Chapter 5

Objectives:

• Name the tissue types composing the epidermis and dermis. List the major layers of each and describe the functions of each layer.

• Describe the structure and function of the hypodermis.

• Describe the factors that contribute to skin color.

• Describe the structure and function of accessory organs including hair follicles, sweat glands, sebaceous glands, nerve endings and nails.

• Differentiate between first, second and third degree burns and be able to approximate surface area involved.

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Describe the origin and warning signs of skin cancers, especially melanoma.

Link the injection sites (intradermal, subcutaneous, intramuscular, intravenous) with the

correct anatomical locations

I. Overview

A. Composition

1. Skin (integument)

2. Skin derivatives (appendages)

1. Sweat (sudoriferous) glands

2. Sebaceous (oil) glands

3. Hairs and hair follicles

4. Nails

B. Skin functions

1. Protection

1. The skin constitutes at least three types of barriers: chemical, physical, and biological

2. Protects deeper tissue from:

i. Mechanical damage ii. Chemical damage iii. Bacterial damage iv. Thermal damage

v. Ultraviolet radiation

Vi. Desiccation

1. Body temperature regulation

2. Cutaneous sensation

3. Metabolic functions (synthesizes vitamin D precursor, etc.)5. Blood reservoir

   a. Can hold ~ 5% of body's total blood volume, which can then be shunted into general circulation for use by vigorously working muscles

   and/or other body organs

   6. Excretion

   a. Elimination of nitrogen-containing wastes (ammonia, urea, uric acid,

   NaCl, H20, etc.

   II. Skin Structure

   A. Epidermis (5 strata)

   1. Stratified squamous epithelium with keratin

   2. Cells tightly connected together by desmososmes

   3. Keratinocytes form several layers

   4. Layers of the epidermis

   a. Stratum basale

   i. Single row of cells that serve as origin of keratinocytes for all superficial strata

   ii. High mitotic activity ili. Contains melanocytes

   1. Accounts for ~10-25% of stratum basale cells

   2. Stratum spinosum

   3. Stratum granulosum

   4. Stratum lucidum

   5. Stratum corneum

   i. 20-30 cell layers thick and accounts for three-quarters of epidermal thickness

   ii. Located at exposed surface of skin

   iii. Protective barrier of dead, durable, and expendable cells

   a. Cells are filled with keratin (literally keratin filled plasma membranes)

   i. Helps give epidermis its protective properties, etc.

   b. Thickness will vary depending on use

   i. Calluses can develop on palms of hands and soles

4. iv. Glycolipids secreted between cells provides waterproofing and preserves some permeability characteristics of the skin

   a. Allows for transdermal medications (nicotine patches, etc.)

   4. Melanin

   1. Pigment produced by melanocytes

   2. Gets packaged in melanosomes and then deposited into the keratinocytes in more superficial layers

   3. Melanin granules then position themselves on superficial (or sunny) side of keratinocyte nucleus to protect against UV radiation

   4. Amount produced depends on genetics and exposure to sunlight

   i. Cell production of tyrosinase (acts on the amino acid tyrosine) is critical for melanin production

   ii. Albinism - failure to produce tyrosinase is the most common form

   1. Strong, flexible connective tissue

   2. Two layers

   a. Papillary layer

   i. Thin, superficial layer of areolar connective tissue ii. Supports and nourishes overlying epidermis iii. Projections called dermal papillae

   a. TSA and serves as basis for friction ridges and fingerprints

   iv. Pain receptors

   v. Capillary loops

   b. Reticular layer

   i. Accounts for ~80% of dermis thickness

   ii. Dense irregular connective tissue with meshwork of collagen and elastic fibers iii. Blood vessels iv. Glands

   v. Nerve receptors

5. Hypodermis (subcutaneous)

   1. Technically not part of the skin

   2. Anchors skin to underlying organs

   3. Composed mostly of adipose tissue (accounts for half of the body's stored fat)

   III. Appendages of the Skin

   A. Sebaceous glands

   1. Produce oil (sebum)

   a. Softens and lubricates the hair and skin

   1. Most with ducts that empty into hair follicles

   2. Distributed body wide except for palms of hands and soles of feet

   3. Glands are activated at puberty (under hormonal control)

   a. Clinical: Acne

   i. Accutane is teratogenic

   B. Sweat (sudoriferous) glands

   1. Widely distributed in skin (up to 3 million body wide)

   2. Two types

   a. Eccrine

   i. Coiled, tubular portion in dermis with opening via duct to pore on skin surface

   ii. Distributed body wide (most numerous)

   iii. Helps dissipate excess heat through evaporative cooling

   b. Apocrine

   i. Ducts empty into hair follicles

   ii. Localized to axillary and pubic (anogenital) areas

   a. Only ~ 2000 in number

   iii. Activated by stress, pain, & sexual excitement; not temp. iv. Fatty acid and protein secretion

   a. Bacteria breakdown produces body odor

   3. Modified sweat glands

   a, Ceruminous glands

   i, Found in lining of external ear canal

   ii, Secretion mixes with sebum to produce cerumen or carwax

   b. Mammary glands (discussed in the reproductive chapter)

