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

 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

 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

 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

 More commonly called skin

 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)

 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

 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

 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

 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)

 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

 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

 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

 Hair Follicles
 Sebaceous Glands
 Nails
 Sweat Glands

 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

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

 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

 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

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

 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

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

 Specialized type of sweat gland that secretes milk in females

 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-moonshaped area at the base of the nail (lunula)
 As nails develop they slide forward over the nail bed; the nail is attached to it

 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

 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

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

 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

 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

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

 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)

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

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

 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

 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