Integumentary System

Integumentary System Overview

• Definition: The integumentary system refers to the skin and its accessory structures, including hair, nails, and associated exocrine glands.
• Functions:
  • Protection
  • Thermoregulation
  • Sensation
  • Vitamin D synthesis

Skin Structure

• General Information:
  • Average human skin surface area: 2 m²
  • Skin thickness varies: 0.5 mm (face) to 5 mm (upper back)
• Skin Layers:
  • Epidermis: 4-5 epithelial layers
  • Dermis: 2 layers of connective tissue
  • Hypodermis: areolar connective tissue and fatty adipose tissue

Epidermis

• Composed of stratified squamous epithelium with 4-5 layers.
• Contains four general cell types:
  • Keratinocytes (90%):
  • Produce keratin protein for protection
  • Form lamellar granules to reduce water loss
  • Melanocytes (8%):
  • Produce melanin pigment
  • Found only in the basal layer of the epidermis
  • Langerhans cells:
  • Macrophages participating in immune response, dispersed throughout all layers
  • Merkel cells:
  • Touch receptors, primarily found in the basal layer.
  • More prevalent in areas like fingertips.

Epidermis Layers

1. Stratum Basale:
   • Single layer of cuboidal keratinocytes.
   • Contains stem cells, melanocytes, and Merkel cells.
   • Attached via hemidesmosomes to the basement membrane.
2. Stratum Spinosum:
   • 8-10 layers of keratinocytes held together by desmosomes.
   • Cells flatten as they move upward; melanin uptake occurs here.
3. Stratum Granulosum:
   • 3-5 layers of flat, dying keratinocytes undergoing apoptosis.
   • Contains lamellar granules for waterproofing.
4. Stratum Lucidum:
   • Present only in thick skin areas (e.g., fingertips, palms).
   • 4-6 layers of clear, dead keratinocytes rich in keratin.
5. Stratum Corneum:
   • Outermost layer, 25-30 layers of flat, dead keratinocytes.
   • Continuously shed, creating a barrier against UV, heat, and chemicals.

Dermis

• Structure:
  • Connective tissue made of collagen and elastic fibers.
  • Contains hair follicles, glands, nerves, and blood vessels.
• Regions:
  • Papillary Region: Loose connective tissue with dermal papillae; contains Meissner’s corpuscles and free nerve endings.
  • Reticular Region: Dense, irregular connective tissue; packed with oil glands, sweat gland ducts, and hair follicles.

Hypodermis

• Composed of loose areolar connective tissue and adipose tissue.
• Physically connects to the dermis above and fascia below.
• Contains larger blood vessels and nerves.

Skin Damage

• Burn Classification:
  • First Degree: Damage only to the epidermis.
  • Second Degree: Damage to the epidermis and papillary layer of the dermis.
  • Third Degree: Damage through the epidermis, dermis, and into the hypodermis.

Skin Pigmentation

• Melanocyte Function:
  • Produce melanin:
  • Eumelanin: Black/brown pigment.
  • Pheomelanin: Yellow-pink-red pigment.
  • Melanin absorbs UV radiation, protecting skin cells.
• All adults have similar melanocyte counts; differences in skin color due to varying melanin production.

Accessory Structures of the Skin

• Hair: Functions include insulation, protection, and sensory enhancement.
• Nails: Extensions of the stratum corneum; protect digits and assist with manipulation.
• Skin Glands:
  • Sebaceous Glands: Produce sebum; prevent drying.
  • Sudoriferous Glands: Produce sweat; includes eccrine (thermoregulation) and apocrine (emotional response) types.

Conclusion

• Understanding the integumentary system's structure, function, and accessories is crucial for comprehending overall skin health and related medical conditions.