Gas Exchange and Transport Flashcards
what is the basic transport and exchange system of o2 and CO2 around the body?
CO2 from tissues to lungs
02 from lungs to tissues
why are lungs such a good gas exchange surface?
- Large surface area for gas exchange.
- Large partial pressure gradients.
- Gases with advantageous diffusion properties.
- Specialised mechanisms for transporting O2 and CO2 between lungs and tissues
What are the partial pressures seen in the different circuits of O2 and CO2?
- Similar volumes of CO2 and O2 move each minute
- The pressure gradient for O2 however is much higher than CO2
describe the alveolar capillary network and its properties?
- Gas exchange occurs through dense mesh-like network of capillaries and alveoli.
- Distance between alveoli and red blood cell 1-2μm
- Ideal environment for gas exchange
- Red blood cells pass through the capillaries in less than 1 second. This is sufficient time in order for complete gas exchange
how is dissolved oxygen transported in the body?
- Only a small percentage of O2 in blood is in the dissolved form.
- Amount of dissolved O2 in blood is proportional to its partial pressure.
- For each mmHg of PO2 there is 0.003 ml O2/100 ml blood.
- Arterial blood (PaO2) = 100 mmHg: contains 0.3 ml O2/100ml blood (3ml O2/litre of blood).
- Transport of O2 in dissolved form NOT adequate for body’s requirements, even at rest.
how is oxygen transported around the body when it is bound to haemoglobin?
- Haemoglobin (Hb) is major transport molecule for O2 found in red blood cells.
- 280 million Hb molecules/red blood cell.
- Binding and dissociation of O2 with Hb occurs in milliseconds to facilitate transport – necessary because red blood cells in capillaries for 1 second only.
what is the oxyhemoglobin dissociation curve?
- Curve illustrates relationship between PO2 in blood and number of O2 molecules bound to Hb.
- O2 binding to Hb is reversible.
what is the clinical significance of the flat portion in the oxyhaemoglobin dissociation curve?
drop in PO2 from 100 to 60 mmHg has minimal effect on Hb saturation.
what is the clinical significance of the steep portion of the oxyhaemoglobin dissociation curve?
large amount of O2 is released from Hb with only a small change in PO2, facilitating release into tissues.
what is oxygen saturation?
- O2 saturation (SaO2) refers to the amount of O2 bound to Hb relative to maximal amount that can bind.
- 100% saturation – all heme groups of Hb molecules fully saturated with O2.
how do we measure oxygen saturation?
- Pulse oximeters used in clinic to measure O2 saturation.
- Measures ratio of absorption of red and infrared light by oxyHb and deoxyHb.
how much CO2 is produced at rate?
- Normal healthy conditions:
- 200 ml CO2 / min produced
- 80 molecules CO2 expired by lung for every 100 molecules of O2
entering.
what is respiratory exchange ratio?
IN normal conditions, respiratory exchange ratio = 0.8 (80 CO2 to 100 O2)
how is CO2 transported in the blood stream?
CO2 carried in blood in three forms:
- 7% dissolved.
- 23% bound to haemoglobin (Hb).
- 70% converted to bicarbonate (this then moves out of RBCs in exchange for a chloride ion)
Outline the reaction to form bicarbonate and and the difference in this between the systemic and pulmonary capillaries
- Direction and speed of the reaction is determined by the concentration gradients
- Rightwards in systemic capillaries – CO2 produced by tissues expelled into blood.
- Leftwards in pulmonary capillaries – CO2 to be expelled into alveoli.
- The CO2 to HCO3- pathway plays a critical role in regulation of H+ ions and in maintaining acid- base balance in body.
explain the formation of the pH balance in the body wrt CO2 and the Henderson Hasselbach Equation
- The concentrations of CO2, bicarbonate and hydrogen ions are linked.
- This means changes in bicarbonate concentrations can be used to stabilise the pH.
- This is a buffer reaction.
- The high bicarbonate concentration makes buffering reaction strong.
what is the Henderson Hasselbach equation?
acidity can be regulated by using ventilation to adjust the PCO2
or
By using the kidneys to regulate the bicarbonate conc
what is the V/Q ratio and why is it important?
- The V/Q ratio is the ratio of ventilation to blood flow and how matched these components are.
- Ratio can be defined for single alveolus, a group of alveoli or entire lung.
- Single alveolus: ratio defined as alveolar ventilation divided by capillary flow.
- Lung: ratio defined as total alveolar ventilation divided by cardiac output.
- This is important in disease processes, where we may see adequate perfusion of alveolar sacs but less blood flow or vice versa.
what is the V/Q ratio in healthy individuals?
- Alveolar ventilation ~ 4-6 L/min
- Pulmonary blood flow ~ 5 L/min
- V/Q FOR LUNG = 0.8-1.2
- V/Q for individual units varies greatly.
- When ventilation exceeds perfusion: V/Q > 1.
- When perfusion exceeds ventilation: V/Q < 1.
- Mismatching of pulmonary blood flow and ventilation results in impaired O2 and CO2 transfer.
how many cell types are in the alveolar capillary networks and what are they?
type 1 epithelial cells
type 2 epithelial cells
alveolar macrophages
what is the distance between red blood cells and alveoli?
- Distance between alveoli and red blood cell 1-2μm due to Type 1 alveolar epithelial cell, capillary endothelial cell and basement membrane.
why is the pressure gradient for O2 much higher Than CO2?
- This is because CO2 is a more diffusible molecule
why is dissolved O2 not adequate for tissue demand?
at rest cardiac output (CO)= 5 L/min. 3ml O2/litre of blood x 5 (CO) = 15 ml/min. BUT tissue requirements at rest 250 ml O2/min.
- E.g., during strenuous exercise CO = 30 L/min. 3ml O2/litre of blood x 30 (CO) = 90 ml/min. BUT tissue requirements may need 3000 ml O2/min.
what is the structure of Haemoglobin?
- Hb: four heme (iron porphyrin compounds) groups joined to globin protein (two α chains and two β chains polypeptide chains).
- Each heme group contains iron in the reduced ferrous form (Fe+++), which is the site of O2 binding.
how many O2 atoms can one molecule of Hb bind?
up to 4
how do we measure dissolved O2 only?
you will need to take an arterial blood gas
what is the respiratory exchange ratio?
ratio of expired CO2 to O2 uptake
