Structure of the Skin Divided into 3 basic

Structure of the Skin �Divided into 3 basic layers: 1. Epidermis 2. Dermis 3. Subcutaneous tissue

Epidermis: top level �Made up of 5 cell layers (from bottom to top): • • • Basal (deep) Spinus Granular Lucidum Corneum (superficial)

Basal cell layer Deepest layer �Cells are continually dividing to produce new skin cells (millions daily) �These cells move towards the skin surface, � �Blood is provided by the dermis below

Spinus cell layer �Cells above the basal cell layer become more irregular in shape

Granular cell layer �Cells are moving away from the blood supply, the cells begin to flatten and die �Keratin begins to form in the cells.

Lucidum cell layer �Clear-ish layer of skin �Only found where the skin is hairless and extra thick �lots keratin to provide water-repellent properties

Stratum Corneum �Layer of skin we SEE �Made up of overlapping squamous cells �Cells are dead and constantly shedding • These cells provide the tough and watertight function of skin

Dermis layer “hide” �Contain many of the structures that are found within our skin. �Arteries and veins run through this layer

Structures of the Dermis �Cutaneous glands Sebaceous gland Sweat glands �Hair �Nails �Nerves �Collagen and elastin fibers

Cutaneous Glands �All exocrine glands that release their secretions to the skin surface via ducts � 2 groups: • Sebaceous glands • Sweat glands

Sebaceous Glands �Glands that secrete sebum (oil) �Ducts empty out into hair follicles

Characteristics of Sebum �Lubricant that keeps skin soft and moist �Prevents hair from becoming brittle �Chemicals that kill bacteria �The gland becomes highly active during adolescence

Acne �Sebaceous gland’s duct becomes blocked by sebum �A whitehead forms on skin surface. �If the material oxidized and dries, it darkens and becomes a blackhead

Sweat Glands �More than 2. 5 million person � 2 types: • Eccrine: found all over the body • Apocrine: found only in genital and axillary regions

Sweat �Made up of water, Na. Cl, vitamin C, metabolic wastes, and lactic acid �Ducts that lead to the surface of the skin are called pores

Sweat Gland Pore

Homeostatic Uses of Sweat �Supplied with nerve endings that cause them to secrete sweat when outside or body temperature is too high

Hair �Earlier humans had more hair for insulation and self defense �Current uses for hair: • Guarding head against minor impact • Shielding the eyes • Keeping particles out of respiratory organs

Structure of the hair �Root: enclosed in the follicle �Shaft: projecting out of the scalp �Hair bulb matrix: Inferior end of the follicle. Where new hair is formed.

Hair Follicles �Where hair forms and attaches to the body �Made of 2 layers: • Inner epidermal layer: forms the hair • Outer dermal sheath: supplies blood and reinforces hair to body

Arrector pili �Small bands of smooth muscle cells �When contracted the hair is pulled upright, dimpling the skin surface “goosebumps”

Nails �Made up of keratinized skin cells �Scale-like modification of the epidermis that corresponds to the hoof or claw of other animals

Subcutaneous layer �The innermost layer of the skin �Composed of fat �thickness varies upon body region �This layer performs 2 major functions: • energy source for the body • helps to insulate the body against temperature.