Biology of Disease

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DISORDERS OF WATER,

ELECTROLYTES AND URATE

BALANCES

Receptor

Regulatory

center

Response

Physiological

value

Change in substance under

homeostatic control

Figure 8.1 A generalized feedback mechanism.

See text for details.

8.1 Introduction

Homeostasis is the maintenance of a stable internal environment within
the body. This stability is necessary for optimum functioning of proteins,
particularly enzymes, cells, tissues, organs and systems. Many substances have
to be maintained at appropriate concentrations, including water, electrolytes,
such as Na+, K+, Ca2+, Mg2+ and Pi, and the acid–base components H+ and HCO 3 –.
In addition, waste products, such as urea and urate, must be kept below
toxic levels. Normally biochemical and physiological mechanisms regulate
and control the concentrations of all these components and, in general,
homeostatic controls involve negative feedback mechanisms. A receptor
detects unacceptable levels of a particular substance under homeostatic
control and sends a signal to a regulatory center that initiates a response that
corrects the imbalance and returns conditions to a physiologically acceptable
state (Figure 8.1). Once normality returns, the receptor is no longer stimulated
and the center ceases to respond. Disorders of homeostasis can occur, often
as a result of failures in the control mechanisms or because of damage to the
regulatory center by external agents.

OBJECTIVES

After studying this chapter you should be able to:

N describe the structure of the kidney;

N list the functions of the kidney;

N describe renal function tests;

N describe the types of renal failure;

N explain the causes and clinical consequences of selected disorders of water,

electrolyte and urate homeostases;

N describe the investigation of selected disorders of water, electrolyte and

urate homeostases;

N discuss the management and treatment of such disorders.