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Anatomy & Physiology: Skin Structure and Function

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  • Layers of the skin

    The skin consists of two layers: the epidermis (outer, avascular epithelial tissue) and the dermis (underlying, vascular dense connective tissue). The subcutaneous tissue (hypodermis) lies beneath but is not part of the skin.

  • Functions of subcutaneous tissue

    Anchors skin loosely to underlying muscles and structures; composed mostly of adipose and areolar connective tissue; part of the integumentary system.

  • Main cell types in the epidermis

    Keratinocytes, melanocytes, dendritic (Langerhans) cells, and tactile (Merkel) epithelial cells.

  • Role of keratinocytes

    Produce fibrous keratin, the protein that protects skin; major epidermal cells; renew epidermis every 25–45 days.

  • Function of melanocytes

    Spider-shaped cells in deepest epidermis; produce melanin pigment packaged in melanosomes; melanin protects keratinocyte nuclei from UV damage.

  • Dendritic (Langerhans) cells function

    Star-shaped macrophages in deep epidermis; ingest foreign substances and activate the immune system.

  • Tactile (Merkel) cells role

    Touch receptors located at the epidermal-dermal junction.

  • Five layers of the epidermis

    Stratum basale, stratum spinosum, stratum granulosum, stratum lucidum (only in thick skin), and stratum corneum.

  • Difference between thick and thin skin

    Thick skin has all five epidermal layers including stratum lucidum; found on palms, fingertips, soles. Thin skin lacks stratum lucidum.

  • Characteristics of stratum basale

    Deepest epidermal layer; single row of mitotic stem cells; attached to dermis; produces daughter cells that migrate upward and die.

  • Stratum spinosum features

    Several layers thick; keratinocytes have pre-keratin filaments attached to desmosomes; cells appear spiky (prickle cells); contains melanosomes and dendritic cells.

  • Stratum granulosum functions

    4-6 flattened cell layers; keratinization begins; cells accumulate keratohyaline granules and lamellar granules (water-resistant glycolipid); cells above die.

  • Stratum lucidum location and structure

    Only in thick skin; thin, translucent layer of 2-3 rows of clear, flat, dead keratinocytes above stratum granulosum.

  • Stratum corneum composition and function

    20-30 rows of flat, anucleated, keratinized dead cells; protects deeper cells, prevents water loss, resists abrasion, and acts as a barrier.

  • Composition of the dermis

    Strong, flexible connective tissue with fibroblasts, macrophages, mast cells, and white blood cells; contains nerves, blood vessels, hair follicles, oil and sweat glands.

  • Papillary dermis characteristics

    Thin, superficial layer of areolar connective tissue with loose collagen and elastic fibers; contains dermal papillae with capillaries, free nerve endings, and tactile corpuscles.

  • Function of dermal papillae

    Fingerlike projections into epidermis; contain capillary loops and sensory receptors; form friction ridges that enhance grip and touch sensitivity.

  • Friction ridges and fingerprints

    Ridges formed by dermal papillae and epidermal ridges; enhance gripping and touch; sweat pores in ridges create unique fingerprint patterns.

  • Reticular dermis composition

    Thick layer of dense irregular connective tissue with coarse collagen and elastic fibers; provides strength, resiliency, and stretch-recoil properties.

  • Dermal vascular plexus

    Network of blood vessels between reticular dermis and subcutaneous tissue supplying skin with nutrients and oxygen.