The Integumentary System

Fundamentals of Anatomy & Physiology: Chapter 5 - The Integumentary System

Learning Outcomes (1 of 3)

  • 5.1 Describe the main structural features of the epidermis, and explain the functional significance of each.
  • 5.2 Describe the structures and functions of the dermis.
  • 5.3 Describe the structures and functions of the subcutaneous layer.

Learning Outcomes (2 of 3)

  • 5.4 Explain what accounts for individual differences in skin color, and discuss the response of melanocytes to sunlight exposure.
  • 5.5 Describe the interaction between sunlight and vitamin D3 production.
  • 5.6 Describe the mechanisms that produce hair, and explain the structural basis for hair texture and color.

Learning Outcomes (3 of 3)

  • 5.7 Discuss the various kinds of glands in the skin, and list the secretions of those glands.
  • 5.8 Describe the anatomical structures of nails, and explain how they are formed.
  • 5.9 Explain how the skin responds to injury and repairs itself.
  • 5.10 Summarize the effects of aging on the skin.

The Integumentary System (1 of 5)

  • Overview: The integumentary system, also known as the integument, is the largest system of the body.
    • Comprises 16% of body weight.
    • Covers approximately 1.5 to 2 m² of surface area.
    • Composed of two major parts:
    • Cutaneous membrane (skin)
    • Accessory structures

The Integumentary System (2 of 5)

  • Components of the Cutaneous Membrane:
    • Outer Epidermis: Superficial epithelium.
    • Inner Dermis: Connective tissues.

The Integumentary System (3 of 5)

  • Accessory Structures:
    • Originate in the dermis and extend through the epidermis to the skin surface.
    • Include:
    • Hair and Hair Follicles
    • Exocrine Glands
    • Nails

The Integumentary System (4 of 5)

  • Additional Features of the integument:
    • Contains blood vessels.
    • Contains sensory receptors.
  • Subcutaneous Layer (Hypodermis):
    • Composed of loose connective tissue.
    • Lies below the dermis.

The Integumentary System (5 of 5)

  • Functions of the Integument:
    • Protection of underlying tissues and organs.
    • Excretion of salts, water, and organic wastes.
    • Maintenance of normal body temperature.
    • Production of melanin (protects against UV radiation).
    • Production of keratin (protects skin)
    • Synthesis of vitamin D.
    • Storage of lipids.
    • Detection of touch, pressure, pain, etc.
    • Coordination of the immune response.

5.1 Epidermis (1 of 12)

  • Structure:
    • Composed of stratified squamous epithelium.
    • Avascular (lacks blood vessels); nutrients and oxygen diffuse from capillaries in the dermis.

5.1 Epidermis (2 of 12)

  • Cells of the Epidermis:
    • Keratinocytes:
    • Most abundant epithelial cells.
    • Contain large amounts of keratin, a protective protein.

5.1 Epidermis (3 of 12)

  • Types of Skin:
    • Thin Skin: Covers most of the body with four layers of keratinocytes.
    • Thick Skin: Covers palms and soles with five layers of keratinocytes.

5.1 Epidermis (4 of 12)

  • Five Strata of Keratinocytes in Thick Skin (from basement membrane to free surface):
    • Stratum Basale
    • Stratum Spinosum
    • Stratum Granulosum
    • Stratum Lucidum
    • Stratum Corneum

5.1 Epidermis (5 of 12)

  • Stratum Basale (stratum germinativum):
    • Attached to the basement membrane by hemidesmosomes.
    • Forms a strong bond between epidermis and dermis.
    • Contains epidermal ridges, lying next to dermal papillae in dermis.
    • Has many basal (germinative) cells, which serve as stem cells that replace superficial keratinocytes.

5.1 Epidermis (6 of 12)

  • Specialized Structures of Stratum Basale:
    • Tactile Discs (Merkel cells):
    • Found in hairless skin, respond to touch.
    • Melanocytes:
    • Contain the pigment melanin, which protects skin from UV damage.

5.1 Epidermis (7 of 12)

  • Stratum Spinosum (spiny layer):
    • Contains 8 to 10 layers of keratinocytes bound by desmosomes.
    • Cells appear spiny in histological sections.
    • Produced by division of cells in stratum basale, some of which continue dividing.
    • Contains Dendritic (Langerhans) Cells involved in immune response.

