Body Tissues, Organs, and Systems Tissue consists of millions of cells that are grouped together to perform a
specific function in the body. Muscle tissue, for example, is one particular type of
tissue. It consists of millions of threadlike muscle cells. In addition to muscle tissue,
there are three other basic types of tissue: nerve, epidermal (skin), and connective
tissue.

Organs are composed of different types of tissues that work together to carry out a

specific body function. For instance, the heart is an organ that consists of muscle
tissue, connective tissue, and nerve tissue. Because these tissues work together, the
organ of the heart is able to pump and circulate blood
throughout the body. Other examples of organs are the eyes, liver, and kidneys. The
skin is the largest organ of the body.

Systems consist of organs that work together. The systems of the body include the
digestive system, nervous system, skeletal system (bones),
muscular system, respiratory system (breathing), endocrine system (glands),
excretory system (waste removal), reproductive system, and circulatory system. The
organs that work together as the digestive system are the mouth, gullet, stomach, and
intestines. Together the brain, spinal cord, and nerves throughout the body function
as the nervous system.

Complete the summary:
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When millions of body cells work together to carry out a certain body function, they are called
tissue, and there are four basic types of tissue.