in the mixture”
What is partial pressure?
The pressure exerted by each individual gas (directly proportional to its % in the total gas mixture)
What is Henry’s law?
“ the amount of gas that dissolves in water is determined by its solubility in water + its partial pressure in air”
- this means that, at equilibrium, the amount of dissolved gas in solution is proportional to the partial pressure of the gas
Oxygen is not very soluble in blood - much less soluble than CO2 - how does it get around this problem?
By binding to haemoglobin to transport it around the bloodstream - 97% of O2 in blood is transported in combo with Hb
What 4 factors control the binding of O2 to Hb in the blood?
- PO2 in the blood
- Blood pH
- temperature
- state of O2 binding of the Hb molecule
How does increasing the pO2 affect binding to Hb?
The higher the pO2, the more O2 combines with Hb
How does decreasing the pH affect the binding of O2 to Hb?
- decreasing pH shifts oxygen dissociation curve to the right - Bohr shift
- allows for better unloading of oxygen
How does temperature affect the binding of O2 to Hb?
- increasing the temperature increases the dissociation of Hb from O2
- allows for more efficient unloading
What are some alternative forms of Hb?
- carboxyhaemoglobin - CO binds much tighter to Hb than O2 (200x tighter) - dramatically reduces ability of O2 to bind to Hb
- foetal haemoglobin - higher affinity for O2 - important for transferring O2 across placenta
What are the 3 ways in which CO2 is transported in bloodstream?
- convert to carbonic acid, then transport in plasma as HCO3- ion (bicarbonate ion)
- bind to Hb - form carbaminohaemoglobin
- dissolve in plasma
How does Hb buffering work?
- Whenever CO2 is converted to HCO3-, it yields an H+ ion
- deoxygenated Hb can consume or release H+ ions to minimise pH changes in blood
Demonstrate the Haldane effect in the lungs
- Hb is oxygenated
- this means it has a lower affinity for H+ ions
- decreases its buffering power
- therefore H+ ions are released
Aids the unloading of CO2 in the lungs
Demonstrate the Haldane effect in the tissues
- Hb is deoxygenated
- therefore has a higher affinity for H+ ions
- increases buffering power
- more H+ ions are uptaken
Aids CO2 transport from tissues
What are the types of sensors that can detect changes in breathing?
Central chemoreceptors - medulla
- detect hypercapnia (too much CO2)
- detect pH changes
Peripheral chemoreceptors - aortic + carotid body
- detect hypercapnia and hypoxia
Mechanoreceptors - lung receptors
- respond to stretch
- has slowly and rapidly adapting receptors
What factors influence rate & depth of breathing?
- exercise (changing body demands in general)
- altitude - acute mountain sickness
- disease
- changing levels of CO2, H+, or O2
How do central chemoreceptors aid in regulating breathing?
- increase in pCO2 = decrease in pH
- detected by chemoreceptors
- increase ventilation
- decrease pCO2
What are some features of peripheral chemoreceptors?
- detect changes in pO2, pCO2 & pH
- Innervated by carotid sinus nerve (CSN) - connects to glossopharyngeal nerve
- vital for response to change in pO2, as this has no effect on central chemoreceptors
What is respiratory acidosis?
- blood pH <7.35 (becomes more acidic)
- lots of H2CO3 -> H+ + HCO3- occurring
Happens as a result of CO2 increasing
What is respiratory alkalosis?
- decrease in H+ ions
- pH increases
Occurs as a result of pCO2 decreasing
What if pO2 changes?
- if pO2 goes up, free radicals are generated which leads to coma and death
- if pO2 goes down, peripheral chemoreceptors increase breathing rate
What are the 3 types of mechanoreceptors in lung tissue + airways?
- slowly adapting (hering-Breuer reflex)
- rapidly adapting (cough reflex)
- c-fibre endings (defence mechanism)
What are the 3 reflexes of the lung tissue + airways?
- hering-breuer reflex - prevents overinflation of lungs
- cough reflex - prevents inhalation of noxious substances
- defence mechanism - response to anything that irritates the airways (e.g. sneeze)
What are some examples of central controller for breathing?
rhythmicity centre (medulla)
- controls automatic breathing
Pneumotaxic and apneustic centres (pons)
- modify firing pattern of medullary centres
