HUMAN BIOLOGY

76 Chapter 4

What are organs and organ systems?

• An organ is a combination of two or more kinds of tissues that
  together perform one or more functions.


• Organ systems consist of two or more organs that together
  perform a specific function.


• The five body cavities contain many major organs.

taKe-hoMe Message

abdominal cavity Body
cavity that contains the
stomach, liver, intestines,
kidneys, and some other
organs.

cranial cavity Body cavity
that encloses the brain.

organ Structure, such as
the heart, built of two or
more kinds of tissue that
together perform one or
more functions.

organ system Combina-
tion of two or more organs
that work in a coordinated
way to carry out a specific
function.

pelvic cavity Body cavity
that encloses reproductive
organs, the bladder, and
rectum.

spinal cavity Body cav-
ity that encloses the spinal
cord.

thoracic cavity Body cavity
that contains the heart and
lungs.

organs and organ systems

thoracic cavity—essentially, inside your chest. Below the

thoracic cavity is the abdominal cavity, which holds your

stomach, liver, pancreas, most of the intestine, and other

organs. Reproductive organs, the bladder, and the rectum

are located in the lower abdominal cavity in a region often

called the pelvic cavity.

In an organ system, two or more organs “cooperate” to

carry out a major body function (Figure 4.10). For example,

interactions between your skeletal and muscular systems

allow you to move about. Blood in the cardiovascular sys-

tem rapidly carries nutrients and other substances to cells

and transports products and wastes away from them. Your

respiratory system delivers oxygen from air to your cardio-

vascular system and takes up carbon dioxide wastes from

it—and so it goes, throughout the entire body.

n The human body’s organs are

organized into eleven organ systems.

n Link to Levels of biological

organization 1.3

An organ is a combination of two

or more kinds of tissue that together

perform one or more functions. As

an example, the stomach contains

all four of the tissue types you have

read about in previous sections (Fig-

ure 4.9A). Its wall is mainly muscle,

and nerves help regulate muscle

contractions that mix and move

food. Connective tissue provides

support, while the stomach lining is

epithelium.

The stomach and many other

major organs are located inside

body cavities shown in Figure 4.9B.

The cranial cavity and spinal

cavity house your brain and spinal

cord—the central nervous system.

Your heart and lungs reside in the

Figure 4.9 Animated! An organ consists of two or more tissues. A The four types of tissue in the stomach. B A side view of

major body cavities where many organs are located. (© Cengage Learning)

Epithelial tissue:

Protection, secretion,

and absorption

Organ system:
A set of organs that interacts to
carry out a major body function

Organ:

Body structure that integrates different

tissues and carries out a specific function

Connective tissue:

Structural support

Muscle tissue:

Movement

Nervous tissue:

Communication,

coordination, and control

Stomach

cranial

cavity

spinal

cavity

thoracic

cavity

abdominal

cavity

pelvic

cavity

A

B

4.8

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