Acid Bases and Disorders

Question 1

What are normal pH ranges and what does an imbalance of these ranges cause?

Answer 1

The normal pH ranges from 7.35-7.45. Optimal pH is required to maintain optimal cellular function. An increase in the concentration of hydrogen ions decreases pH and the environment becomes more acidic. A decrease in the concentration of hydrogen ions increases pH and makes the environment more alkalotic.

Question 2

What are acids?

Answer 2

Acids enter the blood from multiple sources continuously and need to be excreted, hence the
need to have mechanisms to maintain the pH balance. Acids are produced in our bodies as a
byproduct of cellular metabolism on a daily basis.

Question 3

What is a byproduct of aerobic metabolism?

Answer 3

Carbonic acid (H2CO3) is part of the
byproduct of aerobic metabolism. The actual byproduct of aerobic metabolism is carbon dioxide
(CO2) which is converted to carbonic acid by the enzyme carbonic anhydrase.

Question 4

What is a byproduct of anaerobic metabolism?

Answer 4

Lactic acid is a byproduct of the anaerobic metabolism of glucose.

Question 5

What does sulfuric acid result from?

Answer 5

Sulfuric acid results from the oxidation of sulfur
containing amino acids.

Question 6

What does phosphoric acid result from?

Answer 6

Phosphoric acid results from the metabolism of phosphoproteins and ribonucleotides which are used as an energy source

Question 7

What are ketone bodies?

Answer 7

Ketone bodies are an acid and result from
the breakdown of fats.

Question 8

What is the formula for acid-base physiology?

Answer 8

CO2 + H20<—> H2CO3<—->H+ + HCO3-

Question 9

What does this equation represent?

Answer 9

The left side of the equation represents what occurs in the lungs. The right side of the equation is the process that occurs in the kidneys

Question 10

What are the control mechanisms of acid-base balance?

Answer 10

The control mechanisms of acid-base balance include the chemical buffer systems, the kidneys
and the lungs

Question 11

What do chemical buffer systems include?

Answer 11

Chemical buffer systems include bicarbonate, phosphate, plasma proteins and
hemoglobin.

Question 12

What is the kidney’s role in acid-base balance?

Answer 12

The kidney’s role in the control of acid-base balance is three parts and includes the reabsorption of filtered bicarbonate, renal excretion of hydrogen, and the excretion of hydrogen as ammonium.

Question 13

What is bicarbonate?

Answer 13

Bicarbonate (HCO3-/CO2 Buffer) is the most important extracellular buffer. It is the first line of
defense against alterations in the acid-base balance

Question 14

How does phosphate act as a chemical buffer?

Answer 14

Phosphates can be either inorganic or
organic. Inorganic phosphate is an extracellular buffer. The chemical formula is as you see it on
your screen (HPO4-2/H2PO4- Buffer). Organic Phosphates operate as intracellular buffers. They
include ATP, ADP, AMP, glucose 1-phosphate, and 2,3 diphosphoglycerate (2,3 DPG).

Question 15

How do plasma proteins act as a chemical buffer?

Answer 15

Plasma Proteins act as extracellular buffers. Albumin is the main plasma protein and it has a
negative charge; therefore, it has a role in buffering H+, which has a positive charge. Albumin
also has a role in binding calcium. Albumin binds approximately 40% of calcium. In acidotic
states, there is an excess of hydrogen ions which causes albumin to bind more hydrogen ions and
consequently, it binds to fewer calcium ions. This results in the calcium ions being displaced and a
higher level of free calcium. In alkalotic states, there is an insufficient amount of hydrogen ions available to bind with albumin. As such albumin binds more calcium thus decreasing the amount of free calcium.

Answer 16

Hemoglobin is the most important intracellular buffer and plays a pivotal role in acid-base homeostasis. After releasing oxygen to the tissues CO2 diffuses into the RBC. Once inside the RBC, CO2, and H2O are combined by carbonic anhydrase and form carbonic acid (H2CO3). Carbonic acid is a weak acid and it immediately dissociates into H+ and HCO3-. H+ is
then buffered by hemoglobin. When the RBC reaches the lung, the process reverses and CO2 and
H2O is then formed. CO2 then diffuses out of the RBC and is expired by the lungs.

Question 17

How much acid is removed from the lungs every day?

Answer 17

The lungs remove 30 liters of carbonic acid from venous blood on a daily basis.

Question 18

What is the first role of kidneys in maintaining acid-base balance?

Answer 18

The first role is the reabsorption of filtered HCO3-. Reabsorption of filtered HCO3- occurs to maintain the buffer. Nearly 100% of filtered bicarbonate is reabsorbed. The majority of filtered HCO3- is reabsorbed in the proximal tubule of the kidney. Much smaller amounts are reabsorbed in the loop of Henle, the distal tubule and the collecting ducts

Question 19

What does acetazolamide do?

Answer 19

This is the site of action for the carbonic anhydrase inhibitor acetazolamide. The medication blocks the
action of carbonic anhydrase and therefore prevents the reabsorption of HCO3-
.

Question 20

What is extracellular fluid volume and its effects on HCO3- reabsorption?

Answer 20

When the extracellular fluid volume is expanded it inhibits the reabsorption of HCO3- in the proximal tubule. A deficit in the extracellular fluid volume results in an increase in the reabsorption of HCO3-. ECF volume deficit also stimulates the renin-angiotensin system. Angiotensin II stimulates the Na+-H+ exchanger in the proximal tubule lining membrane, thus increasing HCO3- reabsorption. This is what causes metabolic alkalosis. This can also occur with the use of loop and thiazide diuretics. Treatment is volume replacement with sodium chloride.

