Chapter 5

List the functions of the skin and relate them to its structure.

• Thick vs Thin Skin

  • Thin skin 

    • Covers most of the body

    • Hair, has both sebaceous oil glands and sweat glands

  • Thick skin

    • Palms of hands, front of fingers, soles of feet, bottom of toes

    • Hairless, no sebaceous oil glands; has sweat glands

    • Adaptive for high friction

• Functions of skin

  • Resistance to trauma and infection

  • Water retention

  • Synthesis of vitamin D

  • Sensation

  • Thermoregulation

  • Nonverbal communication

Describe the histological structure of the epidermis, dermis, and subcutaneous tissue.

• Epidermis:

  • Stratum basale

    • Only one cell thick - touches basement membrane

    • Varied cell types present here

    • This layer is sometimes called the stratum germinativum to indicate its role in the formation of new cells

    • When this layer of the epidermis is destroyed, new skin cannot regenerate

  • Stratum spinosum

    • AKA “prickle” cells

    • Several layers of cells; often thickest layer of epidermis

    • Cells begin to actively synthesize keratin which builds up in the cells

  • Stratum granulosum

    • As cells move through this layer, keratin is replacing their nuclei and organelles causing cell death

  • Stratum lucidum

    • Only in thick skin

    • Composed a few layers of dead, flattened, translucent keratinocytes

  • Stratum corneum 

    • Lamellar granules in this layer make it water repellant

    • These dead cells are shed constantly and being replaced by the process described prior

• Dermis

  • Papillary layer

    • Superficial, thin layer

    • Areolar connective tissue

    • Rich in blood vessels

  • Reticular layer

    • Deep, thick layer

    • Dense irregular connective tissue

    • Striae (stretch marks): stretching of the dermal collagen

• Hypodermis

  • Not a layer of the skin!

  • Located below the dermis

  • Contains adipose (subcutaneous fat) and areolar tissue

  • Functions

    • Energy storage

    • Thermal insulation

    • Connection to deeper tissue

Describe the normal and pathological colors that the skin can have and explain their causes.

• Melanin: produced by melanocytes

• Eumelanin: brownish black

• Pheomelanin: reddish yellow

• Across individuals, skin tones vary due to type and distribution of melanin (not number of melanocytes)

• Hemoglobin: red pigment of blood

• Carotene

  • Yellow orange

  • Concentrates in stratum corneum

• Diagnostic Skin Colors

  • Cyanosis - blueness; lack of oxygen

  • Erythema - redness; increased blood flow

  • Pallor - pale or ashen; reduced blood flow

  • Albinism - no pigment/white; genetic lack of melanin

  • Jaundice - yellow; liver and bilirubin

  • Hematoma - bruise/multiple colors

Describe the common markings of the skin.

• Friction ridges of fingertips 

• Aid in sensitivity to texture and ability to grasp

• Cause fingerprint pattern

• Flexion lines (creases)

• Where skin near joint attaches to deeper tissue

• Freckles

• Flat, melanized patches

• Vary with heredity and UV exposure

• Mole (nevus)

• Elevated patch of melanized skin

• Beauty marks

Distinguish between three types of hair.

• Downy hair (lanugo)

  • fine downy, unpigmented hair of the fetus

• Veullus hair

  • Fine unpigmented

  • 2/3rds hair of women

  • 1/10th hair of men

  • All hair of children except eyebrows, eyelashes, and scalp

• Terminal

  • Coarse, pigmented

  • Eyebrows, eyelashes, and scalp

  • After puberty

Describe the histology of a hair and its follicle.

• 3 zones along length of hair

  • Bulb

    • Swelling at base where hair originated in dermis

    • Dermal papilla - provides nutrition

    • Hair matrix - hair growth center (mitosis)

  • Root

    • Remainder of hair within follicle

    • Dead tissue

  • Shaft

    • Portion above the skin’s surface

    • Dead tissue

    • 3 concentric layers to a hair

• Medulla

  • Internal layer

  • Loosely arranged cells and air spaces

• Cortex

  • Bulk of hair

  • Several layers of long cells

• Cuticle

  • Outer layer

  • Overlapping scaly cells

• Hair follicle

  • Diagonal tube extending in dermis or as deep as hypodermis

  • 2 layers

    • Epithelial root sheath (inner layer)

    • Connective tissue root sheath (derived from dermis)

  • Hair receptors

    • Nerve fibers that respond to hair’s movement

  • Arrector muscle (arrector pili)

    • Smooth muscle that causes “goose bumps”

Discuss some theories of the purposes served by various kinds of hair.

• Anagen (growth, multiplication of cells, early and mature phases)

• Catagen (degenerative phase, club hair forms)

• Telogen (rest phase and hair loss)

Describe the structure and function of nails.

• Derivative of the stratum corneum

• Composed of very thin, dead, scaly cells with parallel rows of keratin

• Primates have flat nails, as opposed to claws, for easier manipulation

• Nail plate

  • Free edge

  • Nail body

  • Nail root

• Nail fold 

  • Nail groove

• Nail bed

  • Hyponychium (secures nail to nail bed)

  • Nail matrix 

  • Lunule

  • Eponychium (cuticle)

Name two types of sweat glands and describe the structure and function of each.

• Eccrine (merocrine) glands

  • Numerous widespread, and especially abundant on palms, soles, and forehead

  • Simple ducts lead to pores at skin surface of epidermis

  • Produce watery (plus salt) perspiration to cool body

  • Also contains some wastes found in urine

• Apocrine glands

  • Found in groin, anal region, axilla, areola and beard

  • Ducts open into hair follicle

  • Produce sweat with many fat molecules

  • Bacterial metabolism of fats causes odor

  • Respond to stress and sexual stimulation

  • Develop in puberty

  • Believed to secrete pheromones

Describe the location, structure, and function of sebaceous and ceruminous glands.

• Sebaceous glands

  • Produce oily secretion called sebum

  • Usually open into hair follicle

  • Keep skin and hair from becoming brittle

• Ceruminous Glands

  • Found in auditory canal

  • Secrete cerumen (aka earwax)

  • Combination of sebum and dead skin cells

  • Keeps eardrum pliable, waterproofs canal, kills bacteria, and coats guard hairs

Discuss the distinction between breasts and mammary glands, and explain their respective functions.

• Mammary Glands

  • Produce human milk in the breast tissue of females

  • Glands develop during pregnancy and lactation, otherwise are very small and nonfunctional

• Breasts do not equal functional mammary gland (males have breast tissue but no mammary glands)

Describe the three most common forms of skin cancer.

• Basal cell carcinoma

  • Most common

  • Least dangerous

  • Hardly metastasizes

  • Arises in stratum basale and invades dermis

• Squamous cell carcinoma

  • Arises from keratinocytes of stratum spinosum

  • Can metastasize to lymph nodes

  • About 20% mortality (death rate)

• Malignant melanoma

  • Most deadly, but only 5% of the cases are malignant melanoma

  • Arises from melanocytes of an existing mole

  • Metastasizes (spreads) quickly hence it being the most lethal skin cancer

Discuss the three classes of burns and the priorities in burn treatment.

• First-degree burn (partial-thickness burn)

  • Only epidermis

  • Usually localized

• Second-degree burn (partial-thickness burn)

  • Epidermis and part of dermis

  • Red, tan, or white

  • Blistered and painful

  • May damage hair follicles, nerve endings, and cutaneous glands

  • Severe sunburns and scalds

• Third-degree (full-thickness burn)

  • Epidermis and dermis are completely destroyed

  • Causes contracture (abnormal fibrosis) and disfigurement