Anatomy & Physiology 1 Integumentary System

2 Major Components of the Integumentary System

Skin (dermis and epidermis)
Accessory Organs (hair, nails, exocrine glands)

Functions of the Integumentary System

1. Protection
2. Excretion of urea and uric acid
3. Heat regulation
4. Vitamin D Synthesis

Thick Skin

Covers palms, soles and corresponding surfaces of fingers and toes. Has sweat glands but no hair follicles or sebaceous glands. 5 layers

Thin Skin

Covers the remaining parts of the body. Has hair follicles, sebaceous glands, and sweat glands. 4 layers

Epidermis

Keratinized stratified squamous epithelium. Lacks blood vessels, avascular. Mostly made up of Keratinocytes.

Cells of the Epidermis

1. Stem Cells
2. Keratinocytes
3. Melanocytes
4. Tactile (Merkel) Cells
5. Dendritic (Langerhans) Cells

Stem Cells

Undifferentiated cells that divide and give rise to keratinocytes.
Location: stratum basale (the deepest layer of the epidermis)

Keratinocytes

Most abundant of epidermal cells. Named for their role in synthesizing keratin. Nearly all visible epidermal cells are keratinocytes.

Melanocytes

Synthesize the brown and black pigment melanin. The pigment shields the DNA from ultraviolet radiation.
Location: stratum basale among the stem cells and the deepest keratinocytes

Tactile (Merkel) Cells

Receptors for touch. Few in number.
Location: basal layer of the epidermis and associated with an underlying dermal nerve fiber.

Tactile (Merkel) Disc

Tactile cell and its nerve fiber

Dendritic (Langerhans) Cells

Immune cells that originate in the bone marrow but migrate to the epidermis and epithelia of the oral cavity, esophagus, and vagina. Stand guard against toxins, microbes, and other pathogens that penetrate into the skin.
Location: stratum spinosum and stratum granulosum

Layers of the Epidermis

1. Stratum Basale
2. Stratum Spinosum
3. Stratum Granulosum
4. Stratum Lucidum
5. Stratum Corneum

Stratum Basale

Single layer of cuboidal to columnar cells resting on basement membrane; site of most mitosis.

Stratum Spinosum

Many layers of keratinocytes, typically shrunken in fixed tissue but attached to each other by demosomes, giving them a spiny look. Dendritic cells are abundant here.

Stratum Granulosum

Two to five layer of cells with dark-staining keratohyalin granules; scanty in thin skin.

Stratum Lucidum

Clear featureless, narrow zone seen only in thick skin

Stratum Corneum

Dead, keratinized stratified squamous epithelium

Dermis

Connective tissue layer beneath the epidermis. Composed mostly of collagen fibers, but also contains elastic and reticular fibers, fibroblasts, and other typical cells of fibrous connective tissue.
All accessory organs are located in the dermis.

2 Layers of Dermis

1. Papillary Layer
2. Reticular Layer

Papillary Layer

Superficial one-fifth of dermis; composed of areolar tissue; often extends upward as dermal papillae.

Reticular Layer

Deeper 4/5 of dermis; dense irregular connective tissue

Hypodermis

Aerolar or adipose tissue between skin and muscle. Also called subcutaneous tissue.

4 Major Types of Cutaneous Glands

1. Sweat Glands (Sudoriferous)
Apocrine and Merocrine
2. Sebaceous Glands
3. Ceruminous Glands
4. Mammary Glands

Apocrine Sweat Glands

Secret sweat by exocytosis, open by ducts into hair follicles. Scent glands
Location: groin, anal region, axilla (armpit), areola, and in beard areas in adult males.

Merocrine (Eccrine) Sweat Glands

Widely distributed over the entire body, especially abundant on the palms, soles, and forehead. Primary function is to cool the body. Open by ducts onto the skin surface.

Sebaceous Glands

Produce oily secretions called sebum. Usually open up to a hair follicle. Sebum keeps the skin and hair from becoming dry, brittle, and cracked.

Ceruminous Glands

Only found in the external ear canal. Their secretions mix with sebum and dead epidermal cell to form earwax (cerumen).

Mammary Glands

Milk producing glands. They are modified apocrine sweat glands that produce a richer secretion and channel it through ducts to the nipple.

Properties of Hair

Function: Protection
Produced by hair matrix
Arrector Pili: smooth muscle cells extending from dermal collagen fibers to the connective tissue foot sheath of the hair follicle

Properties of Nails

Function: Protection
Used for grasping things
Produced by the nail matrix

Degrees of Burns

1st Degree
2nd Degree
3rd Degree

1st Degree Burns

Involve only the epidermis and are marked by redness, slight edema, and pain. They heal in a few days and seldom leave scars. Most sunburns are first-degree burns.

2nd Degree Burns

Involve the epidermis and part of the dermis but leave at least some of the dermis intact. A second-degree burn by be red, tan, or white and is blistered and very painful. It may take from 2 weeks to several months to heal and may leave scars.

3rd Degree Burns

Also called full-thickness burns. Epidermis, all of the dermis and often some deeper tissue such as muscles and bone are destroyed. Since no dermis remains, skin regeneration can only occur on the outside edges of the wound. Often skin grafts are required. Destroys nerve endings as well.

Types of Skin Cancers

1. Basal Cell Carcinoma
2. Squamous Cell Carcinoma
3. Malignant (Melanoma) Carcinoma

Basal Cell Carcinoma

Most common type of skin cancer. Arises from cells of the stratum basale and eventually invades the dermis. Attacks basal cells.

Squamous Cell Carcinoma

Arises from keratinocytes of the stratum spinosum. Attacks the squamous cells

Malignant (Melanoma) Carcinoma

Arises from the melanocytes. Extremely aggressive and drug-resistant type of skin cancer. Attacks everything.