Layers of the Skin

Protection

Abrasion/UV Light, Barrier against microorganisms, Reduces water loss from the body

Sensation

Contains receptors for temperature, pressure, pain and touch

Production

Vitamin D, keratin and melanin

Temperature regulation

Regulates temperature in the body

Excretion

Small amounts of water/salts/urea

Epidermis

Contains 4 different cell types

Epidermis

Superficial layer of Epithelial tissue; lacks blood vessels/nerves

Keratinocytes

Produces keratin, a protein that accumulates within cells of the epidermis as they age causing them to die, but forming a hard waterproof layer

Keratinocytes

Releases waterproof lipid sealer for skin

Melanocytes

Produces the pigment melanin; transferred to keratinocytes by dendritic extensions of the melanocytes. Melanin granules cluster together in keratinocytes to protect nucleus/DNA.

Melanin

Pigment that contributed to skin, hair and eye color and absorbs UV radiation. Albinos lack enzyme needed to produce melanin.

Langerhans cell

Participates in immune responses to microbes that invade the skin; act as phagocytic macrophages.

Merkel cells

Least numerous found in the deepest layers of the epidermis

Stratum Basale

• Deepest layer

• Single row of Columnar Keratinocytes

• Some stem cells

• Develop into new keratinocytes

• Contains melanocytes, merkel cells, langerhans cells.

Stratum Spinosum

• 8-10 layers of many sided keratinocytes that fit closely together.

• Most prevalent location of Langerhans cells.

Stratum Granulosum

• 3-5 layers of flattened keratinocytes

• Undergoing apoptosis (cell death); cells lose nucleus and organelles as keratin accumulates.

• Cells contain membrane bound granules which produce a lipid-rich secretion that enters the extracellular space and waterproofs layers of cells.

Stratum Lucidum

• Present only in thick skin

• 3-5 layers of flat, clear, dead keratinocytes with large amounts of keratin.

Stratum Corneum

• 25-30 layers of dead/flat keratinocytes

• Continually shed/replaced

• Completely filled with keratin and lipid secretion from lamellar granules.

Keratinization

When newly formed cells are pushed upwards and make and accumulate keratin and are eventually sloughed off. 

Dermis

• Mainly Connective tissue that contains collagen and elastic fibers

• Cell types include : fibroblasts/macrophages/adipocytes

• Contains blood vessels, nerves, glands and hair follicles

Stria

Stretchmarks; small tears in the dermis due to extreme stress.

Papillary Region (Superficial)

• Upper 20%

• Increased surface area due to small upward projections into the epidermis called dermal papillae.

Dermal papillae

• Forms papillary ridges (fingerprints) on surface of fingers and toes

• Contains sensory nerves (signals that produce sensations of warmth, coolness, pain, tickling and itching)

Meissner Corpuscles

Touch receptors that are found in some dermal papillae which are sensitive to light touch.

Reticular Region (Deep)

• Lower 80%

• Dense Irregular Connective Tissue

• Collagen and Elastic Fibers

• Contains adipose cells, hair follicles, nerves, capillaries, sebaceous (oil) glands, and suderoficious (sweat) glands.

Hypodermis

• Loose Connective tissue and adipose

• Not a layer of skin

• Attaches dermis to underlying tissues/organs

• Cointans nerve endings called lamellated (Pacinian) corpuscles which are sensitive to pressure.