BAMS: Respiration (gas transport) Flashcards
respiratory and circulatory systems function together to transport CO2 and O2 in what direction?
O2 from lungs to tissues
CO2 from tissues to lungs
how does gas move through the respiratory system?
diffusion
what are the 4 unique anatomical and physiological properties that facilitate gas diffusion in respiratory and circulatory systems?
- Large surface area in lungs for gas exchange (The tiny alveolar sacs – create large surface area)
- Large partial pressure gradients (advantageous for diffusion of the gases)
- Gases have advantageous diffusion properties
- Specialised mechanisms for transporting O2 and CO2 between lungs and tissues (within the blood system)
what are the 2 forms in which O2 is carries in blood?
- dissolved
- bound to hemoglobin
how is dissolved O2 measured clinically?
in an arterial sample PaO2 (arterial blood)
the amount of dissolved O2 in blood is proportional to what?
its partial pressure
(for each mmHg of PO2, there is 0.003ml O2/100ml blood)
Is the transport of O2 in dissolved form adequate for the body’s requirements?
no, even at rest
- not enough oxygen dissolved in blood to meet the body’s requirements
how is enough oxygen transported into the tissues and cells in order for the body to function optimally?
haemoglobin (second transport system in place)
how many heme groups are in haemoglobin?
4
(two alpha and two beta polypeptide chains)
what does each heme group in haemoglobin contain?
iron in the reduced ferrous form (Fe+++)
what is the site of O2 binding in haemoglobin?
iron
how many oxygen molecules can bind to one haemoglobin molecule?
4
is binding and dissociation of O2 with Hb fast or slow?
occurs incredibly quickly (in milliseconds)
- necessary because RBCs in capillaries for 1 second only
what graph illustrates the binding relationship between O2 and Hb molecules?
oxyhaemoglobin dissociation curve
what does the oxyhaemoglobin dissociation curve demonstrate?
the curve illustrates the relationship between the partial pressure of O2 (PO2) in blood and the number of O2 molecules bound to Hb
is O2 binding to Hb reversible or irreversible?
reversible
what is the clinical significance of the S-shape of the oxyhemoglobin dissociation curve?
flat portion: means body can withstand a degree of decrease in partial pressure before there is a decrease in % saturation of Hb (e.g., from 100-60mmHg PO2) - signifies that the % saturation of Hb is fairly stable
steep gradient: large amount of O2 is released from Hb with only a small change in PO2 - facilitating release into tissues
what factors affect the relationship between the PO2 and how O2 binds to the Hb molecules?
pH and temperature
what does O2 saturation refer to?
the amount of O2 bound to Hb relative to the maximal amount that can bind
(e.g., 100% saturation - all heme groups of Hb molecules are fully saturated with O2)
what is the total O2 capacity transported by Hb in the blood?
211 ml O2/ 1L of blood
what method of O2 transport is better for carrying large amount of O2 around the body - Hb-bound or dissolved?
Haemoglobin
what is used in clinics to measure O2 saturation?
pulse oximeters
(non-invasive way to get idea of the Hb saturation within the blood)
(good way to determine the oxygen-carrying capacity of Hb)
what is the respiratory exchange ratio?
the ratio of expired CO2 to O2 uptake
in normal conditions, what is the respiratory exchange ratio?
0.8 (80 CO2 to 100 O2)
