Acid - Base regulation

Question 1

What are two common types of organic acids?

Answer 1

• lactic acid - produced by white, fast-twitch muscle during anaerobic glycolysis
• keto acids - produced in hepatocytes during amino acid metabolism. These are typically high in concentration during starvation or untreated diabetes mellitus. examples include acetoacetic acid and beta-hydroxybutyric acid

Question 2

What are the three ways that H+ can be secreted into the renal tubular lumen?

Answer 2

• H+ ATPase
• K+/H+ ATPase
• Na+/H+ exchanger (coupled facilitated diffusion) - these exchangers are mostly present on the cells lining the proximal convoluted tubule and the Loop of Henle

Question 3

Two ways hydrogen ions are trapped in the tubular lumen?

Answer 3

monobasic phosphate (H2PO4-) - dibasic phosphate (H2PO42-) binds to H+ in the lumen 
ammonium (NH4+) - formed from the deamination of glutamine in the cells lining the proximal tubule. 
- the trapping means that the newly formed molecule with H+ attached CANNOT be reabsorbed into the interstitial fluid and is thus excreted.

Question 4

Where is ammonium secreted in the renal lumen?

Answer 4

The the cells lining the proximal tubule. When glutamine is deaminated, NH4+ is released and is transported using couple facilitated diffusion. Na+ enters the cell and NH4+ exits into the lumen. This process increases when acid production is high. Glutamine can enter the cell through the renal tubular lumen or through the blood circulation (interstitial fluid)

Question 5

What are normal plasma bicarbonate concentrations?

Answer 5

24 mmol/L

Question 6

Which metabolic disturbances are chronic and which are acute?

Answer 6

They are all considered chronic because they all take relatively long to develop unlike respiratory illesses.

Question 7

What is the diagonal line on the davenport diagram called?

Answer 7

Non-carbonate buffering line (mmol/L/pH unit). Slope = 26 mmol/L/pH unit of whole blood. All of the disturbances are relative to the acid base conditions in the arterial blood.

Question 8

What are the normal body conditions of pH, HCO3-, and pCO2?

Answer 8

pH = 7.4 HCO3- = 25 mmol/L
pCO2 = 40 mmHg

Question 9

metabolic acidosis

Answer 9

No change in pCO2 but both pH and HCO3- decrease. Caused by excess organic acids - non carbonate source. Causes a base deficit because some of the added H+ reacts with HCO3- - causing removal of the base! More common that metabolic alkalosis

Question 10

metabolic alkalosis

Answer 10

No change in pCO2. Too much acid secretion or base retention. Result is an increase in both pH and HCO3- – gives a base EXCESS

Question 11

What triggers respiratory compensation

Answer 11

Chemosensors, sensitive to changes in plasma proton concentration, are present in the carotid bodies (located in the bifurcation of the internal and external carotid arteries) and the aortic bodies (present in the aortic arches)

Question 12

What does a rise in plasma H+ concentration trigger?

Answer 12

Hyperventilation to lower levels of CO2. High H+ triggers chemoreceptors which send signal to the medulla oblongata to increase breathing rate

Question 13

What does a drop in plasma H+ concentration trigger?

Answer 13

Hypoventilation to increase CO2 levels.

Question 14

What detects changes in pCO2?

Answer 14

Central chemoreceptors in the medulla. CO2 diffuses through the blood-brain barrier and affects the pH of the cerebrospinal fluid. The change in the presence of free H+ will tell the chemosensitive part of the medulla what the pCO2 change is.

Question 15

What does respiratory compensation correct?

Answer 15

Acute respiratory disturbances, metabolic disturbances

Question 16

Acute respiratory acidosis compensation?`

Answer 16

Following this disturbance, the respiratory compensation will be to increase ventilation to shift the reaction to the left. HYPERVENTILATION

Question 17

Acute respiratory alkalosis compensation?

Answer 17

Following the disturbance, ventilation will decrease to increase CO2 and shift the reaction to the right. HYPOVENTILATION

Question 18

Metabolic acidosis compensation?

Answer 18

Following the disturbance, hyperventilation will help return levels back to normal.

Question 19

Metabolic alkalosis compensation?

Answer 19

Following the disturbance, hypoventilation will help return levels back to normal.

Question 20

What are the two ways that the kidneys are able to compensate for acid base disturbances?

Answer 20

1. Adjusting the reabsorption of the filtered HCO3-

2. Adjusting the secretion of H+

Question 21

How is new bicarbonate formed?

Answer 21

HCO3- is secreted into the interstitium following the dissociation of H2CO3 in the cell. H+ is secreted into the lumen, new bicarbonate is secreted into the interstitium
- new HCO3- can also be formed during NH4+ secretion into the renal tubules - When glutamine is deaminated, NH4+ is released and sent to the lumen via the Na+/NH4+ exchanger. HCO3- is also a bi-product of this deamination. It is sent into the interstitial fluid

Question 22

What triggers renal compensation?

Answer 22

Changes in the pCO2 of the plasma and changes in the pH of the plasma.

Question 23

What compensates for chronic respiratory disturbances?

Answer 23

renal compensation

Question 24

How to correct for chronic respiratory acidosis?

Answer 24

Renal tubules increase secretion of monobasic phosphate and ammonium into the lumen to trap H+ and new bicarbonate is formed and transported into the circulation - causes a base excess!