Download Section 5

‫فیزیولوژی تکمیلی‬
Advanced Physiology
(part 5, Acid-base Balance)
By: A. Riasi
(PhD in Animal Nutrition & Physiology)
Animal Sci. Dep. Isfahan University of Technology
http://riasi.iut.ac.ir
Acid-base balance

Three aspects that ECF and ICF are crucial to the whole
animal and to its individual cells:

The osmotic balance

Total fluid volume of the body
 Acid
–base status
Acid-base balance

If balance is to be maintained, input must equal output
Adapted from Animal Physiology by Sherwood et al. 2013
Acid-base balance

The
balance
extremely
important
in
maintaining
homeostasis.

Some
constituents
undergo
frequent
and/or
large
disturbances.

Salt and H2O can be lost to the terrestrial environments to
varying degrees through the:

Digestive tract (vomiting, diarrhea)

Skin (sweating)

Lungs (panting)
Acid-base balance

Hydrogen ions are uncontrollably generated internally
(especially during muscle activity) and added to body fluids.

If possible, compensatory adjustments must be made for these
uncontrolled changes.
Acid-base balance
Adapted from Animal Physiology by Sherwood et al. 2013
Acid-base balance

The composition of the ECF as a whole differs considerably
from that of the ICF in all animals.

Among the major differences between the ECF and ICF are:

Cellular proteins that cannot permeate the plasma membranes to leave
the cells.

Cellular organic osmolytes (typically higher in the ICF than in the
ECF).

Na+and K+ and their attendant anions:

In most organisms, Na+ is the primary ECF cation, and K+ is the primarily ICF
cation.
Acid-base balance

The majority of the ECF and ICF ions are electrically
balanced.

In the ECF, Na+ is accompanied primarily by the anion Cl− and to a
lesser extent by HCO3− (bicarbonate).

In
the
ICF,
K+
is
accompanied
primarily
by
the
anion
PO43−(phosphate) and by the negatively charged proteins trapped
within the cell.
Acid-base balance

The acid-base balance refers to the precise regulation of free
hydrogen ion (H+) and hydronium ion (OH-) concentration
in the body fluids.
 Acids
A
are a special group of hydrogen-containing substances.
strong acid has a greater tendency to dissociated in solution than
does a weak acid.
Acid-base balance

Acid-base balance in body fluids
Adapted from Animal Physiology by Sherwood et al. 2013
Acid-base balance

The normal pH of arterial and venous blood

Acidosis exists whenever the blood pH falls below 7.3

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
Adapted from Animal Physiology by Sherwood et al. 2013
Acid-base balance

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

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
CO2 + H2O
H2CO3
CA
CO2 + OH-
H2O
H+ + HCO3-
HCO3-
H+ + OH-
Acid-base balance

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

Three line of defense against changes in [H+]:

Chemical buffer systems

Respiratory mechanisms of pH control

Excretory mechanisms of pH control
Acid-base balance

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
Acid-base balance

The Co2-HCO3- buffer system in
the ECF.
Adapted from Animal Physiology by Sherwood et al. 2013
Acid-base balance

The most plentiful buffers on the ICF are the cell proteins.

The most important buffering amino acid is histidine.

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.
Acid-base balance

The respiratory system plays an important role in acid-base
balance through its ability to alter ventilation
Acid-base balance

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-
Acid-base balance

The kidneys control the pH of the body fluids by adjusting
three interrelated factors:

H+ excretion

H2CO3- excretion
 Ammonia
secretion
Acid-base balance

Hydrogen ion excretion by the kidneys

The kidneys eliminate H+ derived from sulfuric, phosphoric, lactic,
and other acids.
Acid-base balance

pH Regulation: Excretion
Adapted from Animal Physiology by Sherwood et al. 2013
Acid-base balance

pH Regulation: Excretion

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.
Acid-base balance

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.
Acid-base balance

pH Regulation: Excretion
Adapted from Animal Physiology by Sherwood et al. 2013