5.1 Epidermis (8 of 12)

  • Stratum Granulosum (granular layer):
    • Contains 3 to 5 layers of keratinocytes produced from stratum spinosum.
    • Most cells stop dividing and produce:
    • Keratin: tough structural protein.
    • Keratohyalin: aids in keratin fiber crosslinking; promotes cellular dehydration.
    • After protein production, cells die.

5.1 Epidermis (9 of 12)

  • Stratum Lucidum (clear layer):
    • Present only in thick skin, covers stratum granulosum.

5.1 Epidermis (10 of 12)

  • Stratum Corneum (horny layer):
    • Exposed surface of epidermis; water resistant.
    • Composed of 15 to 30 layers of keratinized cells.
    • Keratinization: The process of forming protective layers filled with keratin.
    • New cells move from stratum basale to stratum corneum in 7 to 10 days; exposed cells are shed after two weeks.

5.1 Epidermis (11 of 12)

  • Water Loss from Skin:
    • Insensible Perspiration:
    • Water diffuses across stratum corneum and evaporates (approx. 500 mL/day).
    • Rate increases if stratum corneum is damaged (e.g., burns).
    • Sensible Perspiration:
    • Water excreted by sweat glands.

5.1 Epidermis (12 of 12)

  • Epidermal Growth Factor (EGF):
    • A peptide growth factor produced by salivary glands and duodenum.
    • Functions of EGF include:
    • Promotes division of basal cells.
    • Accelerates keratin production.
    • Stimulates epidermal repair.
    • Stimulates glandular secretion.

5.2 The Dermis (1 of 8)

  • Structure:
    • Located between epidermis and subcutaneous layer; anchors epidermal accessory structures (hair follicles, sweat glands).
    • Composed of two components:
    • Outer Papillary Layer
    • Deeper Reticular Layer.

5.2 The Dermis (2 of 8)

  • Papillary Layer:
    • Composed of areolar tissue; contains capillaries, lymphatic vessels, and sensory neurons.
    • Named for dermal papillae that project between epidermal ridges.
    • Becomes inflamed in dermatitis, which can produce itching or pain due to factors like infection or chemical irritants.

5.2 The Dermis (3 of 8)

  • Reticular Layer:
    • Composed of dense irregular connective tissue; contains collagen and elastic fibers.
    • Houses all cells of connective tissue proper.

5.2 The Dermis (4 of 8)

  • Dermal Strength and Elasticity:
    • Collagen Fibers:
    • Provide strength and resist stretching.
    • Allow bending or twisting but limit flexibility to prevent damage.
    • Elastic Fibers:
    • Allow stretching and return to original length, providing flexibility.
    • Together, fibers and water provide flexibility and resilience, known as skin turgor.

5.2 The Dermis (5 of 8)

  • Skin Damage:
    • Loss of skin turgor can be caused by:
    • Dehydration (reversible).
    • Aging.
    • Hormonal changes.
    • UV radiation exposure.
    • Excessive skin distortion can lead to stretch marks.

5.2 The Dermis (6 of 8)

  • Tension Lines (Cleavage Lines):
    • Produced by parallel bundles of collagen and elastic fibers in the dermis, which resist applied forces.
    • A cut parallel to a tension line heals well, while a cut at a right angle tends to pull open and scar.

5.2 The Dermis (7 of 8)

  • Dermal Blood Supply:
    • Cutaneous Plexus: Deep arteries network along the reticular layer.
    • Subpapillary Plexus: Small arteries network within papillary layer.
    • Capillaries drain into small veins, leading to larger veins in subcutaneous layer.
    • Contusion (Bruise): Caused by damage to blood vessels in dermis.

5.2 The Dermis (8 of 8)

  • Innervation of Skin:
    • Nerve fibers in skin control blood flow, gland secretion rates, and sensory receptor response.
    • Sensory receptors respond to:
    • Light Touch: Tactile (Meissner) corpuscles in dermal papillae.
    • Deep Pressure and Vibration: Lamellar (Pacinian) corpuscles in reticular layer.

5.3 The Subcutaneous Layer

  • Subcutaneous Layer (Hypodermis):
    • Lies deep to the dermis and is connected to it by connective tissue.
    • Stabilizes the skin's position.
    • Primarily adipose tissue; large arteries and veins are present in the superficial region.
    • Common site for subcutaneous injections (hypodermic needles).
    • Distribution of subcutaneous fat is influenced by sex hormones.

