Integument

Integument = skin and associated structures (hair, glands, nails)

Skin (epidermis + dermis) is an organ, the largest of body;

The integument (skin and associated structures) is a system: "Integumentary System."

Key protein is keratin which is specialized for protection --

found in skin and skin derivatives such as hair, feathers and nails.

Layers of the Integument: Epidermis, Dermis, Hypodermis (Subcutaneous)

Skin can be non-keratinized, e.g., internal linings such as oral mucosa

Or skin can be keratinized, e.g., external surfaces

Epidermis:

30-50 cell-thick layer. Outermost layers are dead, keratinized cells.

Avascular. Protective. Specializations include hair shafts and nails.

4-5 Zones or "Strata," depending on location.

1) Stratum basale: single row of cells; melanocytes present; mitosis.

2) S. spinosum: multiple layer; mitotic.

3) S. granulosum: granular layer, Keratinization begins.

4) S. lucidum: clear, 1 cell thick layer--only on palms and soles of feet.

5) S. corneum: outermost, fully keratinized or cornified layer.

S. basale + S. spinosum = S. germinativum (constantly dividing cells)

Melanocytes = melanin containing cells.

In S. basale. Melanin is a protective pigment--absorbs ultraviolet radiation.

Tyrosine (amino acid) ----tyrosinase------> melanin

Pigmentation determined by:

Dermis:

Vascular. Serves as blood supply for epidermis.

A bruise is the result of damaged vessels in dermis.

Elastic. Has collagen, elastin and reticular fibers.

Sensory. Has receptors for pain, temperature and pressure.

Effectors. Glands and small muscles (for blood vessels, arrector pili, and arector pili with follicle).

2 layers of Dermis:

• Papillary. Outermost zone, basis of friction ridges.
• Reticular: Inner layer. Dense array of fibers--can be stretched considerably.

Stretch marks (striae): from over-stretching of dermis and tearing of fibers.

Damage can be influenced by hormones (e.g., in pregnancy, steroids) in addition to generally elasticity of skin (age-related).

Langer's lines (aka lines of cleavage or tension lines) have surgical implications.

Hypodermis or Subcutaneous layer:

Loose fibrous connective tissue. Connects dermis to underlying muscles or bone. Site of adipose tissue which is used for insulation and storage. Deposition of fat is influenced by hormones (male Vs. female pattern).

Functions of Integument:

1) Protective: Inhibits microorganisms (physical and physiological barriers). Immune cells present. Langerhans Anti-Bacterial actions (physical and chemical) Absorbs UV radiation which damages DNA (melanocytes) Waterproof

2) Nutrition: Source of Vitamin D. UV light is necessary for its formation.

Converts 7-dehydrocholesterol into vitamin D3.

Vitamin D is necessary for calcium absorption from intestine. Deficiency results in weakened bones -- rickets  in children, bone loss in adults (osteomalacia).

Vitamin D may reduce some cancers. Epidemiologic studies suggest that vitamin D from fish oils and from sun exposure reduces the rate of colon and breast cancer.

3) Temperature Regulation: Dilation and constriction of blood vessels dissipates or retains heat.

Sweat is a way of dissipating body heat and serves to cool body (evaporative cooling).

4) Sensory: Free nerve endings or specialized receptors

E.g., Meissner's corpuscles and Pacinian corpuscles

Communicates environmental information.

5) Communication: Facial expressions and scents. Pheromones.

Burns:

1st Degree -- epidermis only

2nd Degree -- epidermis and superficial dermis. Blistering.

3rd Degree -- Full thickness destruction. Loss of sensation.

Risks from Burns

Rule of 9's for estimating extent of burns.

Skin Cancer:

Basal cell carcinoma or epithelioma

Squamous cell carcinoma (S. spinosum)

Malignant melanoma.)It is the most dangerous because of its greater tendency to spread (metastasize)

ABCD rule for recognizing melanoma

Epidermal Derivatives:

Hair: Characteristic of mammals. Protective (physical & temp. regulation).

Structure of Hair: Outside cuticle; middle cortex and inside medulla.

Cortex has pigments which give hair its color.

Two types of hairs: Vellus and Termimal. They differ in length and structure.

Hair growth is cyclic and has three phases:

1) anagen - active growth

2) catagen - resting stage

3) telogen - hair stops growing and is shed.

Movement of hairs by arrector pili -- under control of sympathetic nervous system (fight or flight system).

For temperature regulation and behavior.

Hair loss (Alopecia) - from multiple factors.

Male pattern baldness - genetic and requires testosterone (DHT)  for expression.

Common treatments are topical minoxidil (Rogaine) and Propecia.

Nails: Protective and used for grasping.

Specialized S. corneum -- same as claws and hooves--keratinized cells. Keratin is of "hard" variety.

Glands: developmentally originate in epidermis but based in dermis (for support, nutrition and control).

Sebaceous glands: associated with hair follicles. Secrete sebum, a lubricating fluid. Inflammation results in acne.

Sudoriferous glands: Sweat glands

Eccrine sweat glands -- for cooling. (Mammary glands are specialized eccrine glands)

Apocrine sweat glands -- odoriferous. Pheromones

Ceruminous: in ear canal, secretes earwax or cerumen. Inhibits parasites.

Effects of Aging on Skin

Aging has a number of effects on the integument. Skin thickness, melanocyte number, vascular supply, and gland activity decrease.

The Skin and Diabetes

Neuropathy and poor peripheral circulation make diabetes prone to skin ulcers, especially in the hands and feet.

Miscellaneous clinical conditions

Decubitus ulcers

Erythema multiforme

Seborrheic dermatitis: inflammation around abnormally active sebaceous glands:

Furuncle or boil

Herpes zoster - Shingles

Impetigo - bacterial

Nevus - aka: mole Vitiligo

Warts