March 26 - Acid Base

Question 1

What is pH?

Answer 1

-log[H+]

Question 2

What is considered basic?

Answer 2

pH>7.6

Question 3

What is considered acidic?

Answer 3

pH<7.2

Question 4

What is the normal blood pH?

Answer 4

7.4 (slightly basic)

Question 5

What are volatile acids?

Answer 5

Acids that are likely to change. Example: the production of bicarbonate and H ions, which can form carbon dioxide and water

Question 6

What is a major source of volatile acids?

Answer 6

Major source is oxidative metabolism of carbohydrates and triglycerides. Metabolism produces carbon dioxide, which converts to carbonic acid and back to carbon dioxide for excretion by the lungs

Question 7

What are non volatile acids?

Answer 7

They are acids that don’t change (you can’t blow these of as carbon dioxide). So they need to excreted by the kidneys. Diets high in protein result in higher non volatile concentrations. They form non carbonic acids (i.e. not broken down into CO2 and excreted by the lungs). Forms sulfuric and hydrochloric acids. Phosphates normally in diet

Question 8

How can losses in bodily fluid affect the pH of the body?

Answer 8

Vomiting results in the loss of H ions
Diarrhea results in the loss of bicarbonate
Urine results in the loss of bicarbonate

Question 9

Describe the relationship between pH, carbon dioxide and bicarbonate

Answer 9

pH is directly proportionate to the concentration of bicarbonate the inversely proportionate to dissolved CO2. So a decrease in CO2 and/or an increase in bicarbonate will increase the pH and a decrease in bicarbonate and/or an increase in CO2 will decrease pH

Question 10

Describe the body’s buffering system

Answer 10

There are buffers in the blood and tissue that are important for acute control of pH and to prevent large shifts in pH

Question 11

What are the blood buffers?

Answer 11

There are plasma buffers (3/4 of plasma buffers are bicarbonate buffers, but there is also plasma proteins and phosphate buffers) and erythrocyte buffers (mostly bicarbonate but also hemoglobin)

Question 12

What are the tissue buffers?

Answer 12

There are skeletal muscle buffers (the skeletal muscle stores a large percentage of the total body’s bicarbonate, to be used during strenuous activity) and bone buffers (large stores of carbonate; main source for neutralizing non carbonic acid. Long-term non carbonic acidosis associated with bone breakdown)

Question 13

Describe respiratory regulation of pH

Answer 13

The respiratory system eliminates carbon dioxide from the blood and shifts the equilibrium away from carbonic acid (and vice versa). If the respiration rate increases, the amount of carbon dioxide decreases, thus pH increases. If respiration rate decreases, the amount of carbon dioxide increases, thus pH decreases

Question 14

Describe the renal regulation of pH

Answer 14

The kidney serves to fine tune the overall acid base balance in the body. The body’s buffering system and respiratory regulation of pH are typically involved in acute changes, whereas renal regulation is more long term

Question 15

What are the three renal mechanisms for responding to pH changes

Answer 15

1. Bicarbonate reabsorption (reclaimation)
2. Formation of new bicarbonate/ammonium:ammonia
3. Excretion of hydrogen ions (ammonia/phosphate)

Question 16

Describe how bicarbonate reabsorption is used to respond to pH changes

Answer 16

This occurs primarily in the proximal tubule (85%)
Some reabsorption in the collecting ducts (10%)
In the process, hydrogen ion is secreted, reabsorbed and secreted (no net hydrogen ion excretion). Also, bicarbonate in the filtrate is broken down and reformed in the cell for reabsorption.
This is important when bicarbonate is required (acidosis)

Question 17

Describe how the formation of new bicarbonate is used to respond to pH changes

Answer 17

This occurs in the proximal tubule. Glutamine is converted into ammonium (NH4+) and bicarbonate.
Bicarbonate is reabsorbed. Ammonium is secreted into the tubule lumen, reabsorbed by the loop of Henle by a Na/K/Cl transporter. In the interstitium, ammonium is converted into ammonia (NH3) and H ion. Ammonia is “stored” for when it is required by the collecting tubule

Question 18

Describe net acid excretion (NAE)

Answer 18

There are three parts to net acid excretion: urine ammonium excretion volume, urine titratable acid excretion volume and urine bicarbonate excretion volume. Urine ammonium excretion volume is the most important because ammonia allows the excretion of large amounts of H ions as ammonium. Urine titratable acid excretion allows the excretion of H ions as H2PO4- (useful but limited). NAE = (UNH4V + UTAV) - UHCO3V

Question 19

Describe how hydrogen ion secretion is used to respond to pH changes

Answer 19

H ions are present in the distal nephron due to the filtration and secretion (but low). The concentration gradient from the plasma to the tubule lumen limits the amount that can be excreted (very little free H ions are excreted). By buffering the H ions in the tubule lumen, net hydrogen excretion is increased (favors H gradient into the tubule). Once the last of the bicarbonate has been used to buffer the H ions, the titratable buffers become important (phosphate and ammonia). Phosphate is limited in the amount but is an effective buffer at higher pHs. Ammonia (present in the interstitium due to Gln metabolism) is the major titratable acid (acts as a buffer). Aldosterone stimulates the H ion secretion

Question 20

How does the kidney respond to acidosis?

Answer 20

1. Increase H ion secretion and increase bicarbonate reabsorption to 100%
2. Increase ammonia production and loss of ammonium
3. Generate new bicarbonate from glutamine

Question 21

How does the kidney respond to alkalosis?

Answer 21

1. Decrease H ion secretion (less secreted)

2. Decrease bicarbonate reabsorption

Question 22

How can you tell if a patient is acidotic or alkalotic?

Answer 22

Look at the pH
Low pH = acidotic
High pH = alkalotic

Question 23

How can you tell if the patient’s acidosis is respiratory or metabolic?

Answer 23

In respiratory acidosis, bicarbonate and carbon dioxide will both be high (respiratory acidosis with compensatory increase in bicarbonate)
In metabolic acidosis, bicarbonate and carbon dioxide will both be low (metabolic acidosis with compensatory decrease in carbon dioxide)

Question 24

How can you tell if the patient’s alkalosis is respiratory or metabolic?

Answer 24

In respiratory alkalosis, bicarbonate and carbon dioxide will both be low (respiratory alkalosis with compensatory decrease in bicarbonate)
In metabolic acidosis, bicarbonate and carbon dioxide will both be high (metabolic alkalosis with compensatory increase in bicarbonate dioxide)

Question 25

How can an anion gap differentiate between the type of metabolic acidosis a patient can have?

Answer 25

Metabolic acidosis can be caused by either primary loss of bicarbonate or it may be due to an increase of acid production or ingestion. If there is an increase in production or ingestion of acid (e.g., diabetes), sodium will couple with it, causing a larger anion gap. If there is a loss of bicarbonate (e.g., diarrhea), the bicarbonate is lost but the body replaces it with chloride, resulting in hyperchloremic metabolic acidosis (anion gap doesn’t change)

Question 26

What is RTA? What are the different types?

Answer 26

Renal tubular acidosis, causing hyperchloremic metabolic acidosis. There is type 2 RTA (proximal tubule fails to reabsorb bicarbonate), type 1 RTA (distal nephron (distal tubule and collecting duct) is unable to secrete H ions) and type 4 RTA (hypoaldosteronism - no excretion of potassium and H ions)