5.4 Skin Color (1 of 5)

  • Main Influencing Pigments:
    • Melanin: Red-yellow or brown-black pigment produced by melanocytes, protecting skin from UV radiation.
    • Carotene: Orange-yellow pigment found in orange vegetables (can convert to vitamin A).

5.4 Skin Color (2 of 5)

  • Melanin Production:
    • Stored in intracellular vesicles called melanosomes and transferred to keratinocytes.
    • Dark-skinned individuals have larger, more numerous melanosomes.
    • Small amounts of UV radiation are beneficial, but excessive exposure can damage DNA and lead to cancer.

5.4 Skin Color (3 of 5)

  • Carotene:
    • Found in epidermal cells, deep dermis, and subcutaneous layer; it is necessary for:
    • Maintenance of epithelial tissues.
    • Synthesis of photoreceptor pigments in the eye.

5.4 Skin Color (4 of 5)

  • Blood Flow and Oxygenation:
    • Hemoglobin, when bound to oxygen, appears bright red, causing reddening of skin upon blood vessel dilation.
    • When blood flow decreases, skin may pale; low oxygen causes cyanosis (bluish skin).

5.4 Skin Color (5 of 5)

  • Illness Impact on Skin Color:
    • Jaundice: Yellow skin due to bile buildup from liver dysfunction.
    • Pituitary Tumor: Causes excess production of melanin (MSH).
    • Addison’s Disease: Stimulates excess ACTH release, resembling MSH.
    • Vitiligo: Loss of melanocytes leading to patches of lost skin color.

5.5 Vitamin D3 Production

  • Vitamin D3 (Cholecalciferol):
    • Produced by epidermal cells in response to UV radiation.
    • Converted in the liver and kidneys into calcitriol, essential for calcium and phosphate ion absorption in the small intestine.
    • Insufficiency can lead to conditions like rickets.

5.6 Hair (1 of 9)

  • Accessory Structures of the Integument:
    • Includes hair, hair follicles, sebaceous glands, sweat glands, and nails.
    • Derived from embryonic epidermis, these structures are located within the dermis but extend to the skin surface.

5.6 Hair (2 of 9)

  • Hair Coverage:
    • Hairs cover nearly all body surfaces, except:
    • Palms of hands, sides of fingers, sides and soles of feet, sides of toes, lips, and certain parts of external genitalia.
  • Functions of Hair:
    • Provides protection and insulation.
    • Guards against particles and insects entering openings.
    • Acts as sensory receptors.

5.6 Hair (3 of 9)

  • Hair Follicles:
    • Extend deep into the dermis and produce nonliving hairs.
    • Wrapped in dense connective tissue sheaths and associated with sensory nerves (root hair plexus).
    • Arrector Pili Muscle:
    • Involuntary smooth muscle; contraction causes hairs to stand up (producing "goose bumps").

5.6 Hair (4 of 9)

  • Regions of the Hair:
    • Hair Root: Portion anchored into the skin.
    • Hair Shaft: The upper part of the hair extending above the skin.

5.6 Hair (5 of 9)

  • Hair Structure:
    • Medulla: Central core of the hair.
    • Cortex: Intermediate layer providing strength and color.
    • Cuticle: Surface layer that protects the hair.

5.6 Hair (6 of 9)

  • Layers of the Follicle:
    • Internal Root Sheath: Surrounds hair root.
    • External Root Sheath: Extends from skin surface to hair matrix.
    • Glassy Membrane: Clear layer surrounding the follicle's connective tissue sheath.

5.6 Hair (7 of 9)

  • Hair Production:
    • Initiates at the hair bulb, at the follicle base, surrounded by the hair papilla (connective tissue containing capillaries and nerves).
    • Epithelial cells form a layer called the hair matrix that produces hair; as they divide, hair is pushed out of the skin.

5.6 Hair (8 of 9)

  • Hair Growth Cycle:
    • Involves periodic growth and shedding:
    • Active follicle growth leads to firmly attached hair roots.
    • Inactive follicles yield "club hairs"; a new cycle starts as follicles produce new hairs and shed club hairs.

5.6 Hair (9 of 9)

  • Types of Hairs:
    • Vellus Hairs: Soft, fine hairs covering most body surfaces.
    • Terminal Hairs: Heavier, pigmented hairs found on the head, eyebrows, and eyelashes; other body areas develop these after puberty.
  • Hair Color: Determined by melanocyte activity in the hair matrix and genetic factors.

