Review Sheet Exercise 7 The Integumentary System

The integumentary system, encompassing the skin, hair, and nails, is the body's largest organ system, serving as a protective barrier against the external environment. Understanding its structure and function is paramount in fields ranging from dermatology to general medicine. This review delves into the intricacies of the integumentary system, exploring its various layers, specialized structures, and crucial physiological roles.

Anatomy of the Integumentary System

The integumentary system is composed of two primary layers: the epidermis and the dermis, which are anchored to the underlying hypodermis (subcutaneous layer). Each layer possesses unique characteristics and contributes to the overall function of the system.

Epidermis: The Outermost Shield

The epidermis, the outermost layer of the skin, is a stratified squamous epithelium composed of four or five distinct layers, depending on the region of the body. It is avascular, meaning it lacks blood vessels, and relies on diffusion from the underlying dermis for nutrients. The primary cell type of the epidermis is the keratinocyte, which produces keratin, a fibrous protein that provides strength and waterproofing to the skin.

• Layers of the Epidermis:

  • Stratum Basale (Basal Layer): The deepest epidermal layer, attached to the basement membrane separating the epidermis from the dermis. It contains actively dividing keratinocytes, melanocytes (producing melanin pigment), and tactile epithelial cells (Merkel cells) associated with sensory nerve endings.
  • Stratum Spinosum (Spiny Layer): Several layers of keratinocytes connected by desmosomes, providing strength and flexibility. Langerhans cells (dendritic cells), immune cells that protect against pathogens, are also present.
  • Stratum Granulosum (Granular Layer): Keratinocytes begin to flatten and accumulate keratohyalin granules, which contribute to keratinization, and lamellar granules, which release lipids to create a water-resistant barrier.
  • Stratum Lucidum (Clear Layer): A thin, translucent layer found only in thick skin (palms and soles). It consists of flattened, dead keratinocytes filled with eleidin, a precursor to keratin.
  • Stratum Corneum (Horny Layer): The outermost layer, composed of 20-30 layers of flattened, dead keratinocytes filled with keratin. These cells are continuously shed and replaced, providing a protective barrier against abrasion, penetration, and water loss.

• Cell Types in the Epidermis:

  • Keratinocytes: The most abundant cell type, producing keratin for strength and waterproofing.
  • Melanocytes: Produce melanin, a pigment that absorbs UV radiation and protects DNA from damage.
  • Langerhans Cells: Immune cells that detect and engulf pathogens.
  • Tactile Epithelial Cells (Merkel Cells): Associated with sensory nerve endings and involved in light touch sensation.

Dermis: The Supporting Layer

The dermis, the layer beneath the epidermis, is a strong, flexible connective tissue layer that supports and nourishes the epidermis. It is richly supplied with blood vessels, nerves, hair follicles, and glands. The dermis is composed of two layers: the papillary layer and the reticular layer.

• Layers of the Dermis:

  • Papillary Layer: The superficial layer of the dermis, consisting of areolar connective tissue with dermal papillae that project into the epidermis. These papillae contain capillaries and sensory nerve endings, providing nutrients and sensation to the epidermis. In thick skin, the papillae form epidermal ridges, which create fingerprints and footprints, enhancing grip.
  • Reticular Layer: The deeper, thicker layer of the dermis, composed of dense irregular connective tissue with collagen and elastic fibers. These fibers provide strength, elasticity, and resilience to the skin. The reticular layer also contains blood vessels, nerves, hair follicles, sebaceous glands, and sweat glands.

• Structures in the Dermis:

  • Collagen Fibers: Provide strength and structural support to the skin.
  • Elastic Fibers: Allow the skin to stretch and recoil.
  • Blood Vessels: Supply nutrients and oxygen to the skin and regulate body temperature.
  • Nerve Fibers: Transmit sensory information, such as touch, pressure, pain, and temperature.
  • Hair Follicles: Structures that produce hair.
  • Sebaceous Glands: Secrete sebum, an oily substance that lubricates the skin and hair.
  • Sweat Glands: Secrete sweat, which helps regulate body temperature.

Hypodermis (Subcutaneous Layer): The Anchor

The hypodermis, also known as the subcutaneous layer, is the layer beneath the dermis. It is composed of adipose tissue (fat) and areolar connective tissue. The hypodermis anchors the skin to the underlying muscles and bones, provides insulation, and stores energy.

