Regulation of pH

What is glutamine metabolized to?

2 HCO3- and 2 NH4+

What is the concentration of HCO3-?

24 mEq/L

How much filtered phosphate is available for buffering H+?

30-40 mEq/day

How much HCO3- do the kidneys filter?

4320 mEq/day (180 L/day x 24 mEq/L)

What is intracellular pH?

6.0 - 7.4

What is the normal pH of arterial blood?

7.4

At steady state, how much dissolved CO2 is there and what is its partial pressure?

At steady state, there is 1.2 mmol/L of dissolved CO2 corresponding to a PCO2 of 40 mmHg

What is the isohydric principle?

The H+ concentration of body fluids impacts all buffer systems simultaneously Thus a change in H+ changes the balance of all buffer systems

Changes in what affect pH?

alveolar ventilation

What is the principle of buffering?

buffers are weak acids that reduce the effect of changes in H+ concentration

The ammonia buffer system is capable of increasing H+ excretion from what to what?

from 40mEq/day to up to 500 mEq/day

What is the most important system during acidosis?

the ammonia buffer system

What is the normal blood H+ concentration?

0.00004 mEq/L or 40 nEq/L

What are the 3 mechanisms used by the kidney to regulate extracellular fluid H+? Where do these processes occur?

1) secretion of H+ 2) reabsorption of filtered HCO3- 3) production of new HCO3- These processes occur in the renal tubules (80% in the proximal tubule)

How many mmol of CO2 generated per day at rest?

At rest, 20,000 mmol of CO2 generated per day

In what forms is CO2 found?

10% of CO2 is dissolved in blood 25-30% carbaminohemoglobin 60-65% converted to HCO3- (carbonic anhydrase in erythrocytes)

How much nonvolatile acids per day does the body produce?

80 mEq of nonvolatile acids per day

A reduction in pH to what stimulates what by how many times? When does it occur? What is its effectiveness? What happens in the kidneys?

As pH decreases from 7.4 to 7.0, alveolar ventilation increases by 4-5X Respiratory response to a sudden decrease in pH occurs within 3-12 minutes It has an effectiveness of 50-75% (feedback gain of -1 to -3) Compensatory changes by the kidneys take over with time

What is the equation showing the isohydric principle?

H+ = K1 x [HA1]/[A1] = K2 x [HA2]/[A2] = K3 x [HA3]/[A3]

How many mEq of H+ are ingested or produced each day? But what is the concentration of H+ in the body fluids? Why?

Normally, approximately 80 mEq of H+ is either ingested or produced each day. However, the concentration of H+ in body fluids is only about 40 nEq/L (0.00004 mEq/L)

What is also an effective urinary buffer and why?

Phosphate since its pK is around 6.8

What is the pH of venous blood and interstitial fluid and why?

Since CO2 is made in cells, pH of venous blood and interstitial fluid is lower = 7.35

By what 3 main systems is pH regulated and what are their relative speeds?

The buffers in the body that serve to minimize pH changes (immediate) The lungs regulate the removal of CO2 from the blood (rapid) The kidneys can alter the pH of urine and thereby regulate the pH of body fluids (slow

How much HCO3- do the kidneys absorb under conditions of alkalosis and acidosis?

Under conditions of alkalosis, kidneys fail to reabsorb all the HCO3- (loss of HCO3- is the same as adding H+) Under conditions of acidosis, kidneys reabsorb all HCO3- and produce new HCO3- which results in a compensatory decrease in extracellular [H]+

Is there more HCO3- or H2CO3?

a lot more HCO3-

Where is carbonic anhydrase found at high levels?

in erythrocytes, the lungs, and in the cells of the renal tubules