5.7 Sebaceous and Sweat Glands (1 of 6)

  • Exocrine Glands in Skin:
    • Sebaceous Glands (oil glands): Holocrine glands that discharge lipid secretion (sebum) into hair follicles to lubricate, protect hair, and inhibit bacterial growth.
    • Sweat Glands: Include:
    • Apocrine Sweat Glands
    • Eccrine Sweat Glands.

5.7 Sebaceous and Sweat Glands (2 of 6)

  • Types of Sebaceous Glands:
    • Simple Branched Alveolar Glands: Associated with hair follicles.
    • Sebaceous Follicles: Large glands discharging sebum directly onto skin surface, located on the face, back, chest, nipples, and external genitalia.

5.7 Sebaceous and Sweat Glands (3 of 6)

  • Apocrine Sweat Glands:
    • Located in armpits, around nipples, and in the pubic region.
    • Secrete products into hair follicles via merocrine secretion; produce a thick, cloudy secretion that serves as a nutrient source for bacteria, leading to odors.
    • Surrounded by myoepithelial cells that help expel secretions in response to hormonal or nervous signals.

5.7 Sebaceous and Sweat Glands (4 of 6)

  • Eccrine (Merocrine) Sweat Glands:
    • Coiled, tubular glands discharging directly onto skin surface; predominantly found on palms and soles.
    • Secretions consist of 99% water, along with salts and other electrolytes.
    • Functions include cooling the skin (thermoregulation), excreting water/electrolytes, and providing protection.

5.7 Sebaceous and Sweat Glands (5 of 6)

  • Other Integumentary Glands:
    • Mammary Glands: Produce milk.
    • Ceruminous Glands: Produce cerumen (earwax), preventing foreign particles from reaching the eardrum.

5.7 Sebaceous and Sweat Glands (6 of 6)

  • Control of Glands:
    • Autonomic Nervous System (ANS): Broadly controls sebaceous and apocrine sweat glands throughout the body; eccrine sweat glands are controlled more precisely.
    • Thermoregulation: Main function of sensible perspiration, involving eccrine sweat glands collaborating with the cardiovascular system to regulate body temperature.

5.8 Nails (1 of 3)

  • Function and Structure of Nails:
    • Protect tips of fingers and toes; consist of dead cells packed with keratin.
    • Metabolic disorders can affect nail structure (e.g., pitted nails due to psoriasis).

5.8 Nails (2 of 3)

  • Anatomical Structure of Nails:
    • Nail Body: Visible portion that covers the nail bed.
    • Lateral Nail Grooves: Lie in lateral nail folds, surrounded by lateral nail folds.
    • Hyponychium: Skin beneath the distal free edge of the nail.

5.8 Nails (3 of 3)

  • Nail Production:
    • Occurs at the nail root, which is an epidermal fold close to the bone.
    • The visible nail emerges from beneath part of the nail root known as the eponychium (cuticle).
    • Near the root, blood vessels are obscured, creating a pale lunula (meaning moon).

5.9 Repair of the Integument (1 of 2)

  • Repair Process Following Injury:
    • Characterized by bleeding, swelling, and pain.
    • Mast cells trigger an inflammatory response.
    • A scab (dried blood clot) stabilizes/protects the area.
    • Macrophages: Clean the area; fibroblasts and endothelial cells divide, producing granulation tissue.

5.9 Repair of the Integument (2 of 2)

  • Further Steps in Repair:
    • Clot begins to dissolve, number of capillaries declines, and noncellular scar tissue forms.
    • Raised scar tissue called a keloid may result.

5.10 Aging and the Integumentary System

  • Effects of Aging on Skin:
    • Epidermis thins, decreasing barrier strength.
    • Fewer dendritic cells lead to reduced immune response.
    • Vitamin D production declines, impacting calcium absorption.
    • Decreased melanocyte and glandular activity.
    • Blood supply to the dermis reduces.
    • Hair follicle function declines, resulting in hair loss.
    • Dermis thins with a shrinking elastic fiber network.
    • Distribution of hair and body fat alters with age.
    • Repair rate slows significantly with age.

Integration of the Integumentary System with Other Body Systems

  • The integumentary system interacts with various body systems, contributing to overall homeostasis and protective mechanisms essential for wellbeing.