The first line of defense Functions Body temperature

The first line of defense

Functions • • • Body temperature regulation Reservoir of blood Protection from external environment Cutaneous sensations Excretion and absorption Vitamin D synthesis

Epidermis • Composed of: 1. Keratinocytes 2. Melanocytes 3. Langerhans’ cells 4. Merkel cells

Layers of epidermis • Stratum basal (germinativum) 1. deepest layer 2. Cells are mitotic 3. contain melanocytes 4. usually one layer of simple columnar epithelium

• Stratum spinosum 1. Several layers thick 2. Cells are filling with keratin 3. Have melanin granules and Langerhans’ cells

• Stratum Granulosum 1. Cells flatten 2. nucleus and organelles desentegrate 3. Lamellated granules coat cell membranes 4. Cells die

• Stratum Lucidum 1. Present only in thick skin 2. Cells become parallel

• Stratum Corneum 1. Outermost cell layer 2. Cells are full of Keratin 3. Provides protection from external environment 4. Flake off

Dermis Second major skin layer • Made of collegen and elastic connective tissue • Contains nerve fibers, blood vessels, and lymphatic vessels • Consists of two layers: Dermal papillae and reticular region

Dermal Papillae • Made of areolar connective tissue, collagen and elastin • Contain capillary loops • Form part of the dermal-epidermal junction • Contain corpuscles of touch (meissner) • Contain free nerve endings that sense: Pain, heat, tickling and itching • Form epidermal ridges that increase grip of hand foot

Reticular Region • Region deep to dermal papillae • Composed of dense irregular connective tissue with collagen and elastin interwoven • Contain a few cells between fibers: muscle fibers, sweat and oil glands, hair follicles, and Pacinian corpuscles

Skin Color • Melanin 1. Polymer made of amino acid tyrosine 2. Range from yellow to reddish-brown to black 3. Protects underlying tissues from UV light • Carotene 1. Yellow orange pigment 2. Most obvious where stratum Corneum is Thickest • Hemaglobin 1. gives pinkish color to pale skin

Sudiferous glands • Eccrine glands 1. Most numerous of sweat glands 2. secreting part found in dermis and excretory part forms pore in skin • Apocrine glands 1. Found mainly in armpit and groin 2. secreting part found in subcutaneous layer and excretory duct opens into hair follicle 3. Do not function until puberty 4. Ceruminous (ear wax) and mammary glands

Sweat • Hypotonic filtrate of blood • Contains water, salts, vitamin C, antibodies, urea, uric acid, amonia, and lactic acid • Regulated by sympathetic division of autonomic nervous system • Prevents overheating of the body

Sebaceous Glands • Connected to hair follicles with secreting portion in dermis • Secrete oily substance called sebum • Coats surface of hair to keep it from becoming dry and brittle • Keeps skin soft • Inhibits growth of some bacteria • Infections by bacteria that thrive on lipid rich sebum causes pimples

Hair structure • Consists of dead keratinized cells • Shaft (superficial portion of hair) • Follicle (epidermal cells that grow down into dermis forming a tube) • Hair papilla (contains germinal layer of cells and blood vessels to nourish growing cells) • Root (developing hair that is contained in the follicle) • Follicle and dermal papillae attached by erector pili muscle

Hair growth • Germinal cells in the hair papilla reproduce, keratinize and die • Scalp hair grows for 2 -6 years then rests for 3 months • When growth stage resumes old hair is shed

Nails • Consist of hard keratinized cells that do not contain melanin • Nail body (visible part of nail) • Cuticle ( fold of skin that protects nail root) • Lanula (White part at base on nail) • Nail bed (epithelial cells that anchor nail body to finger tip • Root ( contain cells that reproduce mitotically to produce new cells