Biology (B)

The Integumentary System

Lesson Objectives

• List the functions of skin.
• Describe the structure of skin.
• Describe the structure of hair and nails.
• Identify two types of skin problems.
• Describe two ways to take care of your skin.

Vocabulary

Your Skin and Homeostasis

Did you know that you see the largest organ in your body every day? You wash it, dry it, cover it up to stay warm or uncover it to cool off. In fact, you see it so often it is easy to forget the important role your skin plays in keeping you healthy.

Your skin is part of your integumentary system, which is the outer covering of your body. The integumentary system is made up of your skin, hair, and nails. Your integumentary system has many roles in homeostasis, including protection, the sense of touch, and controlling body temperature.

Functions of Skin

Your skin covers the entire outside of your body. Your skin is your body's largest organ, yet it is only about 2 millimeters thick. It has many important functions. The skin:

• Provides a barrier. It keeps organisms that could harm the body out. It stops water from leaving the body, and stops water from getting into the body.
• Controls body temperature. It does this by making sweat, a watery substance that cools the body when it evaporates.
• Gathers information about your environment. Special nerve endings in your skin sense heat, pressure, cold and pain.
• Helps the body get rid of some types of waste, which are removed in sweat.
• Acts as a sun block. A chemical called melanin is made by certain skin cells when they are exposed to sunlight. Melanin blocks sun light from getting to deeper layers of skin cells, which are easily damaged by sunlight.

Structure of Skin

Your skin is always exposed to your external environment, so it gets cut, scratched, and worn down. You also naturally shed many skin cells every day. Your body replaces damaged or missing skin cells by growing more of them. Did you know that the layer of skin you can see is actually dead? The dead cells are filled with a tough, waterproof protein called keratin. As the dead cells are shed or removed from the upper layer, they are replaced by the skin cells below them.

As you can see, two different layers make up the skin — the epidermis and the dermis. A fatty layer, called subcutaneous tissue, lies under the dermis, but it is not part of your skin.

The color, thickness and texture of skin vary over the body. There are two general types of skin:

1. Thin and hairy, which is the most common type on the body.
2. Thick and hairless, which is found on parts of the body that experience a lot of contact with the environment, such as the palms of the hands or the soles of the feet.

Lesson Summary

• Skin acts as a barrier that keeps particles and water out of the body.
• The skin helps to cool the body in hot temperatures, and keep the body warm in cool temperatures.
• Skin is made up of two layers, the epidermis and the dermis.

Review Questions

1. Identify two functions of skin.

2. How does the integumentary system help maintain homeostasis?

3. What are the two layers of the skin?