Chemistry, Solutions, and Acid/Base Balance

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Chemistry, Solutions, and Acid/Base Balance
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Water is Cohesive
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Concentrations of Solutions

• solutions
• Molarity
• Osmolarity
• Tonicity
• Equivalents

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RBCs in Different Solutions
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urea
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Diffusion
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Diffusion Factors

• Size of particle
• Concentration gradient
• Temperature
• Surface area
• Medium

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Fluid Compartments
Figure 26.1
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Electrolyte Composition of Body Fluids
Figure 26.2
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Continuous Mixing of Body Fluids
Figure 26.3
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Water Balance and ECF Osmolality

• To remain properly hydrated, water intake must
  equal water output
• Water intake sources
• Ingested fluid (60) and solid food (30)
• Metabolic water or water of oxidation (10)

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Water Balance and ECF Osmolality

• Water output
• Urine (60) and feces (4)
• Insensible losses (28), sweat (8)
• Increases in plasma osmolality trigger thirst and
  release of antidiuretic hormone (ADH)

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Water Intake and Output
Figure 26.4
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Regulation of Water Intake Thirst Mechanism
Figure 26.5
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Mechanisms and Consequences of ADH Release
Figure 26.6
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Disorders of Water Balance Dehydration
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ECF osmotic pressure rises
Cells lose H2O to ECF by osmosis cells shrink
Excessive loss of H2O from ECF
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(a) Mechanism of dehydration
Figure 26.7a
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Disorders of Water Balance Hypotonic Hydration
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H2O moves into cells by osmosis cells swell
ECF osmotic pressure falls
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Excessive H2O enters the ECF
(b) Mechanism of hypotonic hydration
Figure 26.7b
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Regulation of Sodium Balance Aldosterone
Figure 26.8
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Mechanisms and Consequences of ANP Release
Figure 26.10
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pH
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Acid-Base Balance

• Normal pH of body fluids
• Arterial blood is 7.4
• Venous blood and interstitial fluid is 7.35
• Intracellular fluid is 7.0
• Alkalosis or alkalemia arterial blood pH rises
  above 7.45
• Acidosis or acidemia arterial pH drops below
  7.35 (physiological acidosis)

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Hydrogen Ion Regulation

• Concentration of hydrogen ions is regulated
  sequentially by
• Chemical buffer systems act within seconds
• The respiratory center in the brain stem acts
  within 1-3 minutes
• Renal mechanisms require hours to days to
  effect pH changes

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Chemical Buffer Systems

• One or two molecules that act to resist pH
  changes when strong acid or base is added
• Three major chemical buffer systems
• Bicarbonate buffer system
• Phosphate buffer system
• Protein buffer system
• Any drifts in pH are resisted by the entire
  chemical buffering system

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Physiological Buffer Systems

• The respiratory system regulation of acid-base
  balance is a physiological buffering system
• There is a reversible equilibrium between
• Dissolved carbon dioxide and water
• Carbonic acid and the hydrogen and bicarbonate
  ions
• CO2 H2O ? H2CO3 ? H HCO3

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Renal Mechanisms of Acid-Base Balance

• Only the kidneys can rid the body of metabolic
  acids (phosphoric, uric, and lactic acids and
  ketones) and prevent metabolic acidosis
• The ultimate acid-base regulatory organs are the
  kidneys

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Respiratory Acidosis and Alkalosis

• Result from failure of the respiratory system
• PCO2 is the single most important indicator of
  respiratory inadequacy
• PCO2 levels
• Normal PCO2 fluctuates between 35 and 45 mm Hg
• Values above 45 mm Hg signal respiratory acidosis
• Values below 35 mm Hg indicate respiratory
  alkalosis

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Metabolic Acidosis

• All pH imbalances except those caused by abnormal
  blood carbon dioxide levels
• Metabolic acid-base imbalance bicarbonate ion
  levels above or below normal (22-26 mEq/L)
• Metabolic acidosis is the second most common
  cause of acid-base imbalance

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Metabolic Alkalosis

• Rising blood pH and bicarbonate levels indicate
  metabolic alkalosis
• Typical causes are
• Vomiting of the acid contents of the stomach
• Intake of excess base (e.g., from antacids)
• Constipation, in which excessive bicarbonate is
  reabsorbed

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Respiratory and Renal Compensations

• Acid-base imbalance due to inadequacy of a
  physiological buffer system is compensated for by
  the other system
• The respiratory system will attempt to correct
  metabolic acid-base imbalances
• The kidneys will work to correct imbalances
  caused by respiratory disease