Question 21

Where and how is H+ excreted?

Answer 21

The renal excretion of H+ as a titratable acid occurs mainly in the distal tubule and collecting ducts. The cells of the distal tubule and collecting ducts contain two active transport systems to secrete H+: H+ATPase and H+-K- ATPase. These mechanisms move H+ into the lumen and move potassium from the lumen into the cells. H+ in the lumen binds with monohydrogen phosphate (HPO4-2) and produces H2PO4 (dihydrogen phosphate). H2PO4- can then be excreted. For every H+ excreted there is one HCO3- reabsorbed into the blood.

Question 22

Where and how is H+ as ammonia excreted?

Answer 22

Renal excretion of H+as ammonium (NH4+) occurs in the proximal tubule, the ascending loop of Henle, and the collecting ducts. The proximal tubule cells produce NH4+.

Question 23

What is HCO3?

Answer 23

Bicarbonate

Question 24

What are normal ranges for serum CO2 and what does it test?

Answer 24

The serum CO2 is typically included in a BMP or a CMP. It is an indirect measurement of the anion HCO3. An elevation reflects an alkalotic state and a decrease would reflect an acidotic state. Normal lab value for the adult and elderly is between 23-30 mEq/L or mmol/L

Question 25

What does a low pH mean?

Answer 25

A low pH is < 7.4 and indicates an acidic state and a
high hydrogen ion concentration.

Question 26

What does a high pH mean?

Answer 26

A high pH is > 7.4 and indicates an alkalotic state and a low hydrogen ion concentration.

Question 27

What does the PaCO2 represent?

Answer 27

The PCO2 reflects the lungs’ role in acid-base balance. A normal value is between 35-45. It reflects ventilation. The higher the CO2 the faster the respirations are and vice versa. It has an
inverse relationship with pH. The higher the pH, the lower the CO2, and the opposite is true.

Question 28

What does HCO3 represent?

Answer 28

It is a direct measurement of the amount of bicarbonate in the blood. It reflects the metabolic
component of acid-base balances, specifically the kidney. It is directly related to pH. As the bicarbonate rises, the pH will rise. The opposite is also true. The normal range is 21-28 mEq/L.

Question 29

What are the three pathological mechanisms that cause metabolic acidosis?

Answer 29

Increased acid production, loss of bicarbonate, or diminished renal excretion of hydrogen.

Question 30

What can occur from metabolic acidosis?

Answer 30

Pathological consequences of acidemia include decreased myocardial contractility, decreased
cardiac output, catecholamine-resistant hypotension (decreased binding of norepinephrine to its receptors), and hyperkalemia.

Question 31

What does a high anion gap mean?

Answer 31

A high anion gap acidosis is most likely caused by lactic acidosis, ketoacidosis, or acute and chronic renal failure.

Question 32

What does a normal anion gap mean?

Answer 32

A normal anion gap acidosis (hyperchloremic acidosis) is most commonly caused by GI losses from diarrhea, large volumes of saline administration, and medications such as NSAIDs, ACE inhibitors, and trimethoprim.

Question 33

How does metabolic alkalosis occur?

Answer 33

Metabolic Alkalosis results from an excess of HCO3-
or deficiency of H-. It is characterized by a pH > 7.4 and bicarbonate > 28. The most common causes are vomiting and diuretic use.

Question 34

What happens to the body in metabolic alkalosis?

Answer 34

Metabolic alkalosis is usually accompanied by hypokalemia (cardiac arrhythmias), hypocalcemia and its associated symptoms, hypoventilation, and an elevated pCO2.

Question 35

What is the pathophysiology behind vomiting?

Answer 35

In normal physiology, the gastric parietal cells
produce hydrogen ions and bicarbonate. H+ and Cl are released into the stomach and HCO3- is released into the blood. H+ then travels into the small intestine thus decreasing the pH of the small intestine. This serves as a trigger for the pancreas to secrete HCO3. The pancreatic HCO3- is obtained from the supply of HCO3- in the blood. In the setting of vomiting, H+ ions are lost and the pH of the small intestine does not change, therefore the pancreas does not release HCO3-. HCO3- then accumulates causing the alkalosis.

Question 36

What is the pathophysiology behind respiratory acidosis?

Answer 36

Respiratory Acidosis results from an excess of arterial carbon dioxide (PaCO2), and a decrease in alveolar ventilation in relation to the metabolic production of carbon dioxide. Lungs are not blowing off enough CO2. The pH will be < 7.4 and the Pco2 > 45.

Question 37

What are some effects of respiratory acidosis?

Answer 37

The effects on the body include increased blood calcium levels (decreased binding to albumin) , increased serum potassium, vasodilation because of CO2, tremors, disorientation, restlessness, muscle twitching, and seizures

Question 38

How does respiratory alkalosis occur?

Answer 38

Respiratory Alkalosis results from a deficiency of PaCO2. It occurs when there is an increase in alveolar hyperventilation. The lungs are blowing off too much CO2. The pH will be > 7.4 and Pco2 will be < 35. It causes neurological signs and symptoms.

Question 39

What are some diseases that occur due to respiratory alkalosis?

Answer 39

It is commonly caused by hypoxemia, pulmonary embolism, congestive heart failure, high altitudes, fever, gm negative sepsis, or severe anemia, psychogenic hyperventilation, hepatic failure, salicylate overdose, drugs such as catecholamines, methylphenidate3, nicotine, progesterone, or mechanical ventilation.