Acid-Base Balance

pH of blood

7.35-7.45

Why must pH be regulated in blood?

To facilitate/preserve enzyme/protein function

Buffer

Combination of weak acid and base. Prevent large/sudden changes in pH by taking up H+ when pH falls or releasing them when pH rises

Respiratory system

• Chemoreceptors regulate the rate and depth of respiration, thereby adjusting pH and oxygen.

• Eliminate Co2 in blood, a volatile acid

Renal system (kidneys)

Eliminate any acid (e.g. H+) and synthesize new bicarbonate and recycle old bicarbonate; allows HCO3- to be excreted or maintained

Systems/mechanisms body uses to regulate pH

Buffers, respiratory system, renal system

Death can occur if pH falls below ____ or rises above ____

6.9; 7.8

PaCO2 reflects

Respiratory function

HCO3- reflects

Renal (metabolic) function

CO2+H2O =

H2CO3 (carbonic acid)

Ratio of bicarbonate to carbonic acid

20:1

What acid can the kidney not eliminate?

Carbonic acid (H2CO3); CO2

When pH rises, respiratory rate

Slows (hypoventilation)

When pH falls, respiratory rate

Increases (hyperventilation)

Compensation is not correction. True or false?

True

Lungs compensate for

Metabolic acid changes.

Defined as a pH below 7.35 and abnormally low HCO3- concentration.

Metabolic Acidosis

Metabolic acidosis is ultimately caused by

Metabolic acid accumulation (e.g. lactic acid buildup)

Defined as a pH above 7.45 and abnormally high HCO3- concentration.

Metabolic alkalosis

What is the pH change caused by metabolic acidosis compensated by?

Hyperventilation; will decrease the PaCO2.

What is the pH change caused by metabolic alkalosis compensated by?

hypoventilation; will increase the PaCO2.

Defined as a pH below 7.35 and an abnormally high PaCO2

Respiratory acidosis

Respiratory acidosis is compensated by

Kidney excretion of H+ and retention of HCO3-.

Defined as a pH above 7.45 and abnormally low PaCO2

Respiratory alkalosis

Respiratory alkalosis is compensated by

Renal retention of H+ and excretion of HCO3-.

Mixed Acid-Base Disorders

defined as two primary acid-base disorders present independently.

• May arise from simultaneous dysfunction of the respiratory system and the kidneys.

• pH may be nearly normal or grossly abnormal

Metabolism of fat produces

Acidic ketone bodies

Loss of HCO3- from diarrhea is another cause of

Metabolic acidosis

Useful indicator of acid-base status of extracellular fluid

Arterial blood gas (ABG)

Normal PaCO2 (arterial) in adults

36-44 mm Hg

Normal PaCO2 (arterial) in infants

30-34 mm Hg

Normal HCO3- (serum) in adults

22-26 mEq/L

Normal HCO3- (serum) in infants

19-23 mEq/L

Normal ABG

35-45 mm Hg

Source of acid in human body

• Production of CO2 during cellular metabolism

• Metabolism of fat producing ketone bodies

• Muscle activity produces lactic acid when sufficient oxygen unavailable

How do the kidneys eliminate H+ ions?

Secrete H+ into renal tubule. This acid is buffered or excreted in the form of ammonium ion (NH4+). Allow HCO3- to be excreted or retained

The concentration of HCO3- in plasma reflects

The relative amount of metabolic acid in the blood.

More HCO3- in plasma =

Less metabolic acid in blood

Less HCO3- in plasma =

More metabolic acid in blood

Kidneys compensate for

Altered carbonic acid changes.

In compensation,

• pH returns to near normal

• PaCO2 and HCO3- are not normal

When insulin is unavailable to permit entry of glucose into cells, fat is metabolized for energy leading to the buildup of ketone bodies. Can cause metabolic acidosis

Ketoacidosis in diabetic

Hypoventilation due to lung disease can cause

Respiratory acidosis

Neuromuscular problems such as hypokalemic muscle paralysis can cause

Respiratory acidosis

Respiratory depression caused by opioid overdose or brainstem injury can lead to

Respiratory acidosis

Vomiting can cause

Metabolic alkalosis

Excessive consumption of antacid medications can cause

Metabolic alkalosis

Pain and anxiety can cause

Respiratory alkalosis

Hypoxemia leads to

Respiratory alkalosis

Mixed Acid-Base disorders may arise from

Simultaneous dysfunction of the respiratory system and the kidneys.

pH may be nearly normal in mixed acid-base disorders. True or false?

True

pH is not grossly abnormal in mixed acid-base disorders. True or false?

False

Caloric and glucose intake is insufficient; body metabolozies fat and ketoacids accumulate in blood → metabolic acidosis

Starvation ketoacidosis