Integumentary System Components

Overview

The integumentary system consists of the skin and its derivatives, including hair, nails, and glands. It serves as the body's primary barrier against the external environment and plays vital roles in protection, sensation, and regulation.

• Skin: Composed of three main layers—epidermis, dermis, and hypodermis.

• Hair: Provides protection and sensory input.

• Nails: Protect the distal phalanges and aid in grasping.

• Glands: Include sweat and sebaceous glands, which regulate temperature and sebum production.

Functions of Skin

Major Functions

The skin performs several essential functions for maintaining homeostasis and overall health.

• Protection: Acts as a physical, chemical, and biological barrier against pathogens, UV radiation, and mechanical injury.

• Body Temperature Regulation: Utilizes sweat glands and blood vessel dilation/constriction to maintain optimal temperature.

• Cutaneous Sensations: Contains sensory receptors for touch, pain, pressure, and temperature.

• Metabolic Functions: Synthesizes vitamin D from sunlight; aids in other metabolic processes.

• Blood Reservoir: Stores up to 5% of the body's blood volume.

• Excretion: Eliminates waste products such as urea, uric acid, and ammonia through sweat.

CT: Insensible vs. Sensible Perspiration

• Insensible Perspiration: Continuous, unnoticeable water loss through the epidermis.

• Sensible Perspiration: Noticeable sweating, especially during heat or exercise.

Skin Structure: Layers and Cells

Epidermis, Dermis, and Hypodermis

The skin is organized into three main layers, each with distinct structures and functions.

• Epidermis: Superficial layer; composed of stratified squamous epithelium.

• Dermis: Middle layer; contains connective tissue, blood vessels, nerves, and glands.

• Hypodermis: Deepest layer; primarily adipose tissue, anchors skin to underlying structures.

Layers of the Epidermis (Deepest to Superficial)

1. Stratum basale (deepest)

2. Stratum spinosum

3. Stratum granulosum

4. Stratum lucidum (only in thick skin)

5. Stratum corneum (most superficial)

Stratum lucidum is present only in thick skin, which is found on the palms of the hands and soles of the feet.

CT: In which layer do cells start to die? Cells begin to die in the stratum granulosum due to loss of nutrients and accumulation of keratin.

Dermis: Layers and Connective Tissue Types

• Papillary layer: Superficial; composed of areolar connective tissue.

• Reticular layer: Deep; composed of dense irregular connective tissue.

Special Features of the Dermis

• Friction ridges: Found in thick skin; responsible for fingerprints.

• Cleavage lines: Natural lines in the skin formed by collagen fibers; important for surgical incisions.

• Flexure lines: Folds at joints where the skin is tightly secured to underlying structures.

Skin Color: Pigments and Conditions

Three Pigments Contributing to Skin Color

• Melanin: Brown to black pigment; produced by melanocytes. Melanin protects cells from UV radiation.

• Carotene: Yellow to orange pigment; obtained from diet, accumulates in the stratum corneum.

• Hemoglobin: Red pigment in blood; gives skin a pinkish hue, especially in fair-skinned individuals.

Conditions such as cyanosis (bluish color), jaundice (yellowish color), and erythema (redness) can alter skin color.

Hair

Structure and Regions

Hair is a filamentous structure composed of keratinized cells. It consists of three main regions:

• Shaft: The visible part above the skin surface.

• Root: The portion embedded in the skin.

• Bulb: The expanded base of the root; site of hair growth.

The hair shaft is composed of three parts:

• Medulla: Central core.

• Cortex: Surrounds the medulla; contains pigment.

• Cuticle: Outermost layer; provides strength.

Hair contains hard keratin, which is tougher and more durable than the soft keratin found in skin.

Types of Hair

• Vellus hair: Fine, pale hair found on children and adult females.

• Terminal hair: Coarse, long hair found on scalp, eyebrows, and after puberty in axillary and pubic regions.

Nails

Structure

Nails are protective coverings on the dorsal surface of fingers and toes. Key structures include:

• Nail plate: Visible part of the nail.

• Nail bed: Skin beneath the nail plate.

• Nail matrix: Site of nail growth.

• Lunula: Crescent-shaped area at the base.

• Cuticle (eponychium): Skin fold at the base.

Nails contain hard keratin.

Sweat and Sebaceous Glands

Types of Glands

• Eccrine sweat glands: Most numerous; produce watery sweat for thermoregulation.

• Apocrine sweat glands: Found in axillary and genital areas; produce thicker, milky secretion; become active at puberty.

• Sebaceous glands: Secrete sebum (oil) into hair follicles; lubricates skin and hair.

Modified apocrine sweat glands include:

• Ceruminous glands: Produce earwax.

• Mammary glands: Produce milk.

Skin Cancers

Types and ABCD(E) Rule

• Basal cell carcinoma: Most common, least malignant; arises from stratum basale.

• Squamous cell carcinoma: Arises from keratinocytes in stratum spinosum; can metastasize.

• Melanoma: Most dangerous; arises from melanocytes.

The ABCD(E) rule is used to identify melanoma:

• A: Asymmetry

• B: Border irregularity

• C: Color variation

• D: Diameter > 6 mm

• E: Evolving (changes over time)

Burns

Classification and Treatment

• Rule of nines: Used to estimate the percentage of body surface area affected by burns.

• First-degree burns: Affect only the epidermis; redness and pain.

• Second-degree burns: Affect epidermis and part of dermis; blistering.

• Third-degree burns: Affect full thickness of skin; may appear white, red, or black; nerve endings destroyed.

Burns are considered critical if:

• Over 25% of body has second-degree burns

• Over 10% of body has third-degree burns

• Third-degree burns on face, hands, or feet

Treatment includes fluid replacement, infection prevention, and skin grafting for severe cases.

Rule of Nines Table

Example: A burn covering the entire left leg and anterior trunk would affect 36% + 18% = 54% of the body surface area.

Additional info: The hypodermis, also known as the subcutaneous layer, is not technically part of the skin but is included in the integumentary system due to its role in fat storage and insulation.