Skin and Structures

Skin

• It’s an organ! In fact it’s the largest organ (8 lbs, 22 sq. ft.)

• Makes up the integumentary system (serves to protect)

• Multiple layers of cells and tissues

• Lots of sensory structures 

Three layers

• Epidermis - avascular (no blood cells)

• Dermis - vascular 

• Hypodermis - very vascular 

Epidermis

• Composed of keratinized (fibrous protein), stratified squamous epithelial

• Avascular

• Four to five layers (five layers only found on palms and soles of feet)

• Deep to superficial: Stratum Basale, Stratum Spinosum, Stratum Granulosum, Stratum Corneum.

• Stratum lucidum found in palms and soles only

• Cells at surface are dead and get sloughed, deeper layers produce cells

Dermis

• Papillary Layer - loose, areolar connective tissues; projects into the stratum basale

• Reticular Layer - thicker, dense, irregular connective tissue

Hypodermis

• “Subcutaneous layer”

• Connects the skin to underlying fascia below

• Loose, well-vascularized, areolar and adipose tissue

Pigmentation

• The color of skin is influenced by pigments: melanin, carotene, and hemoglobin

• Melanin transferred into skin layers via a vesicle

• Exposure to UV rays creates a build up of melanin in skin to protect the DNA

Accessory Structures

Hair

• Made of dead, keratinized cells

• Hair Follicle - epidermal penetration of the dermis

• Hair Shaft - exposed portion but not anchored 

• Basal cells of the hair divide and push cells outward

• External hair completely dead and made of keratin

• Serves as protection, sensory input, thermoregulation, and communication

• Color from melanin types

Nails

• Composed of densely packed keratin

• Forms at the nail root

• Rich in blood vessels hence why it appears pink

• Lunula - white crescent shaped region; visible part of the matrix; white because its a thicker epidermis that blocks the color of the blood vessels

Sweat Glands

• AKA: Sudoriferous Glands

• Two Types:

  • Eccrine Sweat Glands - hypotonic (mostly water) releasing glands for thermoregulation; found in palms of hands, soles of feet and forehead

  • Apocrine Sweat Glands - associated with fair follicles in densely hair regions; armpits and genital regions; larger, deeper and sweat include organic compounds which decompose and smell

Functions (of int system)

Protection

• Protection against basic elements: wind, water, UV rays

• Prevents water loss

• First line of defense against abrasions

• Antibiotic qualities (via sweat and oils)

Sensory

• The movement of hairs on your skin is detected in the follicle and sends information to the central nervous system

• All three layers of the skin have specialized nervous structures have the ability to detect touch, temperature, and pain; more concentrated on the fingers

Thermoregulation

• Works with the sympathetic nervous system (fight or flight part) to regulate temperature

• Sweating and dilation of arterioles help cool the body down and release heat

• During cold weather the arterioles constrict in order to reduce heat loss and protect the internal organs

Vitamin D

• Epidermal layer of the skin synthesizes vitamin D when exposed to UV radiation (essential for absorption of calcium and phosphorus for bones and general immunity)