8.4 Transport of Oxygen And Carbon Dioxide In The Blood Flashcards
What are the key adaptations of an erythrocyte?
-Biconcave shape
-No nuclei
-Contain haemoglobin
Why does an erythrocyte have a biconcave shape?
To give it a large surface area, so more area available for diffusion of gases. Also helps them to pass through narrow capillaries
Why does an erythrocyte have no nucleus?
To maximise the amount of haemoglobin that can fit into the cell (however this also reduces its lifespan)
Why does an erythrocyte contain haemoglobin?
Allows RBC to carry oxygen because it binds to it.
What is haemoglobin? (Simple answer, no protein)
A red pigment that carries oxygen, and gives erythrocytes their colour.
How many oxygen molecules can each haemoglobin bind to?
4
What is haemoglobin? (In terms of proteins)
Large globular protein, conjugated, made up of 4 peptide chains, each with an iron-containing prosthetic group
What is formed when oxygen binds to haemoglobin?
Oxyhaemoglobin
State the symbol equation for oxygen binding to haemoglobin.
Hb + 4O2 ⇌ Hb(O2)4
What is loading/association?
Haemoglobin binding to oxygen at gas exchange surfaces
What is unloading/dissociation?
Haemoglobin releases oxygen to respiring tissues
What is affinity?
How readily/easily haemoglobin binds to or releases oxygen
If haemoglobin has high affinity, what does it do?
Loads easily, unloads less easily
What is partial pressure?
The individual pressure of a gas in a mixture of gases (kind of like concentration)
What are the oxygen levels like in the lungs?
High than the red blood cells, to make a step concentration gradient
How does the structure of haemoglobin make it easy for oxygen to bind to it?
As soon as one oxygen molecule binds to a haem group, the molecule changes shape, making it easier for the next oxygen to bind. Called CONFORMATIONAL CHANGE / POSITIVE COOPERATIVITY
What is positive cooperativity?
Where the change in shape of the first subunit makes the binding of substrate to the second subunit easier. Found in haemoglobin
How is a steep oxygen concentration gradient in an erythrocyte maintained despite having oxygen bound to haemoglobin?
The oxygen is bound to the haemoglobin (not the actual erythrocyte), so the free oxygen concentration in the RBC stays low.
What is the difference in oxygen concentration between the cells of the body tissues and the red blood cells?
Conc. of oxygen in the cytoplasm of the body cells is lower than in the erythrocytes.
What is the name of the binding involving oxygen binding to haemoglobin?
Co-operative binding
What does the oxygen dissociation curve show?
The affinity of haemoglobin for oxygen
What is the shape of the oxygen dissociation curve?
A sigmoidal curve.
Why does a small change in partial pressure of oxygen make a significant difference to the saturation of the haemoglobin with oxygen?
-Because once a molecule becomes attached, the change in the shape of the haemoglobin molecule means other oxygen molecules are added rapidly.
When does the oxygen dissociation curve level out? Why?
-At the highest partial pressures of oxygen, because all of the haem groups are bound to oxygen and cannot take up anymore.
What does the levelling out of the oxygen dissocation curve represent?
The red blood cells in the capillaries surrounding the lungs being rapidly filled with oxygen from the lungs (with a high partial pressure of oxygen)
What does a large decrease in saturation of haemoglobin as a result of a relatively small drop in the partial pressure of oxygen represent?
Oxygen releasing rapidly from the haemoglobin to diffuse into body tissues.
When you are not very active, what % of the oxygen carried in your erythrocytes is released into the body cells?
Only about 25%
What is the Bohr effect?
The process describing how the binding of oxygen to haemoglobin changes as carbon dioxide and pH levels change.
What happens as the partial pressure of carbon dioxide rises?
-pH is slightly DECREASED, which causes the shape of haemoglobin to change, and the affinity for oxygen is lower
-So haemoglobin unloads oxygen more readily
-The oxygen dissociation curve is shifted to the RIGHT
Why does haemoglobin change shape when pH changes?
