Biology of Disease

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DISORDERS OF THE

ENDOCRINE SYSTEM

OBJECTIVES

After studying this chapter you should be able to:

N list the different types of hormones and give examples;

N outline the structure and roles of the endocrine system;

N describe general mechanisms underlying hormone actions;

N explain how disorders of the endocrine system occur;

N discuss the causes, investigation and management of some endocrine

disorders.

7.1 Introduction

The endocrine system is one of two major control systems in the body, the
other being the nervous system, that help control the activities of the body. It
consists of a number of ductless glands (Figure 7.1) that produce hormones.
Hormones are molecules that circulate in the blood and excite or inhibit the
metabolic activity of target tissues or organs. These responses maintain and
regulate body functions, such as growth and development, responses to stress
and injury, reproduction, homeostasis and energy metabolism (Figure 7.2).

Hormones can be divided into three chemical groups: amines, peptides and
proteins, and steroids (Table 7.1). Many amine hormones, such as adrenaline
(epinephrine) and those produced by the thyroid gland, are derivatives of
tyrosine. The majority of hormones are peptides and proteins, examples being
insulin and growth hormone. A number of protein hormones, for example
thyroid stimulating hormone, are glycoproteins in that they have carbohydrate
groups covalently attached to them. All steroid hormones are derivatives of
cholesterol and include cortisol and testosterone. Figure 7.3shows examples
of each type of hormones.

Class Examples Associated

glands

Amines adrenaline

noradrenaline

thyroid hormones

T 3 and T 4

adrenal medulla

thyroid gland

Peptides

and proteins

insulin,

growth hormone

islets of

Langerhans

anterior

pituitary

Steroids cortisol

aldosterone

testosterone

adrenal cortex

Table 7.1A structural classification of hormones with

selected examples