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Chapter 33: Acid-Base Balance

Terms in this set (49)

Acid-base
balance is one of the most important of most of the body's homeostatic mechanisms
Acid-base balance refers to regulation of
hydrogen ion concentration in body fluids
Precise regulation of pH at the cellular
is necessary for survival
Slight pH changes
have dramatic effects on cellular metabolism
Acidosis
used to describe an arterial blood pH of less than 7.35
Alkalosis
used to describe an arterial blood pH greater than 7.45
Cranberries are
direct acid-forming food
pH is a symbol
negative logarithm of hydrogen ion concentration of a solution
pH indicated degree of
acidity or alkalinity of a solution
Chemical buffers
immediately combine with any added acid or alkali that enter the body fluids and thus prevents drastic changes in hydrogen ion concentration and pH.
Carbonic acid
formed by aerobic glucose metabolism
Lactic acid
formed by anaerobic glucose metabolism
Sulfuric acid
formed by oxidation of sulfur containing amino acids
Phosphoric
formed in the breakdown of phosphoproteins and ribonucleotides
Acidic ketone bodies
formed in the breakdown of fats
Acidic ketone bodies include
-acetone
-acetoacetic acid
-beta-hydroxybutyric acid
Acid-forming potential of foods
determined by chloride, sulfur, and phosphorus content
Acid-forming potential of foods are all
abundant in high-protein food such as, meat, fish, poultry and eggs.
Maintain the body pH
chemical & physiological
Chemical Mechanisms
rapid-action system
-bicarbonate buffer system
-phosphate buffers system
-protein buffer system
Physiological Mechanisms
delayed-action buffers
-respiratory response
-renal response
If immediate action chemical buffers cannot stabilize pH
the physiological buffers serve as a secondary defense against harmful shift in pH of the body fluids
pH control
-buffers
-respiration
-kidney excretion of acids and bases
Effectiveness of pH control mechanisms
range of pH - extremely effective, normally maintain pH within a very narrow range of 7.36 to 7.40
Buffers defined 1:
substances that prevent a marked change in pH of a solution when an acid or base is added to it
Buffers defined 2:
consist of a weak acid (or its acid salt) and a basic salt of that acid
Buffer pairs present in body fluid:
mainly carbonic acid, proteins, hemoglobin, acid phosphate, and sodium and potassium salts of these weak acids
Buffers consist of two kinds of substance and are therefore often referred
to buffer pair
Chloride shift
the process of exchanging a bicarbonate ion formed in the red blood cell with a chloride ion from plasma
The chloride shift makes it possible for carbonic acid to be:
buffered in the red blood cell and then carried as bicarbonate in the plasma
Nonvolatile acid
such as hydrochloric acid, lactic acid and ketone bodies, buffered mainly by sodium bicarbonate
Volatile acid
chiefly carbonic acid, buffered mainly by potassium salts of hemoglobin and oxyhemoglobin
Bases buffered
mainly by carbonic acid (when homeostasis of pH at 7.4 exists)
Base-to-acid-ratio of
(buffer actions that prevent marked changes in pH of body fluids)
40:1 is critical
Compensation
process of adjustment of pH balance to maintain ratio, such as 40:2 or 10:0.5
Uncompensated alkalosis or acidosis
occurs when base-to-acid ratio is abnormal (unbalanced at a proper ratio)
Correction
occurs when components of buffer pair return to normal 20:1 ratio
Evaluation of the role of buffers in pH control
cannot maintain normal pH without adequate functioning of the respiratory and urinary pH control mechanisms
Amount of blood carbon dioxide
directly relates to the amount of carbonic acid and therefore to the concentration of H+
With increased respirations
less carbon dioxide remains in blood, hence less carbonic acid and fewer H+ ions; with decreased respirations, more dioxide remains in blood, hence more carbonic acid and more h+ ions
If CO2 in arterial blood increases or decreases beyond set level,
(respiratory adjustment to counter pH imbalance of arterial blood)
respiratory center is stimulated and respiration increases in rate and/or depth
Carotid chemoreflexes also
cause respiration adjustment
Acidosis trigger hyperventilation
which increases rate of CO2/H2CO3 loss from the body and thus reduces blood H+ and restores homeostasis
Prolonged hyperventilation
by decreasing blood H+ excessively, may produce alkalosis
Alkalosis triggers hypoventilation
which tends to correct alkalosis by increasing blood co2 and therefore blood H2CO3 and H+
Prolonged hypoventilation,
by eliminating too little co2 causes an increase in blood H2CO3 and consequently in blood H+, thereby producing acidosis
General principles concerning urinary mechanisms
plays a vital role in acid-base balance because kidneys can eliminate more H+ from the body while reabsorbing more base when pH tends toward the acid side and eliminates fewer H+ while reabsorbing less base when pH tends toward the alkaline side
Secretion of H+ into urine
when blood CO2, H2CO3, and H+ increases above normal, distal tubules secrete more H+ into urine to displace basic ion (mainly sodium) from a urine salt and then reabsorb sodium into blood in exchange for the H+ excreted
Secretion of NH3
when blood hydrogen ion concentration increases, distal tubules secrete more NH3, which combines with H+ of urine to form ammonium ion, which displaces a basic ion (mainly sodium from a salt, the basic ion is then reabsorbed back into blood in exchange for the ammonium ion excreted
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