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Integumentary System

Chapter Overview

This chapter discusses the Integumentary System, focusing primarily on the skin, its structure, function, and various appendages.

Skin (Integument)

Definition

  • Skin (Integument): Composed of two distinct regions:
    (1) Epidermis: Superficial region made of epithelial tissue.
    (2) Dermis: Deeper layer made of mostly fibrous connective tissue.

Hypodermis

  • Hypodermis (Superficial fascia):

    • Not part of the skin.

    • Composed mostly of adipose tissue.

    • Functions: Absorbs shock, insulates, anchors skin to underlying structures (mostly muscles).

Skin Structure

Components of Skin

  • Epidermis: Outermost layer.

  • Dermis: Beneath the epidermis.

  • Hypodermis: Subcutaneous tissue behaving as an anchor for the skin.

Detailed Skin Structure

Epidermis

  • Structure:

    • Keratinized Stratified Squamous Epithelium: Comprising four to five distinct layers.

    • Cell Types:

    1. Keratinocytes: Produce keratin, tightly connected by desmosomes.

    2. Melanocytes: Produce melanin and provide color.

    3. Dendritic (Langerhans) cells: Act as immune system macrophages.

    4. Tactile (Merkel) cells: Function as touch receptors.

Layers of the Epidermis

  1. Stratum Basale:

    • Deepest layer; actively mitotic stem cells.

    • Melanocytes are present (10-25%).

    • New cells migrate upwards, takes 25-45 days to reach the surface.

  2. Stratum Spinosum:

    • Several layers thick with cells unified by desmosomes.

    • Contains abundant melanosomes and dendritic cells.

  3. Stratum Granulosum:

    • Cells start to flatten; organelles disintegrate.

    • Keratinization begins; cells accumulate keratohyaline and lamellar granules (water-resistant).

  4. Stratum Lucidum:

    • Present only in thick skin; translucent.

  5. Stratum Corneum:

    • Outermost layer; consists of 20-30 rows of dead, keratinized cells.

    • Protects deeper tissue and acts as a barrier against physical, chemical, and biological damage.

Cells of the Epidermis

Cell Types and Functions

  • Keratinocytes:

    • Form 90% of the epidermis.

    • Produce keratin, an essential fibrous protein.

  • Melanocytes:

    • Present in the stratum basale.

    • Produce melanin, which protects keratinocyte nuclei from UV damage.

  • Dendritic (Langerhans) Cells:

    • Act as macrophages in the epidermis, key players in the immune response.

  • Tactile (Merkel) Cells:

    • Involved in touch sensation.

Layers of the Dermis

Overview

  • Dermis: Strong, flexible connective tissue consisting of:

    • Cells: Including fibroblasts, macrophages, and occasionally mast cells.

    • Contains: Nerve fibers, blood, and lymphatic vessels.

    • Has accessories: Hair follicles, oil glands, and sweat glands.

Layers of the Dermis

  • Papillary Layer:

    • Composed of areolar connective tissue.

    • Contains dermal papillae (peg-like projections that contain capillary loops and touch receptors).

  • Reticular Layer:

    • Comprises ~80% of dermis thickness.

    • Contains dense fibrous connective tissue allowing for strength, elasticity, and provides a structural network.

Skin Markings and Characteristics

Types of Skin Marks

  • Flexure Lines: Locations where the dermis is tightly secured to underlying structures, leading to deep creases (common visible on joints).

  • Striae: Stretch marks caused by dermal tears during extreme stretching.

  • Blisters: Formed by acute trauma leading to fluid-filled pockets separating layers of skin.

Skin Color

Contributing Factors

  • Melanin: Main pigment produced in skin, helps protect against UV radiation.

    • Variations increase with sun exposure.

  • Carotene: Yellow to orange pigment accumulates in the stratum corneum and fat layers,
    significant for vitamin A synthesis.

  • Hemoglobin: Contributes to a pinkish hue in fair skin.

