Chemistry, Solutions, and Acid/Base Balance

Water is Cohesive

Concentrations of Solutions  % solutions  Molarity  Osmolarity  Tonicity  Equivalents  % solutions  Molarity  Osmolarity  Tonicity  Equivalents

RBCs in Different Solutions

urea

Diffusion

Diffusion Factors  Size of particle  Concentration gradient  Temperature  Surface area  Medium  Size of particle  Concentration gradient  Temperature  Surface area  Medium

Fluid Compartments Figure 26.1

Electrolyte Composition of Body Fluids Figure 26.2

Continuous Mixing of Body Fluids Figure 26.3

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%)  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%)

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

Water Intake and Output Figure 26.4

Regulation of Water Intake: Thirst Mechanism Figure 26.5

Figure 26.6 Mechanisms and Consequences of ADH Release

Figure 26.7a Disorders of Water Balance: Dehydration Excessive loss of H 2 O from ECF ECF osmotic pressure rises Cells lose H 2 O to ECF by osmosis; cells shrink (a) Mechanism of dehydration

Figure 26.7b Disorders of Water Balance: Hypotonic Hydration Excessive H 2 O enters the ECF 1 2 ECF osmotic pressure falls 3 H 2 O moves into cells by osmosis; cells swell (b) Mechanism of hypotonic hydration

Regulation of Sodium Balance: Aldosterone Figure 26.8

Figure Mechanisms and Consequences of ANP Release

pH

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)  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)

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  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

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  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

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 CO 2 + H 2 O  H 2 CO 3  H + + HCO 3 ¯  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 CO 2 + H 2 O  H 2 CO 3  H + + HCO 3 ¯

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  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

Respiratory Acidosis and Alkalosis  Result from failure of the respiratory system  P CO2 is the single most important indicator of respiratory inadequacy  P CO2 levels  Normal P CO2 fluctuates between 35 and 45 mm Hg  Values above 45 mm Hg signal respiratory acidosis  Values below 35 mm Hg indicate respiratory alkalosis  Result from failure of the respiratory system  P CO2 is the single most important indicator of respiratory inadequacy  P CO2 levels  Normal P CO2 fluctuates between 35 and 45 mm Hg  Values above 45 mm Hg signal respiratory acidosis  Values below 35 mm Hg indicate respiratory alkalosis

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  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

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  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

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  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