Because haemoglobin is a globular protein, and proteins’ structures are affected by changes in pH.
Is carbon dioxide acidic or alkali?
Acidic
What happens as the partial pressure of carbon dioxide decreases?
-pH is slightly increased, so the affinity of Hb for oxygen is LOWER (Hb unloads oxygen more readily)
-The oxygen dissociation curve is shifted to the LEFT
Is the partial pressure of CO2 in the lungs high or low?
Low
Is the partial pressure of CO2 in respiring tissue high or low?
High
How does the body ensure there is always sufficient oxygen for respiring tissues? (Model Answer)
-If the rate of respiration in tissues is high, more CO2 will be produced
-The pH of the tissues is reduced
-This causes the shape of the haemoglobin to change
-As a result, the affiinity of haemoglobin for oxygen is reduced
-So, more oxygen is unloaded at the tissues
-So more oxygen is available for aerobic respiration
How does a fetus recieve oxygen while it is developing?
-Oxygenated blood from teh mother runs close to the deoxygenated fetal blood in the plasma
-Fetal haemoglobin has a higher affinity for oxygen than adults, so the mother can remove oxygen from the maternal blood and pass it on as the blood moves past eachother
Is maternal circulation and fetal circulation counter-current or parallel?
Parallel
Does fetal haemoglobin have a higher or lower affinity for oxygen than adult haemoglobin?
Higher
What percent of carbon dioxide is carried in the plasma?
5%
What happens to CO2 in erythrocytes that do not react with water?
They are combined with amino groups in the polypeptide chains of haemoglobin to form a compound called CARBAMINOHAEMOGLOBIN
What is the name of the product formed when CO2 combines with amino acids in Hb?
CARBAMINOHAEMOGLOBIN
What are the 3 different pathways for CO2 transported to the lungs from the tissues?
-Carried in the plasma
-Combined with amino groups in Hb to form carbaminohaemoglobin
-Converted to hydrogen carbonate ions in the cytoplasm of erythrocytes
When carbon dioxide reacts slowly with water, what is formed?
Carbonic acid (H2CO3)
How is carbonic acid (H2CO3) formed?
When carbon dioxide reacts slowly with water in the cytoplasm of RBCs
What is the next step for carbonic acid once it is formed?
Then dissociated to form hydrogen ions (H+) and hydrogencarbonate ions (HCO3-)
What enzyme catalyses the reaction between Carbon Dioxide and Water?
Carbonic Anhydrase
What chemical dissociates to form Hydrogen Ions and Bicarbonate?
Carbonic Acid
What is the chloride shift?
When the HCO3- ions move out of the erythrocytes into the plasma by diffusion, so negatively charge chloride ions move into the RBCs, which maintains the electrical balance of the cell
Why is important that the chloride shift takes place?
To maintain the electrical balance of the cell
What happens to the H+ ions in erythrocytes?
They are accepted by the haemoglobin, which acts as a buffer and prevents changes in pH. The haemoglobin and hydrogen ion form haemoglobinic acid
What is produced when haemoglobin accepts a hydrogen ion?
Haemoglobinic acid
Why is it important that CO2 is removed and converted to HCO3- in erythrocytes?
So that a steep concentration gradient can be maintained for carbon dioxide to diffuse from respiring tissues
What happens to HCO3- in the blood once it has reached the lung tissue?
-It diffuses back into the erythrocytes, and reacts with a hydrogen ion to form more H2CO3.
-This is broken down by carbonic anhydrase to release free carbon dioxide
-This diffuses out of the blood into the lungs
What happens to Chlorine ions once HCO3- has been converted back to CO2 and removed via the lungs?
They diffuse out of the erythrocytes and back into the plasma down an electrochemical gradient
What name is given to a change in the oxygen dissociation curve due to increasing carbon dioxide concentration?
The Bohr Effect