Skin Color in Diagnosis

  • Cyanosis: Blue color indicates low oxygen levels.

  • Erythema: Redness due to various conditions like fever or inflammation.

  • Pallor: Underlying blood issues or emotional states cause paleness.

  • Jaundice: Yellowing indicates liver dysfunction.

Appendages of the Skin

Types of Skin Appendages

  • Hair and Hair Follicles: Forms from keratinized cells, providing functions like insulation and protection.

  • Nails: Offer protection and support for fingers and toes.

  • Sweat and Sebaceous Glands: Provide moisture control and sebum production, respectively.

Hair Structure and Characteristics

  • Hair: Composed of dead keratinized cells, not found on certain areas like palms and soles.

  • Types: Vellus (fine body hair) and Terminal hair (coarser, thicker hair).

  • Growth: Average hair growth is approximately 2.25 mm per week.

Functions of the Integumentary System

  1. Protection: Forms barriers against chemical, physical, and biological assaults.

  2. Temperature Regulation: Adjusts blood flow and sweat output to regulate body temperature.

  3. Sensation: Contains receptors for touch, pressure, and pain.

  4. Metabolic Functions: Synthesizes essential molecules like Vitamin D.

  5. Blood Reservoir: Stores a significant volume of blood.

  6. Excretion: Removes waste products via sweat.

Skin Cancer

Types

  1. Basal Cell Carcinoma: Most common, arises from stratum basale, rarely metastasizes.

  2. Squamous Cell Carcinoma: Second-most common, arises from keratinocytes, higher risk of metastasis.

  3. Melanoma: Most dangerous, originating from melanocytes, highly metastatic.

Detection and Treatment

  • Early detection critical; use the ABCD rule for moles:

    • Asymmetry,

    • Border irregularity,

    • Color variation,

    • Diameter greater than 6 mm (size of a pencil eraser).

Burns

Classification

  1. Partial-Thickness Burns:

    • First Degree: Only epidermal damage, redness/pain.

    • Second Degree: Epidermis and part of dermis affected, blisters appear.

  2. Full-Thickness Burns:

    • Involving entire thickness of skin with possibly deeper tissue.

Severity and Treatment

  • Evaluated using the Rule of Nines to estimate fluid loss.

  • Critical if extensive body surface is affected, treatment may include skin grafts.

Conclusion

The integumentary system plays a crucial role in protection, sensation, and regulating body processes. Understanding its structure and functions is essential for diagnosing skin conditions and potential diseases. This knowledge empowers healthcare professionals and promotes personal skincare and health practices.

Study Guide Questions
1. What are the Integumentary system’s components?

The Integumentary system's primary components are the skin (integument), which consists of two distinct regions: the Epidermis (superficial region of epithelial tissue) and the Dermis (deeper layer of mostly fibrous connective tissue). Additionally, the Hypodermis (superficial fascia), though not technically part of the skin, is closely associated with it, composed mostly of adipose tissue. The system also includes various Appendages of the Skin, such as hair and hair follicles, nails, and sweat and sebaceous glands.

2. Structure of the skin. Describe briefly the types of cells present in the Epidermis. What is the function of Stratum Basale, Stratum granulosum and Stratum Corneum?

Structure of the Skin
The skin is composed of two main layers: the Epidermis and the Dermis.

  • Epidermis: The outermost layer, a keratinized stratified squamous epithelium.

  • Dermis: Located beneath the epidermis, it is a strong, flexible connective tissue layer.

  • Hypodermis: Located below the dermis, it anchors the skin to underlying structures and provides insulation and shock absorption.

Types of Cells Present in the Epidermis
The epidermis contains four main cell types:

  1. Keratinocytes: Produce keratin, an essential fibrous protein, forming 90% of the epidermis.

  2. Melanocytes: Produce melanin, a pigment that protects keratinocyte nuclei from UV damage, found in the stratum basale.

