Module 5 The Integumentary System

Module 5: The Integumentary System

Introduction to the Integumentary System

  • The integumentary system encompasses the skin, the largest organ of the body, consisting of three layers and accessory structures.

Layers of the Skin

  • The skin consists of three primary layers:
    • Epidermis
    • Dermis
    • Hypodermis (subcutaneous layer)

The Epidermis

  • The epidermis is made up of 4 to 5 layers of stratified squamous epithelium:
    • Stratum Corneum
    • Stratum Lucidum (variable presence)
    • Stratum Granulosum
    • Stratum Spinosum
    • Stratum Basale
  • The outermost layers primarily consist of keratinocytes, cells that produce keratin, a protein that imparts hardness and water resistance to hair, nails, and skin.
  • Cells of the Stratum Basale include:
    • Basal cells: Mitotic, cuboidal cells responsible for the genesis of keratinocytes.
    • Merkel cells: Specialized cells that communicate with sensory nerves for touch perception.
    • Melanocytes: Cells that produce melanin, contributing to skin and hair color, and offering protection against UV radiation.
The Different Layers of the Epidermis in Detail
  • Stratum Basale:
    • Deepest layer, anchored to the dermis.
    • Contains basal cells, Merkel cells, and melanocytes.
    • Unique feature: Fingerprints originate here.
  • Stratum Spinosum:
    • Contains keratinocytes and Langerhans cells (macrophages).
    • Thickness: 8 to 10 cells.
    • Initiates keratin synthesis.
  • Stratum Granulosum:
    • Comprises flattened keratinocytes; organelles begin to disintegrate.
    • Thickness: 3 to 5 cells; low vascularity.
    • Produces keratin and keratohyalin (from lamellar granules); function: waterproofing.
  • Stratum Lucidum:
    • Composed of dead keratinocytes.
    • Present only in thick skin; cells are filled with eleidin, making them translucent.
  • Stratum Corneum:
    • Outermost layer, made up of dead keratinocytes.
    • Thickness: 15 to 30 cells.
    • Provides waterproofing through the presence of glycolipids between cells.

The Dermis

  • The dermis consists of two main layers of connective tissue:
    • Papillary Layer:
    • Composed of fibroblasts, adipocytes, small blood vessels, phagocytes, lymphatic vessels, and neurons with touch receptors (Meissner corpuscles).
    • Features loose areolar connective tissue; projects into the stratum basale; superficial and thin.
    • Reticular Layer:
    • Mainly contains fibroblasts.
    • Composed of dense irregular connective tissue, including collagen, elastin, and reticular fibers, providing structural integrity and moisture retention.

The Hypodermis

  • Located deep to the dermis, the hypodermis connects the skin to underlying tissues.
  • Highly vascular and consists of areolar and adipose tissue, serving primarily as fat storage.

Accessory Structures of the Skin

  • Hair:

    • Matrix: Contains basal cells responsible for hair growth.
    • Papilla: Connective tissue, also contains blood vessels and nerve endings.
    • Arrector Pili: Smooth muscle causing goosebumps upon contraction.
    • Hair structure: Comprises keratinous filaments arising from hair follicles in the dermis; consists of a shaft (visible part) and root (below the surface), culminating in the bulb.

  • Nails:

    • Comprised of keratinocytes; the nail body forms on the nail bed, providing protection for the tips of fingers and toes.
    • Nail Bed: Highly vascular, giving nails a pinkish hue. Contains the lunula, the white crescent shape that signifies the area of growth.
    • Cuticle: Junction where the nail meets the skin finger.

  • Sweat and Sebaceous Glands:

    • Sudoriferous (sweat) glands produce sweat:
    • Eccrine sweat glands: Responsible for producing hypotonic sweat crucial for thermoregulation; comprise coiled glands in the dermis with ducts extending to the skin surface.
    • Apocrine sweat glands: Associated with hair follicles in regions with dense hair (e.g., armpits, genital areas); modified hormonal control with roles in pheromone release.
    • Sebaceous glands: Produce oil (sebum) to lubricate and waterproof both skin and hair.

Functions of the Integumentary System

  • Protection:

    • Functions as a barrier against environmental threats.
    • Melanin production, serving as a protection against UV radiation.
    • Physical barriers help retain water and defend against abrasion; hosts immune function via components that deter microbial over-colonization:
    • Sudoriferous glands: Deter microbes.
    • Sebum: Antimicrobial properties.
    • Langerhans cells and dermal macrophages: Serve in immune response.

  • Sensory Reception:

    • Contains specialized sensory nerve structures which detect:
    • Touch (Meissner's corpuscle)
    • Vibration (Pacinian corpuscle)
    • Pain and temperature (via other sensory nerves).
    • Hairs originating from hair follicles also serve sensory functions, with the root plexus acting as a mechanoreceptor.

  • Thermoregulation:

    • Active sweating: Approximately 0.5 L/day to 1.5 L/hour when necessary.
    • Blood vessels in the dermis play a vital role in heat conservation; vasoconstriction occurs in cold environments, which may lead to frostbite.

  • Vitamin D Synthesis:

    • Vitamin D is produced from cholesterol upon sunlight exposure, crucial for normal calcium and phosphorus absorption.
    • Insufficient vitamin D can result in rickets, characterized by misshapen bones.
    • Vitamin D is important for overall immunity against infections.
    • Recent studies suggest associations between low vitamin D levels and various health issues, including cancer and depression.

Skin Cancer

  • Skin Cancer: Results from UV exposure that increases rapidly dividing cell populations.
    • Basal Cell Carcinoma: Most common form, low lethality.
    • Squamous Cell Carcinoma: Grows quickly but generally has a high cure rate; typically affects scalp, ears, and lip.
    • Melanoma: Rarest but most lethal; commonly arises from moles.

Diagnosing Melanoma

  • Employ the ABCDEFG rule for identification:
    • A) Asymmetry: Non-matching sides.
    • B) Border Irregularity: Non-smooth borders.
    • C) Color: Variations including black, red, brown, tan.
    • D) Diameter: Greater than 6 mm.
    • E) Evolving: Changes in shape or size over time.
    • F) Firmness: Elevated or hard texture.
    • G) Growth: Increasing in size.

Acne and Skin Disturbances

  • Acne: Skin disorder prevalent in sebaceous gland-rich areas (face and back); often onset during puberty, can be present from infancy and continue through adulthood.

Injuries to the Skin

  • Partial Thickness Burns:

    • First-Degree Burns: Involve only the epidermis; result in pain and swelling and generally heal within a few days; example: mild sunburn.
    • Second-Degree Burns: Affect both the epidermis and partial dermis; leads to swelling and painful blisters, requiring cleanliness to prevent infection with healing taking several weeks.

  • Full Thickness Burns:

    • Third-Degree Burns: Extend into both epidermis and dermis; may destroy tissue and impact nerve endings, resulting in numbness. They appear white, red, or black and necessitate medical treatment due to their slow healing.
    • Fourth-Degree Burns: Extend even deeper, affecting muscle and bone; similar to third-degree burns in terms of pain levels and healing concerns.

Calluses and Scars

  • Calluses: Develop when basal stem cells are activated to increase skin thickness at abrasion sites, enhancing protection against further damage.
  • Scars: Form as collagen-rich tissue following wound healing that differs from normal skin; generated primarily by fibroblasts producing collagen-rich scar tissue, contributing to the skin’s healing process.

Administrative Announcements

  • Module 5 Homework: Due on October 6 at 8:00 AM.
  • Module 5 Quiz: Scheduled for October 6 at the end of class.
  • Queries should be posted on the discussion board.
  • Exam 2: Scheduled for October 22.