A & P Ch. 5 The Integumentary System and Skin

The Integumentary System

Overview

The integumentary system consists of the skin and its accessory structures, including hair, nails, and glands. It is the largest organ system of the body and serves multiple protective and regulatory functions.

• Skin is composed of different tissues joined together to perform specific functions.

• Accessory structures include hair follicles, sweat glands, sebaceous glands, and nails.

Structure of the Skin

Main Regions of the Skin

• Epidermis: Outermost layer; composed of keratinized stratified squamous epithelium.

• Dermis: Deeper layer; consists of connective tissue, blood vessels, nerves, and accessory structures.

• Hypodermis (subcutaneous layer): Not technically part of the skin; made of adipose and areolar tissue, provides insulation and energy storage.

Functions of the Hypodermis

• Anchors skin to underlying tissues.

• Stores fat and provides insulation.

• Shock absorption.

Cells of the Epidermis

Principal Cell Types

• Keratinoctyes: Most abundant; produce keratin, a fibrous protein that provides protection.

• Melanocytes: Produce melanin, the pigment responsible for skin color; found in the deepest layer.

• Epidermal Dendritic Cells (Langerhans cells): Immune cells that help protect against pathogens.

• Tactile (Merkel) Cells: Sensory receptors for touch.

Layers of the Epidermis

Stratum Basale

• Deepest layer; single row of stem cells attached to the dermis.

• Cells are highly mitotic, producing new keratinocytes.

• Contains melanocytes and Merkel cells.

Stratum Spinosum

• Consists of 8-10 layers of keratinocytes with desmosomes.

• Provides strength and flexibility.

• Contains Langerhans cells.

Stratum Granulosum

• Thin layer of 3-5 rows of keratinocytes undergoing keratinization.

• Cells begin to die and lose nuclei.

Stratum Lucidum

• Only present in thick skin (palms, soles).

• Consists of a few rows of clear, flat, dead cells.

Stratum Corneum

• Most superficial layer; 20-30 rows of dead, keratinized cells.

• Accounts for most of the epidermal thickness.

• Constant friction can lead to callus formation.

Dermis

Layers of the Dermis

Layer	Composition	Functions
Papillary	Superficial; areolar connective tissue	Contains capillaries, nerve endings, and forms dermal ridges (fingerprints)
Reticular	Deeper; dense irregular connective tissue	Provides strength, elasticity, and houses accessory structures

Structural Basis of Skin Color

Major Pigments

• Melanin: Only pigment made in the skin; ranges from reddish-yellow to brown-black. Produced by melanocytes and transferred to keratinocytes.

• Carotene: Yellow-orange pigment from plants; accumulates in the stratum corneum and hypodermis.

• Hemoglobin: Red pigment from circulating red blood cells; gives skin a pinkish hue, especially in fair skin.

Clinical Indications

• Cyanosis: Blue color indicates low oxygenation of hemoglobin.

• Erythema: Redness indicates fever, hypertension, inflammation, or allergy.

• Jaundice: Yellow skin indicates liver disorders.

Skin Glands

Sebaceous (Oil) Glands

• Attached to hair follicles; secrete sebum (oil) onto hair and skin.

• Function: Lubricates skin and hair, prevents water loss, inhibits bacterial growth.

Sweat (Sudoriferous) Glands

• Eccrine Sweat Glands: Widely distributed; secrete watery sweat via skin pores; important for temperature regulation.

• Apocrine Sweat Glands: Found in axillary and anogenital areas; secrete into hair follicles; begin functioning at puberty.

Hair

Structure and Function

• Composed of dead, keratinized cells.

• Hair follicle anatomy includes the bulb and arrector pili muscle.

• Growth occurs in cycles; longer growth phase produces longer hair.

• Functions: Protection from sunlight, heat loss, and physical trauma.

Functions of the Integumentary System

Major Functions

• Protection: Physical, chemical, and biological barriers against pathogens, abrasions, and harmful chemicals.

• Body Temperature Regulation: Sweat secretion and blood vessel dilation/constriction help regulate heat loss and retention.

• Cutaneous Sensation: Sensory receptors detect touch, pressure, pain, and temperature.

• Metabolic Functions: Synthesis of vitamin D for calcium absorption; activation by sunlight.

• Excretion: Minor role in excreting water and salts.

• Blood Reservoir: Skin can hold up to 5% of the body's blood supply.

Burns

Types of Burns

• First-degree burns: Affect only the epidermal layer.

• Second-degree burns: Affect the epidermis and dermis.

• Third-degree burns: Affect the entire thickness of the skin (epidermis, dermis, and hypodermis).

Serious burns are determined by depth and extent. Critical if >25% of body is 2nd degree, >10% is 3rd degree, or 3rd degree on face, hands, feet.

First threat to a burn is fluid loss and infection.

Skin Cancer

Types of Skin Cancer

Type	Origin	Characteristics
Basal Cell Carcinoma	Stratum basale	Most common, least malignant, slow growing, cured by excision
Squamous Cell Carcinoma	Stratum spinosum	Second most common, grows rapidly, can metastasize, good prognosis if treated early
Melanoma	Melanocytes	Most dangerous, highly metastatic, resistant to chemotherapy, treated by excision and immunotherapy

ABCDE Rule for Melanoma Detection

• A: Asymmetry

• B: Border irregularity

• C: Color variation

• D: Diameter > 6 mm

• E: Evolving shape or size

Additional info: Some explanations and definitions have been expanded for clarity and completeness based on standard Anatomy & Physiology curriculum.