Process of gas exchange in the lung Flashcards
Which process facilitates the transfer of oxygen and carbon dioxide?
Diffusion
List factors that contribute towards the rate of diffusion
- Large surface area
- Short diffusion distance
- High concentration gradient
- High solubility of gas in membrane
What is the typical pressure gradient of oxyegn in the alveoli and capillaries?
Alveoli: 100
Capillary: 45
What is the typical pressure gradient of carbon dioxide at the alveoli and capillaries?
Alveoli: 40
Capillary: 45
Therefore net movement from Capillary into Aveoli
Describe the differences in partial pressure of oxygen and carbon dioxide at the pulmonary artery and pulmonary veins
Pulmonary Veins: O2 - 40 co2 - 46
Pulmonary Artery: O2 - 102 Co2 - 40
Define partial pressure
The pressure exerted by a gas in a given mixture
What value is normal atmospheric pressure
760mmHG
State the two ways oxygen can be transported in the body
- Dissolved in blood
- Bound to Haemoglobin in red blood cells
Oyxgen and carbon dioxide have limited solubilities in blood plasma. What is the max amount of O2 per 100ml of plasma?
0.3ml
Every 100ml of blood leaving the alveoli carries approximately how much oxygen? (free and haemoglobin bound)
20ml
Describe the structure of hemoglobin
- 2 alpha and 2 beta chains
- Each of the 4 chains contains a single Heme group, a non-protein compont with Iron in the middle - the haem group gives the blood it’s colour
- Therefore a single hameoglobin can bind four oxygen
The binding of one oxygen to a haem group increases the affinity of the other 3 haem groups for oxygen. What is the name of this principle?
Protein cooperativity
The percentage of heme units containing bound oxygen at any given moment is known as what?
hemoglobin saturation
Many factors affect levels of Hemoglobin saturation. What is the single most important factor?
The partial pressure of oxygen in blood.
Describe what what happens to haemoglobiin saturation as the partial pressure of oxygen changes
- As partial pressure of oxygen increases, Hameoglobin saturation increases
- As partial pressure of oxygen decreases, Haemoglobin saturation decreases
Why is the oxyhaemoglobin saturation graph a curve rather than a straight line?
Since the affinity of haemoglobin for oxygen increases each time after an oxygen binds to a haem group.
The relationship between partial pressure of oxygen and hemoglobin saturation provides a mechanism for automatic regulation of oxygen deliver. Inactive tissues have little demand for oxygen, as the Partial pressure of oxygen is arround 40. Under these conditions hemoglobin does not release much oxygen (In this case, hemoglobin would go from around 97% saturation to 75%, meaning the remaining blood will have a large oxygen reserve. . Active tissues use oxygen at a much higher rate, so hemoglobin saturation may go from 97% to around 20%.
Describe how pH can effect hemoglobin saturation
- Decrease in pH reduces levels of Hemoglobin saturation compared to normal conditions - this is because at lower pH, hemoglobin has a reduced affinity for oxygen
- Increase in pH levels increase levels of Hemoglobiin saturation compared to normal conditions - this is because at higher pH hemoglobin has a reduced affinity for oxygen
Define the Bohr effect
The Bohr Effect refers to the observation that increases in the carbon dioxide partial pressure of blood or decreases in blood pH result in a lower affinity of hemoglobin for oxygen.
What compound is primarily responsible for the bohr effect (reduced affinity for oxygen at lower pH)
carbon dioxide
Explain how temperature affects hemoglobin saturation
- As temperature increases, hemoglobin affinity for oxygen decreases and hemoglobin saturation decreases
- As temperature decreases, hemoglobin affinity for oxygen inreases and hemoglobin saturation increases
In what tissues is the effect of temperature on oxyhemoglobin saturation?
Tissues that generate lots of heat - muscles. As blood warms
Explain how 2,3 bisphopsphoglycerate (2,3 BPG) affects oxyhemoglobin saturation
2,3BPG is produced by erythrocyes as a by-product of glycolysis. The higher the levels of BPG decrease oxyhemoglobin saturation.
Production of BPG decreases with age - meaning ability to release oxygen even when tissue levels of oxygen are critically low can be impaired.
The RBCs of a developing fetus contain fetal hemoglobin. The structure of fetal hemoglobin differs, giving it a much higher affinity for oxygen than adult hemoglobin. Explain why this the case
This greater affinity for oxygen is explained by the lack of fetal hemoglobin’s interaction with 2,3-bisphosphoglycerate (2,3-BPG) In adult red blood cells, this substance decreases the affinity of hemoglobin for oxygen. 2,3-BPG is also present in fetal red blood cells, but interacts less efficiently with fetal hemoglobin than adult hemoglobin
List the 3 ways carbon dioxide can be transported
- Bind to hemoglobin
- Converted to carbonic acid
- Dissolves in plasma
About 23% of carbon dioxide is transported by being bound to hemoglobin. What is the resulting complex called?
Carbaminohemaglobin
Roughly 70% of carbon dioxide absorbed by blood is transported as molecules of carbonic acid. Which enzyme does this?
Carbonic anhydrase.
Carbonic acid formed by carbonic anhydrase acting on carbon dioxide. It then dissociates into what two ions?
Hydrogen and bicarbonate.
Most of the hydrogens then bind to hemoglobin, in order to prevent drop in blood pH. The bicarbonate ions move into the plasma in exhange for CHLORIDE - this resulting movement of chloride into RBCs is called the Chloride shift. The hydrogen ions are removed by buffers like hemoglobin.
