Anatomy of Skin

Anatomy of the Skin

Largest and heaviest organ

3 layers
-Epidermis (Stratified Squamous Epithelium)
-Dermis (Connective Tissue Layer)
-Hypodermis (Subcutaneous Tissue)

Thickness of skin
Skin thickness varies from 0.5mm to 6mm. Difference due mainly to variation in the thickness of the dermis. However, skin is classified as thick or thin based on thickness of epidermis alone.

Thick skin covers palms, soles and surfaces of fingers/toes. (Epidermis alone is 0.5mm due to thick surface of dead cells called stratum corneum). Thick skin has sweat glands but no hair follicles or sebaceous glands.

Thin skin covers the rest of the body. (0.1mm thick epidermis with thin stratum corneum). Has hair follicles, sebaceous glands and sweat glands

Epidermis
Keratinized stratified squamous epithelium.

Layers of epidermis from the top
-stratum corneum
-stratum lucidum
-stratum granulosum-keratohyalin granules
-stratum spinosum-desmosomes attaches keratinocyte
-stratum basale

Cells of epidermis
Stem cells
-undifferentiated cells that divide and give rise to keratinocytes. Found in stratum basale.

Keratinocytes
-makes up most of epidermal cells
-synthesize keratin

Melanocytes
-found in stratum basale
-synthesize brown to black pigment called melanin (shields DNA from UV radiation)

Tactile Cells
-receptors for sense of touch

Dendritic Cells/Langerhans cells
-found in stratum granulosum and stratum spinosum
-originate in bone marrow but migrates to epidermis
-guard against toxins, microbes and other pathogens by alerting immune system

Dermis
-composed of collagen, elastic and reticular fibers, fibroblasts
-rich with blood vessels, sweat glands, sebaceous glands and nerve endings
-hair follicles and nail roots are embedded in dermis
-smooth muscles associated with hair follicles contract in response to stimuli which causes the hair to stand, goosebumps and wrinkles.
-skeletal muscles on face attach to dermal collagen fibres-wrinkle,lifting eyebrow, smiling

2 zones of dermis
Papillary Layer
-thin zone of areolar tissue in and near dermal papillae
-mobility of leucocytes and other defenses against foreign substances
-rich in small blood vessels

Reticular layer
-deeper and much thicker
-consists dense irregular connective tissue
-collagen forms thicker bundles-less room for ground substance
-small clusters of adipocytes

Hypodermis
-has more areolar and adipose tissue
-binds skin to underlying tissue

Subcutaneous fat
-hypodermis composed of adipose tissue
-energy reservoir and thermal insulation