skin - biology

General Facts:

A.First line of defense

B.Vital to homeostasis

C.Largest body organ

Functions of the skin:

1. Protection

2. Regulate body temperature

3. Decrease water loss

4. Contains sensory receptors

5. Synthesize biochemicals

6. Excrete waste

Regions

Epidermis – outermost layer

Dermis – middle layer

Subcutaneous– deepest layer

Epidermis

• Composed of cells in four or five layers

• Lacks blood vessels

• Outer portion of the skin that is exposed to the external environment and functions in protection

Cells of the Epidermis

• Most cells in the epidermis produce the fibrous protein keratin

• Some cells produce the brown pigment melanin

• Some cells turn on the immune system

• Some cells function as touch receptors in association with sensory nerve endings

Skin ColorThree pigments contribute to skin color•Melanin – yellow to reddish-brown to black pigment, responsible for dark skin colors•Carotene – yellow to orange pigment, most obvious in the palms and soles of the feet•Hemoglobin – reddish pigment responsible for the pinkish hue of the skin

Sunlight causes the melanin production to increase.

Circulation with dermal blood vessels affects skin color.

Dermis

• Second major skin region containing strong, flexible connective tissue (collagen fibers) and blood vessels that carry nutrients to upper layers of skin and help regulate body temperature

Also consists of nerves, hair follicles, sweat glands, oil glands and muscles.

Subcutaneous (Hypodermis)

• Deepest layer of the skin

• Composed of a fatty layer and loose connective tissue

• It binds the skin to underlying organs and contains the blood vessels that supply the skin.

• There is no sharp boundary between the dermis and the hypodermis