Integumentary System - Part 1 Lecture Notes

Introduction

• Lecture on the integumentary system, focusing on the skin.
• Comparison: Skin as a valuable jacket with features like waterproof, stretchable, washable, self-repairing.
• Main Idea: Skin is a complex organ system providing protection, sensory functions, and more.

Skin as an Organ

• Misconception: Many do not consider skin an organ like heart or liver.
• Definition: An organ is a structure with several tissues working together.
• Skin is the largest organ, accounting for 7% of total body weight.
• Varies in thickness: 1.5 mm (e.g., forearm) to 4 mm (e.g., palms, soles).

Structure of the Skin

• Epidermis: Upper layer, composed of epithelial tissue, primarily keratinized stratified squamous epithelium.
• Dermis: Below the epidermis, made of connective tissue.
• Hypodermis: Not part of the skin, composed mainly of fat tissue, anchors skin to underlying structures.

Functions of the Skin

• Protection: Barrier against mechanical damage, pathogens, and UV radiation.
• Thermoregulation: Vasodilation and vasoconstriction manage heat loss/gain.
• Excretion: Sweat glands excrete waste products like urea and salts.
• Sensation: Contains receptors for touch, pain, temperature, and pressure.

Layers of the Epidermis

1. Stratum Basale: Deepest layer, single cell layer, contains keratinocytes, melanocytes, and Merkel cells.
2. Stratum Spinosum: Several cell layers thick, contains keratinocytes and Langerhans cells.
3. Stratum Granulosum: 1-5 cell layers, cells contain keratohyalin and lamellated granules.
4. Stratum Lucidum: Found only in thick skin (palms/soles), few rows of dead keratinocytes.
5. Stratum Corneum: Outermost layer, many dead keratinized cells providing a tough protective layer.

Cell Types in the Epidermis

• Keratinocytes: Most abundant, produce keratin.
• Melanocytes: Produce melanin, protect against UV damage.
• Merkel Cells: Touch receptors.
• Langerhans Cells: Part of the immune system, present antigens.

Dermis Structure

• Composed of areolar and dense irregular connective tissue.
• Papillary Layer: Upper 20%, contains dermal papillae which create fingerprints.
• Reticular Layer: Lower 80%, network of collagen fibers.

Blood Supply and Thermoregulation

• Two blood vessel networks: Cutaneous Plexus (deep) and Subpapillary Plexus (superficial).
• Involved in temperature regulation by controlling blood flow.

Hypodermis

• Not part of the skin but shares some functions.
• Composed mostly of adipose tissue, aids in insulation and anchoring the skin.

Skin Color

• Determined by three pigments: melanin, carotene, and hemoglobin.
• Melanin: Produced by melanocytes, provides UV protection.
• Carotene: Yellow-orange pigment found in certain foods.
• Hemoglobin: Red pigment in blood contributing to skin color.
• Variations based on genetics and environmental exposure (e.g., UV light exposure).

Conclusion

• This lecture covered the structure, function, and importance of the integumentary system.
• The integumentary system is vital for protection, sensation, and overall homeostasis.

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This concludes part one of the integumentary system lecture. Part two will continue exploring this topic.