Lecture on Human Skin and Integumentary System

Introduction

• Skin is the largest organ of the human body.
• Functions: protection against infection and extreme temperatures, fluid balance, vitamin D synthesis.
• Sensory role: nerve endings allow sensation of the external world.
• Communication role: blushing, flushing, sweating.
• Accounts for 3-5 kg of body weight, covering up to 2 square meters.
• Part of the integumentary system along with hair, nails, sweat, and oil glands.

Structure of Skin

• Three main layers:
  • Epidermis: Only visible layer, made of stratified squamous epithelial tissue.
  • Dermis: Middle layer, responsible for most skin functions like sweating, blood circulation, sensation.
  • Hypodermis (Subcutis): Bottom layer, composed of adipose tissue, provides insulation and energy storage.

Epidermal Cells

• Keratinocytes: Form keratin, provide durability and waterproofing.
• Melanocytes: Produce melanin, determine skin color.
• Langerhans Cells: Immune cells, originate from bone marrow, ingest invaders.
• Merkel Cells: Sensory receptors for touch.

Differences in Skin Thickness

• Thick Skin: Found on palms and soles, consists of five layers.
• Thin Skin: Covers the rest of the body, consists of four layers.

Layers of the Epidermis

1. Stratum Corneum: Outermost, roughest layer of dead keratinocytes.
2. Stratum Lucidum: Clear layer found only in thick skin.
3. Stratum Granulosum: Granular layer, living keratinocytes forming keratin.
4. Stratum Spinosum: Spiny layer, active cell regeneration.
5. Stratum Basale: Basal layer, cell factory, connects epidermis to dermis.

Dermis

• Papillary Layer: Upper layer with peg-like dermal papillae, forms fingerprints.
• Reticular Layer: Thick, made of dense, irregular connective tissue.
• Houses capillaries, nerve fibers, parts of hair follicles, glands.

Hypodermis

• Composed mainly of adipose tissue.
• Functions: insulation, energy storage, shock absorption, anchors skin.

Skin Health and Protection

• Importance of sun protection: UV radiation can damage skin, risk of skin cancer.
• Immune system in the epidermis can be temporarily depressed by sunburn.

Tattoos

• Needles must reach the dermis to make tattoos permanent.

Conclusion

• Overview of skin structure, layers, functions.
• Upcoming lesson topics: effects of lotion, deodorant, and hair care.

Acknowledgments

• Written by Kathleen Yale, edited by Blake DePastino.
• Consultant: Dr. Brandon Jackson.
• Directed and edited by Nicholas Jenkins.
• Graphics by Dot Cafe.