Integumentary System Anatomy & Physiology

Integumentary System

Overview of the Integumentary System

• Definition: The integumentary system covers the body and consists of skin and accessory tissues, including nails, hair, sweat glands, and sebaceous glands.

• Terminology:

  • Integument: another term for skin.

  • Cutaneous membrane: also refers to the skin.

• Function:

  • Acts as a barrier to the outside world.

  • Serves as a visual indicator of physiology and health.

• Field of Study: Dermatology is the medical specialty that focuses on the study of skin.

Layers of the Integument

• Components:

  • Outer: Epidermis

  • Middle: Dermis

  • Inner: Subcutaneous layer

• Structures:

  • Hair shaft, sweat pore, hair follicle, sebaceous glands, arrector pili muscles, sensory nerve fibers, blood vessels (veins and arteries), and various types of connective tissues.

Detailed Look at the Epidermis

• Structure:

  • Composed of multiple layers of keratinized cells.

  • Contains distinct strata:

  • Stratum Basale:

    • Deepest layer of the epidermis, single layer of cuboidal to low columnar cells.

    • Cell Types:

    1. Keratinocytes:

       • Found in all layers; in stratum basale, they are stem cells responsible for generating new cells and synthesizing keratin.

       • Keratin: a protein that strengthens the epidermis.

    2. Melanocytes:

       • Scattered among keratinocytes; produce and store melanin, a pigment that protects against UV radiation by transferring melanosomes to keratinocytes.

    3. Tactile cells (Merkel cells):

       • Few in number; sensitive to touch and release chemicals to stimulate sensory nerve endings.

  • Stratum Spinosum:

    • Several layers of polygonal keratinocytes connected by desmosomes.

    • Contains epidermal dendritic cells (Langerhans cells) that initiate immune responses against pathogens.

  • Stratum Granulosum:

    • 3 to 5 layers of keratinocytes undergoing keratinization, resulting in cell death as they fill with keratin.

  • Stratum Lucidum:

    • 2 to 3 layers, translucent, found only in areas of thick skin (palms and soles).

    • Contains eleidin, a precursor to keratin.

  • Stratum Corneum:

    • Outermost layer, composed of 20-30 layers of dead, anucleate, keratinized cells, providing protective barrier functions against abrasion and infection.

Types of Skin

• Thick Skin: Found on palms and soles, contains all five epidermal strata including the stratum lucidum.

• Thin Skin: Covers most other body areas, lacks stratum lucidum, and has fewer layers overall.

Production of Melanin

• Melanocyte Structure: Contains melanin stored in melanosomes, which are transferred into keratinocytes, providing protection against UV radiation.

Friction Ridges

• Function: Enhance grip and tactile feedback, visible as patterns on thick skin.

UV Radiation and Skin Health

• Types of UV Radiation: UVA, UVB, and UVC (UVC is absorbed by the atmosphere).

• Sunscreens: Designed to block UVA and UVB rays, protecting the skin from damage.

• Sunless Tanners: Provide skin color without UV exposure, but do not offer UV protection.

Dermis Overview

• Location: Deep to the epidermis.

• Composition: Composed of connective tissue proper with blood vessels, sweat glands, sebaceous glands, hair follicles, and nerve endings.

• Layers:

  • Papillary Layer: Superficial, made of areolar connective tissue, containing dermal papillae that interlock with epidermal ridges.

  • Reticular Layer: Deeper layer, composed of dense irregular connective tissue supporting various structures.

Functions of the Integumentary System

1. Protection: Shields body from injury, pathogens, and harmful substances.

2. Prevention of Water Loss/Gain: Epidermis is water resistant; however, it facilitates loss through sweating.

3. Vitamin D Synthesis: Initiates formation of Vitamin D3, aiding in calcium absorption.

4. Excretion: Removes waste products through sweating.

5. Absorption: Selective permeability allows absorption of certain substances.

6. Temperature Regulation: Blood vessels in dermis enable heat conservation or release.

7. Immune Function: Dendritic cells initiate immune responses and help protect against pathogens.

8. Sensory Reception: Contains sensory receptors for touch, pressure, and temperature.

Hair Structure and Function

• Components: Hair shaft, follicle, root, medulla, cortex, cuticle, and associated arrector pili muscles.

• Functions: Provide protection, assist in thermal insulation, sensory function, and visual identification.

Exocrine Glands of the Skin

• Sweat Glands:

  • Merocrine: Most common, involved in thermoregulation, releasing a watery secretion.

  • Apocrine: Found in specific areas (axillae, nipples), produce viscous secretions activated at puberty.

• Sebaceous Glands: Produce sebum, an oily substance that lubricates and has antibacterial properties, activated by hormones, especially during puberty.

Repair and Regeneration of the Integumentary System

• Processes: Involves either regeneration (replacement with same tissue type) or fibrosis (scar formation).

• Stages of Wound Healing:

  1. Hemostasis: Bleeding occurs; blood clot forms.

  2. Inflammation: White blood cells (leukocytes) clean the wound.

  3. Granulation: Tissue forms as blood vessels regrow.
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