Integumentary System Notes

The Integumentary System

Learning Outcomes

• Describe the tissue structure and functions of the integument.

• Describe the structural features of the epidermis and their functional significance.

• Explain individual differences in skin color.

• Explain tissue damage and loss of homeostasis due to burns.

• Explain the structural configurations of different kinds of skin cancer.

• Explain the causes of common skin disorders.

Introduction

• The integumentary system includes the skin, hair, oil and sweat glands, nails, and sensory receptors.

  • Largest organ of the body

• The skin (integument) accounts for approximately 16% of total body weight.

• Skin surface area: 1.5 - 2.0 m^2 .

• The skin is constantly exposed to wear, microorganisms, sunlight, and environmental chemicals.

• Skin is composed of two major components:

  • Cutaneous membrane

  • Accessory structures

• Functions:

  • Body’s first line of defense against the environment.

  • Helps maintain body temperature.

  • Converts inactive vitamin D to its active form.

  • Provides sensory information.

  • Helps maintain homeostasis.

• Specific Functions:

  • Protection against impact, abrasion, fluid loss, and chemical attack.

  • Excretion of salts, water, and organic wastes by integumentary glands.

  • Maintenance of normal body temperature via insulation or evaporative cooling.

  • Production of melanin for UV radiation protection.

  • Production of keratin for abrasion resistance and water repellency.

  • Synthesis of vitamin D3 (converted to calcitriol) for calcium metabolism.

  • Storage of lipids in adipocytes in the dermis and hypodermis.

  • Detection of touch, pressure, pain, and temperature stimuli and relaying information to the nervous system.

Sensory Function

The integument contains many sensory receptors:

1. Free nerve endings: numerous encapsulated nerve endings for pain and temperature detection.

2. Merkel cells: extend from the dermis into the stratum basale of the epidermis responsible for stimulating sensory nerves that the brain perceives as touch. These cells are especially abundant on the surfaces of the hands and feet.

3. Meissner’s corpuscles (tactile corpuscle): receptors located in the dermal papillae; responsible for the detection of light touch.

4. Pacinian corpuscles (lamellated corpuscle): receptors located in the reticular layer of the dermis; responsible for detection of vibration and deep pressure.

Components of the Integumentary System

The skin is composed of layers:

• Epidermis: made of closely packed epithelial cells.

• Dermis: made of dense, irregular connective tissue that houses blood vessels, hair follicles, sweat glands, and other structures.

• Hypodermis: composed mainly of loose connective and fatty tissues.

The Epidermis

• Composed of four layers in thin skin and five layers in thick skin (from deep to superficial):

  • Stratum basale

  • Stratum spinosum

  • Stratum granulosum

  • Stratum lucidum (only present in thick skin)

  • Stratum corneum

Stratum Corneum

• The “horny layer”; outermost layer.

• Cells in the surface layer remain about 2 weeks before being shed or washed away.

• 15–30 layers of dead keratinized cells held together by desmosomes.

• Water-resistant, not waterproof, due to insensible perspiration (unable to see or feel) and sensible perspiration (sweat).

  • The stratum corneum makes your skin water-resistant, but it is not completely waterproof because:

    • It constantly lets some water out (insensible perspiration).

    • It allows sweat to pass through when your body needs to cool down (sensible perspiration).

Stratum Lucidum

• “Clear layer.”

• Flattened, densely packed dead cells filled with keratin.

Stratum Granulosum

• “Granular layer.”

• 3–5 layers of keratinocytes that have stopped dividing and started producing keratin.

• Cells grow thinner and flatter, and the cell membrane becomes less permeable.

Stratum Spinosum

• “Spiny layer.”

• Composed of 8–10 layers of keratinocytes bound together by desmosomes.

• Contains dendritic (Langerhans) cells defending against microorganisms and superficial skin cancers.

Stratum Basale

• “Basement layer”; innermost layer.

