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The Integumentary System

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Introduction:

Organs are body structures composed of two or more different tissues.

The skin and its accessory organs make up the integumentary system.

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Skin and Its Tissues

The skin is a large organ responsible for: temperature regulation protection of underlying tissues Slowing the rate of water loss housing sensory receptors synthesizing certain chemicals excreting wastes

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The skin consists of an outer epidermis and a dermis, connected to underlying tissue by the subcutaneous layer (hypodermis).

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Epidermis

The epidermis is made up of stratified squamous epithelium and lacks blood vessels.

The layer of reproducing cells (the stratum basale), which lies at the base of the epidermis, is well-nourished by blood vessels from the deeper dermal layer.

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Cells are pushed outward as new cells are formed, and become keratinized as they die.

Layers of the Epidermis: Stratum corneumStratum lucidumStratum granulosumStratum spinosumstratum basale

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Skin Color

Specialized cells in the epidermis called melanocytes produce melanin, a dark pigment that provides skin color.

Differences in skin color result from differing amounts of melanin and in the size of melanin granules.

The amount of melanin produced is affected by genetics and environmental factors.

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Dermis

The dermis binds the epidermis to underlying tissues.

It consists of dense connective tissue with tough collagen and elastic fibers within a gel-like ground substance.

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Dermal blood vessels carry nutrients to upper layers of skin and help to regulate temperature.

The dermis also contains nerve fibers, sensory fibers, hair follicles, sebaceous glands, and sweat glands.

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Subcutaneous Layer

The subcutaneous layer (hypodermis) is composed of loose connective tissue and insulating adipose tissue.

It binds the skin to underlying organs and contains the major blood vessels that supply the skin.

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Accessory Organs of the Skin

Hair Follicles

Hair can be found in nearly all regions of the skin.

Hairs develop from cells at the base of the hair follicle, an area of the lower epidermis that dips down into the dermis.

As new cells are formed, old cells are pushed outward, become keratinized, and die forming the hair shaft.

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Hair color is determined by genetics; melanin from melanocytes is responsible for most hair colors; red hair contains an additional pigment.

A bundle of smooth muscle cells, called the arrector pili muscle, attaches to each hair follicle. These muscles cause goose bumps when cold or frightened.

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Sebaceous Glands

Associated with hair follicles and secrete an oily substance that waterproofs and moisturizes the hair shafts.

Nails

Nails consist of stratified squamous epithelial cells overlying the nail bed.

As new cells are produced, older ones are pushed outward and become keratinized.

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Sweat Glands Each gland consists of a tiny tube that originates

as a ball shaped coil lined with sweat secreting epithelial cells.

Cells respond to body temperature and stress

Modified Sweat GlandsModified sweat glands, called secrete wax in the

ear canal.

Mammary glands, another modified type of sweat glands, secrete milk.

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Regulation of Body Temperature

The skin plays a key role in the homeostatic mechanism that regulates body temperature.

Response to increased body temperature Heat from cellular metabolism or the environment is

transferred to the blood and carried to the hypothalamus of the brain.

The hypothalamus signals the dermal blood vessels to dilate and sweat glands to secrete.

Increased blood flow to the skin and evaporation of sweat results in a release of heat from the body.

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Response to decreased body temperature

Hypothalamus detects decrease in body temperature

Hypothalamus stimulates dermal blood vessels to constrict and sweat glands to remain inactive.

Decreased blood flow to the skin and lack of sweat reduce amount of heat loss.

Skeletal muscles may also be stimulated (shivering) which increases cellular metabolism and thus, heat production.

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Healing of Wounds and Burns

The body’s initial response to skin trauma is inflammation.

Inflammation-

The dilation of blood vessels in affected area become more permeable, fluids leave the blood vessels and enter the damaged tissues. This provides the tissues with increased nutrients and oxygen necessary for healing.

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Healing the wound

Shallow wounds are healed as epithelial cells along the margin of the wound divide more rapidly than usual and fill the gap.

Wounds that affect the dermis &/or hypodermis result in a blood clot and “scab” that cover and protect the underlying tissues. Fibroblasts form collagenous fibers that bind the edges of the wound together.

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Skin cancerSquamous cell carcinoma

Basal cell carcinoma

Common, slow growing form of skin cancer, usually linked to over exposure to sun, usually curable

Melanoma

develop in melanocytes, lesion becomes dangerous when it spreads downward into deeper layers, survival rate low once this type of growth occurs.

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