Renal Acid-Base Balance

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.

72

pH

HCl

H + Cl-

H + Cl-

H + Cl-

H + Cl-

H + Cl-

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.

72

pH

H + Cl-

H + Cl-

H + Cl-

H + Cl-

H + Cl-NaOH Na+ OH-

Na+ OH-

Na+ OH-

Na+ OH-

Acids and basis neutralize eachother

72

pH

Na+ Cl-

Na+ Cl-

Na+ Cl-Na+ Cl-

H+ OH- H2O

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

Acids are being created constantly through metabolism

• Anaerobic respiration of glucose produces lactic acid

• Fat metabolism yields organic acids and ketone bodies

• Carbon dioxide!!!!!

Acids must be buffered, transported away from cells, and eliminated from the body

Phosphate: important renal tubular bufferHPO4

- + H+ H2PO 4

Ammonia: important renal tubular bufferNH3 + H+ NH4

+

Proteins: important intracellular and plasma buffersH+ + Hb HHb

Bicarbonate: most important Extracellular buffer

Buffering is good, but it is a temporary solution. Excess acids and bases must be

eliminated from the body

H2O + CO2 H2CO3 H+ + HCO3 -CA

Lungs eliminate carbon dioxide

Kidneys can remove excess non-volatile acids and bases

gas aqueous

Excessive Acids and Bases can cause pH changes---denature proteins

• Normal pH of body fluids is 7.40• Alkalosis or alkalemia – arterial blood pH rises above

7.45• Acidosis or acidemia – arterial pH drops below 7.35

(physiological acidosis)• For our class, we will stick to 7.40 as normal!

• 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

HPO4-

NH3

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 Alkalosis (less than 35mmHg- lowered CO2)

• Hyperventilation syndrome/ psychological (fear, pain)

• Overventilation on mechanical respirator

• Ascent to high altitudes• Fever

What if your metabolism changed? • Metabolic acidosis • Bicarbonate levels

below normal (22 mEq/L)

• Metabolic alkalosis• bicarbonate ion levels higher

(greater than 26mEq/L)

• Ingestion, infusion or production of more acids (alcohol)

• Salicylate overdose (aspirin)

• Diarrhea (loss of intestinal bicarbonate)

• Accumulation of lactic acid in severe Diabetic ketoacidosis

• starvation

• Excessive loss of acids due to ingestion, infusion, or renal reabsorption of bases

• Loss of gastric juice during vomiting

• Intake of stomach antacids

• Diuretic abuse (loss of H+ ions)

• Severe potassium depletion

• Steroid therapy

Acidosis: pH < 7.4

- Metabolic: HCO3 -

- respiratory: pCO2

Alkalosis: pH > 7.4- Metabolic: HCO3 -

- respiratory: pCO2

How can you tell if the acid-base balance is from a kidney disorder or

a lung disorder?

Compensation

• If the kidneys are the problem, the respiratory system can compensate.

• If the kidneys are secreting too much H+

(which makes too much bicarbonate, causing metabolic alkalosis), breathing will become slower so that less CO2 (an acid) is lost.

• If the kidneys are reabsorbing too much H+

(metabolic acidosis), breathing will become faster.

Compensation• If the respiratory system is the problem, the

kidneys can compensate.

• If breathing is too rapid (too much CO2, an acid, is lost, leaving the blood in respiratory alkalosis), Kidneys respond by reabsorbing more H+.

• If breathing is too shallow (not enough CO2 is lost, leaving the blood in respiratory acidosis), Kidneys respond by secreting more H+.

Clinical Problem 1a• Your patient’s blood pH is too low (acidosis).

• This can be caused by either respiratory acidosis or metabolic acidosis. Let’s say it was respiratory acidosis.

• We need to look at the patient’s partial pressures of carbon dioxide and bicarbonate to see if they are compensating.

• If blood carbon dioxide levels are elevated (too much blood acid) and urine bicarbonate levels are elevated (H+ is being secreted to make bicarbonate). That means that the original problem of elevated carbon dioxide ( pCO2) is being compensated for by the kidneys, which are secreting more H+ to make more bicarbonate.

• Since this patient’s bicarbonate levels are also elevated, they are compensating already.