• Functions of the Hypodermis:

  • Anchoring: Connects the skin to underlying structures.
  • Insulation: Adipose tissue provides thermal insulation, helping to regulate body temperature.
  • Energy Storage: Adipose tissue stores energy in the form of fat.
  • Cushioning: Provides cushioning and protection for underlying tissues and organs.

Accessory Structures of the Integumentary System

The integumentary system includes several accessory structures, such as hair, nails, and glands, which are derived from the epidermis and extend into the dermis. These structures perform specialized functions that contribute to the overall health and protection of the body.

Hair: Protection and Sensation

Hair is a flexible, filamentous structure composed of dead, keratinized cells. It is found all over the body, except for the palms, soles, lips, nipples, and parts of the external genitalia. Hair provides protection against UV radiation, insulates against heat loss, and provides sensory input.

• Structure of Hair:

  • Hair Follicle: A tube-like invagination of the epidermis that extends into the dermis or hypodermis.
  • Hair Root: The portion of the hair within the follicle.
  • Hair Shaft: The portion of the hair that projects above the skin surface.
  • Hair Bulb: The expanded base of the hair follicle, containing the hair matrix where new hair cells are produced.
  • Arrector Pili Muscle: A small smooth muscle attached to the hair follicle that contracts to raise the hair, creating "goosebumps."

• Functions of Hair:

  • Protection: Protects the scalp from UV radiation and the eyes from debris.
  • Insulation: Traps a layer of air near the skin surface, providing insulation against heat loss.
  • Sensation: Hair follicles are associated with sensory nerve endings, providing sensory input.

Nails: Protection and Manipulation

Nails are hard, keratinized plates that cover the distal ends of the fingers and toes. They protect the fingertips and toes from injury and aid in grasping and manipulating objects.

• Structure of Nails:

  • Nail Plate: The visible portion of the nail, composed of dead, keratinized cells.
  • Nail Bed: The skin beneath the nail plate.
  • Nail Matrix: The proximal portion of the nail bed, where new nail cells are produced.
  • Lunula: The white, crescent-shaped area at the base of the nail, where the nail matrix is visible.
  • Eponychium (Cuticle): A fold of skin that covers the nail root.
  • Hyponychium: The area beneath the free edge of the nail.

• Functions of Nails:

  • Protection: Protects the fingertips and toes from injury.
  • Manipulation: Aids in grasping and manipulating objects.

Glands: Secretion and Regulation

The integumentary system contains several types of glands, including sebaceous glands, sweat glands, and mammary glands. These glands secrete various substances that lubricate the skin, regulate body temperature, and provide nourishment.

• Sebaceous Glands:

  • Function: Secrete sebum, an oily substance that lubricates the skin and hair, preventing them from drying out. Sebum also has antibacterial properties.
  • Location: Found all over the body, except for the palms and soles. Most abundant on the face and scalp.

• Sweat Glands:

  • Eccrine Sweat Glands:
    • Function: Secrete sweat, a watery solution containing salts, urea, and other waste products. Sweat helps regulate body temperature through evaporative cooling.
    • Location: Found all over the body, especially on the palms, soles, and forehead.
  • Apocrine Sweat Glands:
    • Function: Secrete a thicker, oily sweat that contains pheromones. These glands become active during puberty and are associated with body odor.
    • Location: Found in the axillae (armpits), groin, and around the nipples.

• Mammary Glands:

  • Function: Secrete milk to nourish infants.
  • Location: Located in the breasts.

Functions of the Integumentary System

The integumentary system performs a wide range of functions that are essential for maintaining homeostasis and protecting the body from the external environment.

Protection: The Primary Defense

The integumentary system acts as a physical barrier that protects the body from a variety of threats, including:

• Mechanical Damage: The skin protects underlying tissues from abrasion, pressure, and trauma.
• Chemical Damage: The skin provides a barrier against harmful chemicals and irritants.
• Infection: The skin prevents the entry of pathogens, such as bacteria, viruses, and fungi. Langerhans cells in the epidermis also play a role in immune defense.
• UV Radiation: Melanin in the epidermis absorbs UV radiation, protecting DNA from damage.
• Dehydration: The skin prevents excessive water loss, maintaining hydration.

Thermoregulation: Maintaining Body Temperature

The integumentary system plays a crucial role in regulating body temperature through several mechanisms:

• Sweating: Eccrine sweat glands secrete sweat, which evaporates from the skin surface, cooling the body.
• Vasodilation: Blood vessels in the dermis dilate, increasing blood flow to the skin surface, allowing heat to dissipate.
• Vasoconstriction: Blood vessels in the dermis constrict, reducing blood flow to the skin surface, conserving heat.
• Insulation: Adipose tissue in the hypodermis provides thermal insulation, helping to retain heat.

