Renal 5: Acid-Base Balance

Buffer systems in blood, extracellular, and intracellular fluid; respiratory system; renal system

Three systems involved in regulating systemic pH

Buffer systems in blood, extracellular, and intracellular fluid

Closed system (no excretion or retention)

Rapid acting (chemical equilibrium, seconds)

Respiratory system

Open system (excretes or retains CO2)

Rapid-acting (seconds to minutes)

Renal system (with some participation of the liver)

Open system (reabsorbs HCO3- or excretes NH4+, protons, or HCO3-)

Slow-acting (hours to days)

Equilibrium constant (Ka)

Also called dissociation constant

At equilibrium, this value equals the products divided by the reactants of a dissociation reaction

Temperature, activity

The value for Ka is a function of ___ when products and reactants are quantified in terms of ___.

Concentration

The ___ of a solution is a measure of how much stuff is dissolved in a liquid.

Activity, concentration

The ___ of a solution is an effective concentration based on the chemical potential. It is always less than the ___ of a solution except in an infinitely dilute solution.

pKa

Negative value of the log to the base 10 of Ka

Acid, base

The pKa (negative value of the log to the base 10 of Ka) represents the pH value where the number of ___ molecules (proton donor) equals the number of ___ molecules (proton taker/acceptor).

Protein structure and therefore protein function must be maintained.

Why is blood pH one of the most tightly-regulated physicochemical entities in biological systems?

6.92

Survival rate decreases in critically ill calves when the blood pH decreases below ___.

Proteins (hemoglobin, plasma proteins, cell proteins)

Buffer system in blood

Bicarbonate

Buffer system in extracellular fluid

Phosphate

Buffer system in intracellular fluid

Buffer

Minimizes the change in pH when an acid or base is added to the solution

1.5

Buffers are effective in a closed system when the buffer pKa is within ±__ pH units of the actual pH.

Proteins, bicarbonate, phosphate

Molecules that can serve as buffers (minimize change in pH when an acid or base is added to the solution)

Histidine

Most important protein buffer

Filteration, reabsorption, secretion, excretion

Functions of kidney

Extracellular fluid volume and osmolality, electrolyte composition of body fluids and osmolality, blood pressure, acid-base balance

What is involved in homeostasis when relating to renal function (regulatory role)?

Homeostasis, acidemia (excreting ammonium ions), acidemia (excreting protons), alkalemia (excreting bicarbonate)

Four ways that kidney maintains systemic acid-base balance

Acidemia

Low blood pH

Acidosis

Disease process that causes low pH

Alkalemia

High blood pH

Homeostasis

Reabsorption of filtered HCO3-

Acidemia

Can be resolved by excreting ammonium (NH4+), which permits the reabsorption of bicarbonate (HCO3-), or by excreting protons (mainly buffered by phosphate and creatinine in urine)

Alkalemia

Can be resolved by excreting bicarbonate (HCO3-)

Activity, proton concentration

pH is best expressed in terms of ___, which more accurately represents the electromotive force of the proton than ___.

Phosphate, creatinine

Buffers in urine

Protons

Buffers in urine minimize the change in urine pH when ___ are added to the filtrate.

Phosphate

Most important buffer in urine

Carnivores, omnivores, 5.0

High urine phosphate concentrations are usually present in ___ and ___ to buffer urine pH from decreasing below pH = __

5.0, Epithelial cells lining urinary tract

Below the urine pH of __ in carnivores and omnivores, the acidity becomes toxic to ___.

Creatinine

Other than phosphate, ___ also exerts a buffering effect in the urine of carnivores and omnivores.

Bicarbonate

___ ions can be present in high concentrations in herbivore urine.

8.5

In herbivores, urine pH is rarely higher than __.

Urine pH

Provides a clinically useful insight into the nutritional acid-base status of healthy animals

Aciduria

Urine pH less than 7.0 in carnivores

Excess sulfur in diet is acidogenic

Alkaluria

Urine pH more than 7.0 in herbivores

Excess potassium in diet is alkalogenic

Acidogenic

Excess sulfur in a diet is ___.

Alkalogenic

Excess potassium in a diet is ___.

6.1

In bovine urine, any pH below __ is that breakpoint for increased ammonium excretion.