18. Chapter 20- Acid/Base Balance

Question 1

What does a pH of 7 mean?
Below?
Above?

Answer 1

Means neutral, 1x10^-7 M of H+
Below is acidic
Above is basic

Normal pH of body is 7.40

Change of 1 pH represents a 10-fold change in H+concentration

Briefly look at slide 16 Feb 8

Question 2

What does very low pH in the body result in?

What does very high?

Answer 2

Low pH (high H+): acidosis- CNS depression, confusion, coma
High pH (low H+): alkalosis- hyperexcitability in sensory neurons and muscles
Sustained respiratory muscle contraction

Question 3

What can pH change result in in proteins?

What is acidosis and alkalosis?

Answer 3

pH changes can denature proteins
Enzymes and membrane channels sensitive to these changes
Changes in the H+ concentration results in disruptions in hydrogen bonds altering the structure (High pH, low H+)

Acidosis- very low pH (excess H+) resulting in CNS depression, confusion, coma
Alkalosis- high pH (low H+) results in hyperexcitability in sensory neurons and muscles and sustained respiratory muscle contraction

Question 4

What are the 3 mechanisms pH homeostasis relies on?

Answer 4

1. Buffers (first line of defence)
2. Ventilation (handles 75% of disturbances) (slide 6 Feb 11)
3. Renal regulation of H+ and HCO3- (slowest)

Question 5

What are buffer systems?

Answer 5

Include proteins, phosphate ions, and HCO3-
A buffer is a molecule that moderates (but doesn’t prevent) changes in pH by combining with or releasing H+
These are found within cells and in the plasma
(Intracellular buffers are cellular proteins (hemoglobin) and phosphate ions)
Slide 4-5 Feb 11

Question 6

How do kidneys handle remaining 25% of pH disturbances? (2 mechanisms)

Answer 6

1. Directly: altering rates of excretion or reabsorption of H+
2. Indirectly: changing rate at which HCO3 buffer is reabsorbed or excreted

Kidneys use ammonia and phosphate buffers (during acidosis, excess H+ is buffered by ammonia within tubule cells or enters lumen and is buffered by phosphate ions)

Slide 7 Feb 11

Question 7

How does the proximal tubule secret H+ and reabsorb HCO3-?

Answer 7

Slide 8 Feb 11

Question 8

What does the distal nephron do in relation to pH balance?

Type A and type B

Answer 8

Distal nephron controls acid excretion
Collecting duct plays significant role

In acidosis, Type A intercalated cells increase H+ secretions and HCO3 reabsorption (hyperkalemia)
In alkalosis, Type B intercalated cells increase H+ reabsorption and HCO3 secretion (hypokalemia)
Examples slide 9-10 Feb 11

Question 9

What is respiratory acidosis?

What is respiratory alkalosis?

Answer 9

R. Acidosis- occurs when alveolar hyperventilation results in CO2 retention and elevated plasma CO2
Slide 13 Feb 11
R. Alkalosis- less common, result of hyperventilation in the absence of increased metabolic CO2 production
Slide 15 Feb 11

Question 10

What is metabolic acidosis?

What is metabolic alkalosis?

Answer 10

M. Acidosis- when dietary and metabolic input of H+ exceeds H+ excretion
Increase ventilation fixes (or HCO3 reabsorbed, H+ excreted)
Slide 15 Feb 11
M. Alkalosis- excessive vomiting of acidic stomach contents or excessive ingestion of bicarbonate-containing antacids
Decrease in ventilation fixes it (or HCO3 excreted, H+ reabsorbed)
Slide 16 Feb 11