Page 468 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

CHAPTER • 19

Fluid, Electrolyte, and Acid-Base

Disturbances in Liver Disease

Joao Felipe de Brito Galvao and Sharon A. Center

Liver disease can influence many metabolic, hormonal, functions as an anatomic barrier to solute diffusion. Trans-
and hemodynamic processes. Changes in hepatic albumin port processes in the basolateral hepatocellular and cana-
synthesis affect oncotic pressure; alterations in renal func- licular membranes determine bile acid uptake and biliary
tion and disturbances in production and metabolism excretion. Active transport of osmotically active solutes
of hormones contribute to water, electrolyte, and acid- into the canaliculus provides the driving force for bile flow.
base imbalances; and stimulation of baroreceptors and Bile salts are the most concentrated organic solutes
osmoreceptors can evoke detrimental changes in effective in bile and a major determinant of bile secretion.
circulating volume and plasma osmolality. Rate-limiting secretory mechanisms involve bile acid
transporters in the canalicular membranes. Bile acids
NORMAL PHYSIOLOGY OF impartunique properties thatattenuate theosmotic forces
THE HEPATOBILIARY SYSTEM in bile. Formation of bile acid micelles (polymolecular
aggregates) protects the intestinal mucosa from highly
concentrated solutes and promotes interaction between
BILE FORMATION: COMPOSITION bile acids and lipids in the intestinal tract, thus facilitating
AND FLOW digestion. Almost all bile acids are conjugated (exclusively

Bile is an aqueous solution containing organic and inor- to taurine in the cat and to taurine or glycine in the dog)
ganic compounds and electrolytes (Table 19-1). 174 Sepa- and exist as organic anions rather than undissociated acids.
rate hepatic and ductular transport mechanisms allow Nonabsorbable constituents of bile (e.g., bile acids,
regulation of bile composition and volume in response phospholipids, cholesterol) are concentrated when water
to changing physiologic needs. 110 Bile acids are amphi- and inorganic electrolytes (e.g., sodium, chloride, bicar-
pathic organic anions synthesized and conjugated by the bonate) are absorbed from the gallbladder and biliary
liver. The hepatocyte is a polarized secretory epithelial cell ducts. Stasis of bile flow or dehydration can promote a
with specific transporters localized in basolateral and can- pathologic thickening of bile (inspissated or sticky consis-
alicular cell membranes. 142 The canaliculus is a confined tency), whereas choleresis (increased bile flow) produces
space formed by a junction between specialized portions watery or dilute bile. The bicarbonate concentration of
of cell membranes from two adjacent hepatocytes. The bile exceeds that of plasma and is largely under the influ-
surfaces defining the canaliculus form a tight junction that ence of secretin. Most of the bicarbonate in bile arises

TABLE 19-1 Flow and Electrolyte Concentrations of Hepatic Bile

Flow Taurocholate
(mL/min/g Na þ K þ Cl HCO 3 (Canalicular Bile)
Species liver) (mEq/L) (mEq/L) (mEq/L) (mEq/L) (mM/L)

Dog 0.19 171 5.1 66 61 37
(n ¼ 24)* (n ¼ 75) (n ¼ 73) (n ¼ 83) (n ¼ 83) (n ¼ 80)
Cat 0.23 163 4.2 109 24 26
(n ¼ 5) (n ¼ 16) (n ¼ 16) (n ¼ 16) (n ¼ 16) (n ¼ 10)
*n ¼ Number of observations reported.

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