Week 2 - Ch. 22: Acid-Base Balance
Why does venous blood have a slightly lower pH than arterial blood?
-Carbon dioxide enters venous blood as a waste product of cellular metabolism. It combines with water in the blood and is converted into carbonic acid by carbonic anhydrase [CA], an enzyme found in red blood cells
Metabolic Acidosis
-Includes all types of acidosis other than those caused by excess CO2 in body fluids a) Causes: -Severe diarrhea -Diabetes mellitus -Strenuous exercise -Uremic acidosis b) Compensations: -Buffers take up extra H+ -Lungs blow off additional H+ generating CO2 -Kidneys excrete more H+ and conserve more HCO3- Patients with metabolic acidosis often have renal disease, uncontrolled diabetes, or prolonged diarrhea or have ingested toxic chemicals, such as antifreeze.
metabolic alkalosis
-Reduction in plasma pH caused by relative deficiency of noncarbonic acids a) Causes: -Vomiting -Ingestion of alkaline drugs b)Compensations: -Chemical buffer systems immediately liberate H+ -Ventilation is reduced -If condition persists for several days, kidneys conserve H+ and excrete excess HCO3- in the urine
Acid-Base Imbalances -4 general categories
-can arise from either respiratory dysfunction or metabolic disturbances 1) respiratory acidosis -During exercise, respirations increase in response to a drop in pH caused by increased CO2 production by muscles. 2) respiratory alkalosis 3) metabolic acidosis 4) metabolic acidosis
What causes respiratory alkalosis?
(Anxiety [hyperventilation syndrome]; overinflation of patients on ventilators; hepatic coma.)
What causes respiratory acidosis?
(Depression of the respiratory center by drugs or anesthesia; pulmonary diseases, such as emphysema and pneumonia.)
From what can metabolic alkalosis result?
(The bicarbonate excess in metabolic alkalosis can result from diuretic therapy, from loss of acid-containing gastric fluid through vomiting or suction, or from certain diseases, such as Cushing syndrome.)
How does holding your breath affect blood pH?
-it affects blood pH because no carbon dioxide leaves the body by way of expired air and the blood's CO2 content increases. This increases the amount of H2CO3 and the hydrogen-ion concentration of blood, which in turn decreases blood pH.
What are the mechanisms that control pH of body fluids?
-pH homeostatic mechanism: three coordinated homeostatic mechanisms act to maintain the normal pH of body fluids and prevent pH swings when excess acids or bases are present a) chemical/ buffer mechanism: fastest, seconds -first line of defense b) respiratory mechanism: takes minutes c) urinary mechanism: takes hours, depends on person's urinary system and how well hydrated
respiratory alkalosis
-primarily due to excessive loss of CO2 from body as result of hyperventilation a) possible causes: -fever -anxiety -aspirin poisoining -physiologic mechanisms at high altitude b) compensations: -chemical buffer systems liberate H+ -if situation continues a few days, kidneys compensate by conserving H+ and excreting more HCO3-
respiratory acidosis
-results of abnormal CO2 retention arising from hypoventilation a) possible causes -lung disease -depression of respiratory center by drugs or disease -nerve or muscle disorders that reduce respiratory muscle activity -holding breath b) compensations -chemical buffers immediately take up additional H+ -kidneys are most important in compensating for respiratory acidosis -The chloride ions of the solution replace the bicarbonate ions and help relieve the bicarbonate excess responsible for the imbalance. -Compensation is a clinically important concept.
Acid-Base Balance -equation
CO2 + H2O <-> H2CO3 <-> H+ + HCO3- -use of carbonate anhydrase a) H+ is continuously added to the plasma from ongoing metabolic activity b) major source of H+ is from CO2 generated H+ c) other sources include production of inorganic and organic acids by metabolism
Chemical Buffers and their Primary Roles
The lungs and kidneys kick in only if the chemical pH control mechanism is unable to stabilize blood pH.
What are the 3 mechanisms for regulation of pH?
a) buffer mechanisms in blood b) respiratory system - CO2 loss -Lungs cannot excrete base. c) urinary system - loss in urine -Kidneys usually excrete acids, but they can excrete bases if necessary. -More acids than bases usually enter the blood.