Clinical Problem 1b• Your patient’s blood pH is too low (acidosis).• This can be caused by either respiratory acidosis or

metabolic acidosis. Let’s say it was respiratory acidosis. • We need to look at the patient’s partial pressures of

carbon dioxide and bicarbonate to see if they are compensating.

• If blood carbon dioxide levels are elevated (too much blood acid) and urine bicarbonate levels are decreased (H+ is being absorbed). That means that the original problem of elevated carbon dioxide ( pCO2) is NOT being compensated for by the kidneys, which should be secreting more H+ to make more bicarbonate.

Clinical Problem 2a• Your patient’s blood pH is too high (alkalosis).

• This can be caused by either respiratory alkalosis or metabolic alkalosis. Let’s say it was respiratory alkalosis.

• We need to look at the patient’s partial pressures of carbon dioxide and bicarbonate to see if they are compensating.

• If blood carbon dioxide levels are low (too little acid) and bicarbonate levels in the urine are low (too little base). That means that the original problem of decreased carbon dioxide ( pCO2) is being compensated for by the kidneys, which need to start reabsorbing more H+ to make more acid in the blood. If they are reabsorbing more H+, they are making less bicarbonate in the urine.

• Since this patient’s bicarbonate levels in the urine are low, they are compensating.

Clinical Problem 2b• Your patient’s blood pH is too high (alkalosis).• This can be caused by either respiratory alkalosis or

metabolic alkalosis. Let’s say it was respiratory alkalosis. • We need to look at the patient’s partial pressures of carbon

dioxide and bicarbonate to see if they are compensating. • If blood carbon dioxide levels are low (too little acid) and

bicarbonate levels in the urine are high (too much base). That means that the original problem of decreased carbon dioxide ( pCO2) is NOT being compensated for by the kidneys, which need to start reabsorbing more H+ to make the blood more acidic. The bicarbonate levels would be low if the kidneys were doing this.

Clinical Problem 3a• Your patient’s blood pH is too low (acidosis).• This can be caused by either respiratory acidosis or metabolic

acidosis. Let’s say it was metabolic acidosis. • We need to look at the patient’s partial pressures of carbon

dioxide and bicarbonate to see if they are compensating. • If urine bicarbonate levels are too low (H+ is being

reabsorbed) and blood carbon dioxide levels are too low (too little blood acid), that means that the original problem of a low bicarbonate level needs to be compensated for by the lungs, which need to hyperventilate, expelling more CO2 (an acid).

• Since this patient’s pCO2 levels are also low, they are compensating already.

Clinical Problem 3b• Your patient’s blood pH is too low (acidosis).• This can be caused by either respiratory acidosis or metabolic

acidosis. Let’s say it was metabolic acidosis. • We need to look at the patient’s partial pressures of carbon

dioxide and bicarbonate to see if they are compensating. • If urine bicarbonate levels are too low (H+ is being

reabsorbed) and blood carbon dioxide levels are too high (too much blood acid), that means that the original problem of a low bicarbonate level needs to be compensated for by the lungs, which need to hyperventilate, expelling more CO2 (an acid).

• However, since this patient’s pCO2 levels are also high (not expelling enough acid), they are NOT compensating.

Clinical Problem 4a• Your patient’s blood pH is too high (alkalosis).• This can be caused by either respiratory alkalosis or

metabolic alkalosis. Let’s say it was metabolic alkalosis. • We need to look at the patient’s partial pressures of carbon

dioxide and bicarbonate to see if they are compensating. • If bicarbonate levels in the urine are high (too much base)

and blood carbon dioxide levels are high (too much acid), that means that the original problem of increased bicarbonate levels need to be compensated by the lungs, which should take shallower breaths so less acid is lost.

• Since this patient’s pCO2 levels are elevated, they are compensating.

Clinical Problem 4b• Your patient’s blood pH is too high (alkalosis).• This can be caused by either respiratory alkalosis or

metabolic alkalosis. Let’s say it was metabolic alkalosis. • We need to look at the patient’s partial pressures of carbon

dioxide and bicarbonate to see if they are compensating. • If bicarbonate levels in the urine are high (too much base)

and blood carbon dioxide levels are low (too little acid), that means that the original problem of increased bicarbonate levels need to be compensated by the lungs, which should take shallower breaths so less acid is lost.

• Since this patient’s pCO2 levels are low, they are NOT compensating.