Integumentary System

Three major regions in the skin:

* Epidermis- outermost superficial region * Dermis- middle region * Hypodermis- deepest region, fatty layer that is composed of loose areolar connective tissue and adipose tissue

Langerhan's cells (Dendritic cells):

* Function as touch receptors in association with sensory nerve endings * Found in the Stratum Spinosum (3rd Layer)

The skin (integument):

* Largest system (organ) of your body * 16% of body weight * You have 21 square feet of it * It weighs ~9 pounds * It contains more than 11 miles of blood vessels * You shed 50,000 cells every MINUTE

Melanocytes:

* Produce the brown pigment melanin * Found in the Stratum Basale (Basal Layer) (4th Layer)

Epidermis

* Superficial region- Outer component of the skin * Epithelial tissue * Thick * Stratified squamous- Keratinized

Dermis

* Deep to the Epidermis- Inner component of the skin * Fibrous connective tissue * Loose and dense

Merkel cells (Tactic epithelial cells):

* Epidermal macrophages that help activate the immune system * Found in the Stratum Basale (Basal Layer) (4th Layer)

Two components to the skin:

* Epidermis * Dermis

Keratinocytes:

* The most abundant epidermal cell * Produce the fibrous protein keratin * Provides protection, produces antibiotics and enzymes that detoxify the harmful chemicals exposed to the skin * Found in all of the layer but are "dead" in the Stratum Lucidum and Stratum Corneum (Horny Layer) (1st layer)

*Sensory reception:

**FIRST LINE OF DEFENSE- Detects sensations- touch, pressure, pain, and temperature: as a "huge sensory receptor", the skin is your constant communication with the outside world** * The skin contains sense organs called sensory receptors that are associated with nerve endings. * By sensing touch, pressure, temperature, and pain, these receptors keep us aware of conditions at the body surface.

Body temperature regulation:

**Insulation and evaporation- releases 3 gallon of sweat each day** * The skin's rich capillary networks and sweat glands regulate the loss of heat from the body, helping to control body temperature.

Protection:

**Protects from infection, desiccation, UV rays** * Cushions and insulates the deeper body organs and protects the body from bumps, scrapes, and cuts. * Protects the body from chemicals and invading microorganisms * The epidermis is waterproof, preventing unnecessary loss of water across the body surface * Cells in the epidermal layer produce pigment to protect the skin from the harmful effects of ultraviolet (UV) radiation.

Excretion:

**Salts, water, and organic waste (glands)** * The skin acts as a miniature excretory system when urea, salts, and water are lost through sweat.

Production of vitamin D:

**Which you need to extract calcium from your diet and incorporate it into your bones** * The epidermal cells use UV radiation to synthesize vitamin D, a molecule necessary for absorbing calcium from the digestive tract.

Epidermis contains 4 distinct types of cells:

1. Keratinocytes 2. Melanocytes 3. Merkel cells (Tactic epithelial cells) 4. Langerhan's cells (Dendritic cells)

Functions of the skin:

1. Protection 2. Body temperature regulation 3. Excretion 4. Production of vitamin D 5. Sensory reception