18 Renal Acid Base Balance

Topics: Carbon dioxide, PH, Acid Pages: 38 (2429 words) Published: April 30, 2015
Renal Physiology

PART
THREE
Renal Acid-Base
Balance

1

Acid





An acid is when hydrogen ions accumulate in a solution.
It becomes more acidic
[H+] increases = more acidity
CO2 is an example of an acid.

HCl
2
H+

H+
ClH+

H+

ClH+

7

ClpH
ClCl-

As concentration of hydrogen
ions increases, pH drops

Base
• A base is chemical that will remove hydrogen ions from
the solution
• Bicarbonate is an example of a base.

NaOH

Na+ OH- H +
ClH+
ClNa+ OHH+
ClH+
Cl- Na+ OHH+
ClNa+ OH-

2

7

pH

Acids and basis
neutralize
eachother

A change of 1 pH unit corresponds to
a 10-fold change in hydrogen ion
concentration

2

Na+

ClNa+

H+

Na+

7

ClH2O

OH-

Na+
Cl-

Cl-

pH

Acids are being created constantly
through metabolism
• Anaerobic respiration of glucose
produces lactic acid
• Fat metabolism yields organic acids and
ketone bodies
• Carbon dioxide is also an acid.

Acids must be buffered, transported away
from cells, and eliminated from the body
Phosphate: important renal tubular buffer
HPO4- + H+
H2PO 4
Ammonia: important renal tubular buffer
NH3 + H+
NH4+
Proteins: important intracellular and plasma buffers
H+ + Hb
HHb
Bicarbonate: most important Extracellular buffer
H2O + CO2 H2CO3

H+ + HCO3 -

Buffering is good, but it is a temporary
solution. Excess acids and bases must be
eliminated from the body
gas

H2O + CO2 H2CO3

aqueous

H+ + HCO3 Kidneys can remove excess
non-gas acids and bases

Lungs eliminate
carbon dioxide

Excessive Acids and Bases can cause
pH changes---denature proteins
• Normal pH of body fluids is 7.40
• Alkalosis (alkalemia) – arterial blood pH rises above 7.45 • Acidosis (acidemia) – arterial pH drops below 7.35
• Acidosis:
– too much acid
– Too little base

• Alkalosis
– Too much base
– Too little acid

Compensation for deviation
• Lungs (only if not a respiratory problem)
– If too much acid (low pH)—respiratory
system will ventilate more (remove CO2)
and this will raise pH back toward set point
– If too little acid (high pH)—respiratory will
ventilate less (trap CO2 in body) and this will
lower pH back toward set point

• Kidneys
– If too much acid (low pH)—intercalated cells
will secrete more acid into tubular lumen
and make NEW bicarbonate (more base)
and raise pH back to set point.
– If too little acid/excessive base (high pH)proximal convoluted cells will NOT reabsorb filtered bicarbonate (base) and will eliminate
it from the body to lower pH back toward
normal.

Acid-Base Balance
• How would your ventilation change if you
had excessive acid?
– You would hyperventilate

• How would your ventilation change if you
had excessive alkalosis?
– Your breathing would become shallow

How can the kidneys control acids
and bases?
• Bicarbonate is filtered and
enters nephron at
Bowman’s capsule
• Proximal convoluted tubule
– Can reabsorb all bicarbonate
(say, when you need it to
neutralize excessive acids in
body)
OR

– Can reabsorb some or
NONE of the bicarbonate
(maybe you have too much
base in body and it needs to
be eliminated)

How can the kidneys control acids
and bases?
• Acidosis
• Intercalated cells
– Secrete excessive
hydrogen
– Secreted hydrogen
binds to buffers in the
lumen (ammonia and
phosphate bases)
– Secretion of hydrogen
leads to formation of
bicarbonate

HPO4NH3

What would happen if the respiratory
system had a problem with ventilation?
Respiratory Acidosis and Alkalosis
Normal PCO2 fluctuates between 35 and 45 mmHg






Respiratory Acidosis (elevated
CO2 greater than 45mmHg)
Depression of respiratory
centers via narcotic, drugs,
anesthetics
CNS disease and depression,
trauma (brain damage)
Interference with respiratory
muscles by disease, drugs,
toxins
Restrictive, obstructive lung
disease (pneumonia,
emphysema)







Respiratory...
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