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THE INTEGUMENTARY SYSTEM

Gross Anatomy of the skin, hair, glands and nails

The Integumentary system includes the skin and the associated accessory structures hair, glands and nails. Note that the skin is a type of membrane, which can be referred to as the cutaneous membrane. Ask yourself, what is a membrane? When examining models, drawings or slides of the skin, keep in mind that the epithelial tissue is superficial and connective tissue is deep to the epithelium. Review the characteristics of epithelial and connective tissues and see that they apply when examining the skin. Examine the accessory structures of the skin (hair, glands, nail) remembering that they are all derived from epithelial tissue but originate in the dermis portion of the skin.

SKIN - The Cutaneous Membrane

A. Epidermis - keratinized stratified squamous epithelium. There are 5 Layers called strata.

Stratum Basale (Germinativum) - single row of cells that make the deepest layer (attached to c.t.) that are about 80 to 90% keratinocytes and 10 to 20% melanocytes. These cells have mitotic potential.

Stratum Spinosum - several cell layers thick. Mostly spindly keratinocytes and scattered Langerhans cells for immunological protection.

Stratum Granulosum - from 3 to 5 layers of flattened keratinocytes containing darkly staining keratohyaline and lamellated granules, waterproofing hydrophobic substances.

Stratum Lucidum - a thin translucent band of a few cells, found in thick skin (palms and soles) only. These cells are dead, as they are too far away from the capillaries in the underlying c.t.

Stratum Corneum - the most superficial (external) layer of the epidermis, it is many cell layers thick and is cornified (horn like).

Cells of the Epidermis:

1) Keratinocytes

2) Melanocytes

3) Merkel cells

4) Langerhans cells

B. Dermis - dense irregular connective tissue and areolar connective tissue.

Papillary Layer (~ top1/5 of Dermis). Composed mostly of areolar c.t.

dermal papillae

fibroblasts

Reticular Layer (~ bottom 4/5 of Dermis). Composed mostly of dense irregular c.t.

blood vessels – filled with RBCs

bundles of collagen fibers (crisscrossing)

fibroblasts

Cells of the Dermis:

Fibroblasts

Adipocytes

Macrophages (fixed, wandering)

Mast cells

Leukocytes

Nerve cells: Meissner's (tactile) corpuscles and Pacinian (lamellated) corpuscles.

C. Hypodermis - subcutaneous layer (is also called superficial fascia).

loose connective tissue

adipose tissue

blood vessels

Accessory Structures of the Skin

1. Hair Follicle & Hair: Cortex & medulla; hair root, bulb; papilla; root sheath (external & internal).

2. Arrector Pili: Smooth muscle attached to hair to make it stand upright, as in "goose bumps".

3. Exocrine Glands: Made from glandular epithelium, they secrete their products onto surfaces or into body cavities through ducts (except the goblet cell).

A. Sebaceous gland - secretes sebum (oil) and is usually associated with hair follicles.

B. Sudoriferous glands (sweat glands). There are 2 types 1) Merocrine and 2) Apocrine.

1) Merocrine (eccrine) sweat glands - secrete thin, watery sweat for thermoregulation

(lysozyme). Most abundant in the body; highest density on palms, soles and forehead.

2) Apocrine sweat glands - in axillary and other regions of the skin, associated with hair

follicle. Secrete thicker, more viscous, lipid rich ‘sweat’ at specific regions of body.

a) Ceruminous - modified apocrine sweat gland secretes cerumen (wax) in external ear

canal. Contains antimicrobial agents to prevent colonization by microbes of canal.

b) Mammary glands - modified apocrine sweat gland in breast tissue.

4. Finger Nail: Free edge; nail bed; nail body; nail root; lunula; eponychium (cuticle); hyponychium.

5. Mechanoreceptors: For the detection of pressure and touch.

Meissner's (tactile) corpuscles in papillary layer of dermis.

Pacinian (lamellated) corpuscle in reticular layer of dermis.