  3. Dendritic (Langerhans) Cells: Act as immune system macrophages, key players in the immune response.

  4. Tactile (Merkel) Cells: Function as touch receptors, involved in touch sensation.

Functions of Epidermal Layers

  • Stratum Basale: The deepest layer, primarily responsible for continuous cell division to produce new keratinocytes that migrate upwards. It also contains melanocytes which produce melanin.

  • Stratum Granulosum: This layer initiates keratinization and the formation of water-resistant lamellar granules. Cells begin to flatten, and organelles disintegrate.

  • Stratum Corneum: The outermost layer, consisting of 20-30 rows of dead, keratinized cells. Its main function is to protect deeper tissue and act as a barrier against physical, chemical, and biological damage, as well as water loss.

3. Describe the structure of the Dermis. What kind of tissue is present in the Papillary layer and/or in Reticular Layer?

Structure of the Dermis
The Dermis is a strong, flexible connective tissue underlying the epidermis. It consists of cells such as fibroblasts, macrophages, and occasionally mast cells. It is richly supplied with nerve fibers, blood, and lymphatic vessels, and houses hair follicles, oil glands, and sweat glands.

Tissue Types in Dermal Layers

  • Papillary Layer: This superficial dermal layer is composed of areolar connective tissue. It contains dermal papillae, which are peg-like projections that house capillary loops and touch receptors.

  • Reticular Layer: This deeper layer comprises approximately 80% of the dermis thickness and is composed of dense fibrous connective tissue. This tissue provides strength, elasticity, and forms a structural network for the skin.

4. What are the friction ridges? Describe briefly the pigments responsible for the skin colors.

Friction Ridges
Friction Ridges are epidermal ridges that lie atop dermal ridges. They are genetically determined, enhance gripping ability, and contribute to unique fingerprints, found on the palms of the hands and soles of the feet.

Pigments Responsible for Skin Colors
Three pigments contribute to skin color:

  1. Melanin: The main pigment produced in the skin by melanocytes in the stratum basale. It ranges in color from reddish-yellow to brownish-black and helps protect against UV radiation. Exposure to sun increases melanin production.

  2. Carotene: A yellow to orange pigment typically found in the stratum corneum and in the fat of the hypodermis. It is especially significant for vitamin A synthesis.

  3. Hemoglobin: A reddish pigment found in oxygenated blood flowing through the dermal capillaries. It contributes to the pinkish hue seen in fair skin.

5. Describe all the differences between Eccrine Sweat Glands, Apocrine Sweat Gland and Sebaceous Glands: location, are they always active during our life? Differences in structure and composition of secretion. Composition of sweat and sebum.

Here are the differences between the major skin glands:

  • Eccrine (Merocrine) Sweat Glands

    • Location: Most numerous, abundant on palms, soles, and forehead.

    • Activity: Always active throughout life, starting shortly after birth.

    • Structure: Simple, coiled tubular gland; ducts open directly onto the skin surface via a pore.

    • Composition of Secretion (Sweat): Primarily 99% water, with salts (NaCl), vitamin C, antibodies, dermcidin (antimicrobial peptide), and metabolic wastes (urea, uric acid, ammonia). It has an acidic pH (between 4 and 6).

  • Apocrine Sweat Glands

    • Location: Confined to the axillary (armpit) and anogenital areas.

    • Activity: Begin functioning at puberty under hormonal influence; not significantly involved in thermoregulation in humans.

    • Structure: Larger than eccrine glands; ducts usually empty into hair follicles.

    • Composition of Secretion: Contains true sweat, plus fatty substances and proteins. It is odorless when secreted, but bacterial decomposition of its organic molecules produces body odor.

  • Sebaceous (Oil) Glands

    • Location: Widely distributed over the entire body, except on palms and soles. Most develop from and secrete into hair follicles.

    • Activity: Relatively inactive during childhood; become very active during puberty, stimulated by androgens (male sex hormones).

    • Structure: Simple branched alveolar glands; holocrine secretion (whole cells rupture).

