transport of carbon dioxide Flashcards
what is carbonic anhydrase
the enzyme that catalyses the combination of carbon dioxide and water
what is the chloride shift
the movement of chloride ions into the erythrocytes to balance the charge as hydrogencarbonate ions leave the cell
what is haemoglobinic acid
the compound formed by the buffering action of haemoglobin as it combines with excess hydrogen ions
where is carbon dioxide released from
respiring tissues
what must happen to the carbon dioxide
it must be removed from the respiring tissues and transported by the blood to the lungs for excretion
give the 3 ways carbon dioxide is transported from the tissues to the lungs
- about 5% is carried dissolved in the plasma
- 10-20% is combined with the amino groups in the polypeptide chains of haemoglobin to form carbaminohaemoglobin
- 75-80% is converted into hydrogen carbonate ions in the cytoplasm of the red blood cells
what does CO2 diffuse into the blood from the cells to the lungs as
hydrogencarbonate ions
what happens to the CO2 in the lungs
all the CO2 in various forms leaves the plasma and haemoglobin and enters the alveoli
what first happens when carbon dioxide in the blood plasma diffuses into the red blood cells
CO2 reacts with water to form carbonic acid (H2CO3). the carbonic acid then dissociates to form hydrogen ions and hydrogen carbonate ions
give the equation for what happens to the carbonic acid
CO2 + H2O ⇌ H2CO3 ⇌ H+ + HCO3-
what helps speed the reaction of carbonic acid
in the cytoplasm of the red blood cells there are high levels of carbonic anhydrase which catalyses this reversible reaction of forming H2CO3 and reforming CO2 and H2O
what happens to the carbon dioxide entering the erythrocytes that escapes being broken down by the carbonic anhydrase
it binds directly with the amino groups of haemoglobin to form carbaminohaemoglobin (about 10-20% of CO2 is carried this way)
what happens to the hydrogen carbonate ions
the negatively charged hydrogen carbonate ions move out of the erythrocytes into the plasma by diffusion down a concentration gradient
what moves into the rbc to maintain the electrical balance of the cell and what is the term
chloride ions - called the chloride shift
why do chloride ions move in
carbonic acid dissociates to form hydrogen and hydrogen carbonate ions. the HCO3- ions are negative so when they move out, the rbc is more positive due to the presence of H+ ions. therefore negative chloride ions move in to maintain the electrical balance of the cell
what is the benefit of removing carbon dioxide and converting it to hydrogen carbonate ions
it maintains a steep concentration gradient in rbc for CO2 to diffuse from respiring tissues into rbcs
what happens when the blood reaches the lung tissue (low concentration of CO2)
carbonic anhydrase catalyses the reverse reaction breaking down carbonic acid into carbon dioxide and water
what happens when carbonic acid is broken down to CO2 and H2O
hydrogen carbonate ions diffuse back into the erythrocytes and react with hydrogen ions to form more carbonic acid. when this is broken down by carbonic anhydrase, it releases free CO2 which diffuses out of the blood into the lungs
what happens to the chloride ions after free CO2 enters the lungs
they diffuse out of the RBC back into the plasma down an electrochemical gradient
what would happen if H+ ions kept building up in the RBC
they could cause the contents of the RBC to become very acidic
how is acidity of the RBC prevented
the H+ ions are taken out of a solution by associating it with haemoglobin in the RBC to form haemoglobinic acid which acts as a buffer
what is a buffer
a substance that maintains pH
what does the haemoglobinic acid do
causes the haemoglobin to release all the oxygen it is carrying. the HCO3- diffuses out of the RBC into the plasma
what does blood entering respiring tissues carry O2 as
oxyhaemoglobin
why is the partial pressure of O2 in the respiring tissues lower than in the lungs
the oxygen has been used in respiration
what does oxyhaemoglobin do
dissociates and releases oxygen to the tissues. haemoglobin is available to take up H+ ions forming haemoglobinic acid. where the tissues are very active, more O2 is released
what does the Bohr effect describe
the effect that an increasing concentration of oxygen has on haemoglobin
what happens when carbonic acid dissociates to release hydrogen ions
they can affect the pH of the cytoplasm making it acidic. these changes in pH can affect the tertiary structure of haemoglobin. the increased acidity alters the tertiary structure of haemoglobin and reduces the affinity of haemoglobin for oxygen. the haemoglobin is unable to hold as much oxygen so releases oxygen from oxyhaemoglobin to the tissues
describe what will happen when tissues respire more
there will be more carbon dioxide, leading to more hydrogen ions in the red blood cells. the oxyhaemoglobin releases more oxygen. the haemoglobin becomes less saturated with oxygen
what happens to the oxygen dissociation curve when there is more carbon dioxide
the curve goes down and right
more oxygen is released when…
when more carbon dioxide is produced in respiration
