Integumentary System Lesson 5

Integumentary System Overview

• Composed of skin (largest organ), sweat glands, sebaceous glands, hairs, and nails.
• Skin also referred to as integument, meaning "covering."

Functions of Skin

• Maintains hydration and prevents loss of essential molecules.
• Acts as a barrier to external elements, protecting against mechanical, chemical, and thermal damage.
• Insulates and cushions internal organs.
• Regulates body heat loss and acts as an excretory system via sweat.
• Manufactures essential immune-related proteins and stores vitamin D precursor.
• Contains sensory receptors for touch, pressure, temperature, and pain.

Principal Layers of Skin

• Epidermis: outer protective layer.
• Dermis: deeper supportive layer.

Epidermis Details

• Superficial layer composed of stratified squamous keratinized epithelium.
• Contains 4-5 layers, with the palms and soles featuring five due to increased friction.

Layers of Epidermis

• Stratum Basale: Base layer with keratinocytes (produce keratin), melanocytes (synthesize melanin), tactile cells (Merkel cells for touch), and Langerhans cells (immune response).
• Stratum Spinosum: Spiny appearance due to keratinocyte shape; limited mitosis occurs here.
• Stratum Granulosum: 3-4 flattened cell layers; presence of keratohyaline granules gives a granular appearance.
• Stratum Lucidum: Clear layer found in thick skin areas; contains eleidin.
• Stratum Corneum: Outermost layer, 25-30 layers of anucleated cells, continuously shed and provides protective cornified layer.

Skin Coloration

• Resulting from three pigments: melanin, carotene, and hemoglobin.

Melanin

• Brown-black pigment from melanocytes, protects against UV rays.
• Increased production due to sun exposure leads to tanning.
• Absence of tyrosinase in albinos results in no melanin production despite normal melanocyte numbers.
• Freckles: aggregates of melanin; vitiligo: localized loss of melanocytes.

Carotene

• Yellowish pigment located in the epidermis and dermis, prominent in certain ethnicities.
• Contributes to yellowish-tan skin tone.

Hemoglobin

• Oxygen-binding pigment in RBCs; contributes to skin's pinkish hue via oxygenated blood in the dermis.

Surface Patterns of Skin

• Congenital Patterns: Fingerprints or friction ridges, formed by elastic fibers, aid in gripping.
• Acquired Lines:
  • Deep flexion creases on palms.
  • Shallow flexion lines on knuckles.
  • Wrinkles from repeated facial muscle contractions.