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Biology
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2. 36–3 The Integumentary System
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3. The Integumentary System
The skin, hair, nails, and a variety of glands make up the integumentary system.
The skin is the largest organ in the body.
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4. The Integumentary System
What are the functions of the integumentary system?
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5. The Integumentary System
serves as a barrier against infection and injury.
helps to regulate body temperature.
removes waste products from the body.
provides protection against ultraviolet radiation from the sun.
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The Skin
The Skin
The skin is made up of two main layers—the epidermis and the dermis.
Beneath the dermis is a layer of fat (hypodermis) and loose connective tissue that insulates the body.
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The Skin
Structures of the Skin
Nerves
Blood vessels
Hair
Sweat pore
Sebaceous gland
Hair follicle
Epidermis
The skin has an outer layer called the epidermis and an inner layer called the dermis.
Dermis
Muscle
Sweat gland
Hypodermis
Fat
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The Skin
Epidermis 
The outer layer of the skin is the epidermis.
The epidermis has two layers.
The outer layer is made up of dead cells.
The inner layer is made up of living cells.
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The Skin
Cells in the inner layer undergo rapid cell division, producing new cells that push older cells to the surface of the skin.
Older cells flatten and their organelles disintegrate.
Older cells also begin making keratin, a tough, fibrous protein.
When these cells die, they form a waterproof covering on the skin’s surface.
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The Skin
The epidermis also contains melanocytes, which are cells that produce melanin, a dark brown pigment.
Melanin protects the skin from sun damage.
Differences in skin color result from different amounts of melanin and where melanocytes are distributed.
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The Skin
Dermis 
The inner layer of the skin is the dermis.
The dermis contains collagen fibers, blood vessels, nerve endings, glands, sensory receptors, smooth muscles, and hair follicles.
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The Skin
The dermis contains two major types of glands:
sweat glands
sebaceous, or oil, glands
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The Skin
If your body gets too hot, sweat glands produce sweat.
When sweat evaporates, it cools the body.
Sweat also gets rid of wastes from the blood, along with water.
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The Skin
Sebaceous glands produce an oily secretion called sebum.
Sebum spreads out along the surface of the skin and helps to keep the skin flexible and waterproof.
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Hair and Nails
Hair 
Hair covers most body surfaces. Hair:
protects the scalp from ultraviolet light from the sun.
provides insulation from the cold.
prevents dirt and other particles from entering the body.
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Hair and Nails
Hair is produced by hair follicles, which are tubelike pockets of epidermal cells that extend into the dermis.
An individual hair is a column of cells that have filled with keratin and died.
The oily secretions of sebaceous glands help maintain the condition of each individual hair.
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Hair and Nails
Nails 
Nails grow from rapidly dividing cells in the nail root.
The nail root is located near the tips of the fingers and toes.
During cell division, cells fill with keratin and produce a platelike nail that covers and protects the fingertips and toes.
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36–3
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36–3
Keratin provides
insulation.
a waterproof covering.
pigmentation.
protection from UV radiation.
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36–3
The dermis contains two types of glands: sweat glands and
sebaceous glands.
pigment glands.
hair follicles.
dermal glands.
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36–3
All of the following are found in the dermis EXCEPT
nerve endings.
blood vessels.
sebaceous glands.
melanocytes.
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36–3
The function of melanin is to
help control the rate of heat loss by the skin.
produce sweat.
produce a waterproof covering on the surface of the skin.
absorb harmful UV radiation.
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36–3
The basic structure of human hair and nails is
melanin.
sebum.
keratin.
dermal cells.
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24. END OF SECTION