• Attached to the basement membrane.

• Most cells here are basal cells, stem cells that divide to replace more superficial keratinocytes.

• Melanocytes and Merkel cells that respond to touch are also found here.

Epidermal Cell Types

The Epidermis contains four major types of cells:

1. Keratinocytes

2. Melanocytes

3. Intraepidermal macrophages (Langerhans cell)

4. Tactile epithelial cells (Merkel cell)

Types of Skin

• Thin (hairy) skin covers all body regions except the palms, palmar surfaces of digits, and soles.

• Thick (hairless) skin covers the palms, palmar surfaces of digits, and soles.

Epidermal Layers (Deep to Superficial)

Stratum Basale

• Attached to basement membrane by hemidesmosomes

  • (multiprotein complexes that facilitate the stable adhesion of basal epithelial cells to the underlying basement membrane).

• Most cells here are basal cells, stem cells that divide to replace more superficial keratinocytes.

• Merkel cells, that respond to touch, are also found here.

Stratum Spinosum “spiny layer”

• Composed of 8–10 layers of keratinocytes bound together by desmosomes.

• Only looks spiny when on a prepared slide.

• Contains dendritic (Langerhans) cells; part of the immune response defending against microorganisms and superficial skin cancers.

Stratum Granulosum “grainy layer”

• Composed of 3–5 layers of keratinocytes.

• Most cells have stopped dividing and started producing keratin and keratohyalin.

• Cells grow thinner and flatter; cell membranes thicken and become less permeable.

Stratum Lucidum “clear layer”

• Found only in thick skin.

• Separates the stratum corneum from underlying layers.

• Flattened, densely packed dead cells filled with keratin and keratohyalin.

Stratum Corneum “cornu, horn”

• Outermost, protective region.

• With 15–30 layers of keratinized cells (filled with keratin); dead cells still tightly connected by desmosomes.

• Water-resistant, not waterproof; loses water through insensible perspiration (unable to see or feel) and sensible perspiration (sweat).

Epidermal Strata Descriptions

• Basale: Deepest layer, composed of a single row of cuboidal or columnar keratinocytes that contain scattered keratin intermediate filaments (tonofilaments); epidermal stem cells undergo cell division to produce new keratinocytes; melanocytes and tactile epithelial cells associated with nonencapsulated sensory corpuscles are scattered among epidermal stem cells.

• Spinosum: Eight to ten rows of many-sided keratinocytes with bundles of keratin intermediate filaments; contains projections of melanocytes and dendritic cells.

• Granulosum: Three to five rows of flattened keratinocytes, in which organelles are beginning to degenerate; cells contain the protein keratohyalin (converts keratin intermediate filaments into keratin) and lamellar granules (release lipid-rich, water-repellent secretion).

• Lucidum: Present only in skin of palms, palmar surfaces of digits, soles, and plantar surfaces of toes; consists of four to six rows of clear, flat, dead keratinocytes with large amounts of keratin.

• Corneum: Few to 50 or more rows of dead, flat keratinocytes that contain mostly keratin.

The Dermis

• Composed of connective tissue containing collagen and elastic fibers.

  • Papillary: Superficial portion of the dermis (about one-fifth); consists of areolar connective tissue with thin collagen and fine elastic fibers; contains dermal ridges that house blood capillaries, tactile corpuscles, and free nerve endings.

  • Reticular: Deeper portion of dermis (about four-fifths); consists of dense irregular connective tissue with bundles of thick collagen and some coarse elastic fibers. Spaces between fibers contain some adipose cells, hair follicles, nerves, sebaceous glands, and sudoriferous glands.

The epidermis supports the epidermis and the hypodermis connects the dermis to the rest of the body.

• Papillary layer

  • Named for dermal papillae in this region

  • Composed of areolar tissue

  • Contains capillaries, lymphatic vessels, and sensory neurons

Fingerprints

• Fingerprints are unique, they are tools of personal identification. Arise from the interaction of an individual’s genes and the developmental environment in the uterus.

