Acid base balance 1

Question 1

What is the pH equation?

Answer 1

pH = log 1/hydrogen

Question 2

pH is a measure of what?

Answer 2

Unbound hydrogen ions and thus the acidity or alkalinity of a solution

Question 3

Which is more acidic venous or arterial blood and why?

Answer 3

Venous blood due to the presence of carbonic acid

Question 4

What is the normal pH range of blood?

Answer 4

7.35-7.45

Question 5

Big changes in pH reflect big changes in hydrogen ion concentration. T/F

Answer 5

False - small changes in pH reflect big changes in hydrogen ion concentration

Question 6

Why is it important to regulate hydrogen ion (i.e pH) levels?

Answer 6

Hydrogen ions affect:

• Enzyme activity
• Nerve activity
• Potassium levels

Question 7

How does nerve activity change with differing levels of hydrogen ions?

Answer 7

Increased hydrogen - depression of CNS

Decreased hydrogen - overexcitibility of peripheral NS (–> CNS)

Question 8

Hydrogen is continually added to the body via three main mechanisms. List them

Answer 8

Carbonic acid formation
Inorganic acids from nutrient breakdown (e.g meat protein)
Organic acids from metabolism

Question 9

How can diabetes mellitus cause an acid base imbalance?

Answer 9

Glucose cannot be broken down so must switch to fat metabolism >
Increased production of ketoacids >
Decreased pH

Question 10

Weak acids dissolve partially in solution. Write this equation

Answer 10

Undissociated weak acid –> hydrogen ion/proton + base

Question 11

Explain a buffer system

Answer 11

Pair of substances where one dissociates to give hydrogen (in deficit) and the other combines with hydrogen (in excess)

Question 12

If acid is added to a buffer system which way does equilibrium shift?

Answer 12

Acids provide hydrogen which combines with the base to form an undissociated acid (thus equilibrium shifts to the left)

Question 13

If base is added to a buffer system which way does equilibrium shift?

Answer 13

Base combines with hydrogen forcing more undissociated acid to dissociate (thus equilibrium shifts to the right)

Question 14

What is the dissociation constant pK? What is it’s equation?

Answer 14

pH at which equilibrium is reached. pK = -log K (where K is the right part of the buffer system over the left)

Question 15

Write the henderson hasselbach equation

Answer 15

pH = pK + log [base/acid]

Question 16

What is the most important physiological buffer system?

Answer 16

Carbon dioxide and bicarbonate

Question 17

Which enzyme is responsible for converting carbon dioxide and water into carbonic acid?

Answer 17

Carbonic anhydrase

Question 18

What version of the henderson hasselbach equation do we use with regard to physiological buffers?

Answer 18

pH = pK + log [bicarb/(solubility coefficient x partial pressure of carbon dioxide) ]

Question 19

What makes the carbon dioxide and bicarbonate buffer system so important?

Answer 19

Bicarb is controlled by the kidneys
Carbon dioxide is controlled by the lungs
Interplay allows for precise control

Question 20

By which two methods does the kidney control bicarbonate levels?

Answer 20

Changes in reabsorption of filtered bicarbonate
Addition of “new” bicarbonate to the blood (i.e higher concentration of bicarb in the renal veins than in renal arteries)

Question 21

What is the kidney control of bicarbonate levels dependent on?

Answer 21

Hydrogen ion secretion into the kidney tubules

Question 22

How is bicarbonate reabsorbed in the proximal tubule?

Answer 22

It must be indirectly reabsorbed:

Carbon dioxide (from interstitium) and water (from tubular fluid) combine within the tubular cells to form carbonic acid >
Carbonic acid dissociates into bicarbonate and hydrogen >
Bicarbonate already within the tubular cell leaves at the basolateral membrane via the sodium bicarbonate cotransporter >
Hydrogen ions secreted into the tubular fluid via sodium hydrogen exchanger >
Bicarbonate in tubular filtrate combines with the hydrogen ions to form carbonic acid >
Carbonic acid dissociates into water and carbon dioxide and water enters the tubular cells

Question 23

Hydrogen ion secretion is driven by the partial pressure of carbon dioxide. T/F

Answer 23

True - increase in partial pressure causes increase in hydrogen secretion

Question 24

What do hydrogen ions combine with when bicarbonate in the tubular fluid is low?

Answer 24

Phosphate (next most plentiful buffer)

Question 25

Which primary active transport mechanisms are present in the collecting ducts?

Answer 25

Hydrogen potassium ATPase
Hydrogen ATPase
Sodium-hydrogen exchanger

Question 26

How does phosphate act as a tubular buffer?

Answer 26

Hydrogen ions which are being pumped from the tubular cell via the sodium hydrogen exchanger combine with phosphate >
Formation of dihydrogen phosphate ion >
Acidic ion is excreted >
Net gain of two “new” bicarbonate ions

Question 27

What is titratable acid? How is titratable acid measured?

Answer 27

Hydrogen excreted as the dihydrogen phosphate ion.

Measure the amount of strong base needed to bring the pH of the urine back to normal

Question 28

How does ammonia act as a tubular buffer? When does ammonia start being used as a buffer?

Answer 28

Glutamine from the liver is broken down to ammonia by glutaminase >
Ammonia enters the tubular fluid >
Hydrogen ions which have been pumped from the tubular cell via the sodium hydrogen exchanger combine with ammonia >
Ammonium is formed >
Ammonium is excreted >
Net gain of two “new” bicarbonate ions

When all the phosphate has been used up

Question 29

Is ammonium a titratable acid?

Answer 29

No

Question 30

What does hydrogen secretion from the kidney tubules do?

Answer 30

Drives reabsorption of bicarbonate
Forms acid phosphate (dihydrogen phosphate ion)
Forms ammonium ion

Question 31

Excretion of TA and NH4 simultaneously rids the body of acid and regenerates buffer stores. T/F

Answer 31

True - remember buffer equation