SKIN AND THE INTEGUMENTARY SYSTEM Chapter 6

Word Roots cut- (skin)  subcutaneous: beneath the skin derm- (skin)  dermis: inner layer of the skin epi- (upon)  epidermis: outer layer of the skin follic- (small bag)  hair follice: tubelike depression in which a hair develops

Word Roots kerat- (horn)  keratin: protein produced as epidermal cells die and harden melan- (black)  melanin: dark pigment produced by certain cells seb- (grease)  sebaceous gland: gland that secretes an oily substance

Introduction Organs - composed of two or more different tissues Skin/accessory organs make up the integumentary system

Skin and Its Tissues Large organ responsible for:  Maintaining homeostasis through temperature regulation  Protection of underlying tissues  Prevention of water loss  Housing sensory receptors  Synthesizing certain chemicals  Excreting wastes

Skin and Its Tissues Skin consists of an outer epidermis and a dermis, connected to underlying tissue by the subcutaneous layer (hypodermis)

The Skin

The Epidermis Stratified squamous epithelium Lacks blood vessels Stratum basale lies at the base - well-nourished by dermal blood vessels Cells pushed outward as new cells are formed, and become keratinized as they die Four or five layers may be seen: stratum basale, stratum spinosum, stratum granulosum, and stratum corneum are always present and the stratum lucidum is found in the thicker palms and soles

The Epidermis Protects against water loss, mechanical injury, chemicals, and microorganisms Melanocytes produce pigment melanin that protects deeper cells from the sun's ultraviolet rays Melanocytes pass melanin to nearby cells through cytocrine secretion

Skin Color Skin color is determined by the amount of melanin produced and how it is distributed Combination of genetic, environmental, and physiological factors

Skin Color Genetic differences in skin color result from differing amounts of melanin and in the size of melanin granules Exposure to sunlight, UV light from sunlamps, or X rays cause darkening of skin as melanin production increases

Skin Color Circulation within dermal blood vessels  Highly oxygenated blood is bright red, blood with lower oxygen concentration is dark red  Cyanosis makes skin appear bluish Eating a lot of beta carotene can make skin appear yellow/orange In newborns, a build up of bilirubin can cause jaundice

The Dermis Binds the epidermis to underlying tissues Epidermal ridges and dermal papillae cause the border to be uneven  Dermal papillae are most abundant in hands and feet, cause fingerprints Consists of connective tissue with collagen and elastic fibers within a gel-like ground substance

The Dermis Dermal blood vessels carry nutrients to upper layers of skin and help to regulate temperature  Interruption of blood flow can kill epidermal cells  Bedsores Also contains nerve fibers, sensory fibers, hair follicles, sebaceous glands, and sweat glands

The Skin

The Subcutaneous Layer Composed of loose connective tissue and insulating adipose tissue Binds the skin to underlying organs and contains the blood vessels that supply the skin No sharp boundary exists

Accessory Structures of the Skin Nails Hair follicles Sebaceous glands Sweat glands

Nails Consist of stratified squamous epithelial cells Nail plate overlies the nail bed, which is continuous with the epithelium of the skin Lunula as the most actively growing region of the nail root As new cells are produced, older ones are pushed outward and become keratinized

Hair Follicles Found in nearly all regions of the skin Individual hairs develop from cells at the base of the hair follicle As new cells are formed, old cells are pushed outward and become keratinized, and die forming the hair shaft

Hair Follicles A bundle of smooth muscle cells, called the arrector pili muscle, attaches to each hair follicle (cause goose bumps) Hair color is determined by genetics - melanin from melanocytes  Dark hair has eumelanin while blonde and red hair have pheomelanin

Sebaceous Glands Holocrine glands associated with hair follicles Secrete sebum that waterproofs and moisturizes the hair shafts Sebum = mixture of fatty material and cellular debris

Sweat Glands Sudoriferous glands Eccrine respond to body temperature – environmental heat or physical activity  Focused in forehead, neck, and back  Sweat is mostly water but also contains small amounts of salts and wastes like urea and uric acid  Secreted through pores

Sweat Glands Apocrine respond to body temperature, stress, and sexual arousal  Become active at puberty, most numerous in axillary regions and groin  Secretions develop a scent as they are metabolized by bacteria Modified sweat glands include:  Ceruminous glands which secrete wax in the ear canal  Mammary glands which secrete milk

Regulation of Body Temperature Active cells produce heat As body temperature rises, nerve impulses stimulate skin structures to release heat Heat lost to the surroundings through radiation Excessive heat causes dilation of dermal blood vessels and sweating

Regulation of Body Temperature Excessive cooling causes constricting dermal blood vessels, inactivating sweat glands, and shivering Hypothalamus controls set point Hypo and hyperthermia p. 125

Healing Wounds Body’s normal response to injury is inflammation, in which blood vessels dilate and become more permeable, causing tissues to become red and swollen More nutrients and oxygen are provided to the area, aiding healing

Healing Wounds

Superficial cuts filled in by reproducing epithelial cells – cells surrounding the break in skin are signaled to reproduce faster than normal to fill the gap Injuries that extend into dermis or subcutaneous layers result in broken blood vessels Escaping blood forms a clot A scab forms from clot and dried tissue fluids – protection

Healing Wounds Fibroblasts migrate to area forming new collagenous fibers around edges Suturing speeds process Under scab, phagocytic cells remove dead cells and debris, allowing tissue to be replaced Eventually scab falls away Scars are present if the wound is extensive Large wounds are often accompanied by granulations that develop in the exposed tissues

Burns Slightly burned skin results in erythema – redness, warm, mild edema Superficial partial-thickness burn (first degree) injures only the epidermis – heals within a few days to a week with no scarring Deep partial-thickness burn (second degree) injures epidermis and dermis – blisters, may appear moist and white/red – healing time varies

Burns Full-thickness burn (third degree) – destroys epidermis, dermis, and accessory structures – skin is dark and leathery, healing only occurs if epithelial cells divide and grow inward from margin of the burn Often requires a transplant:  Autograft – skin from unburned region of body  Homograft – skin from a cadaver  Skin substitute – amniotic membrane from fetus, artificial membrane, tissue-engineered skin

Other Topics Skin Cancer – p. 121 Clinical Connection – p. 126 Common Skin Disorders – p. 126