Transcript Section 3

‫فیزیولوژی تکمیلی‬
Advanced Physiology
(part 3, Acid-base balance)
By: A. Riasi
(PhD in Animal Nutrition & Physiology)
Isfahan University of Technology (IUT)
 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. 2013
 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. 2013
 Acid-base balance in body fluids
 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
CO2 + H2O
H2CO3
CO2 +
OH-
H2O
CA
H+ + HCO3-
HCO3-
H+ + OH-
 Acid-base balance in body fluids
 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
 pH Regulation: Buffers
 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.
Adapted from Animal Physiology by Sherwood et al. 2013
 pH Regulation: Buffers
 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.
 pH Regulation: Respiration
 The respiratory system plays an important role in acid-base
balance through its ability to alter ventilation
 pH Regulation: Excretion
 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
Adapted from Animal Physiology by Sherwood et al. 2005
 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
cells.
within the tubular
 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
Adapted from Animal Physiology by Sherwood et al. 2013