Advanced PhysiologyAdvanced Physiology(part 3, Acid-base balance)(part 3, Acid-base balance)

By: A. Riasi (PhD in Animal Nutrition & Physiology)Isfahan University of Technology (IUT)

فیزیولوژی تکمیلی

Introduction

Three aspects of the ECF and ICF that are crucial to the

whole animal and to its individual cells:

The osmotic balance

Total fluid volume of the body

Acid –base status

Introduction

The term of acid-base balance refers to the precise regulation

of free hydrogen ion (H+) and hydronium ion (OH-)

concentration in the body fluids.

Acids are a special group of hydrogen-containing substances.

A strong acid has a greater tendency to dissociated in solution

than does a weak acid.

Acid-base balance in body fluids

�َAdapted from Animal Physiology by Sherwood et al. 2005

Acid-base balance in body fluids

The normal pH of arterial and venous blood

Acidosis exists whenever the blood pH falls below 7.35

Alkalosis occurs when the blood pH is above 7.45

Death can occur if arterial pH falls outside of the range of 6.8-8.0

Acid-base balance in body fluids

�َAdapted from Animal Physiology by Sherwood et al. 2005

Fluctuations in hydrogen ion concentration have profound

effect on body chemistry.

Even small changes in [H+] have dramatic effect on proteins.

The most prominent whole body consequences of fluctuations in

[H+] are changes in excitability of nerves and muscle cells.

Acid-base balance in body fluids

Hydrogen ions are continually being added to body fluids

Metabolic activities are main source for H+ in the body fluids

Normally, H+ is continually being added to the body fluids by:

Carbonic acid formation

Inorganic acid produced during the breakdown of nutrients

Organic acid resulting from intermediary metabolism

Acid-base balance in body fluids

Acid-base balance in body fluids

CO2 + H2O H2CO3 H+ + HCO3-

CO2 + OH- HCO3-CA

H2O H+ + OH-

Sulfuric acid and phosphoric acid are produced in the body.

Fatty acids and lactic acid that are produced during

intermediary metabolism partially dissociate to yield free H+.

In certain disease additional acids may be produced.

Acid-base balance in body fluids

Three line of defense against changes in [H+]:

Chemical buffer systems

Respiratory mechanisms of pH control

Excretory mechanisms of pH control

Acid-base balance in body fluids

There are four buffer system in the vertebrate body:

CO2-HCO3- buffer system

The peptide and protein buffer system

The hemoglobin buffer system

The phosphate buffer system

pH Regulation: Buffers

The Co2-HCO3- buffer system in the ECF.

pH Regulation: Buffers

�َAdapted from Animal Physiology by Sherwood et al. 2005

The most plentiful buffers on the ICF are the cell proteins.

The most important buffering amino acid is histidine.

pH Regulation: Buffers

Hemoglobin (Hb) in erythrocytes buffers the H+ generated.

The phosphate buffer system consists of an acid phosphate

slat (NaH2PO4) and a basic phosphate salt (Na2HPO4).

The phosphate system serve as an excellent urinary buffer.

The respiratory system plays an important role in acid-base

balance through its ability to alter ventilation

pH Regulation: Respiration

The excretory organs are the third line of defense against

changes in [H+] in body fluids.

In mammals, the kidneys are the most potent acid-base

regulatory mechanism.

The kidneys can remove of H+ from any source

The kidneys can variably conserve or eliminate HCO3-

pH Regulation: Excretion

The kidneys control the pH of the body fluids by adjusting

three interrelated factors:

H+ excretion

H2CO3- excretion

Ammonia secretion

pH Regulation: Excretion

Hydrogen ion excretion by the kidneys

The kidneys eliminate H+ derived from sulfuric, phosphoric,

lactic, and other acids.

pH Regulation: Excretion

pH Regulation: Excretion

�َAdapted from Animal Physiology by Sherwood et al. 2005

The H+ secretary process begins in the tubular cells with

CO2 that has come from three sources:

The CO2 diffused from plasma

The CO2 diffused from the tubular fluid

CO2 that has been metabolically produced within the tubular

cells.

pH Regulation: Excretion

The kidneys adjust H+ excretion to compensate for changes

in both carbonic and noncarbonic acids.

The kidneys regulate plasma [HCO3-] by two mechanisms:

Variable reabsorption of the filtered HCO3- back to the plasma.

Variable addition of new HCO3- to the plasma.

pH Regulation: Excretion

pH Regulation: Excretion

�َAdapted from Animal Physiology by Sherwood et al. 2005

pH Regulation: Excretion

�َAdapted from Animal Physiology by Sherwood et al. 2005