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Chapter 5: The Integumentary System – Structured Study Notes

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The Integumentary System

Overview

The integumentary system is the largest organ system in the human body, accounting for approximately 16% of total body weight and covering 1.5 to 2 square meters of surface area. It consists of two major components: the cutaneous membrane (skin) and accessory structures.

  • Cutaneous membrane: Includes the outer epidermis (superficial epithelium) and inner dermis (connective tissue).

  • Accessory structures: Originate in the dermis and extend through the epidermis to the skin surface, including hair and hair follicles, exocrine glands, and nails.

  • Subcutaneous layer (hypodermis): Lies below the dermis, composed of loose connective tissue and adipose tissue.

Functions of the Integumentary System

  • Protection: Shields underlying tissues and organs from mechanical damage, pathogens, and chemical exposure.

  • Excretion: Removes salts, water, and organic wastes through sweat.

  • Temperature Regulation: Maintains normal body temperature via sweat and blood flow.

  • Melanin Production: Protects against ultraviolet (UV) radiation.

  • Keratin Production: Provides water resistance and strength.

  • Vitamin D3 Synthesis: Essential for calcium and phosphate absorption.

  • Lipid Storage: Stores energy in adipose tissue.

  • Sensory Detection: Detects touch, pressure, pain, and temperature.

  • Immune Coordination: Initiates immune responses to pathogens.

Structure of the Skin

Cutaneous Membrane

  • Epidermis: Stratified squamous epithelium; avascular; receives nutrients and oxygen via diffusion from the dermis.

  • Dermis: Located between the epidermis and subcutaneous layer; anchors accessory structures.

  • Subcutaneous Layer (Hypodermis): Primarily adipose tissue; stabilizes skin position; site for subcutaneous injections.

Accessory Structures

  • Hair and Hair Follicles

  • Exocrine Glands

  • Nails

Layers of the Epidermis

Types of Skin

  • Thin Skin: Covers most of the body; four layers of keratinocytes.

  • Thick Skin: Covers palms and soles; five layers of keratinocytes.

Layers of the Epidermis

Layer

Characteristics

Stratum basale (germinativum)

Deepest layer; attached to basement membrane; contains basal (stem) cells, epidermal ridges, tactile (Merkel) cells, and melanocytes.

Stratum spinosum

8-10 layers of keratinocytes; bound by desmosomes; contains Langerhans (dendritic) cells for immune response.

Stratum granulosum

3-5 layers; cells stop dividing and produce keratin and keratohyalin; cells die after protein production.

Stratum lucidum

Only in thick skin; clear layer covering stratum granulosum.

Stratum corneum

15-30 layers of keratinized cells; exposed surface; water resistant; cells are shed after two weeks.

Water Loss from Skin

  • Insensible perspiration: Water diffuses across stratum corneum and evaporates (about 500 mL/day).

  • Sensible perspiration: Water excreted by sweat glands.

The Dermis

Layers of the Dermis

  • Papillary Layer: Areolar tissue; contains capillaries, lymphatic vessels, and sensory neurons; involved in dermatitis.

  • Reticular Layer: Dense irregular connective tissue; contains collagen and elastic fibers; provides strength and elasticity.

Dermal Strength and Elasticity

  • Collagen fibers: Resist stretching, provide strength.

  • Elastic fibers: Allow stretching and recoil.

  • Skin turgor: Flexibility and resilience due to fibers and water.

Skin Damage

  • Loss of skin turgor caused by dehydration, aging, hormones, or UV radiation.

  • Excessive distortion (pregnancy, weight gain) may cause stretch marks.

Tension Lines (Cleavage Lines)

  • Produced by parallel bundles of collagen and elastic fibers.

  • Incisions parallel to tension lines heal better; perpendicular incisions may scar.

Dermal Blood Supply

  • Cutaneous plexus: Deep arteries in reticular layer.

  • Subpapillary plexus: Small arteries in papillary layer.

  • Contusion (bruise): Damage to dermal blood vessels.

Innervation of Skin

  • Nerve fibers control blood flow, gland secretion, and monitor sensory receptors.

  • Sensory receptors: Tactile (Meissner) corpuscles for light touch; Lamellar (Pacinian) corpuscles for deep pressure and vibration.

The Subcutaneous Layer (Hypodermis)

Structure and Function

  • Lies deep to dermis; stabilizes skin position.

  • Primarily adipose tissue (adipocytes).

  • Contains large arteries and veins.

  • Site for subcutaneous injections.

  • Fat distribution influenced by sex hormones.

Skin Color

Pigments Influencing Skin Color

  • Melanin: Red-yellow or brown-black pigment produced by melanocytes; stored in melanosomes and transferred to keratinocytes. Protects against UV radiation.

  • Carotene: Orange-yellow pigment from vegetables; accumulates in epidermal cells and subcutaneous layer; can be converted to vitamin A for epithelial maintenance and photoreceptor synthesis.

Additional info:

  • Blood flow and oxygenation also affect skin color (e.g., hemoglobin).

  • Conditions such as jaundice, pituitary tumors, Addison's disease, and vitiligo can alter skin color.

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