Respiration - Gas Transport Flashcards
Describe the pulmonary circuit
O2 enters the blood, CO2 leaves
What is the systemic circuit
O2 leaves the blood, CO2 enters the blood
Describe the gas concentration gradient in the pulmonary capillary
PO2 100(alveolar air) > 40 (venous blood)
PCO2 40 (alveolar air) < 47 (venous blood)
What are the anatomical and physiological properties to facilitate gas diffusion
1) large surface area for gas exchange
2) large partial pressure gradients
3) gases with advantageous diffusion properties
4) specialised mechanisms for transporting O2 and CO2 between lungs and tissues
What is partial pressure
Concentration of a particular gas within a mixture of gases
What ways are oxygen transported
1) dissolved
2) bound to haemoglobin (Hb)
Describe dissolved oxygen
Only a small percentage of O2 in blood is dissolved in the dissolved form, the amount is proportional to its partial pressure, for each mmHg PO2 there is 0.003ml O2/100ml of blood
How much oxygen is dissolved on average in atrial blood
Arterial blood (PaO2) = 100mmHg, contains 0.3ml O2/100ml blood
Is dissolved oxygen in the blood enough to meet the body’s oxygen requirements
No
What is the average cardiac output at rest
5L/min
What are the oxygen requirements at rest
250ml O2/min
What is the oxygen requirements during strenuous exercise
3000ml O2/min
What molecule transports oxygen
Haemoglobbin
Describe the structure of haemoglobbin
Four haem groups joined to a globin protein (2 alpha chains, 2 beta chains)
Where does oxygen bind on haemoglobbin
To the iron molecules in the haem groups, one haemoglobbin can transport 4 oxygen molecules
What many haemoglobbin molecules per red blood cell on average
280 million Hb molecules/red blood cell
Describe how haemoglobin works so efficiently
Binding and dissociation of O2 with Hb occurs in milliseconds to facilitate transport which is necessary because red blood cells are in capillaries for one second only
What two things can impact the binding of oxygen to haemoglobin
- temperature
- pH
Is oxygen binding to Hb reversible
Yes
What is the average partial pressure of oxygen PO2 in the blood
The partial pressure of oxygen in the blood is 100mmHg
Describe what happens to oxygen and Hb saturation when partial pressure drops
You can withstand a drop from about 100 to 60 in partial pressure without the haemoglobin mechanism being majorly affected
What happens when the partial pressure of oxygen drops below 60
The partial pressure of oxygen in the blood is quite low, which means there isn’t enough oxygen being transported around the body, not all the Hb molecules are saturated
What is the oxygen carrying capacity of haemoglobin
211mls O2/1L of blood
Better than oxygen being dissolved in the blood
What does oxygen saturation refer to
Refers to the amount of O2 bound to Hb relative to maximal amount that can bind
How is oxygen saturation measured
Using a pulse oximeter, this measures the ratio of absorption of red and infrared light by oxyHb and deoxyHb
Basically measures how much oxygen is bound to Hb
What is the normal amount of CO2 expired per minute
200ml CO2 / min produced
What is the Normal respiratory exchange ratio
80 molecules CO2 expired for every 100 molecules O2 entering
0.8 in normal adults
How is CO2 carried around the blood
1) 7% will remain dissolved in the blood plasma
2) 23% bound to haemoglobin (Hb)
3) 70% converted to bicarbonate
What happens to the majority of carbon dioxide in the blood
Converted to bicarbonate, which can alter the pH of the blood
Bicarbonate is converted into water and carbon dioxide by what
Pulmonary capillaries
Bicarbonate is converted into H+ and HCO3- by what
Systemic capillaries
Why is the majority of CO2 in the blood converted into bicarbonate
To maintain the acid base of the blood
Henderson hasslebach equation for respiration
Pk = log (HCO3)/Pco2*sol
