chapter 6: the integumentary system. integumentary system composed of the cutaneous membrane with...

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 MembranesLine 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 membranesLine 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 membranesForm 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 MembraneMore 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 colorMelanin – 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

DermisBinds 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 layerAlso 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 skinHair 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 & distributionFunctions 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 & distributionHair is distributed over the entire skin surface

except: Palms, soles, and lips Mammaries & portions of the external genitalia

Sebaceous glandsSimple 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 GlandsCan 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 glandsAre exocrine glands

Different types prevent overheating of the body

Eccrine Glands

Apocrine Glands

Ceruminous Glands

Mammary Glands

Eccrine Sweat GlandsMost 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 GlandsBecome 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 glandsModified apocrine gland

Found in the external ear canal

Secretes earwax

Mammary glandSpecialized 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 CancerThe 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 carcinomaArises 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

MelanomaCancer of melanocytes is the most dangerous

type of skin cancer because it is: Highly metastatic Resistant to chemotherapy

Ex) moles

MelanomaMelanomas 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)

MelanomaTreated by a wide surgical excision

accompanied by immunotherapy

Chance of survival is poor if the lesion is over 4 mm thick

BurnsFirst-degree – only the epidermis is damaged

Symptoms include localized redness, swelling, and pain

Ex) sunburn

Can be caused by heat, chemicals, friction, electrical

BurnsSecond-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

burnsThird-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