Chapter 6: The integumentary System

Integumentary System  Composed of the cutaneous membrane with certain accessory organs  4 Major Types of Membranes  Serous membrane  Mucous membranes  Synovial membranes  Cutaneous membrane

Serous Membranes  Line body cavities that lack openings to the outside of the body  Form the inner linings of the thorax and abdomen  Consists of a layer of simple squamous epithelium & a thin layer of loose connective tissue  Cells of a serous membrane secrete watery serous fluid which lubricates membrane surfaces

Mucous membranes  Line cavities & tubes that open to the outside of the body  Include the oral & nasal cavities & the tubes of the digestive, respiratory, urinary, and reproductive systems  Specialized cells within a mucous membrane secrete mucus

Synovial membranes  Form inner linings of the joint cavities between the ends of bones at freely movable joints (synovial joints)  Usually include dense connective tissue that overlies loose connective tissue and adipose tissue  Cells secrete a thick, colorless synovial fluid into the joint cavity  this lubricates the ends of the bones within the joint

Cutaneous Membrane  More commonly called skin

Skin & its tissues (figure 6.1)  The skin is the largest and one of the more versatile organs of the body  Plays a major role in maintaining the body’s homeostasis  Includes 2 distinct tissue layers:  Epidermis  outer layer, composed of stratified squamous epithelium  Dermis  inner layer, thicker than the epidermis & it contains connective tissue, epithelial tissue, smooth muscle tissue, nervous tissue, & blood Basement membrane that is anchored to the dermis separates the two skin layers Masses of loose connective & adipose tissues that bind the skin to the underlying organs  these tissues form the subcutaneous layer (hypodermis)

Epidermis  Lacks blood vessels but the deepest layer of epidermal cells (stratum basale) is close to the dermis and is nourished by its blood vessels  As the cells divide and grow, the older cells are pushed away from the dermis toward the skin surface  The farther away, the poorer the nutrient supply becomes, in time they die  Older cells (keratinocytes) harden in a process called keratinization  Cytoplasm fills with strands of a tough, fibrous, waterproof keratin protein  Many layers accumulate in the outer epidermis  this forms the stratum corneum (outermost layer of the epidermis)  Dead cells are often rubbed away

Epidermis  Important protective functions:  Shields moist underlying tissues against excessive water loss, mechanical injury, and the effects of harmful chemicals  Keeps out disease-causing microorganisms when unbroken

Epidermis  Melanocytes – specialized cells that produce melanin (a dark pigment that provides skin color)  Absorbs light energy which helps protect deeper cells from the damaging effects of ultraviolet radiation in sunlight  Melanocytes lie in the deepest portion of the epidermis & in connective tissue of the dermis

Skin color  Due largely to melanin  Differences in skin color result from:  Differences in the amount of melanin produced  Genetics  Environmental and physiological factors  Blood may also affect skin color as physiological changes occur  Well oxygenated blood has hemoglobin that is bright red  pinkish color in light-complexioned people  Low concentration of oxygen in blood causes hemoglobin to be dark red  makes the skin appear blue (cyanosis)

Skin color  Melanin – yellow to reddish-brown to black pigment, responsible for dark skin colors  Carotene – yellow to orange pigment, most obvious in the palms and soles of the feet  Hemoglobin – reddish pigment responsible for the pinkish hue of the skin

Dermis  Binds the epidermis to underlying tissues  Composed largely of dense connective tissue that includes tough collagenous fibers & elastic fibers in a gel-like ground substance  Gives the skin its toughness & elasticity  Dermal blood vessels supply nutrients to all skin cells and help regulate body temperature  Nerve fibers carry impulses out from the brain to dermal muscles & glands  Sensory fibers carry impulses away from specialized sensory receptors to the brain (ex touch receptors)  Contain hair follicles, sebaceous (oil-producing) glands, & sweat glands

Subcutaneous layer  Also called the hypodermis (beneath the dermis)  Consists of loose connective & adipose tissues  The adipose tissue insulates which helps conserve body heat and impedes the entrance of heat from the outside

Accessory Organs of the skin  Hair Follicles  Sebaceous Glands  Nails  Sweat Glands

Hair (figure 6.4)  Filamentous strands of dead keratinized cells produced by hair follicles  Contains hard keratin which is tougher and more durable than soft keratin of the skin  Made up of the shaft projecting from the skin, and the root embedded in the skin  Consists of a core called the medulla, a cortex, and an outermost cuticle  Pigmented by melanocytes at the base of the hair

