Book Feb 1, 2025

Page 1: Epidermis, Dermis, and Subcutaneous Tissue

Epidermis

  • The outer layer of skin that is tough and water-repellent, consisting of four to five stratified layers of epithelial cells.

  • Key Cell Types:

    • Keratinocytes: Constitute about 90% of the epidermal cells and undergo keratinization.

    • Melanocytes: Produce melanin, which protects the nuclei of keratinocytes from UV damage.

    • Dendritic Cells: Migratory cells that engulf pathogens and start immune responses.

    • Tactile Epithelial Cells: Located deep in the epidermis, serving as touch receptors.

Layers of the Epidermis (from deep to superficial):

  1. Stratum Basale:

    • A single layer of columnar or cuboidal cells adjacent to the dermis, where new keratinocytes are produced via mitosis.

  2. Stratum Spinosum:

    • Contains 8-10 rows of keratinocytes with a spiny appearance; dendritic cells are most abundant here.

  3. Stratum Granulosum:

    • Composed of 3-5 rows of flattened keratinocytes with visible granules, crucial for keratin production. Cells begin to undergo apoptosis.

  4. Stratum Lucidum:

    • Presents in thick skin (e.g., palms, soles); consists of 3-5 rows of flattened, dead keratinocytes. Appears clear/transparent in fresh samples.

  5. Stratum Corneum:

    • Up to 30 layers of flattened, dead keratinocytes packed with keratin, forming a tough barrier.

Dermis

  • A thick, vascular layer of skin comprising connective tissue, containing accessory organs like hair follicles and glands.

Layers of the Dermis:

  1. Papillary Layer:

    • Thin layer of loose connective tissue, with dermal papillae forming skin ridges; adjacent to the stratum basale.

  2. Reticular Layer:

    • The dense, dominant part of the dermis composed of irregular connective tissue with abundant collagen and elastic fibers.

Subcutaneous Tissue (Hypodermis)

  • Contains adipose tissue and loose connective tissue with numerous blood vessels, serving to attach skin to underlying structures and providing cushioning, insulation, and lipid storage.

Page 2: Accessory Organs

Hair and Hair Follicles

  • Hair is present except on palms, soles, and certain regions. Hair follicles are epithelial sheaths extending from the epidermis into the dermis.

  • Arrector Pili Muscle: Smooth muscle that can elevate hair.

  • Hair Structure:

    • Hair Shaft: Visible, non-living part.

    • Hair Root: Non-living part within the follicle.

    • Hair Bulb: Enlarged base of the hair composed of living cells.

    • Dermal Papilla: Supplies nourishment to the hair bulb.

    • Hair Matrix: Active area where cell division occurs for hair growth.

Nails

  • Composed of keratinized structures emerging from the stratum corneum.

  • Nail Structure:

    • Nail Plate: Hard portion.

    • Nail Root: Extends under the skin.

    • Nail Body: Visible portion.

    • Free Border: Extends beyond the fingertip.

    • Nail Bed: Epidermis under the nail.

    • Nail Matrix: Growth region at the nail's proximal end.

  • Lunule: White crescent at the proximal end, indicates nail matrix position.

  • Cuticle (Eponychium): Skin covering the proximal nail body.

Glands in Skin

  • Sebaceous Glands: Produce oily sebum through ducts into hair follicles to lubricate skin.

  • Sweat Glands:

    • Eccrine Glands: Widespread and active from birth; help cool the body by sweat secretion.

    • Apocrine Glands: Larger glands in specific areas (e.g., axillary); activated at puberty and contribute to pheromone signaling.

Sensory Receptors

  • Tactile Corpuscles: Located in the papillary layer for light touch and texture awareness.

  • Lamellar Corpuscles: Found in the reticular layer and detect pressure, itch, tickle, and vibration.

Page 3: Structure of Skin (Images)

  • Image (a): Section of thin skin showing hair structures.

  • Image (b): Enlarged view of hair bulb structures including hair matrix, dermal papilla, and hair bulb components.

Page 4: Layers of Skin (Images)

  • Image (a): Layers of the epidermis under magnification.

  • Image (b): Displays epidermal layers alongside dermis and subcutaneous tissue.

Page 5: Exercise 7.3 - Examining Nails

  • Nail growth is similar to the epidermis, where new cells push older cells upward, leading to keratinization.

    1. Labeling Exercise: Use provided terms to label the nail anatomy in Figure 7.5.

    2. Identification Exercise: Locate listed nail structures on yourself or a partner.

Page 6: Labeling Skin Structures

  • Interactive labeling of various skin structures including glands and sensory receptors in a skin model.