RMS Quiz 2 - Gas Exchange Stuff Flashcards
How does gas exchange occur in the alveoli using the partial pressures to explain
The PO2 in the alveoli is 100mmHg, the PO2 in the blood coming in from the periphery is 40mmHg, so O2 diffuses from the alveoli to the blood. And vice versa for CO2
What layers does the O2 have to cross to reach the blood form the alveoli
Alveolar epithelial layer ANd the capillary endothelial layer
What types of cells line the alveoli
Type I alveolar cells - thin and flat to allow diffusion
Type II alveolar cells - secrete and produce pulmonary surfactant (reduces surface tension, preventing the alveoli from collapsing)
BOTH of these cells are known as PNEUMOCYTES
What 2 ways is O2 transported
1) dissolved in blood (2%)
2) combined with haemoglobin (98%)
What’s Henry’s law
Solubility of a gas in a liquid is directly proportional to pressure of that gas above the liquid
What’s decompression sickness (DCS)
When bubbles of nitrogen form in the blood - leading to dizziness, sickness or paralysis
How many subunits does haemoglobin have (and therefore how many oxygen can bind)
4
Describe the normal oxygen dissociation curve
At around 40mmHg, haemoglobin has a low affinity for oxygen but once one O2 binds, the haemoglobin undergoes a conformational change and this causes it to have increased affinity for oxygen
BUT once the third O2 has bound, the graph plateaus because it becomes difficult for O2 to find a vacant subunit as it is almost saturated
Describe the oxygen dissociation curve with temperature changes
As the temperature INCREASES the graph shifts to the right , thus haemoglobin has a LOWER affinity for oxygen as temp increases
This is beneficial as it means oxygen is more readily released from the haemoglobin to the tissues
E.g. whilst exercising temp will increase as respiration increases, meaning graph will shift to the right and oxygen will be more readily released to respiring tissues
Describe the oxygen dissociation curve when pH changes
As pH DECREASES the graph shifts toward the right , meaning oxygen is more readily released
This usually occurs due to more H+ (acidic) from increased CO2 levels (Bohr effect), lactic acid buildup - during strenuous exercise, etc…
Causes more O2 to unload and
Describe the oxygen dissociation curve when CO2 levels change
As CO2 levels increase the graph shifts toward the RIGHT - Bohr effect
Causes O2 to be more readily unloaded
What happens when CO2 levels are low
Usually occurs in high altitude areas - causes hyper ventilation and o2 dissociation curve shifts to the LEFT, holding onto the oxygen more tightly
What is special about fetal haemoglobin
It has a higher affinity for O2 at lower PO2 - for developmental reasons
What are the 3 ways CO2 is carried
1) dissolved in the blood
2) as bicarbonate (most common 60%)
3) as carbo-amino compounds
How does bicarbonate in the blood form
CO2 dissolves in the plasma then diffuses into a erythrocyte
Then combines with water to form carbonic acid
This then converts immediately into bicarbonate + H+ ion
How do carboamino compounds form in the blood
CO2 dissolves in the blood and binds reversibly with haemoglobin to form carbohaemoglobin
Describe how is CO2 unloaded and removed from the blood
HCO3- (bicarbonate) recombines with H+ (from haemoglobin) to form carbonic acid
The carbonic acid dissociates back into CO2 + H2O via the enzyme carbonic anhydrase
CO2 is then diffused into the alveoli and breathed out
What’s hypoxic hypoxia
Low arterial pO2 caused by high altitude, hyper ventilation, etc..,
What’s anemic hypoxia
Decreased total amount of O2 bound to haemoglobin - caused by blood loss (anemia) or carbon monoxide poisoning
What’s ischemic hypoxia
Reduced blood flow - caused by heart failure or thrombosis
What’s histotoxic hypoxia
Failure of cells to use O2 bc cells have been poisoned - caused by cyanide poisoning
Does CO have a low or high affinity for haemoglobin binding sites
VERY HIGH
what happens during CO poisoning
It has a very high affinity for the binding site on haemoglobin so
It reduces the amount of O2 that can bind
O2 dissociation curve shifts to the LEFT = increased affinity and O2 remains bound
It can lead to death, headache, convulsions, and blue tinted skin
What’s anemia
Low content of functional haemoglobin in RBC = reduced O2 carrying capacity
May be due to gene mutation or loss of RBCs
What is cyanosis
Deficient supply of o2 to the tissues = blue skin
There is increased amount of de-oxyhaemoglobin causing the blue tint
What are the 2 types of cyanosis + causes
1) peripheral cyanosis = reduced blood flow = hypoxic tissue = blue hands and feet (peripheries). Causes of reduced blood flow= low temp, poor arterial supply, cardiovascular shock, etc…
2) central cyanosis = arterial hypoxaemia = reduced o2 content in buccal mucosa & lips. Caused by COPD or right to left heart shunts (leading to reduced o2 saturation)
What are the 2 main reasons for low alveolar pO2
1) inspired air has abnormally low oxygen (e.g. due to altitude)
2) alveolar ventilation is inadequate due to increased lung compliance or increased airway resistance or overdose of drugs
What conditions involve low alveolar pO2
Emphysema ( form of COPD)
FLD
What’s Dalton’s law
Total pressure = sum of all individual partial pressures
What happens to air water saturation when temp increases
It increases because more water evaporates into the air making it more saturated - inspired air will warm and saturate quickly - decreasing partial pressure exerted on other gases
What is partial pressure
Activity of a GAS in a SOLUTION (e.g. o2 in haemoglobin is not in a solution so has no partial pressure)
Is O2 or CO2 more soluble at lower partial pressure
CO2 is more soluble in arterial blood despite having a lower partial pressure than oxygen
Why is pO2 slightly lower in the arterial than in the alveoli
1) mixing of some blood from the bronchial vein resulting in lower pO2 because this blood is not oxygenated
2) some coronary venous blood drains directly into left ventricle lowering pO2
Why is low capillary pO2 dangerous
Diffusion gradient lowers meaning less o2 enters and reaches the respiring tissues = hypoxia
Where is PCO2 highest
At site of production = mitochondria
What 3 things causes insufficient reduced gas transfer
1) reduction in alveolar capillary membrane area e.g. due to emphysema (collapsed alveoli)
2) increased alveolar - capillary membrane thickness e.g. due to pulmonary oedema
3) anaemia
What causes gas transfer to be more efficient and increase
1) increased pulmonary blood flow and volume e.g. due to exercise
2) polycythaemia = increased RBC count and thus increased haemoglobin content
What enzyme is responsible for converting carbonic acid into CO2 + H2O
Carbonic anhydrase
