The Integumentary System

Skin is a multilayered organ that covers and protects the body.

The skin on the tips of fingers and toes is thick and is composed of curving ridges that form the basis of fingerprints. Fingerprints were first used in criminal investigations in 1860 by Henry Faulds, a Scottish medical missionary. Your skin is not just a simple covering that keeps your body together. It

is complex and is essential for your survival. Your ridges are uniquely yours!

The Structure of Skin

The integumentary (ihn TEG yuh MEN tuh ree) system is the organ system that covers and protects the body. Skin is the main organ of the integumentary system and is composed of four types of tissues: epithelial tissue, connective tissue, muscle tissue, and nerve tissue. Epithelial tissue covers body surfaces, and connective tissue provides support and protection. Muscle tissue is involved in body movement. Nerve tissue forms the body’s communication network.

The epidermis the two main layers of skin as seen through a microscope. The outer superficial layer of skin is the epidermis. The epidermis consists of epithelial cells and is about 10 to 30 cells thick, or about as thick as this page. The outer layers of epidermal cells contain keratin (KER uh tun), a protein which waterproofs and protects the cells and tissues that lie underneath. These dead, outer cells are constantly shed.  As much as an entire layer of skin cells can be lost each month.

Skin is an organ because it consists of different types of tissues joined together for specific purposes.

The inner layer of the epidermis contains cells that continually are dividing by mitosis to replace cells that are lost or die. Some cells in the inner layer of the epidermis provide protection from harmful ultraviolet radiation by making a pigment called melanin. Melanin is a pigment that absorbs light energy, which protects deeper cells from the damaging effects of ultraviolet rays of sunlight. The amount of melanin that is produced also influences the color of a person’s skin. A suntan

results when melanin is produced in response to exposure to the ultraviolet radiation in sunlight.

The dermis Directly beneath the epidermis is the dermis, the second layer of skin. The thickness of the dermis varies but usually is 15–40 times thicker than the epidermis. The dermis consists of connective tissue, a type of tissue that prevents the skin from tearing and also enables the skin to return to its normal state after being stretched. This layer contains other structures including nerve cells, muscle fibers, sweat glands, oil glands, and hair follicles. Beneath the dermis is the subcutaneous layer, a layer of connective tissue that stores fat and helps the body retain heat.

Hair and nails Hair, fingernails, and toenails also are parts of the integumentary system. Both hair and nails contain keratin and develop from epithelial cells. Hair cells grow out of narrow cavities in the dermis called hair follicles. Cells at the base of a hair follicle divide and push cells away from the follicle, causing hair to grow. Hair follicles usually have sebaceous or oil glands associated with

them, as shown in Figure 32.3. Sebaceous glands lubricate skin and hair. When glands produce too much oil, the follicles can become blocked. The blockage can close the opening of a follicle, causing a whitehead, blackhead, or acne—an inflammation of the sebaceous glands.

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Functions of the

Integumentary System

Skin serves several important functions including regulation of body Temperature, production of vitamin D, protection, and perception of one’s surroundings.

Temperature regulation What happens when a person is working outside on a hot summer day? In order to regulate body temperature, the person sweats. As sweat evaporates it absorbs body heat, thereby cooling the body. What happens to skin when a person gets cold or frightened? “Goose bumps” are caused by the contraction of muscle cells in the dermis. In other mammals, when these muscles contract, the hair (fur) stands on end. Notice the frightened cat in This also is a mechanism for trapping air, which insulates or warms the mammal. Humans do not have as\ much hair as most other mammals, but “goose bumps” are caused by the same type of muscles that make a cat’s fur stand on end. Humans rely on fat in the subcutaneous layer instead of hair to keep warm.