chapter 5

Integumentary System Overview

Introduction to the integumentary system and its role as the first organ system covered in class.
Composed primarily of skin and associated accessory structures (hair, nails, sweat glands, oil glands).

Skin: Largest organ by surface area and weight.
- Area: approximately 2 square meters (22 square feet).
- Weight: 4.5 to 5 kg (10 to 11 pounds), around 7% of body weight.
- Thickness: ranges from 0.5 to 4 mm, thinnest on eyelids, thickest on heels of feet.
Accessory Structures: Includes hair, nails, sweat glands, oil glands, blood vessels, muscles, and nerves.
- Connective, epithelial, muscle, and nervous tissues are present in the integumentary system.

Thermoregulation: Controls body temperature through sweating and blood flow adjustments.
Blood Reservoir: Dermal blood vessels hold 8-10% of total blood volume; regulates body temperature.
Protection: Acts as a barrier against pathogens, chemicals, and dehydration.
Cutaneous Sensations: Contains sensory receptors that detect various stimuli (touch, pressure, heat, cold, pain).
Excretion: Minor role in excreting waste products like urea through sweat.
Absorption: Limited absorption of materials from the environment due to the barrier function of the skin.
Synthesis of Vitamin D: Requires adequate sunlight exposure (about 30 minutes a week) to produce vitamin D.
- Vitamin D aids in calcium absorption; synthesis involves skin, liver, and kidneys to form calcitriol (active form of vitamin D).

Two Main Layers:
- Epidermis (outer layer): Composed of keratinized stratified squamous epithelium.
- Dermis (underlies the epidermis): Composed primarily of dense irregular connective tissue.
Hypodermis (Subcutaneous Layer): Below dermis, contains fat tissue, but not technically part of the skin.

Cell Types in the Epidermis:
- Keratinocytes: Most numerous; produce keratin, contribute to the barrier function.
- Melanocytes: Produce melanin; protect skin from UV radiation.
- Langerhans Cells: Immune response; phagocytize foreign pathogens.
- Merkel Cells: Sensory receptors for touch/discriminative touch.

Stratum Basale: Deepest layer; where mitosis occurs to produce new keratinocytes.
Stratum Spinosum: Contains several layers of keratinocytes; home to Langerhans cells.
Stratum Granulosum: Contains keratinocytes undergoing keratinization.
- Granules contain keratohyalin, a precursor to keratin.
Stratum Lucidum: Thin, clear layer only present in thick skin (palms/soles).
Stratum Corneum: Outermost layer; consists of dead, keratinized cells that are shed regularly.

Process of keratinocytes moving to the surface while dying, leaving keratin behind.
Calluses: Result from increased friction; lead to hyperkeratinization.
Dandruff: Excessive keratinization leads to flaking.

Two Types of Melanin:
- Eumelanin: Brown to black.
- Pheomelanin: Yellow to reddish.
Melanin protects skin cells from UV radiation damage that can lead to skin cancer.
Tanning: Body's response to UV exposure leads to increased melanin production; serves as protective mechanism.

Nevi (Moles): Benign overgrowths of melanocytes.
Malignant Melanoma: Most severe skin cancer; originates from melanocytes.
Albinism: Genetic inability to produce melanin; sensitive to sun, increased risk of skin damage.
Vitiligo: Loss of melanin in patches due to autoimmune issues.

Composed mainly of collagen and elastic fibers.
Regions:
- Papillary Region: Upper layer with loose areolar connective tissue; contains Meissner's corpuscles for touch sensation.
- Reticular Region: Denser, thicker layer; contains sweat glands, sebaceous glands, and hair follicles.

Hair: Composed of dead keratinized cells; functions in sensation, protection, and insulation.
- Hair Follicles: Deep structures housing hair roots; contain matrix for hair growth.
- Types of Hair:
- Lanugo: Fine fetal hair.
- Vellus: Fine body hair.
- Terminal: Coarser, pigmented hair (e.g., scalp, beard).
Sebaceous Glands: Produce sebum; provide lubrication and inhibit bacterial growth.
Sweat Glands: Two types:
- Eccrine: Found all over; secrete watery sweat, regulate temperature.
- Apocrine: Located in limited areas; produce viscous sweat that leads to body odor.
Nails: Composed of hard keratinized cells; grow from a nail matrix; important for grasping and health indicators.

Thick Skin: Found on palms and soles; has an additional stratum lucidum; contains no hair follicles or sebaceous glands.
Thin Skin: Covers most of the body; contains hair follicles and glands.

Types of Wound Healing:
- Epidermal Healing: Superficial wounds; prompted by mitosis in stratum basale.
- Deep Wound Healing: Involves dermis; results in scarring due to collagen deposition.

Most skin cancers result from UV exposure; mutations in DNA lead to uncontrolled cell division.
Types:
- Basal Cell Carcinoma: Most common, slow-growing, typically non-invasive.
- Squamous Cell Carcinoma: Less common, moderate prognosis, can metastasize.
- Malignant Melanoma: Least common but most aggressive; poor prognosis when advanced.

Burn Classification: First-degree (epidermis), second-degree (into dermis, blisters), third-degree (through dermis to subcutaneous).
Rule of Nines: Quick estimation of burn extent based on body surface area affected.
Pressure Sores: Result from prolonged pressure on areas where bones are near the surface; can lead to severe tissue damage and infection.