Hair function & distribution  Functions of hair include:  Helping to maintain warmth  Alerting the body to presence of insects on the skin  Guarding the scalp against physical trauma, heat loss, and sunlight

Hair function & distribution  Hair is distributed over the entire skin surface except:  Palms, soles, and lips  Mammaries & portions of the external genitalia

Sebaceous glands  Simple alveolar glands found all over the body (except palms & soles)  Soften skin when stimulated by hormones  Secrete an oily secretion called sebum  Keeps the hair and skin soft, pliable, and waterproof

Sebaceous Glands  Can be found next to hair follicles  Functions:  Lubricates hair & skin, collects dirt, layer of protection, kills bacteria, prevents water loss  Acne – gland becomes blocked because too much sebum is produced  Androgens – hormone that stimulates sebum production  Ex) puberty  Pimple forms when pore is infected & inflammation occurs

Sweat glands  Are exocrine glands  Different types prevent overheating of the body  Eccrine Glands  Apocrine Glands  Ceruminous Glands  Mammary Glands

Eccrine Sweat Glands  Most numerous of the sweat glands  Respond when the body experiences elevated temperatures due to heat or physical exercise  Found on the forehead, neck, and back

Apocrine sweat Glands  Become active when a person is emotionally upset, frightened, stressed, or in pain  Can activate during physical activity or elevated body temperature  Found in axillary regions and groin

Ceruminous glands  Modified apocrine gland  Found in the external ear canal  Secretes earwax

Mammary gland  Specialized type of sweat gland that secretes milk in females

Nails  Protective coverings on the ends of fingers and toes  Consist of keratinized stratified squamous epithelial cells w/ very hard keratin  Form by cell division in the nail root  The most active growing region of the nail is the whitish half-moon- shaped area at the base of the nail (lunula)  As nails develop they slide forward over the nail bed; the nail is attached to it

Healing of wounds  The specific events in healing depend on the severity and extent of the injury  A shallow break in the skin causes epithelial cells to divide more rapidly than usual so the cells fill the gap  Deeper breaks into the dermis or subcutaneous layer may break blood vessels  Escaping blood forms a clot in the wound which dries and forms a scab covering the wound  Fibroblasts migrate into the injured area and begin forming new collagenous fibers that bind the edges of the wound together  If the wound is extensive, newly formed connective tissue may appear on the surface as a scar

Skin cancer  Most skin tumors are benign and do not metastasize  A crucial risk factor for non-melanoma skin cancers is the disabling of the p53 gene  Newly developed skin lotions can fix damaged DNA

Skin Cancer  The three major types of skin cancer are:  Basal cell carcinoma  Squamous cell carcinoma  Melanoma

Basal cell carcinoma  Least malignant and most common skin cancer  Stratum basale cells proliferate and invade the dermis and hypodermis (located in the stratum basale)  Slow growing and do not often metastasize  Can be cured by surgical excision in 99% of the cases  Develops a central ulcer  Attracts blood vessels which then take away nutrients from the body

Squamous cell carcinoma  Arises from keratinocytes of stratum spinosum  Arise most often on scalp, ears, and lower lip  Grows rapidly and metastasizes if not removed  Prognosis is good if treated by radiation therapy or removed surgically

Melanoma  Cancer of melanocytes is the most dangerous type of skin cancer because it is:  Highly metastatic  Resistant to chemotherapy Ex) moles

Melanoma  Melanomas have the following characteristics (ABCD rule)  A: Asymmetry; the two sides of the pigmented area do not match  B: Border is irregular and exhibits indentations  C: Color (pigmented area) is black, brown, tan, and sometimes red or blue  D: Diameter is larger than 6 mm (size of a pencil eraser)

Melanoma  Treated by a wide surgical excision accompanied by immunotherapy  Chance of survival is poor if the lesion is over 4 mm thick

Burns  First-degree – only the epidermis is damaged  Symptoms include localized redness, swelling, and pain Ex) sunburn Can be caused by heat, chemicals, friction, electrical

Burns  Second-degree – epidermis and upper regions of dermis are damaged  Symptoms mimic first-degree burns, but blisters also appear  Takes 3-4 weeks to heal  Little scarring occurs

burns  Third-degree – entire thickness of the skin is damaged  Burned area appears gray-white, cherry red, or black; there is no initial edema or pain (since nerve endings are destroyed)  Skin graft is usually needed