7: Acid-Base Balance

CO2

A deep exhalation will effectively expel which substance from the human body?

Increase

If the VCO2 increases and the VA is unchanged, what will happen to the partial pressure of CO2 in arterial blood?

Kidney

Which organ is used to most regulate bicarbonate and H+ levels in the blood on a time scale of hours to days?

Lung

Which organ is used to most regulate CO2 levels in the blood on a time scale of minutes?

ATP

Excretion of H+ in the DCT cells of the kidney requires...

3 multiple choice options

Increased pH, decreased HCO3-

Which lab values best represent an individual who is hyperventilating?

3 multiple choice options

Decreased pH, decreased HCO3-

An individual who has diabetes has run out of insulin. Furthermore, the individual ate something that caused diarrhea. The most likely lab values would show:

3 multiple choice options

7.35-7.45

Normal blood pH

Strong acids

On a mixed diet, pH is threatened by the production of ______ _____.

HCO3-

Strong acids are buffered by chemical buffer bases, such as _____ in the ECF.

Kidneys

The ________ eliminate H+ ions and anions in the urine.

HCO3-

Kidneys add _____ to replace that consumed in buffering strong acids.

Volatile acids

CO2 produced by the normal metabolism of dietary carbohydrates, lipids, and some amino acids as part of aerobic respiration

Acidifies

CO2 _________ blood because most of it is hydrated to carbonic acid which dissociates into bicarbonate and a proton.

Nonvolatile acids

From catabolism of sulfur-containing amino acids to yield H2SO4

From catabolism of purines to yield uric acid

From phosphoproteins and phospholipids to yield H3PO4

From incomplete oxidation of carbohydrates and fats to yield lactic acid and keto acids

Lactic acid and keto acids

Nonvolatile acids: from incomplete oxidation of carbohydrates and fats to yield...

Cannot

Lactic acid and keto acids ______ be expelled directly by the lungs and generate a net acid load of 40 mmol per day.

Body fluid buffers

Lungs

Chemosensors in the circulation and brain

Kidney

How do we neutralize the daily 70 mmol of acid?

Chemical buffers

Small fluctuations in the acid content of the blood are most readily handled by _________ ________ in the blood, the most abundant of which is bicarbonate.

pK where [HCO3-]/[CO2] = 1

The best buffering capacity is at the __.

False

T/F: The bicarb buffer is particularly effective at normal blood pH.

VCO2 / VA

PaCO2 =

Decrease

Increased alveolar ventilation can ________ arterial PaCO2.

Increase

Depressed alveolar ventilation can _________ arterial PaCO2.

Aortic and carotid bodies

Respond to changes in PaCO2 and pH in arterial blood

IX and X

Signals from aortic and carotid bodies reach the respiratory centers in the brain via which cranial nerves to regulate VA?

Increase

_________ in PaCO2 and H+ result in an increase in VA.

Kidneys

Reabsorb bicarbonate from and excrete H+ into the urine

PCT

Where is most of the filtered HCO3- reabsorbed?

Na+/H+ antiporter

Filtered HCO3- combines with H+ by PCT cells via an ______ __________ to form carbonic acid that dissociates rapidly into CO2 and water.

Carbonic anhydrase

Both the luminal and intracellular reactions are catalyzed by ________ _________.

Na+/HCO3- symporter

The CO2 readily diffuses into the PCT cell and the reaction is reversed to re-form H+ and HCO3- which can diffuse into the peritubular blood via a _______ ___________.

ATPase H+ pump

H+/K+ ATPase that reabsorbs K+ in exchange for H+

Two types of active transporters secrete H+ ions:

Acid; HCO3-

The increased PCO2 in the distal tubule cells drive the production of more ____, which is secreted and new _____ which is reabsorbed.

Distal tubule

Where is acid produced and new HCO3- produced?

Phosphate, ammonia

The luminal buildup of H+ ions in the DCT/CD is prevented by urinary buffers, especially _________ and _______.

False

T/F: Blood normally has appreciable amounts of ammonia.

Ammonia

Kidney glutaminase produces _______.

Acidosis

Condition or process that lowers the pH level

Alkalosis

Condition or process that elevates the pH level

Acidemia

Specifically refers to a blood pH ≤ 7.35

Alkalemia

Refers to a blood pH ≥ 7.45

Respiratory acidosis/alkalosis

Processes that affect pulmonary ventilation and skew the value of the PCO2

Metabolic acidosis/alkalosis

Non-respiratory processes that directly alter the H+ or HCO3-

Respiratory acidosis

Decreased pulmonary ventilation raises the PaCO2 and drives the reaction below to the right thereby increasing H+ and HCO3-

Decreased

Respiratory acidosis involves _________ pulmonary ventilation.

Respiratory alkalosis

Increased pulmonary ventilation lowers the PCO2 and drives the reaction below to the left thereby decreasing H+ and HCO3-

Metabolic acidosis

Addition of H+ from a non-volatile source consumes large amounts of HCO3-

Thus H+ increases and HCO3- decreases

Anion gap

The Na+ levels minus the levels of Cl- and HCO3- must equal the concentration of the unmeasured ions which is called the ____ ____.

[Na+] - {[Cl-] + [HCO3-]}

Typically about 6-10 mg/L

Anion gap =

Metabolic alkalosis

An increase in HCO3- resulting from excessive intake of alkali (e.g. antacids) or by loss of acid (e.g. HCl loss from vomiting, excessive use of some diuretics)

Respiratory acidosis

pH decreased

HCO3- increased

Metabolic acidosis

pH decreased

HCO3- decreased

Respiratory alkalosis

pH increased

HCO3- decreased

Metabolic alkalosis

pH increased

HCO3- decreased

Respiratory acidosis

pCO2 > 45 mm

Metabolic acidosis

HCO3- < 22

Respiratory alkalosis

pCO2 < 35 mm

Metabolic alkalosis

HCO3- > 26

Respiratory acidosis

Elevated net renal H+ excretion with increased serum HCO3- is compensation for...

Metabolic acidosis

Hyperventilation causing lower pCO2 is compensation for...

Respiratory alkalosis

Lower net renal H+ excretion with decreased serum HCO3- is compensation for...

Metabolic alkalosis

Hypoventilation producing higher pCO2 is compensation for...

pH = pK + log {[HCO3-] / [CO2]}

H-H equation for bicarbonate buffer system

20

In order for the pH to be 7.4, the HCO3-/CO2 ratio must be __.