6. Hair

   1. Distributed body wide except for palms, soles, lips, nipples, and part of external genitalia

   2. Strand of dead, hard keratinized epithelial cells projecting from an invaginated tunnel in the epidermal and dermal layers called the hair follicle

   3. Hair follicle

   1. Tubular invaginations of the epidermis

   2. Formed by mitotically active stratum basale cells

   3. Melanocytes provide pigment for hair color

   c. Dermal capillaries provide blood supply

   4. Parts:

   1. Bulb - growth zone at inferior end of hair follicle

   2. Root - part of the hair enclosed in hair follicle

   3. Shaft - visible part of hair; projects from surface of skin

   1. Arrector pili (smooth muscle)

   2. Clinical: Minoxidil (Rogaine)

   D. Nails

   1. Nail structures

   1. Nail fold (lateral and proximal skin coverings)

   2. Eponychium (cuticle)

   3. Nail body

   i. Sheet of hard keratin attached to nail bed

   ii. Lanula - crescent shaped vascular area at proximal end of the nail bed and visible through the nail. Used for visual check of oxygen status in patients

   2. Clinical: Eponychiitis, ingrown toenail

   IV. Clinical Applications

   A. Injection Sites

   1. Intradermal (ID)

   2. Subcutaneous ("subcue" or SQ)

   3. Intramuscular (IM)

   4. Intravenous (IV)

   B. Blisters

   1. Fluid-filled pocket between epidermis and dermisC. Lines of Cleavage

   1. Formed by uniform alignment of collagen and elastic fibers

   1. Stretch marks

   2. Decubitus ulcers or "bed sores"

   1. Blood supply restricted → ischemia (O2 reduced) → necrosis (tissue death)

   2. Bacterial infections result, difficult to heal, secondary intention

   3. Areas of highest risk are least padded (elbow, heels, backbone)

   4. Patients of high risk: elderly (less body fat for padding) in care homes

   5. Importance of rotating patient positions, artificial padding and clean bedding

   F. Burns

   1. Tissue damage inflicted by heat, electricity, UV radiation, or chemicals that denature proteins and cause cell death in affected areas

   2. Associated dangers

   a. Catastrophic loss of body fluids that can lead to:

   i. Dehydration ii. Electrolyte imbalance iii. Renal failure iv. Circulatory shock

   b. Infection

   i. Sepsis (widespread bacterial infection) is leading cause of death in burn victims

   3. Rule of Nines

   1. Way to approximate the extent of burns

   2. Special tables are used when greater accuracy is desired

   4. Severity of burns a, 1s degree

   i. Only epidermis is damaged ii. Redness, pain, and swelling (inflammation) ili. Usually heals 2-3 days

   b. 2 degree

   i, Damage to epidermis and dermis

   ii. Same symptoms as 1" degree (redness, pain, and inflammation), but also blistering ili, Usually requires 3-4 weeks to healc. 3гd degree

   i. Total tissue destruction epidermis, dermis, and even hypodermis)

   ii. Tissue becomes discolored, but no edema, pain, etc. iii. Usually requires skin graft

   G. Skin Cancer

   1. Most common type of cancer

   2. Skin cancer types

   a. Basal cell carcinoma

   i. Least malignant but most common type

   a. Accounts for ~80% of all skin cancers

   ii. Arises from stratum basale cells that then go on and invade the underlying dermis and hypodermis

   iii. Results in a shiny, dome-shaped nodule most commonly found in sun-exposed regions of the face iv. Slow growing and therefore metastasizes seldom

   v. Full cure by surgical excision in 99% of cases

   b. Squamous cell carcinoma

   i. Arises from stratum spinosum

   ii. Results in a scaly reddened papule most commonly on the head (scalp, ears, and lower lip) and hands

   iii. Tends to grow rapidly and will metastasize if not removed iv. Chance of complete cure is good if caught early and removed by surgery or radiation

   c. Malignant melanoma

   i. Most deadly of skin cancers

   a. Accounts for only ~5% of all skin cancers but 90% of skin cancer deaths due to metastasis and resistance to chemotherapy

   ii. Cancer of melanocytes

   iii. Metastasizes rapidly to lymph and blood vessels iv. Can occur body wide

   v. Most appear spontaneously, but about 1/3 from preexisting moles (wherever there is pigment)vi. Key to survival is early detection, so strongly encouraged to evaluate moles regularly using the ABCD and sometimes ABCD(E) rule

   A (asymmetry)

   B (irregular border)

   C (color)

   D (larger than 6mm in diameter...about the size of a pencil eraser)

   E (elevation above the skin surface and evolution...changes over time)