Skin, Scalp, and Bone Histology

Epidermis

Outer avascular layer made of keratinized stratified squamous epithelium.

Stratum corneum

Top layer of the epidermis made of dead, keratin-filled cells.

Stratum basale

Bottom layer of the epidermis containing living stem cells and melanocytes.

Dermis

Middle skin layer composed of connective tissue divided into two layers.

Papillary layer

Upper dermis made of areolar connective tissue; forms dermal papillae and fingerprints.

Reticular layer

Deep dermis made of dense irregular connective tissue providing structural strength.

Hypodermis

Under-skin layer composed of adipose tissue providing insulation and padding.

Sebaceous gland

Dermis gland that secretes oil (sebum) into hair follicles.

Arrector pili

Smooth muscle attached to hair follicles that causes goosebumps.

Sudoriferous (sweat) gland

Gland located in the dermis/hypodermis that releases watery sweat to the surface.

Osteon

The cylindrical unit of compact bone that appears as a target on models.

Osteocyte

Mature bone cell living in a lacuna that maintains the matrix.

Haversian (central) canal

Canal in the middle of an osteon carrying vessels and nerves lengthwise.

Volkmann (perforating) canal

Sideways canal linking Haversian canals to each other and the periosteum.

Periosteum

Tough membrane wrapping bone involved in growth, repair, and attachment.

Sharpey's fibers

Collagen pegs extending from the periosteum into bone to anchor it.

Spongy bone

Bone structure with trabeculae and marrow spaces (no osteons) for lightweight support.

Thin vs. thick skin (Scalp)

Scalp is thin (hairy) skin containing visible hair follicles and sebaceous glands.

Ground bone slide view

Microscopic view where an osteon appears as a bullseye.