9 - Removal of Molecules from the Body

Summary

LEARNING OBJECTIVES

After reading this chapter, you should:

• Understand the role of the excretory systems in eliminating wastes and toxins and maintaining body balances.

• Understand the concept of biotransformation and the role of the liver in accomplishing the removal of compounds by both direct excretion (through the biliary system) and biotransformation.

• Understand the basic anatomy of the kidney and its functional unit, the nephron.

• Understand the basic processes that underlie kidney function: filtration, reabsorption, and secretion.

• Understand the biophysical processes responsible for filtration and regulation of filtration in the glomerulus.

• Understand the concept of clearance and be able to calculate clearances for typical solutes.

• Understand how proteins in the membrane of tubular epithelial cells—such as channels, active transporters, co-transporters, and exchangers—are responsible for reabsorption and secretion of compounds.

• Understand the role of osmotic pressure as a driving force for water reabsorption in the tubules.

Prelude

Each person ingests a large number of molecules per day with meals and snacks (Figure 9.1). A similarly large number of molecules enters the body through respiration (Figure 9.2). Body processes—such as building proteins, producing energy, and replenishing lost nutritional stores—use many of these molecules (recall Table 7.1). But a sizeable number of ingested chemicals are either not usable or not needed by the body, and therefore must be eliminated. In addition, metabolic processes generate waste products that are toxic if they accumulate in body tissues. These molecules must also be eliminated.