Renal Physiology Lecture 3: Acid-Base Balance General Considerations

Question 1

How is body pH tightly regulated?

Answer 1

• Body Hydrogen ion concentration normally kept low
• Normal body pH: ~7.4 (7.38-7.42) → slightly alkaline
• Certain compartments (i.e. GI) feature varying pH related to function
• Urine pH varies: 4.5-8.5

Question 2

Why must stable plasma pH be maintained?

Answer 2

Stable pH supports enzyme, membrane protein function

• Fluctuating H+ altered protein structure & function
• Alters neuronal function

Question 3

Effect of altered pH on neuronal function

Answer 3

• i.e. acidosis render sneurons less excitable, CNS depression
• i.e. alkalosis renders neurons highly excitable → can lead to tetanus

Question 4

Intake & outake of acids & bases

Answer 4

• Sources of H+
  
  • Food, internal metabolism
  • Organic acids → aa, FA, etc.
  • CO2 → aerobic respiration
• Intake balanced by excretion
• Diet & metabolism do not add much base
• Homeostatic mechanisms focused on acid excretion

Question 5

How does CO2 contribute to H+ intake?

Answer 5

aerobic respiration

Question 6

What are the 3 key processes in pH homeostasis?

Answer 6

• Buffer systems
• Ventilation
• Renal regulation of hydrogen & bicarbonate ions

Question 7

Buffer systems in pH homeostasis

Answer 7

First line of defense → Always present, rapidly prevents pH fluctuation and any change will cause the reaction change to reach equalibrium

• Modulates pH in response to disturbance (not prevention)
• Combine with/release H+
  
  • Mostly combine with H+

Question 8

Where are buffer systems located?

Answer 8

In cells:

• Cellular proteins, phosphate ions, hemoglobin

In plasma

• i.e.HCO3- produced by CO2 released in metabolism which can then leave with Cl- transporter

Question 9

Buffer system changes

Answer 9

Question 10

What does acidosis induce?

Answer 10

respiratory compensation

• Respiratory compensation is the modulation by the brainstem respiratory centers, which involves altering alveolar ventilation to try and bring the plasma pH back to its normal value (7.4) in order to keep the acid-base balance in the body.

Question 11

Respiratory compensation mechanism

Answer 11

Question 12

What can ventilation cause?

Answer 12

acid base imbalance

Question 13

hypoventilation

Answer 13

• Carbon dioxide increases
• Acidotic state → increased pH

Question 14

Hyperventilation

Answer 14

• Carbon dioxide decreases
• pH increases