Download Acid-Base Balance Text Chapter 27 pages 1046-1052 Acid

Acid-Base Balance
Text Chapter 27 pages 1046-1052
Acid-Base Balance gives you an ideal opportunity to pull what you know about the overall
physiology of the body systems together. Think specifically and broadly at the same time.
I.
Introduction
A.
Regulation of acid-base balance actually means regulation of H+ concentration in
body fluids.
B.
When H+ concentration is greater than normal, it is said to be acidic
C.
When H+ concentration is lower than normal, it is said to be alkaline
D.
Typically, cellular metabolism produces more acids than bases and therefore we lean
toward acidification of the blood.
E.
An important homeostatic challenge is to keep H+ concentration (pH) within
acceptable, normal levels.
II.
Background information
A.
An acid is a substance that has a large number of free H+ when dissolved in water.
B.
A base is a substance that has a large number of hydroxyl ions (OH-) dissolved in
water.
C.
A base is often called an alkali. Therefore an excess base in the blood is called
alkalosis. Also, an excess amount of acid in the blood is called acidosis.
D.
Acids and bases tend to neutralize each other.
H+ + OH- -----------> H2O
E.
Hydrogen ion concentration is usually expressed in terms of pH.
1.
The normal pH of extracellular fluids and blood is 7.4 and may range within
the narrow margins of 7.35—7.45
2.
A pH less than 7.4 is on the acidic side.
3.
A pH greater than 7.4 is on the basic side.
ACIDOSIS
NORMAL pH
ALKALOSIS
7.0 <-------------------7.35—7.4—7.45 ----------------------- >7.8
Survival Range
Normal Range
Survival Range
III.
Effects of acidosis and alkalosis on body functions.
A.
H+ ion concentration, although present in low levels, is one of the most important
controlling factors in most metabolic reactions of the cells.
B.
Therefore an increase or decrease in H+ ion concentration greater than or less than
normal causes serious derangements in overall function of the body.
C.
Acidosis
1. Generally depresses synaptic transmission and therefore central nervous system
activity that can lead to coma and death
2. Severe diarrhea (excessive loss of alkaline digestive juices) or diabetes mellitus
(fatty acid catabolism) can cause this.
3. Usually a person goes into coma when pH of extracellular fluid is less than 7.
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Acid-Base Balance
Text Chapter 27 pages 1046-1052
D.
IV.
V.
VI.
Alkalosis
1.
H+ concentration is decreased to less than normal (ph 7.8) which leads to
severe over excitability of central and peripheral nervous systems.
2.
This often results in excessive, spontaneous initiation of signals in many
areas of brain and peripheral nerves.
3.
These signals can produce generalized nervousness, agitation, muscle
spasms, and tetanic contractions of muscles that can kill a person by causing
convulsions or other derangements of the nervous system.
Metabolic processes that serve as sources of hydrogen ions:
A.
Aerobic respiration of glucose: O2 + C6H12O6 Æ CO2 + H2O + E
and carbonic acid
CO2 + H2O Æ H2CO3 Æ H+ + HCO3B.
Anaerobic respiration of glucose: C6H12O6 ÆPyruvic acidÆ Lactic Acid
C.
Oxidation of sulfur containing amino acids
D.
Sulfuric acid (H2SO4)
E.
Protein digestion Æ amino acids
F.
Fat digestion Æ fatty acids
G.
Ketones (ketosis)
Three mechanisms by which the body can regulate pH of body fluids
A.
Chemical buffers quickly bind to H+ to remove it from solution and make it less
acidic, but it is not eliminated from the body through this mechanism.
B.
Exhalation of carbon dioxide by increasing the rate and depth of breathing can fairly
quickly remove the source of H+. Remember, respiratory disorders that cause one
to retain CO2 can cause one to become acidotic.
C.
Kidneys excrete H+ through the urinary system. This is a slow process, but it can
compensate for failure of other systems.
Regulation of Acid-Base Balance by Chemical Buffers
A.
The body's first line of defense against changes in hydrogen ion concentrations.
B.
Occur in all body fluids.
