Acid-Base Regulation

Front 1

What are acid/base disorders?

What's the normal [H] concentration of the ECF?

Back 1

*Acid base disorders are disorders of the concentration of hydrogen ion (H) in the extracellular fluid.

*In the extracellular fluid, the normal H concentration is 40 nEq/L.

Front 2

If the H concentration is 40 nEq/L, what is the pH?

Back 2

7.4. This is normal blood pH.

Front 3

What are the [H] ranges for acidemia and alkalemia, in both nEq/L and in pH?

Back 3

*Keep in mind that [H] falls as pH rises.

Front 4

How abundant is H compared to other cations?

Back 4

*It's not. [Na] is thousands of times more abundant.

Front 5

What happens As H+ rises and pH falls?

Back 5

*Myocardial contractility decreases.

*Vascular responsiveness to catecholamines decrease (hypotension due to decreased arteriolar function).

*Renal and hepatic plasma flow decrease.

*Skeletal muscle contractility decreases.

*Protein degradation increases, protein synthesis decreases.

*K+ leaves the intracellular space and hyperkalemia increases in the extracellular fluid.

*Calcium dissociates from albumin, increasing the level of ionized (bioactive) calcium in the extracellular fluid.

Front 6

What happens As H+ falls and pH rises?

Back 6

*Increased vasoconstriction.

*Increased muscular contraction.

*K+ enters the intracellular space and hypokalemia develops in the extracellular fluid.

*Calcium binds to albumin, decreasing the level of ionized (bioactive) calcium in the extracellular fluid.

*Decreased oxygen release by erythrocytes, decreasing tissue oxygenation.*

Front 7

At what pH and [H] is life possible?

Back 7

*Outside of 7.3 and 7.5, life is only possible for a few hours.

Front 8

What two processes constantly increase the H+ concentration?

Back 8

Front 9

What happens to H2CO3 when it is added to the body?

Back 9

It is converted to CO2 and water: CO2 diffuses from alveolar capillaries to alveolar space in the lung and is expired.

Front 10

What happens to dietary acids when we take them in?

Back 10

An acid added to the ECF is buffered by HCO3, producing H2CO3 and a molecule of the salt of the added acid, consuming a H2CO3 molecule in the process.

HA + NaHCO3 --> NaA + H2CO3

H2SO4 + NaHCO3 --> NaHSO4 + H2CO3
H3PO4 + NaHCO3 --> NaH2PO4 + H2CO3

*H2CO3 then --> CO2 + H2O and is expired.



Front 11

How do the concentrations of H2CO3 and CO2 affect [H]?

How does HCO3 level affect the [H]?

Back 11

*Note normal PCO2 level.
*Note normal bicarb level.

*H2CO3=CO2

Front 12

What is the HH equation for the human body?

Back 12

Front 13

What's more important for us to know than the HH equation for understanding the level of acidity of the blood?

Back 13

*States that pH and H+ are dependent on pCO2 and HCO3. Normal body values are listed in the image.
*Note the measurement units of all the values in this equation. Note that the constant is a value of 24.

Front 14

So...what are the 4 ways that your pH can become ABNORMAL?

Back 14

*Increase in H+ (ACIDEMIA):
1) Increase in pCO2
2) Decrease in HCO3-

*Decrease in H +(ALKALEMIA):
3) Decrease in pCO2
4) Increase in HCO3-

Front 15

WHAT DO THESE 4 CHANGES LEAD TO?

*Increase in H+ (ACIDEMIA):
1) Increase in pCO2
2) Decrease in HCO3-

*Decrease in H +(ALKALEMIA):
3) Decrease in pCO2
4) Increase in HCO3-

Back 15

*Increase in H+ (ACIDEMIA):
1) Increase in pCO2: RESPIRATORY ACIDOSIS
2) Decrease in HCO3: METABOLIC ACIDOSIS

*Decrease in H +(ALKALEMIA):
3) Decrease in pCO2: RESPIRATORY ALKALOSIS
4) Increase in HCO3: METABOLIC ALKALOSIS

Front 16

You are in the emergency room and an unidentified man, who appears to be in his twenties, is brought to the critical care area after passing out at a bar. An arterial pH is done and is 7.28. The pO2 is 97 mmHg and the pCO2 is 36 mmHg. The HCO3- level is 31 mEq/L. What is the acid base disturbance?

a) metabolic acidosis
b) metabolic alkalosis
c) respiratory acidosis
d) respiratory alkalosis
e) a mixed acidosis and alkalosis
f) the lab values must be incorrect.

Back 16

*The lab values must be incorrect.

*THE POINT: this is an impossible combination of lab numbers.

Front 17

What 3 organ systems determine the body's pH?

Back 17

*The normal, or physiologic [H] in the extracellular fluid is 40 nEq/L; this correlates to a pH of 7.40. The [H] is determined (as per the Henderson equation) by the [HCO3] and the partial pressure of CO2 (pCO2).

*The [HCO3] is regulated to be closely around a value of 24 mEq/L, the pCO2 is closely regulated around a value of 40 mmHg.

*The lungs are responsible for the pCO2 level and the gastrointestinal and renal systems determine the HCO3 level. Therefore, three organ systems: pulmonary, GI, and renal, regulate and determine the [H] and pH of the ECF.

Front 18

How is pH maintained in the upper GI tract?

Back 18

*As parietal cells secrete HCl into the lumen of the upper GI tract, NaHCO3 is simultaneously transported into the capillaries that line the stomach. Therefore, neutrality is maintained.

Front 19

How is pH maintained in the lower GI tract?

Back 19

*In the jejunum, ileum, and proximal large intestine, the reverse process occurs: NaHCO3- is secreted into the intestinal lumen, and HCl- diffuses into the surrounding capillaries. Neutrality is maintained.

Front 20

What happens to bicarb in the proximal tubule?

Back 20

*It's freely filtered by the glomerulus (negative charge, small size).
*One molecule of bicarb combines with one molecule of secreted [H]; H2CO3 is formed.
*It dissociates, and CO2 and H20 diffuse freely into the cell. H2CO3 is formed again. This H2CO3 dissociates into HCO3- and H+.
*The H+ gets secreted into the TF, and the bicarb is reabsorbed.

Front 21

What happens to bicarb in the distal tubule and the proximal CCD?

Back 21

*Restores our pH by secreting acid that was taken in in the diet, regenerating the bicarb that gets used up.
*Occurs in INTERCALATED cells.

*Distal tubular cell:
1) Secretion of H+ into the tubular lumen (as free H+, as titratable acid, or as ammonium (NH4+).
2) In this process, there is regeneration of HCO3- and passage of HCO3- into the systemic circulation.
3) Both of the above processes stimulated by aldosterone.