INTEGUMENTARY

UNIT 3: INTEGUMENTARY SYSTEM

Learning Outcomes

  • At the end of the session, students will be able to:

    1. Describe the structures of the integumentary system.

    2. Explain the functions of the skin:

      • Thermoregulation

      • Protection

      • Sensation

      • Excretion and absorption

      • Synthesis of vitamin D

1. Structure of the Integumentary System

  • Skin / Cutaneous Membrane (major component):

    • Composed of three layers:

      • Epidermis

      • Dermis

      • Hypodermis

  • Accessory Structures:

    • Hair (pili)

    • Nails

    • Glands (sebaceous & sudoriferous)

    • Arrector pili muscle

    • Blood vessels

    • Nerves

2. Epidermis

  • Characteristics:

    • Outer/topmost layer; composed of keratinized stratified squamous epithelium

    • Varies in thickness; thickest at palms and soles

    • Avascular (lacks blood vessels) and contains no nerves.

3. Cells of the Epidermis

  • Five Types of Cells:

    1. Stem Cells:

      • Undifferentiated cells that develop into keratinocytes; located in the basal stratum.

    2. Keratinocytes:

      • Comprise 90% of cells; produce keratin for protection and lamellar granules for water resistance.

    3. Melanocytes:

      • Produce melanin, influencing skin color and UV protection.

    4. Langerhans Cells:

      • Immune cells, act against pathogens; susceptible to UV rays.

    5. Merkel Cells:

      • Tactile epithelial cells that detect touch sensation.

4. Layers of the Epidermis

  • Five Layers:

    1. Stratum Corneum:

      • Contains ≥25 layers of dead cells; topmost layer.

    2. Stratum Lucidum:

      • Found only in thick skin; 3-5 layers of dead, transparent cells.

    3. Stratum Granulosum:

      • 2-5 layers of flattened cells undergoing apoptosis.

    4. Stratum Spinosum:

      • 8-10 layers of nucleated cells joined by desmosomes; keratin synthesis occurs here.

    5. Stratum Basale:

      • Deepest layer with cuboidal or columnar keratinocytes; contains stem cells for mitosis.

5. Dermis Structure

  • Between Epidermis & Hypodermis:

    • Composed of connective tissue:

      • Loose (areolar) & dense (irregular) fibers.

    • Contains blood vessels, nerves, glands, and hair follicles.

  • Two Layers:

    • Papillary Layer:

      • Superficial layer (~1/5); contains dermal papillae (fingerprints), Meissner corpuscle, and free nerve endings.

    • Reticular Layer:

      • Deeper layer (~4/5); consists of dense irregular connective tissue, providing strength and elasticity.

6. Accessory Structures

  • Hair / Pili:

    • Composed of dead keratinized epidermal cells.

    • Structure includes hair shaft, hair root, and hair follicle (with hair root plexus).

    • Functions: Protection, reducing heat loss, and light sensation.

  • Nails:

    • Comprised of tightly packed dead keratinized cells.

    • Structure includes free edge, body, lunula, and root.

    • Functions include protection and aiding in manipulation.

  • Glands:

    1. Sebaceous (Oil) Glands:

      • Secrete oil to prevent water loss and protect against microbes.

    2. Sudoriferous (Sweat) Glands:

      • Eccrine: Secretes sweat for thermoregulation.

      • Apocrine: Activated after puberty; associated with emotional responses.

    3. Ceruminous Gland:

      • Modified sweat gland producing earwax (cerumen) for protection.

7. Functions of the Skin

  1. Thermoregulation:

    • Controlled by sweat production and blood vessel dilation/constriction based on environmental temperature.

  2. Protection:

    • Keratin, sebum, melanin, and sensory receptors help guard against environmental damage and microbial invasion.

  3. Sensation:

    • Contains sensory receptors for touch, pressure, vibration, pain, and temperature.

  4. Excretion & Absorption:

    • Excretes waste products through sweat; absorbs substances like topical medications.

  5. Vitamin D Synthesis:

    • Keratinocytes synthesize vitamin D when exposed to sunlight; crucial for calcium and phosphorus absorption.

Revision Questions

  1. Explain functions of skin.

  2. Describe ways of heat loss from body.

  3. State types of cells in the epidermis layer.

  4. List accessory structures of the integumentary system.