A&P ch5 pt2

Melanin

The primary determinant of skin color.

Melanocytes

Cells in the stratum basale that produce melanin.

Tyrosine

The amino acid from which melanin is derived, catalyzed by the enzyme tyrosinase.

Melanosomes

Vesicles in which melanin synthesis occurs.

Primary function of melanin

Protect keratinocyte DNA from UV radiation-induced mutations.

Transfer of melanin to keratinocytes

Melanosomes are released by melanocytes and taken into keratinocytes.

Position of melanin in keratinocytes

On the superficial side of the nucleus, like an umbrella, to shield DNA from UV damage.

Continuous production of melanin

Melanin degrades after a few days, requiring constant replenishment to maintain skin color.

Effect of UV exposure on melanin

Melanin synthesis increases, leading to tanning.

Immediate effect of UV radiation on skin pigmentation

Oxidation of existing melanin, which darkens the skin quickly.

Delayed effect of UV radiation

DNA damage in melanocytes stimulates increased melanin production (visible after ~72 hours).

Limitations of melanin

Melanin cannot absorb unlimited UV radiation; all skin types are susceptible to sunburns and skin cancer.

Secondary function of melanin

Reduces vitamin D synthesis to regulate calcium absorption and maintain homeostasis.

Geographic UV exposure and skin color evolution

High UV areas (e.g., Africa) → darker skin to prevent excess vitamin D; low UV areas (e.g., northern Europe) → lighter skin to allow adequate vitamin D synthesis.

Melanocyte concentration

All humans have the same number of melanocytes; skin tone differences come from melanin type, amount, and tyrosinase activity.

Freckles

Localized areas of increased melanin production.

Moles (nevi)

Local proliferation of melanocytes (not increased melanin synthesis).

Healthy tan

There is no such thing as a healthy tan; all tanning damages DNA and increases cancer risk.

UVA rays

UV rays associated with tanning and aging of skin.

UVB rays

UV rays associated with sunburn.

Long-term effects of tanning

Damages melanocytes and skin structures, prematurely ages skin, and increases cancer risk.

Carotene

A yellow-orange pigment from foods (egg yolks, orange vegetables) that accumulates in the stratum corneum.

Hemoglobin

An iron-containing protein in red blood cells that binds oxygen; oxidized hemoglobin gives skin a red/pink tint based on dermal blood flow.

Accessory structures of the integument

Hair, nails, and glands (all derived from epithelium).

Locations without hair

Thick skin, lips, and parts of external genitalia.

Main parts of hair

The two main parts of hair.

Shaft

Above skin, composed of dead keratinized cells.

Root

Embedded in dermis, contains living cells.

Hair papilla

A projection of blood vessels into the hair root that nourishes it.

Hair bulb

The root plus the hair papilla.

Matrix of the hair

Keratinocytes at the base of the root that actively divide to produce new hair cells.

Epithelial root sheath

From epidermis, surrounds the hair root.

Dermal root sheath

Connective tissue support surrounding the hair root.

Arrector pili muscles

Smooth muscle bands attached to hair follicles that contract to cause piloerection ('goosebumps').

Regions of a hair strand (cross-section)

Medulla (soft keratin, only in thick hair), cortex (hard keratin for strength), cuticle (outer protective layer of overlapping cells).

Stages of hair growth

Growth stage (mitosis in matrix, hair lengthens) and resting stage (mitosis stops, hair falls out and is replaced).

Types of hair

Lanugo (fetal, thin and nonpigmented), terminal hair (thick, coarse, pigmented), and vellus hair (thin, nonpigmented, found on most of body).

Hair color determination

Melanin produced in the matrix by melanocytes.

Hair color with aging

Melanocytes produce less melanin → hair turns gray or white, often with air bubbles inside.

Nails

Made of stratified squamous epithelium filled with hard keratin.

Parts of the nail plate

Nail body (visible portion) and nail root (under skin, contains nail matrix).

Nail matrix

Actively dividing cells that produce nail growth.

Cuticle (eponychium)

A fold of stratum corneum at the proximal nail edge.

Lunula

The pale, half-moon region of the proximal nail where keratin accumulates.

Primary function of nails

Protect fingertips and toes from trauma and assist in precise gripping.

Types of skin glands

Sweat (sudoriferous) glands and sebaceous glands.

Sweat gland secretion method

Merocrine secretion (via exocytosis).

Types of sweat glands

Eccrine, apocrine, ceruminous, and mammary.

Eccrine sweat glands

The most numerous sweat glands; secrete water, electrolytes, and waste directly onto the skin surface.

Apocrine sweat glands

Found in axillae, anal area, and areolae; secrete a protein-rich fluid into hair follicles that becomes odoriferous after bacterial metabolism; activated at puberty.

Ceruminous glands

Secrete cerumen (ear wax), which traps particles and lubricates the ear canal.

Mammary glands

Produce milk (a modified sweat secretion).

Sebaceous glands

Most abundant in face and scalp (absent on palms and soles); secrete sebum (waxy, oily lipid mixture) by holocrine secretion (cells rupture and release contents).

Function of sebum

To lubricate and protect the skin.

Hydrophobic barrier

Provides hydrophobic barrier, prevents water loss, and inhibits/kills bacteria.

Testosterone

Hormone that influences sebaceous gland activity; activity increases significantly after puberty.

Wound

Any disruption in the skin's integrity, including lacerations, burns, and cancers.

Burns

Wounds caused by heat, cold, electricity, chemicals, or radiation.

Classification of burns

By the extent and depth of tissue damage: first-degree, second-degree, and third-degree.

First-degree burn

Affects only the epidermis.

Symptoms of a first-degree burn

Redness (erythema) and mild pain, with no permanent damage.

Second-degree burn

Affects the epidermis and part or all of the dermis.

Symptoms of a second-degree burn

Pain, blistering, and possible scarring.

Third-degree burn

Affects the epidermis, dermis, hypodermis, and possibly deeper tissues (muscle, bone).

Pain in third-degree burns

Often not painful at first because nerve endings in the skin are destroyed.

Complications of third-degree burns

Major tissue damage, scarring, loss of hair follicles, reduced keratin production, dehydration from fluid loss, and high infection risk.

Cancer at the cellular level

Caused by mutations in DNA that cause loss of control over the cell cycle.

Metastasis

The spread of cancer cells through blood or lymphatic vessels to other tissues.

Basal cell carcinoma

The most common type of skin cancer, originating from keratinocytes in the stratum basale.

Appearance of basal cell carcinoma

A nodule with a central crater.

Metastasis of basal cell carcinoma

Rarely metastasizes and can usually be cured by surgical removal.

Squamous cell carcinoma

The second most common type of skin cancer, originating from keratinocytes in the stratum spinosum.

Appearance of squamous cell carcinoma

Scaly plaques that may ulcerate and bleed, often on the head and neck.

Metastasis of squamous cell carcinoma

More likely to metastasize than basal cell carcinoma, but can still be treated effectively with surgical removal.

Malignant melanoma

The most dangerous form of skin cancer, originating from melanocytes.

Danger of malignant melanoma

Cancerous melanocytes extend 'arms' into the dermis and spread through blood vessels, making it highly metastatic.

Treatment of malignant melanoma

Surgical removal, radiation therapy, and chemotherapy.

Prognosis factors of malignant melanoma

Tumor size, depth of dermal invasion, and whether metastasis has occurred.

ABCDE rule

Used to distinguish melanoma from other skin cancers or moles: A: Asymmetry, B: Border irregularity, C: Color variation, D: Diameter larger than 6 mm, E: Evolving.