Integumentary System

Integumentary System Anatomy and Physiology

Skin • Called cutaneous membrane or integument • Integument and its appendages form the integumentary system • Hair • Nails • Largest organ in human body • Covers entire surface of the human body • Skin has two distinguished regions; three layers • Hypodermis • Dermis • Epidermis

Skin • Functions • Protection • Internal organs • Waterproof, cushions, and insulates • Protects against heat, bacteria, and UV rays • Regulates body heat • Facilitates water retention and loss • Site of sensory receptors

Skin—Hypodermis • A subcutaneous (below the skin) tissue layer • Also called superficial fascia • Not considered skin • Fatty tissue which stores fat and anchors skin • Different patterns of fat accumulation in men and women • Connects to underlying muscle tissue when muscle is present if not connects directly to bone

Skin—Epidermis • The outer and thinner region of skin • Made of stratified squamous epithelium divided into five separate layers • Stratum basale—single row of cells attached to dermis; youngest cells • Stratum spinosum—bundles of protein that resist tension • Stratum granulosum—layers of flattened cells producing keratin (hair and nails are composed of it) • Stratum lucidum—only found on the palms and soles • Stratum corneum—thick layers made of dead cells • Avascular and made of tightly-packed cells

Skin—Epidermis • Stratum basale • Cells of this layer not supplied with nutrients and oxygen, so they die off • Contains melanocyte cells that produce melanin, which gives skin its color. • Sensory nerves are found in the stratum basale • Free nerve endings – supply pain and temperature sensations to the brain • Tactile cells (Merkel cells) – signal the brain that an object has touched the skin

Skin - Dermis • Strong and flexible connective tissue • Contains rich supply of nerves and vessels • Critical role in temperature regulation (the vessels) • Two layers • Papillary – areolar connective tissue; includes dermal papillae, which is responsible for fingertip patterns • Reticular – network of collagen and reticular fibers

Hair • Found on all body parts except the palms, soles, lips, nipples, and portions of the external reproductive organs • Projects from structures called hair follicles (formed from epidermis cells) • Hair follicles are located in the dermis • Each hair has oil glands also called sebaceous glands that empties into the hair follicle

Hair • Functions • Warmth • Sense • Protection for scalp • Made of hardened keratin • Three concentric layers • Medulla—core • Cortex—surrounds medulla • Cuticle—overlapping single layers

Nails Grow from special epithelial cells at base of nail called nail root Cells become keratinized as they grow out over nail bed Visible portion of nail is called nail body Cuticle is a fold of skin that hides nail root The whitish color of the “half-moon” shaped base is called a lunula

Glands—Sweat • Also called sudoriferous glands • Present in all regions of skin • Two types • Apocrine glands • Open into hair follicles in the anal region, groin, and armpits • Glands begin to secrete after puberty • Eccrine glands • Open onto surface of the skin • Become active when person is hot to lower body temperature • Sweat is mostly water, salts, and a waste substance called urea • Ears have modified sweat glands that produce earwax

Glands—Sebaceous Most sebaceous glands are associated with hair follicles Glands secrete sebum, which lubricate hair and skin and kill bacteria on skin surface Glands may fail to secrete sebum and accumulation of sebum causes whiteheads and blackheads to appear on skin surface Most common form of acne, Acne vulgaris, is the inflammation of sebaceous glands

Glands—Other • Mammary Glands • Modified apocrine sweat glands • Produce milk after childbirth • Ceruminous Glands • Modified apocrine sweat glands • Secrete earwax, or cerum

Disorders of the Skin • Athlete’s Foot • Caused by a fungal infection that involves skin of the toes and soles • Impetigo • Highly contagious disease that is caused by bacterial infection that results in pustules • Eczema • Inflammation of the skin caused by sensitivity to certain chemicals, fabrics, and dryness or heat • Dandruff • Skin disorder caused by an accelerated rate of keratinization in certain areas of the scalp – causes flaking and itching. • Hives • An allergic reaction characterized by the appearance of reddish, elevated patches and itching.

Disorders—Skin Cancer • Categorized as melanoma or non-melanoma • Begins with mutation of skin cell DNA • Non-melanoma • Basal cell carcinoma • Most common type of skin cancer • Begins when ultraviolet radiation causes epithelial basal cells to form a tumor • Squamouscell carcinoma • Begins in the epidermis • Triggered by excessive UV exposure • Melanoma • Associated with skin aging, UV exposure, and overproduction of melanin in melanocytes which causes an unusual mole • Most dangerous type of skin cancer

Disorders—Burns • Burns • Catastrophic loss of body fluids • Dehydration and fatal circulatory shock • Infection • Types • First degree • Occurs in epidermis • Most common—skinburn • Second degree • Occurs in epidermis and upper dermis • Commonly blisters • Third degree • Occurs in epidermis, dermis, and sometimes as deep as hypodermis • Worst and most dangerous type of burn

Wounds and Healing • A wound is characterized by redness, swelling, heat, and pain • A wound that punctures a blood vessel will fill with blood • Chemicals cause the blood to clot • Blood clots will harden and create a scab when exposed to air • Fibroblasts pull skin together to regenerate tissue • Scar tissue is a tissue composed of many collagen fibers

Aging • As skin ages, the rate of cell reproduction decreases • Dermis becomes thinner and is held less tightly to the epidermis causing loose skin • Wrinkling • Epidermis is loose • Fibers are fewer and scarce • Hypodermis has less padding • Melanocytes decrease causing hair to turn gray and skin becomes paler • Many changes due to sun damage

Homeostasis • Used to regulate water loss and gain • Regulates body temperature as well • Disorders • Hypothermia • Body temperature falls below normal • Hyperthermia • Body temperatures rises above normal

Integumentary System