Sensation: Responding to the Environment

The integumentary system contains a variety of sensory receptors that detect touch, pressure, pain, and temperature. These receptors allow the body to respond to changes in the external environment.

• Tactile Epithelial Cells (Merkel Cells): Detect light touch.
• Tactile Corpuscles (Meissner's Corpuscles): Detect light touch and texture.
• Lamellar Corpuscles (Pacinian Corpuscles): Detect deep pressure and vibration.
• Bulbous Corpuscles (Ruffini Endings): Detect sustained pressure and stretch.
• Free Nerve Endings: Detect pain, temperature, and itch.

Vitamin D Synthesis: Essential for Bone Health

The skin synthesizes vitamin D when exposed to UV radiation. Vitamin D is essential for calcium absorption, which is necessary for bone health.

Excretion: Eliminating Waste Products

The integumentary system excretes small amounts of waste products, such as salts, urea, and ammonia, through sweat.

Clinical Significance of the Integumentary System

The integumentary system is susceptible to a variety of disorders and conditions, ranging from minor skin irritations to life-threatening diseases. Understanding these conditions is crucial for diagnosis and treatment.

Common Skin Disorders

• Acne: A common skin condition characterized by pimples, blackheads, and whiteheads. It is caused by clogged hair follicles and inflammation.
• Eczema (Atopic Dermatitis): A chronic inflammatory skin condition characterized by itchy, red, and inflamed skin.
• Psoriasis: A chronic autoimmune disease characterized by thick, scaly patches of skin.
• Skin Cancer: The most common type of cancer, caused by uncontrolled growth of skin cells. There are three main types: basal cell carcinoma, squamous cell carcinoma, and melanoma.
• Infections: Bacterial, viral, and fungal infections can affect the skin, causing a variety of symptoms.

Burns

Burns are injuries to the skin caused by heat, radiation, chemicals, or electricity. They are classified based on their depth:

• First-Degree Burns: Affect only the epidermis, causing redness and pain.
• Second-Degree Burns: Affect the epidermis and part of the dermis, causing blisters and pain.
• Third-Degree Burns: Affect the epidermis, dermis, and underlying tissues, causing severe damage and potential nerve damage.

Aging and the Integumentary System

As the body ages, the integumentary system undergoes several changes:

• Decreased Collagen and Elastin: The skin loses elasticity and becomes thinner, leading to wrinkles and sagging.
• Decreased Melanin Production: The skin becomes more susceptible to UV damage.
• Decreased Sweat Gland Activity: The body becomes less efficient at regulating temperature.
• Decreased Blood Flow: The skin becomes paler and heals more slowly.

Review Questions and Answers

Question 1: What are the layers of the epidermis in order from superficial to deep?

Answer: Stratum corneum, stratum lucidum (only in thick skin), stratum granulosum, stratum spinosum, stratum basale.

Question 2: What is the function of melanin?

Answer: Melanin absorbs UV radiation and protects DNA from damage.

Question 3: What are the two layers of the dermis?

Answer: Papillary layer and reticular layer.

Question 4: What type of tissue is found in the hypodermis?

Answer: Adipose tissue and areolar connective tissue.

Question 5: What are the functions of hair?

Answer: Protection, insulation, and sensation.

Question 6: What is sebum and what gland secretes it?

Answer: Sebum is an oily substance that lubricates the skin and hair. It is secreted by sebaceous glands.

Question 7: What are the two types of sweat glands and what are their functions?

Answer: Eccrine sweat glands secrete sweat for thermoregulation. Apocrine sweat glands secrete a thicker, oily sweat that contains pheromones.

Question 8: How does the integumentary system help regulate body temperature?

Answer: Through sweating, vasodilation, vasoconstriction, and insulation.

Question 9: What are the functions of the integumentary system?

Answer: Protection, thermoregulation, sensation, vitamin D synthesis, and excretion.

Question 10: What are the three main types of skin cancer?

Answer: Basal cell carcinoma, squamous cell carcinoma, and melanoma.

Conclusion

The integumentary system is a complex and vital organ system that protects the body from the external environment, regulates body temperature, provides sensation, and performs a variety of other essential functions. Understanding the structure and function of the integumentary system is crucial for maintaining health and preventing disease. This review provides a comprehensive overview of the integumentary system, covering its anatomy, physiology, and clinical significance.