Anatomy and Phisiology Unit 3

Organ definition

Two or more kinds of tissues grouped together performing specialized functions.

Integumentary system

Covers the body; includes skin and accessory tissues (nails, hair, sweat glands, sebaceous glands). Functions as a barrier and indicator of health.

Dermatology

The study of skin.

Skin

Largest organ of the body, about 1/6 of body weight, covering ~20 sq ft in adults.

Layers of skin

Epidermis, Dermis, Subcutaneous (hypodermis).

Functions of skin

Protection, homeostasis, retards water loss, regulates temperature, houses receptors, immune cells, synthesizes chemicals, excretes waste, helps produce Vitamin D.

Keratinocytes

Cells producing keratin and substances stimulating white blood cell development.

Skin pH role

Normal acidic pH protects from pathogens, supports microbiota, aids wound healing, maintains barrier integrity.

Factors disturbing skin acidity

Harsh soaps, excessive washing, aging, diet/systemic disease, environment, medications, infections.

Diseases with increased skin pH

Eczema, dermatitis, dry skin, diabetes, chronic renal failure, cardiovascular disease.

Epidermis

Keratinized stratified squamous epithelium; 5 strata: basale, spinosum, granulosum, lucidum, corneum.

Stratum basale

Deepest layer; single row cuboidal/columnar cells; keratinocytes, melanocytes, tactile cells.

Keratinocytes

Stem cells producing keratin; regenerate new cells.

Melanocytes

Produce melanin in response to UV; transfer pigment to keratinocytes to shield DNA.

Tactile (Merkel) cells

Few in number; sensitive to touch; stimulate sensory nerves when compressed.

Stratum spinosum

Several layers of keratinocytes; connected by desmosomes; contains Langerhans cells for immunity.

Stratum granulosum

3-5 layers keratinocytes; keratinization begins, cells die and flatten.

Stratum lucidum

2-3 translucent layers; only in thick skin of palms/soles; cells contain eleidin.

Stratum corneum

20-30 layers dead keratinized cells; protective barrier.

Thick vs Thin skin

Thick skin has all 5 layers (palms, soles, no hair/sebaceous glands). Thin skin lacks lucidum, covers rest of body.

Hemoglobin

Oxygen-binding protein in blood; gives skin red tint.

Melanin

Pigment produced by melanocytes; eumelanin (brown/black), pheomelanin (tan/red).

Carotene

Yellow-orange pigment from vegetables; builds up in stratum corneum and fat.

Albinism

Inherited condition with no melanin production.

Nevus

Mole; localized melanocyte overgrowth.

Freckles

Localized spots of increased melanocyte activity.

Hemangiomas

Benign blood vessel tumors causing skin discoloration.

Friction ridges

Dermis/epidermis folds; fingerprints.

Dermis

Below epidermis; dense irregular connective tissue; contains blood vessels, hair follicles, glands, sensory receptors.

Papillary layer

Superficial dermis; areolar CT; dermal papillae interlock with epidermis.

Reticular layer

Deeper dermis; dense irregular CT; cleavage lines present.

Lines of cleavage

Collagen bundles alignment; important for surgical healing.

Stretch marks

Collagen fiber tears due to overstretching (pregnancy, weight gain).

Tattoo

Ink injected into dermis; permanent unless removed by lasers.

Subcutaneous layer

Hypodermis; areolar + adipose tissue; insulation, energy storage, drug injection site.

Protection

Protects against injury, microbes, UV, harmful substances.

Water regulation

Prevents excessive water loss/gain; epidermis water-resistant.

Vitamin D synthesis

Skin makes Vitamin D3, converted to calcitriol for calcium absorption.

Secretion

Sweat and sebum excretion.

Absorption

Selectively permeable; allows some drugs via transdermal patches.

Immune function

Epidermal dendritic cells trigger immune response.

Temperature regulation

Vasoconstriction conserves heat; vasodilation releases heat.

Sensory reception

Receptors for touch, pressure, pain, temperature.

Nail plate

Composed of nail root, nail body, free edge.

Nail bed

Living epidermis covered by nail body.

Lunula

Whitish semilunar region at nail base.

Nail matrix

Growth zone at nail base; produces new cells.

Cuticle (eponychium)

Band of epidermis covering nail margin.

Hyponychium

Thickened stratum corneum under free edge.

Hair

Keratinized filament growing from follicle; functions in protection, sensory reception, heat retention.

Lanugo hair

Fine, unpigmented hair on fetus.

Vellus hair

Fine hair covering most of body.

Terminal hair

Coarse, pigmented hair (scalp, brows, lashes, beards, axillae, pubic).

Hair bulb

Swelling at hair base, contains living cells and papilla.

Hair root

Extends from bulb to surface; embedded portion.

Hair shaft

Portion projecting beyond skin.

Hair matrix

Growth zone where cells divide to produce new hair.

Medulla

Core with soft keratin.

Cortex

Hard keratin around medulla.

Cuticle

Outer protective single-cell layer.

Hair follicle

Oblique tube in dermis; epithelial and connective tissue sheaths.

Arrector pili

Smooth muscle attaching follicle to dermis; causes goosebumps.

Hair functions

Protection, heat retention, sensation, identification.

Hair color

Due to melanin; grays with age, turns white when melanin stops.

Hair growth cycle

Anagen (growth), Catagen (regression), Telogen (rest/shedding).

Alopecia areata

Autoimmune hair loss in patches.

Diffuse hair loss

General thinning due to hormones, drugs, nutrition.

Hirsutism

Excessive hair growth.

Male pattern baldness

Genetic/hormonal hair loss from scalp crown.

Sweat glands

Eccrine (merocrine) and apocrine; coiled glands with ducts.

Merocrine glands

Most numerous; watery sweat; thermoregulation.

Apocrine glands

Axillae, groin, nipples; thicker sweat; bacteria cause odor; active at puberty.

Sebaceous glands

Secrete oily sebum into hair follicles; lubricates, antibacterial; stimulated at puberty.

Ceruminous glands

External ear canal; produce cerumen (earwax).

Mammary glands

Modified apocrine glands; produce milk in females.

Normal body temp

37°C (98.6°F); regulated by hypothalamus.

Hyperthermia

Abnormally high body temperature.

Hypothermia

Abnormally low body temperature.

Heat loss

Radiation, conduction, convection, evaporation.

Regeneration

Replacement with same cell type; restores function.

Fibrosis

Scar tissue replaces damaged tissue; function not restored.

Wound healing steps

1. Bleeding/clotting, 2. Inflammation/leukocytes clean wound, 3. Granulation tissue forms, 4. Regeneration and fibrosis.

Psoriasis

Autoimmune; rapid keratinocyte growth; scaly patches; treated with steroids/UV/meds.

First-degree burn

Epidermis only; redness, pain.

Second-degree burn

Epidermis + part dermis; blisters, pain, slight scarring.

Third-degree burn

Full-thickness; epidermis, dermis, subcutaneous; severe scarring; needs grafts.

Rule of Nines

Method to estimate % body surface burned.

Integument development

Week 7: ectoderm forms epidermis; week 21: stratum corneum, friction ridges; week 32: nails; week 20: sweat/sebaceous glands.

Aging skin

Thinner epidermis/dermis, less collagen, reduced glands, less melanin, wrinkles, impaired healing, less Vitamin D activation.

Botox

Botulinum toxin type A; blocks nerve signals to muscles; reduces wrinkles temporarily.

Granulation tissue

Vascular CT forming in wound during healing.

UV rays and aging

UV damages DNA, accelerates aging, promotes cancer.