lecture recording on 13 March 2025 at 09.49.37 AM

Introduction

• Acknowledgment of the session and reminder about the quiz deadline.

• Overview of today's topics:

  • Structure and functions of skin

  • Skin types and contributions

Integumentary System Overview

• Definition: Integumentary system includes skin, hair, oil glands, sweat glands, nails, and sensory receptors.

• Importance: Protects against infection, disease, and injury.

• Skin Weight: Approximately 3.5 kg in an average human, making it the largest organ.

• Thermoregulation: Skin helps maintain constant body temperature.

Functions of the Skin

• Six Main Functions:

  • Thermoregulation: Maintaining body temperature through vasodilation (expansion of blood vessels) and vasoconstriction (narrowing of blood vessels).

  • Protection: Provides a barrier against UV radiation, bacteria, viruses, etc.

  • Sensation: Contains nerve receptors for detecting touch, temperature, and pain.

  • Blood Storage: Approximately 10% of blood volume can be stored in the dermis.

  • Excretion and Absorption: Excretes substances like sweat (primarily water and salt) and can absorb small molecules (e.g., creams).

  • Vitamin D Synthesis: Skin synthesizes Vitamin D upon UV exposure, essential for calcium absorption.

Skin Structure

• Layers of Skin:

  • Epidermis: Outer layer, composed mainly of keratinocytes. Includes layers such as:

    • Stratum basale (young, mitotically active cells)

    • Stratum spinosum (spiny-shaped cells for strength)

    • Stratum granulosum (granular cells, waterproof lipids)

    • Stratum corneum (outermost layer of dead, keratinized cells).

  • Dermis: Contains connective tissue, blood vessels, and sensory receptors. Divided into:

    • Papillary layer (loose connective tissue)

    • Reticular layer (dense connective tissue).

  • Hypodermis (Subcutaneous Layer): Composed mainly of adipose tissue; functions in insulation, energy storage, and protection.

Skin Cells

• Keratinocytes: Main cell type, produce keratin. Renew every 30 to 35 days.

• Melanocytes: Produce melanin, the pigment responsible for skin color.

• Merkel Cells: Function as touch receptors.

• Langerhans Cells: Immune cells that respond to environmental threats.

Accessory Structures of the Skin

• Hair: Extensions of epidermis; consists of root and shaft. Contains:

  • Hair follicle: Invagination of epidermis.

  • Erector pili muscle: Causes hair to stand on end (goosebumps).

• Nails: Hard plates of keratin that protect fingertips, grow from the nail matrix under the cuticle.

• Glands:

  • Sebaceous Glands: Produce sebum to moisturize skin.

  • Sweat Glands: Include eccrine (regulating body temperature) and apocrine (associated with body odor).

Thermoregulation

• Mechanisms:

  • Vasodilation: Expands blood vessels to increase blood flow and heat loss when hot.

  • Vasoconstriction: Narrows blood vessels to conserve heat when cold.

• Role of Hypothalamus: Acts as a thermostat regulating body temperature.

Vitamin D and Homeostasis

• Vitamin D synthesis involves sunlight conversion in skin, liver, and kidneys.

• Plays critical roles in calcium absorption, bone health, and overall metabolic functions.

Wound Healing

• Types: Superficial (epidermal) and deep wounds.

  • Epidermal Wound Healing: Simple process requiring mitosis of stratum basale cells.

  • Deep Wound Healing: Involves four phases:

    1. Hemostasis: Stopping blood flow.

    2. Inflammation: Redness and swelling as immune response.

    3. Proliferation: Rebuilding tissue.

    4. Remodeling: Fine-tuning and strengthening of the new tissue.

Summary and Conclusion

• Understanding the structure and functions of the integumentary system is crucial for knowledge of skin biology, health, and disease.

• Ensure to watch supplementary videos for deeper insights and visuals on skin anatomy and functions.