Acid base balance Flashcards
Why must H+ concentrations be regulated in the human body?
Metabolic reactions are highly sensitive to changes in pH.
What is the range of blood pH?
7.35-7.45
What is it called when blood pH is below what it should be?
Acidosis.
What is it called when blood pH is above what it should be?
Alkalosis.
What substances are a H+ ion input?
Fatty acids, amino acids, CO2, lactic acid and ketoacids.
What are H+ buffers in the body?
HCO3- ions in the extracellular fluid, proteins, haemoglobin, phosphates in cells and phosphates and ammonia in the urine.
What are the two main ways to output H+? (fast and slow)
Ventilation (fast) and renal (slow).
What does carbonic anhydrase do?
It catalyses the combination of carbon dioxide and water to form carbonic acid.
What is the equilibrium equation for the interconversion between carbon dioxide, water, carbonic acid and bicarbonate ions?
CO2 + h20 -> H2CO3 -> Hco3- + H+.
How can hyperventilation or hypoventilation affect the blood pH?
It can cause an excess of CO2 to be lost or too much CO2 to remain.
What are some of the tissues that carbonic anhydrase is expressed in?
Lung, kidney, eyes, intestine and red blood cells.
What other organisms express carbonic anhydrase?
Plants and corals.
What are the ways in which CO2 can be carried around the body?
Dissolved CO2 in the tissues/red blood cells, carbonic acid in the red blood cells. combined with haemoglobin as haemoglobinic acid.
What is the chloride shift?
When the pH is balanced (due to HCO3- and H+ ions) by chloride ions diffusing into the red blood cells when HCO3- diffuses out.
Why can the CO2 in the blood diffuse into the alveoli?
The concentration of CO2 in the blood is greater than in the alveoli, so there is a concentration gradient.
What happens to the H+ in the red blood cell?
It combines with HBo2 to form HbH and oxygen.
What are the two ways in which ventilation can be controlled?
Peripheral chemoreceptors located in the bifurcation of the common carotid artery and arch of the aorta. There are also central chemoreceptors in the medulla.
Can CO2 get through the blood-brain barrier?
Yes.
What do peripheral chemoreceptors respond to?
An increase in arterial H+ concentration due an increase in CO2.
What do both central and peripheral chemoreceptors stimulate?
Medullar inspiratory neurons to create ventilation.
What are non-CO2 dependent changes that occur in pH?
Increase in lactic acid.
Why does H+ only activate the peripheral chemoreceptors?
They cannot pass the blood brain barrier.
What happens if there is a decrease in the H+ concentration?
There is depression of peripheral chemoreceptor firing.
How can the kidneys regulate H+ concentration?
They can alter plasma HCO3- levels.
What happens when bicarbonate ions enter the nephron?
It is completely filtered but most of it will get reabsorbed in the PCT, loop of henle and cortical collecting duct. The collecting duct can also secrete HCO3-.
What is the bicarbonate ions in the filtrate exposed to when it enters the nephron?
Renal carbonic anhydrase .
What are the two types of carbonic anhydrase found in the kidney?
Intracellular - in kidney epithelial cells lining tubules and extracellular such as in the brush border surface.
Why do filtered bicarbonate ions want to be reabsorbed?
So they can continue to be used as a buffer.
What happens with the carbonic acid in the tubular epithelial cells?
It dissociates into HCO3- and H+. The H+ diffuses into the tubular lumen and combines with HCO3- which is then broken down into H2O and CO2. This CO2 can pass the membrane and diffuse back into the cell.
How does HCO3- get from the tubular epithelial cell to the interstitial fluid?
It is transported by facilitated diffusion.
What are the two ways that hydrogen ions can be excreted into the lumen from a PCT cell?
From ATPase and sodium proton pump.
What happens to excreted H+ ions from a PCT cell?
It combines with bicarbonate to form CO2 and H2O.
What is the purpose of the intracellular carbonic anhydrase on the basal lateral side?
It forms new carbonate ions that are transported out of this side to enter the blood.
What happens in the case of acidosis?
The kidney excretes H+ and reabsorbs HCO3-. to increase the pH.
What happens in the case of alkalosis?
The kidney excretes K+ and HCO3- and reabsorbs H+ to lower the pH.
What happens when all of the filtered bicarbonate has been reabsorbed?
Additional buffering can be gained with new bicarbonate ions that are synthesized in the tubule cells, as long as there is a sink for hydrogen ions. In this case it is HPO42-. There is a net gain in HCO3-.
What is the process that occurs when all of the filtered bicarbonate has been reabsorbed?
H2O and CO2 combine (with the presence of carbonic anhydrase) to form carbonic acid, which dissociates into H+ and HCO3-. The HCO3- enters the interstitial fluid, and the H+ combines with HPO42- to form H2PO4- , which is excreted.
What is the other method in which new bicarbonate ions can be synthesised?
Catalysis of the amino acid glutamine. This is a non-CO2 dependent pathway.
What happens when glutamine is broken down?
It forms HCO3- ions and NH4+.
What happens to the NH4+ produced from the breakdown of glutamine?
It is exchanged for sodium into the tubular lumen and then excreted.
What is the net result of the renal response to acidosis?
More HCO3- is added to blood and plasma and the bicarbonate is increased. The urine will be acidic.
What is the net result of the renal response to alkalosis?
Plasma bicarbonate is decreased which compensates for the alkalosis. The urine will be alkaline.
