Skin - 1st line of defense, prevents water loss, waterproofs the body
Hair - insulates the body, receptor for touch
Nails - protects distal phalanx (fingers /toes)
Sebaceous glands - lubricates the skin, discourages growth of bacteria
Sweat glands - temperature regulation
The Skin
A. The largest organ of the body and vital in maintaining homeostasis
B. Two distinct layers, some say three
1. Epidermis a. most superficial layer b. half the thickness of a piece of paper c. varies in thickness(eyelids--sole of foot) d. avascular, it is nourished by the blood vessels in the dermis e. keratinization is when the older cells harden, the cytoplasm of the skin cell fills with the protein keratin f. specialized cells known as melanocytes produce melanin
1) melanin is a dark pigment in the deeper layers of the epidermis that absorbs light energy and so protects the deeper cells from UV light
2) skin color is due to the amount of melanin produced but color is also influenced by environmental and physiological factors
2. Dermis a. binds the epidermis to underlying tissue (basement membrane) b. gives skin its strength and elasticity c. vascular which supply nutrients to all skin cells

heat, pain) d. nerve fibers are scattered throughout as well as sensory receptors (touch, pressure,
3. Subcutaneous layer
a. aka Hypodermis b. adipose tissue which insulates
(conserves body heat and keeps out outside heat) tissue
c. vascular that supplies skin and adipose
Hair Follicles
A. Hair is present on all skin surfaces except...
B. hair develops from a group of skin cells at the base of a tube called a hair follicle
1. follicle extends from the dermis to the surface and contains the hair root (bulb) follicle a. a bundle of smooth muscle cells form the arrector pili muscle that is attached to each b. the hair stands on end when the muscle contracts
2. hair shaft extends away from the surface a. this is dead cells b. process of keratinization
Nails
3. sebaceous glands usually are attached to hair follicles
4. hair color
A. unguis, onych
B. protective covering at the ends of fingers and toes
C. consist of keratinized stratified squamous cells with very hard keratin
D. form by cell division in the nail root

1. whitish half-moon-shaped area at the base of the nail is the lunula and is the growing region
2. skin at base is the eponychium (cuticle)
3. as the nail develops it slides forward over a layer of epithelium called the nail bed (matrix)
Sebaceous Glands
A. aka oil glands
B. usually attached to hair follicles
C. they are holocrine glands
1. secrete an oily mixture called sebum through small ducts into the hair follicle
2. Sebum helps keep the hair and skin soft, pliable, and waterproof
Sweat Glands
A. aka sudoriferous glands
B. exocrine glands that are widespread in the skin but are most numerous in the ____
C. each gland consists of a tiny tube that originates as a ball-shaped coil in the deeper dermis or superficial subcutaneous layer
D. fluid (sweat) is carried away in a duct, which opens at the surface as a pore
E. sweat is mostly water, but it also contains small quantities of salt and wastes (urea, uric acid)
Regulation of Body Temperature
Healing of Wounds