Guyton Chapter 30 Acid base Regulation

Question 1

What is an acid?

Answer 1

Molecules containing hydrogen atoms that can release hydrogen ions in solutions.

Question 2

What is a base?

Answer 2

An ion or molecule that can accept an H+.

Question 3

Which 3 primary systems regulate the H+ concentration in the body fluids to prevent acidosis or alkalosis?

Answer 3

1. The chemical acid-base buffer systems of the body fluids which immediately combine with acid or base to prevent excessive changes in H+ concentration.
2. The respiratory centre which regulates the removal (and therefore H2CO3) from the extracellular fluid.
3. The kidneys which can excrete either acid or alkaline urine thereby readjusting the extracellular fluid H+ concentration toward normal during acidosis or alkalosis.

Question 4

What does the bicarbonate buffer system consist of?

Answer 4

It consists of a water solution that contains two ingredients
1. A weak acid, H2CO3 and
2. A bicarbonate salt such as NaHCO3
H2CO3 is formed in the body by the reaction of Co2 with H2O with the help of the enzyme carbonic anhydride. This enzyme is especially abundant in the walls of the lung alveoli where Co2 is released.
The second component of the system, bicarbonate salt occurs predominantly as sodium bicarbonate (NaHCO3) ionises almost completely to form HCo3- and Na+.

Question 5

Which is the most important extracellular buffer?

Answer 5

Bicarbonate buffer system

Question 6

Name two reasons why the phosphate buffer is especially important in the tubular fluids of the kidney?

Answer 6

1. Phosphate usually becomes greatly concentrated in the tubules thereby increasing the buffering power of the phosphate system.
2. The tubular fluid usually has a considerable lower pH than the extracellular fluid does bringing the operating range of the buffer closer to the pK (6.8) of the system.

Question 7

Through which 3 mechanisms do the kidneys regulate extracellular fluid H+ concentration?

Answer 7

1. Secretion of H+
2. Reabsorption of filtered HCO3-
3. Production of new HCO3-

Question 8

In which part of the kidney does hydrogen ion secretion and HCO3- reabsorption occur?

Answer 8

In virtually all parts of the tubules except the descending and ascending thin limbs of the loop of Henle.
About 80-90% of the bicarbonate reabsorption occurs in the proximal tubule.

Question 9

What is secreted when HCO3- is reabsorbed?

Answer 9

H+ (by sodium-hydrogen counter transport)