In-Depth Notes on Skin Structure and Function

Overview of Skin Layers

• The skin is the outer covering of the body made up of multiple layers.
  • Epidermis: The outermost layer of skin.
  • Dermis: Located beneath the epidermis, composed of connective tissue.

Dermis Structure

• The dermis has two primary layers:
  1. Papillary Layer:
  • Composed of areolar tissue with loosely arranged collagen and elastic fibers.
  • Contains dermal papillae which project into the epidermis, including free nerve endings and tactile Meissner's corpuscles.
  1. Reticular Layer:
  • Composed of dense irregular connective tissue with densely packed collagen and elastic fibers.
  • Provides strength and elasticity to the skin; contains hair follicles, sweat glands, sebaceous glands, and sensory receptors.

Functions of the Dermis

• Storage: Stores water.
• Regulation: Helps regulate body temperature.
• Vitamin D Production: Participates in synthesizing vitamin D.
• Cushioning: Acts as a cushion for underlying structures.
• Nutrition: Supplies blood to the epidermis.

Sensory Receptors

• Tactile (Meissner's) Corpuscles: Found in dermal papillae; sensitive to light touch.
• Lamellar Corpuscles: Respond to pressure and vibration, located in various organs (mammary glands, joints).
• Free Nerve Endings: Detect pain, temperature, itch, and tickle sensations.

Glandular Structures in the Skin

• Sebaceous (Oil) Glands:
  • Exocrine glands producing sebum, an oily substance comprising triglycerides, cholesterol, and proteins.
  • Functions:
  • Moisturizes skin and hair.
  • Reduces water loss.
  • Inhibits bacterial growth.
• Sweat Glands (Pseudoriferous):
  • Eccrine Sweat Glands: Most common, located throughout the body; important for thermoregulation through perspiration.
  • Apocrine Sweat Glands: Located in armpits and groin; activated during emotional sweating and can produce odor due to bacterial activity.

Hair Structure

• Components:
  • Root: Embedded in the dermis.
  • Shaft: Projects above the epidermis.
  • Follicle: Sheath surrounding the root, with a bulb at the base.
  • Erector Pili Muscles: Attached to the follicle; contract to raise hair and create goosebumps.
• Hair Variability:
  • Length, thickness, and color influenced by genetics and environment.
  • Variation in hair texture is due to the shape and size of hair follicles and bulbs.

Healing Process in the Skin

• Phase 1 - Hemostasis: Platelets form a clot after injury to halt bleeding.
• Phase 2 - Inflammation: Mast cells release histamine, increasing blood flow and attracting white blood cells (neutrophils, macrophages) to clean debris.
• Phase 3 - Proliferation: Fibroblasts secrete collagen, forming granulation tissue that resembles the original tissue.
• Phase 4 - Remodeling: Tissue reorganizes and matures, regaining functional integrity.

Summary

• The skin serves critical protective and regulatory functions, composed of the epidermis and dermis with complex structures that include hair, glands, and sensory receptors. The healing process integrates multiple phases crucial for recovery from injury.