C.
Convert strong acids, which tend to release large quantities of hydrogen ions, to
weak acids, which release relatively fewer hydrogen ions.
D.
Convert strong bases into weak ones.
E.
Remember, even though we tend to be constantly fighting acidic conditions, buffers
can move the pH in either direction depending on pH of the fluid.
F.
Three most important acid-base chemical buffer systems.
1.
Bicarbonate (HCO-3)
a.
called bicarbonate/carbonic acid buffer system
b.
in all body fluids
c.
strong acid added to body fluids
d.
strong base added to body fluid
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Text Chapter 27 pages 1046-1052
VII.
2.
Protein Buffer System
a.
Most important buffer system in plasma and intracellular fluid.
b.
Consists of plasma proteins and various proteins within the cells.
c.
Albumin is the most important plasma protein buffer.
d.
Hemoglobin of red blood cells—Hb + H+ ÆHHb buffers H+.
e.
Proteins are chains of amino acids.
f.
Some amino acids within the chain have groups of atoms called
carboxyl groups (-COOH) freely exposed that can become ionized
and release a hydrogen ion—responds to alkalitic conditions causing
plasma to become more acid (pH decreases)
g.
Some amino acids within protein molecules contain freely exposed
amino groups (-NH2) that can accept hydrogen ions—responds to
adid conditions causing plasma to become more alkaline (pH
increases).
3.
Phosphate Buffer System
a.
Extracellular and intracellular fluids (especially intracellular fluids).
b.
Regulator of H+ concentration in tubular fluid of nephrons and urine.
c.
Two phosphate compounds
(1)
One acts with strong acid converting it to weak acid and
NaCl.
(2)
The other reacts with strong base converting it to a weak base
and water.
The Respiratory Center as a Mechanism for Control of H+ Concentration
A. Secondary line of defense, but very important because most H ions appearing in body
fluids originate from carbonic acid produced when CO2 reacts with water.
B.
CO2
+
H2O ---------------> H2CO3
Cells increase production of CO2 resulting in more H2CO3
↓
H2CO3 Æ H+ + HCO3↓
H+
Respiratory Center is Stimulated
↓
Rate and depth of Breathing Increases
↓
More CO2 is eliminated through lungs
↓
Concentration of CO2 and H+ in body fluids decreases
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Text Chapter 27 pages 1046-1052
VIII.
The Kidneys as a Mechanism for Control of H+ Concentration
A.
Secondary line of defense
B.
Kidney Nephrons help regulate H+ concentration of body fluids by secreting H+
C.
H+ secreted into urine of renal tubules mainly by epithelial cells that line proximal
and distal convoluted tubules and collecting ducts
D.
Important in balancing quantities of sulfuric acid, phosphoric acid, and other organic
acids in body fluid accumulating from metabolic activity
E.
High intake of protein
↓
Increased metabolism of
amino acids
↓
Increased formation of
sulfuric acid and
phosphoric acid
Decreased concentration
of H+ in body fluids
↑
Increased concentration
of H+ in urine
↑
Increased secretion of
H+ into fluid of
renal tubules
↓
Increased concentration of
↑
H+ in body fluids -----------------------------------------Æ
G.
Therefore, a diet high in protein results in excessive production of acids
(Remember: our diets usually tend to lower pH or increase acidity; so our bodies are
continually trying to adjust for this)
H.
Kidneys secrete more H+ into urine
I.
H+ in urine are buffered by phosphates that were filtered into fluid of renal tubules
J.
Ammonia (NH3) also aids in buffering
1.
Due to prolonged increase in H ion concentration there is an increase in ammonia
production by the cells of the renal tubule by deamination of certain amino acids.
2.
Ammonia diffuses readily through the cell membrane into urine
3.
Ammonia is a weak base so it accepts H+ and is converted to ammonia ions (NH4+)
H+ + NH3 ------------> NH4
4.
The cell membrane is impermeable to the ammonium ion so they are trapped in
urine.
5.
Ammonia therefore helps to transport excess H+ out of the body via the urine and at
the same time helps to control the pH of the urine.