    • Composition of Secretion (Sebum): An oily secretion composed of lipids (triglycerides, cholesterol), fatty acids, and fragmented cells. Its functions include softening and lubricating hair and skin, preventing hair from becoming brittle, slowing water loss, and providing bactericidal properties.

6. List and describe all the functions of the Integumentary System. Be able to describe the Chemical, physical and biological barriers.

The Integumentary System performs several crucial functions:

  1. Protection: Forms barriers against various environmental threats.

    • Chemical Barrier: Skin secretions (sweat's acid mantle, dermcidin; sebum; melanin) protect against microbes and UV radiation. The low pH inhibits bacterial growth.

    • Physical Barrier: The continuity of the epidermal layers, especially the hardened keratinized cells of the stratum corneum tightly linked by desmosomes, provides a durable barrier against trauma, pathogen invasion, and water loss (aided by glycolipids).

    • Biological Barrier: Epidermal dendritic cells (macrophages) engulf foreign antigens and present them to lymphocytes. Dermal macrophages dispose of viruses and bacteria. DNA also absorbs UV radiation, acting as a shield.

  2. Temperature Regulation: Adjusts blood flow through the dermal vascular plexus and controls sweat production via eccrine glands to dissipate heat or conserve it.

  3. Sensation: Contains numerous sensory receptors for touch, pressure, temperature (cold and heat), and pain, allowing the body to interact with its environment.

  4. Metabolic Functions: Synthesizes Vitamin D (cholecalciferol) upon exposure to sunlight. Keratinocyte enzymes can also activate hormones and detoxify certain chemicals.

  5. Blood Reservoir: Stores approximately 5% of the body's total blood volume in the extensive dermal vascular plexus, which can be shunted to other organs when needed.

  6. Excretion: Removes limited amounts of nitrogenous wastes (ammonia, urea, uric acid) in sweat, along with water and salts.

7. Types of skin cancer. ABCD rule.

Types of Skin Cancer

  1. Basal Cell Carcinoma: The most common type, originating from cells in the stratum basale. It is slow-growing and rarely metastasizes.

  2. Squamous Cell Carcinoma: The second most common type, arising from keratinocytes of the stratum spinosum. It grows rapidly and has a higher risk of metastasis if not removed.

  3. Melanoma: The most dangerous type, originating from melanocytes. It is highly metastatic and resistant to chemotherapy, making early detection critical.

ABCD Rule for Detection
For early detection of melanoma, the ABCD rule is used for moles:

  • Asymmetry: The two halves of the mole do not match.

  • Border irregularity: The edges are notched, indented, or scalloped.

  • Color variation: The pigment is not uniform; it may have shades of tan, brown, black, red, or blue.

  • Diameter: The spot is greater than 6 mm in diameter (about the size of a pencil eraser).

8. Burns: evaluation of burn severity (Fig 5.9). First, second, third-degree burns (Fig 7.10)

Classification of Burns

  1. Partial-Thickness Burns

    • First-Degree Burns: Only the epidermis is damaged. Symptoms include localized redness, swelling, and pain. Healing typically occurs in 2-3 days without special treatment.

    • Second-Degree Burns: Involve damage to the epidermis and the upper part of the dermis. Symptoms include redness, swelling, pain, and the appearance of blisters. Healing usually takes 3-4 weeks if infection is prevented.

  2. Full-Thickness Burns

    • Third-Degree Burns: Involve the entire thickness of the skin, and sometimes deeper tissues. The burned area may appear gray-white, cherry red, or blackened. The area is numb because nerve endings are destroyed. Third-degree burns typically require skin grafting for healing.

Evaluation of Burn Severity (Rule of Nines)
Burn severity is evaluated using the Rule of Nines, a method to estimate the percentage of total body surface area (TBSA) affected by burns, which aids in assessing fluid loss and guiding treatment. Specific criteria define burns as critical:

  • Over 25% of the body has second-degree burns.

  • Over 10% of the body has third-degree burns.

  • Third-degree burns are located on the face, hands, or feet.