Integumentary System Functions and Structure

Integumentary System

• Consists of the cutaneous membrane (skin) and accessory structures such as hair follicles, nails, and exocrine glands.
• Skin is composed of two layers: the epidermis (superficial layer) and dermis (deeper layer).
• Hypodermis (subcutaneous layer) lies beneath the skin, composed of loose connective tissue and is not considered part of the integument.

Functions of Skin and Hypodermis

• Protection: from impact, abrasion, fluid loss, chemicals.
• Excretion: of salts, water, and organic waste.
• Temperature regulation: helps maintain body temperature.
• Synthesis of Vitamin D3: converted to calcitriol, a hormone essential for calcium absorption from the intestine.
• Storage of lipids: in adipocytes of the hypodermis.
• Sensation: innervated with tactile receptors sensitive to touch, pressure, and vibration.
• Production of melanin: protects cells from UV radiation.
• Production of keratin: protects from dehydration.

Epidermis

• Composed of stratified squamous epithelium, avascular, and lacks blood vessels.
• Superficial cells are dead and inert, stem cells are located in the deepest layer.
• Pressure, wear, and tear stimulate rapid cell division, leading to thickening of the epidermis.
• Blisters form when friction or damage from extreme temperatures cause layers of the epidermis to separate, and the gaps fill with fluid.

Cell Types in Stratum Germinativum

• Basal cells: stem cells responsible for producing new epidermal cells.
• Melanocytes: pigment producing cells that synthesize melanin, providing protection against UV radiation.
• Merkel cells: sensitive to light touch, activating nerve endings by releasing chemicals.

Layers of the Epidermis

• Stratum spinosum: 8-10 layers of keratinocytes joined by desmosomes, containing Langerhans cells (phagocytes) that engulf and destroy damaged cells and pathogens.
• Stratum granulosum: 3-5 layers of keratinocytes that produce keratin, a protective protein.
• Stratum lucidum: a clear layer found only in thick skin, densely packed with keratin and devoid of organelles.
• Stratum corneum: the outermost layer, composed of 15-30 layers of dead, keratinized cells tightly interconnected by desmosomes, creating a water-resistant barrier.

Skin Color

• Carotene: an orange-yellow pigment found in orange vegetables and stored in adipocytes.
• Melanin: a yellow-brown pigment produced from the amino acid tyrosine by melanocytes.
• Hemoglobin: the oxygen-carrying pigment in red blood cells, contributes to skin color.
• Melanin is packaged into vesicles called melanosomes and passed to keratinocytes.
• The rate of melanin breakdown determines skin color.
  • Lighter skin: melanosomes break down in the stratum germinativum and spinosum, leading to a faster breakdown and lighter pigment.
  • Darker skin: melanosomes break down in the stratum granulosum, leading to a slower breakdown and darker pigment.

Hair

• Insulates and protects the scalp from damage.
• Protects nostrils and ear canals from debris.
• Detects movement through the hair plexus sensory nerve.
• Arrector pili muscle causes hair to stand up (goosebumps).

Hair Growth Cycle

• Active phase: hair grows continuously for 2-5 years.
• Regression phase: follicle begins to shrink and transition to the resting phase.
• Resting phase: hair loses its attachment to the follicle and becomes a club hair.
• Shedding phase: the club hair is shed, and the hair matrix begins producing a replacement hair.

This quiz covers the integumentary system, including the structure and functions of skin and its associated components. Learn about how the skin protects the body, regulates temperature, and contributes to sensory perception. Test your understanding of the layers of skin and the role of the hypodermis.