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1. Back to Basics: Renal Physiology
Normal Acid base balance
Mohammed Abdel Gawad
Nephrology Consultant - Alexandria
MD Nephrology - Mansoura University
drgawad@gmail.com

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4. Henderson–Hasselbalch equation
4
pH = log 1 / H+

5. 5
Lactic acid Sulphuric acid
Carbonic acid
Phosphoric acid
Threats to pH
• 1. Volatile acids: Carbon dioxide:
• 2. Fixed-non volatile acids:
▫ a- Sulphuric acid:
 an end product of the oxidation of sulphur containing aminoacids, methionine and cysteine.
▫ b- phosphoric acid:
 formed in the metabolism of phospholipids, nucleic acids, phosphorproteins and
phosphoglycerides.
• 3. Organic acids:
▫ Lactic acid, acetoacetic acid and B-OH-butyric acid
 formed during the metabolism of carbohydrates and fats.

6. Friday, January 24, 2020 6

7. Defense against changes in H+ concentration
• I. Acid-base buffer systems in body fluids, within seconds.
• II. The respiratory system, within minutes.
• III. The kidneys, within hours.
7

8. Defense against changes in H+ concentration
• I. Acid-base buffer systems in body fluids, within seconds.
• II. The respiratory system, within minutes.
• III. The kidneys, within hours.
8

9. Defense against changes in H+ concentration
• I. Acid-base buffer systems in body fluids, within seconds.
9
• A. The bicarbonate buffer system
• B- The phosphate buffer system
• C- The protein buffer system
• D- Bone salts (calcium carbonate and calcium phosphate)

10. Defense against changes in H+ concentration
• I. Acid-base buffer systems in body fluids, within seconds.
10
• A. The bicarbonate buffer system
• B- The phosphate buffer system
• C- The protein buffer system
• D- Bone salts (calcium carbonate and calcium phosphate)

11. I-ACID-BASE BUFFERS
A. The bicarbonate buffer system
• consists of a mixture of:
• carbonic acid (H2CO3) and sodium bicarbonate (NaHCO3) in the same body fluid.
• It is the most important buffer system in the body because:
• 1- present in all the body fluids, both ECF & ICF.
• 2- concentration of its components (CO2 & HCO3)can be independently regulated
11

12. Defense against changes in H+ concentration
• I. Acid-base buffer systems in body fluids, within seconds.
12
• A. The bicarbonate buffer system
• B- The phosphate buffer system
• C- The protein buffer system
• D- Bone salts (calcium carbonate and calcium phosphate)

13. I- ACID-BASE BUFFERS
B- The phosphate buffer system:
• composed of:
• more effective in ICF than in ECF:
• The total concentration of phosphate is much greater in ICF than ECF.
• also effective in buffering the tubular fluid in the kidneys because:
• Phosphate becomes greatly concentrated in the tubular fluid due to the reabsorption of
water in excess of phosphate.
13

14. Defense against changes in H+ concentration
• I. Acid-base buffer systems in body fluids, within seconds.
14
• A. The bicarbonate buffer system
• B- The phosphate buffer system
• C- The protein buffer system
• D- Bone salts (calcium carbonate and calcium phosphate)

15. I- ACID-BASE BUFFERS
C- The protein buffer system
• 1) Proteins of the cells and the plasma:

16. I-ACID-BASE BUFFERS
C- Protein buffer system
2) Haemoglobin
v

17. Defense against changes in H+ concentration
• I. Acid-base buffer systems in body fluids, within seconds.
17
• A. The bicarbonate buffer system
• B- The phosphate buffer system
• C- The protein buffer system
• D- Bone salts (calcium carbonate and calcium phosphate)
In the short term, bicarbonate is, by far, the most
important, though bone buffers play a more
significant role in chronic acidosis

18. Defense against changes in H+ concentration
• I. Acid-base buffer systems in body fluids, within seconds.
• II. The respiratory system, within minutes.
• III. The kidneys, within hours.
18

19. II- RESPIRATORY REGULATION OF ACID-BASE BALANCE
central chemoreceptors in the medulla
oblongata
peripheral
chemoreceptors in aortic
and carotid bodies
↑ CO2 → H+ (in blood)
→ H+ (in CSF)

20. Defense against changes in H+ concentration
• I. Acid-base buffer systems in body fluids, within seconds.
• II. The respiratory system, within minutes.
• III. The kidneys, within hours.
20

21. 21

22. 22

23. Defense against changes in H+ concentration
23
1. Reabsorption (reclamation) of the filtered bicarbonate by proximal tubules.
2. Generation of new bicarbonate
A- ammonia
B- phosphoric, sulphuric acid
III. The kidneys

24. Defense against changes in H+ concentration
24
1. Reabsorption (reclamation) of the filtered bicarbonate by proximal tubules.
2. Generation of new bicarbonate
A- ammonia
B- phosphoric, sulphuric acid
III. The kidneys

25. 1- Reabsorption of the filtered bicarbonate
25

26. 1- Reabsorption of the filtered bicarbonate
26

27. Defense against changes in H+ concentration
27
1. Reabsorption (reclamation) of the filtered bicarbonate by proximal tubules.
2. Generation of new bicarbonate
A- ammonia
B- phosphoric, sulphuric acid
III. The kidneys

28. 2. Generation of new bicarbonate
A- ammonia (PCT & DCT)
Na Na
Cl

29. Defense against changes in H+ concentration
29
1. Reabsorption (reclamation) of the filtered bicarbonate by proximal tubules.
2. Generation of new bicarbonate
A- ammonia
B- phosphoric, sulphuric acid
III. The kidneys

30. 2. Generation of new bicarbonate
B- phosphate (DCT)
Na Na
Filtered
Na2HPO4

31. 2. Generation of new bicarbonate
B- phosphate (DCT)
NaHPO4 +
Filtered
Na2HPO4
Na Na
Na

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