Integumentary System Lecture Notes

Introduction

• The integumentary system is the outermost system of the human body.
• It includes the skin, its derivatives (certain glands), hair, and nails.

Skin Structure and Function

• Skin as a Protective Organ

  • Acts as the first line of defense against environmental elements.
  • Keeps bacteria out, retains water and heat.

• Layers of Skin

  • Epidermis: Thin outer layer; avascular, receives nutrients via diffusion.

    • Composed of keratinized stratified squamous epithelium.
    • Contains four cell types in five layers:
      • Stratum Basale: Deepest layer; contains keratinocytes (dividing cells) and melanocytes (produce melanin).
      • Stratum Spinosum: Contains prickly cells with intermediate filaments and dendritic cells (immune function).
      • Stratum Granulosum: Keratinization begins here; cells become tougher as they move up.
      • Stratum Lucidum: Clear layer; consists of dead keratinocytes.
      • Stratum Corneum: Outermost layer; cells are dead, anucleated, rich in keratin.

  • Dermis: Below epidermis, made of connective tissue.

    • Papillary Layer: Thin, areolar connective tissue with dermal papillae.
    • Reticular Layer: Dense fibrous connective tissue.

  • Hypodermis: Subcutaneous layer, anchors skin to underlying structures, composed of adipose tissue.

Skin Color

• Determined by three pigments:
  • Melanin: Provides UV protection.
  • Carotene: Yellow-orange pigment.
  • Hemoglobin: Red pigment when oxygenated.

Hair Structure and Function

• Hair is a flexible strand of dead, keratinized cells.

• Hair structure:

  • Medulla: Innermost layer with soft keratin.
  • Cortex: Middle layer of flattened cells.
  • Cuticle: Outer layer, most keratinized.

• Hair Follicle

  • Composed of peripheral connective tissue sheath, glassy membrane, and epithelial root sheath.
  • Contains hair bulb, where hair growth occurs.
  • Arrector Pili: Muscle causing goosebumps.

Nail Structure

• Nails are modifications of epidermis, contain hard keratin.
• Structure:
  • Free Edge: Tip of nail.
  • Body: Visible part.
  • Root: Embedded in skin.
  • Nail Bed: Epidermis under nail.
  • Nail Matrix: Area of growth.
  • Nail Folds: Overlapping skin.
  • Hyponychium: Under nail’s free edge.

Glands

• Sweat Glands (Sudoriferous Glands)

  • Eccrine Glands: Found throughout body; regulate temperature.
  • Apocrine Glands: Found in specific areas, cause body odor.
  • Ceruminous and Mammary Glands: Types of apocrine glands.

• Sebaceous Glands (Oil Glands)

  • Produce sebum to lubricate skin and hair, slow water loss, and kill bacteria.

Summary

• The integumentary system protects, regulates temperature, and responds to external stimuli.