Integration of pH Control Mechanism
a) Elevated CO2 levels result in increased formation of carbonic acid in red blood cells. The resulting increase in hydrogen ions, coupled with elevated CO2 levels, results in an increase in respiratory rate and secretion of hydrogen ions by the kidneys, thus helping to regulate the pH of body fluids.
The Respiratory System with pH
a) SECOND LINE OF DEFENSE against changes in pH -acts in a matter of minutes -acts at a moderate speed b) regulates pH by controlling rate of CO2 removal CO2 + H2O <-CA-> H2CO3 <-fast-> H+ + HCO3-
Acid-Base Balance a) venous blood pH b) arterial blood pH c) acidosis d) alkalosis
a) about 7.35 --> lower due to more presence of CO2 (more acidic) b) about 7.45 -arterial pH less than 6.8 or greater than 8.0 is not compatible with life c) occurs when blood pH falls below 7.35 d) occurs when blood pH falls above 7.45 -*very narrow range* - only rarely does it fall low to 7.0 (neutrality) --> death will occur first
Acid-Base Balance a) sources of H+ in body b) what does exercise do in this relationship?
a) carbonic acid formation from metabolic activity -inorganic nutrients produced during breakdown of nutrients -organic acids resulting from intermediary metabolism b) exercise is a major source of acids and thereby improves BUFFERING capacity as an ADAPTION -exercise leads to better buffering acids which can lead to less fatigue when working out --ex: some top athletes drink baking soda (base) to balance acids because some overwork the buffering adaptation (already adapted to as much as they can)
Acid-Base Balance -what are some consequences of fluctuations in pH
a) changes in excitability of nerve and mm. cells b) marked influence on ENZYME ACTIVITY -affects skeletal contraction (seen as muscle fatigue) due to increase in metabolism (aka increase H+ = acidosis) c) changes influence K+ levels in body -sodium potassium pump
Acid-Base Balance
a) designation used to express the [H+] b) pH 7 = neutral c) ph < 7 = acidic d) pH > 7 = basic (alkaline) -moving 1 unit multiples the relative H+ concentration by 10x
What is an acid?
a) group of H+ containing ions substances that dissociate in solution to release free H+ and anions b) a STRONG ACID HAS A GREATER TENDENCY TO DISSOCIATE IN A SOLN THAN A WEAK ACID DOES
Lactic Acid Buffered by Sodium Bicarbonate
a) illustrates lactic acid buffered by sodium bicarbonate. Lactic acid (H • lactate) and other "fixed" acids are buffered by NaHCO3 in the blood. Carbonic acid (H • HCO3, or H2CO3, a weaker acid than lactic acid) replaces lactic acid. As a result, fewer H+ ions are added to blood than would be added if lactic acid were not buffered.
Describe the Chemical Buffer System
a) minimizes changes in pH by binding with or yielding free H+ b) FIRST LINE OF DEFENSE c) based on buffers in blood/RBCs and body fluids d) acts immediately
What is the Removal of Carbonic Acid?
a) once carbonic acid is formed, it needs to be removed because it will create metabolic acidosis CO2 + H2O <-> H2CO3 <-> H+ + HCO3- b) beyond what the chemical buffer system can absorb, the lungs remove over 30L of carbonic acid each day eliminating CO2 c) this acid is buffered well to keep the pH of venous blood close to that of arterial blood
What is acid-base balance?
a) refers to precise regulation of free H+ concentration in body fluids
Respiratory Mechanism of pH Control
a) respirations remove some CO2 from blood as blood flows through lung capillaries b) amount of H2CO3 in blood is decreased and thereby its H+ concentration is decreased, and this in turn increases blood pH from its venous to its arterial level c) respiratory control centers in brainstem react to dropping pH and promote increased respirations; when pH increases, then breathing slows
Acidosis
a) resulted from increased metabolic activity (exercise) or decreased respirations -when holding your breath too long, the brainstem detects the dropping pH and rising CO2; this forces you to inhale as a survival mechanism
Alkalosis
a) results from anything that causes increased respirations over time or loss of acids
What is a base?
a) substances that can combine with free H+ and remove it from solution
Urinary Mechanism of pH control
a) third line of defense against change in hydrogen ion concentration b) kidneys require hours to days to compensate for changes in body-fluid pH c) kidneys are the body's most effective regulator of blood pH -H+ excretion -HCO3- excretion (base) - pH is too high -ammonia secretion
