Organization of Body Parts

Organization of Body Parts

The structure of the body can be studied 

at different levels of organization (Fig. 1.1). 

First, all substances, including body parts, 

are composed of chemicals 

made up of submicroscopic particles called atoms. 

Atoms join to form molecules, 

which can in turn join to form macromolecules. 

For example, 

molecules called amino acids 

join to form a macromolecule called protein, 

which makes up the bulk of our muscles.

Macromolecules are found in all cells, 

the basic units of all living things. 

Within cells are organelles, 

tiny structures that perform cellular functions. 

For example, 

the organelle called the nucleus 

is especially concerned with cell reproduction;

another organelle, called the mitochondrion, 

suppliesthe cell with energy.

Tissues are the next level of organization. 

A tissue is composed of similar types of 

cells and performs a specific function.

An organ is composed of several types of tissues and 

performs a particular function within an organ system. 

For example, 

the stomach is an organ that is a part of the digestive system. 

It has a specific role in this system, 

whose overall function is to supply the body 

with the nutrients needed for growth and repair. 

The other systems of the body also have specific functions.

All of the body systems together make up

the organism—such as, a human being.

Human beings are complex animals,

but this complexity can be broken down and

studied at ever simpler levels.

Each simpler level is organized and constructed

in a particular way.