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IX.
Respiratory and Metabolic Acidosis and Alkalosis—Study Table 27.4 carefully.
A.
Acidosis and alkalosis
1.
Acidosis results from an accumulation of acids or a loss of bases.
2.
Alkalosis results from a loss of acids or an accumulation of bases.
3.
Two major types of acidosis are respiratory and metabolic acidosis.
4.
Two major types of alkalosis are respiratory and metabolic alkalosis.
5.
The respiratory system and the urinary system work together to maintain
proper pH of the blood and body fluids.
6.
One system may compensate for the failure of the other—this means that the
pH becomes adjusted to within the normal range, but pCO2 or HCO3- is NOT
within homeostatic levels.
B.
Respiratory acidosis
1.
↑ pCO2 > 45 and pH < 7.35 with no compensation
2.
Caused by factors which promote an accumulation of carbon dioxide, such
as injury to or suppression of the respiratory center, obstructed air passages,
and respiratory diseases (emphysema) resulting in hypoventilation.
3.
Symptoms include depression of the central nervous system and signs of
respiratory insufficiency.
4.
Results in excessive concentration of H+ (lower pH).
5.
Shift in pH is resisted by chemical buffers
6.
Renal compensation through ↑secretion of H+ and ↑reabsorption of HCO3-.
7.
Compensation = normal pH but ↑pCO2
C.
Respiratory Alkalosis
1.
↓pCO2 (below 35), pH > 7.45 with no compensation
2.
Develops as a result of hyperventilation, which is accompanied by a decrease
in carbon dioxide concentration and therefore H+ concentration
3.
Occurs during periods of anxiety, CVA, fever, or salicylate poisoning
(aspirin-salicylic acid).
4.
May occur in high altitudes when the respiratory center is stimulated by low
oxygen pressure.
5.
Symptoms include light-headedness, dizziness, tingling sensations, and
tetany
6.
Shift in pH is resisted by buffer systems.
7.
Renal compensation through ↓ secretion of H+, ↓reabsorption of HCO38.
Compensation = normal pH but ↓pCO2
D.
Metabolic Acidosis
1.
↓ HCO3-, pH < 7.35 with no compensation
2.
Involves an accumulation of non-respiratory acids or the loss of bases (loss
of HCO3-).
3.
May be caused by kidney disease (loss of protein buffers), prolonged
vomiting (loss of alkaline digestive secretions), prolonged diarrhea (loss of
alkaline digestive secretions), and diabetes mellitus, anorexia nervosa, high
protein/fasting diets (fatty acid catabolism, ketosis).
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4.
5.
6.
7.
E.
Symptoms are similar to those of respiratory acidosis.
Shift in pH is resisted by buffer systems.
Respiratory compensation through hyperventilation.
Compensation = normal pH but ↓ HCO3-
Metabolic alkalosis
1.
↑HCO3-, and pH > 7.45 with no compensation
2.
Results from excessive loss of H+ or a gain of bases.
3.
May occur following a loss of gastric secretions by drainage or vomiting,
excessive intake of alkaline drugs
4.
Symptoms include shallow breathing, irritability, and tetany.
5.
Shift in pH is resisted by buffer systems.
6.
Respiratory compensation through hypoventilation.
7.
Compensation = normal pH but ↑HCO3-
READ and OUTLINE:
• Acid-Base Imbalances (pp. 1049-1050 & Tables 27.3 and 27.4) = summary of above and it
they are very important!!!
• Clinical Application—Diagnosis of Acid—Base Imbalances (page 1050) (very important)
• Aging and Fluid, Electrolyte, and Acid-Base Balance (page 1051-1052)
Some parts of Chapter 27 (pages 1039-1041) revisit aspects of ADH, ANP and Renin-AngiotensinAldosterone Pathway (cardiovascular and also endocrine system chapters). Revisit these hormones
and see how they apply here (you might find thirst/dehydration, water intoxication, and enemas, tap
water/ hypotonic vs. hypertonic commercial preparations interesting reading—even if not
interesting…read and think about these concepts).
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