Acid base balance

Question 1

Why must H+ concentrations be regulated in the human body?

Answer 1

Metabolic reactions are highly sensitive to changes in pH.

Question 2

What is the range of blood pH?

Answer 2

7.35-7.45

Question 3

What is it called when blood pH is below what it should be?

Answer 3

Acidosis.

Question 4

What is it called when blood pH is above what it should be?

Answer 4

Alkalosis.

Question 5

What substances are a H+ ion input?

Answer 5

Fatty acids, amino acids, CO2, lactic acid and ketoacids.

Question 6

What are H+ buffers in the body?

Answer 6

HCO3- ions in the extracellular fluid, proteins, haemoglobin, phosphates in cells and phosphates and ammonia in the urine.

Question 7

What are the two main ways to output H+? (fast and slow)

Answer 7

Ventilation (fast) and renal (slow).

Question 8

What does carbonic anhydrase do?

Answer 8

It catalyses the combination of carbon dioxide and water to form carbonic acid.

Question 9

What is the equilibrium equation for the interconversion between carbon dioxide, water, carbonic acid and bicarbonate ions?

Answer 9

CO2 + h20 -> H2CO3 -> Hco3- + H+.

Question 10

How can hyperventilation or hypoventilation affect the blood pH?

Answer 10

It can cause an excess of CO2 to be lost or too much CO2 to remain.

Question 11

What are some of the tissues that carbonic anhydrase is expressed in?

Answer 11

Lung, kidney, eyes, intestine and red blood cells.

Question 12

What other organisms express carbonic anhydrase?

Answer 12

Plants and corals.

Question 13

What are the ways in which CO2 can be carried around the body?

Answer 13

Dissolved CO2 in the tissues/red blood cells, carbonic acid in the red blood cells. combined with haemoglobin as haemoglobinic acid.

Question 14

What is the chloride shift?

Answer 14

When the pH is balanced (due to HCO3- and H+ ions) by chloride ions diffusing into the red blood cells when HCO3- diffuses out.

Question 15

Why can the CO2 in the blood diffuse into the alveoli?

Answer 15

The concentration of CO2 in the blood is greater than in the alveoli, so there is a concentration gradient.

Question 16

What happens to the H+ in the red blood cell?

Answer 16

It combines with HBo2 to form HbH and oxygen.

Question 17

What are the two ways in which ventilation can be controlled?

Answer 17

Peripheral chemoreceptors located in the bifurcation of the common carotid artery and arch of the aorta. There are also central chemoreceptors in the medulla.

Question 18

Can CO2 get through the blood-brain barrier?

Answer 18

Yes.

Question 19

What do peripheral chemoreceptors respond to?

Answer 19

An increase in arterial H+ concentration due an increase in CO2.

Question 20

What do both central and peripheral chemoreceptors stimulate?

Answer 20

Medullar inspiratory neurons to create ventilation.

Question 21

What are non-CO2 dependent changes that occur in pH?

Answer 21

Increase in lactic acid.

Question 22

Why does H+ only activate the peripheral chemoreceptors?

Answer 22

They cannot pass the blood brain barrier.

Question 23

What happens if there is a decrease in the H+ concentration?

Answer 23

There is depression of peripheral chemoreceptor firing.

Question 24

How can the kidneys regulate H+ concentration?

Answer 24

They can alter plasma HCO3- levels.

Question 25

What happens when bicarbonate ions enter the nephron?

Answer 25

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-.

Question 26

What is the bicarbonate ions in the filtrate exposed to when it enters the nephron?

Answer 26

Renal carbonic anhydrase .

Question 27

What are the two types of carbonic anhydrase found in the kidney?

Answer 27

Intracellular - in kidney epithelial cells lining tubules and extracellular such as in the brush border surface.

Question 28

Why do filtered bicarbonate ions want to be reabsorbed?

Answer 28

So they can continue to be used as a buffer.

Question 29

What happens with the carbonic acid in the tubular epithelial cells?

Answer 29

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.

Question 30

How does HCO3- get from the tubular epithelial cell to the interstitial fluid?

Answer 30

It is transported by facilitated diffusion.

Question 31

What are the two ways that hydrogen ions can be excreted into the lumen from a PCT cell?

Answer 31

From ATPase and sodium proton pump.

Question 32

What happens to excreted H+ ions from a PCT cell?

Answer 32

It combines with bicarbonate to form CO2 and H2O.

Question 33

What is the purpose of the intracellular carbonic anhydrase on the basal lateral side?

Answer 33

It forms new carbonate ions that are transported out of this side to enter the blood.

Question 34

What happens in the case of acidosis?

Answer 34

The kidney excretes H+ and reabsorbs HCO3-. to increase the pH.

Question 35

What happens in the case of alkalosis?

Answer 35

The kidney excretes K+ and HCO3- and reabsorbs H+ to lower the pH.

Question 36

What happens when all of the filtered bicarbonate has been reabsorbed?

Answer 36

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-.

Question 37

What is the process that occurs when all of the filtered bicarbonate has been reabsorbed?

Answer 37

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.

Question 38

What is the other method in which new bicarbonate ions can be synthesised?

Answer 38

Catalysis of the amino acid glutamine. This is a non-CO2 dependent pathway.

Question 39

What happens when glutamine is broken down?

Answer 39

It forms HCO3- ions and NH4+.

Question 40

What happens to the NH4+ produced from the breakdown of glutamine?

Answer 40

It is exchanged for sodium into the tubular lumen and then excreted.

Question 41

What is the net result of the renal response to acidosis?

Answer 41

More HCO3- is added to blood and plasma and the bicarbonate is increased. The urine will be acidic.

Question 42

What is the net result of the renal response to alkalosis?

Answer 42

Plasma bicarbonate is decreased which compensates for the alkalosis. The urine will be alkaline.