Biology 12

6.1 The Endocrine System and Homeostasis

168 MHR • Unit 2 Homeostasis

In Chapter 5, you studied the role of the human

nervous system in maintaining homeostasis. This

chapter focuses on the endocrine system, which

comprises the hormone-producing glands and

tissues of the body. As mentioned previously,

hormonesare chemical substances that circulate

through the blood and exert some measure of control

over virtually every organ and tissue in the body.

In conjunction with the nervous system, the

endocrine system acts as a complex internal

communication network that continuously monitors

and responds to the body’s ever-changing internal

environment. This system regulates critical

physiological processes and plays a key role in

homeostasis. Some of the regulatory functions of

the endocrine system include the control of heart

rate, blood pressure, immune response to infection,

reproduction, emotional state, and the overall growth

and development of the body. Hormone production

and secretion fluctuate in response to nervous

system activity, stimulation by other hormones,

and changing concentrations of salt, glucose, and

other essential constituents in the blood.

Abnormal endocrine function can seriously

disrupt the body’s normal metabolic functions.

However, as you will see in this chapter,

endrocrinology — the scientific study of the

endocrinesystem — is a very active field of

medical research. This field continually yields new

and exciting discoveries about the unique functions

of endocrine glands and the hormones they

produce. New and effective medications and

procedures are constantly being developed for

many endocrine disorders.

Components of the

Endocrine System

As Figure 6.1 illustrates, the endocrine system

is composed of a number of glands and tissues.

This system consists of the pituitary, thyroid,

parathyroid, adrenal, thymus, and pineal glands,

as well as the pancreas and reproductive tissues

(ovaries and testes). Many other organs, such as the

liver, skin, kidney, and parts of the digestive and

circulatory systems, produce hormones in addition

to their other physiological functions.

Figure 6.1Anatomical location of major endocrine glands in

the body

hypothalamus

pituitary gland

thymus

adrenal

gland

pancreas

thyroid

gland

pineal gland

parathyroid

gland

ovary

testis

EXPECTATIONS

Describe the anatomy and physiology of the endocrine system and explain

its role in homeostasis.

Describe and explain homeostatic processes involved in maintaining

equilibrium in response to both a changing environment and medical

treatments (for example, describe the effect of disorders of the

endocrine system).