Accessory Structures Of The Skin

Hair

Keratinous filament growing out of the epidermis.

Primarily dead keratinized cells.

Hair Follicle

Originating point for strands of hair in an epidermal penetration of the dermis ; where the hair grows.

Hair Shaft

Part of hair not anchored to the follicle, exposed at the skins surface.

Hair Root

Hair anchored in the follicle, lies below the surface of the skin.

Hair Bulb

Deep in the dermis, where the hair root ends; enlarged base of the follicle.

Hair Matrix

Mitotically active basal cell layer that produces new hair.

Hair Papilla

Made of connective tissue, contains blood capillaries and nerve ends from the dermis; surrounded by the hair bulb.

Medulla

Forms the central core of the hair, which is surrounded by the cortex.

Cortex

Compressed keratinized cell layer covered by hard keratinized cells called the cuticle.

Hair texture

Determined by shape & structure of the cortex, and to the extent of presence, the medulla. The cortex and medulla shape & structure are determined by the shape of the hair follicle.

Walls of the hair follicle

• 3 concentric layers of cells (share common axis or center)

• Internal Root Sheath - Surrounds the root of the growing hair and extends just up to the hair shaft.

• External Root Sheath - An extension of the epidermis, encloses the hair root, made of basal cells at the base of the hair root.

• Glassy Membrane - Thick, clear connective tissue sheath covering the hair root, connecting it to the tissue of the dermis.

Arrector Pili Muscle

Smooth muscle each hair root connects to that contracts in response to nerve signals from the sympathetic nervous system, making external hair shaft “stand up”.

• Primary purpose of trapping air to add insulation.

Hair Growth - 3 Phases

1. Anagen: Cells divide rapidly at hair root, pushing hair shaft out (2-7 years)

2. Catagen: Transition from hair follicles active growth (About 2-3 weeks)

3. Telogen: Hair follicle is at a rest and no new growth happens (2-4 months)

• Hair grows about 0.3mm/day in anagen.

• About 50 hairs are lost+replaced/day.

Nails

Specialized structure of the epidermis found at the tips of finger & toes.

Nail body

• Formed on the nail bed

• Protects tips of our fingers and toes, our farthest extremities that receive the most mechanical stress

• Forms back-support for picking up small objects with fingers

  • Composed of densely packed dead keratinocytes

Nail Root

Has matrix of proliferating cells from stratum basale that enabled nails to grow continuously.

Nail Fold

Lateral fold that overlaps the nail on the sides, helping anchor the nail body.

Nail cuticle

Formed from the nail fold that reaches the proximal end of the nail body; also called the eponychium.

Nail Bed

• Rich in blood vessels

  • Epithelium over the nail matrix forms a crescent, white shaped region called lunula.

Hyponychium

Area beneath free edge of nail; consists of thickened layer of stratum corneum.

Sudoriferous Glands

Produces sweat to cool the body when the body gets warm.

• Glands develop from epidermal projections into the dermis and are classified as merocrine glands.

Merocrine Glands

Secretions by exocytosis through a duct without affecting the cells of that gland.

Eccrine Sweat Gland

• Produces hypotonic sweat for thermoregulation.

• Lie deep in dermis

• Duct rises to surface

Apocrine Sweat Gland

• Associated with hair follicles in densely hairy places likes pits or genitals

• Larger than eccrine and deeper in dermis

• Thicker sweat, smell, bacterial decomp

• Duct normally empties into hair follicle

• Falls under nervous + hormonal control

Sebaceous Gland

Oil gland all over that helps lubricate and waterproof skin and hair

• Largely inactive during puberty

Sebum

Generated by sebaceous glands; a mix of lipids that lubricate skin and hair, reduces water loss, protects skin, and keeps stratum corneum pliable. Stimulated by hormones.