• Impression made by the papillary ridges on the ends of the finger and thumb.

  • Genes determine general characteristics of patterns that are used for fingerprint classification.

  • As the skin on the fingertip differentiates, it expresses these general characteristics.

  • The area around growing cells on the fingertip is in flux and is always slightly different from hand to hand and finger to finger.

  • Their effect is amplified by the differentiating cells and produces the larger differences that enable the fingerprints of even identical twins to be differentiated.

Skin Layers

The skin has 2 major layers:

• Epidermis – the most superficial layer

• Dermis – a layer deep to the epidermis

• Hypodermis – also called the subcutaneous (subQ) layer; located deep to the dermis but not a layer of the skin; composed of areolar and adipose tissue

Dermis

The dermis supports the epidermis and the hypodermis connects the dermis to the rest of the body.

Papillary layer

• Named for dermal papillae in this region

• Composed of areolar tissue (check)

• Contains capillaries, lymphatic vessels, and sensory neurons

The dermis is beneath the epidermis and is composed of connective tissue. It contains the lymphatics, nerves, nerve endings, blood vessels, sebaceous and sweat glands, elastic fibers, and hair follicles.

Two layers

• Papillary layer

  • Projections called dermal papillae

  • Pain receptors

  • Capillary loops

• Reticular layer

  • Blood vessels

  • Glands

  • Nerve receptors

Hypodermis

• Deep to the dermis is the hypodermis.

• Not part of the skin.

• Anchors skin to underlying organs.

• Composed mostly of adipose tissue.

• Separates skin from deeper structures and stabilizes position of skin relative to underlying tissues; allows independent movement.

• Dominated by adipose tissue and it is an important energy storage site.

Epidermal Layers Overview

• Entire epidermis lacks blood vessels, cells get oxygen and nutrients from capillaries in the dermis.

• Cells with the highest metabolic demand are closest to the dermis.

• It takes about 7–10 days for cells to move from the deepest stratum to the most superficial layer.

• Cells in the surface layer (stratum corneum) remain about 2 weeks before being shed or washed away.

Functions of Skin (lecture video 2)

Thermoregulation

• Sweat

• Blood flow to the dermis

Blood Reservoir

• The dermis has so many blood vessels that it can hold about 8–10% of total blood flow while an adult is at rest!

Protection entity

• Keratin

• Lipids released by lamellar granules

• Sebum

• Acidic sweat

• Melanin

• Macrophages

Cutaneous Sensations

• The skin contains different types of sensory receptors found in different layers

  • Tactile sensations – touch, pressure, vibration, tickle

  • Thermal sensations – warm, cool

  • Pain

Excretion and Absorption

• Excretion – elimination of substances from the body

• Absorption – passage of materials from the external environment into body cells

• Transdermal drug administration

Synthesis of Vitamin D

• Ultraviolet rays activate the precursor molecule (calcitriol) that allows vitamin D to be made.

• Vitamin D aids in the absorption of calcium from foods in the gastrointestinal tract

Pigmentation

Skin Pigmentation

• The relative coloration of the skin depends on the amount of melanin produced by melanocytes in the stratum basale and taken up by keratinocytes.

Factors influencing skin color include

• Epidermal pigmentation via melanin and carotene

• Dermal circulation.

Skin Pigments

• Melanin - produced by melanocytes in the stratum basale

  • Pheomelanin (yellow to red)

  • Eumelanin (brown to black)

• Hemoglobin – red pigment in red blood cells; oxygen content determines the extent of red coloring.

  • Cyanosis - Low oxygen content creates a bluish appearance

• Carotene – yellow-orange pigment stored in the stratum corneum and adipose tissue

Melanin

• Pigment (melanin) produced by melanocytes.

• Color is yellow to brown to black.

• Melanocytes are mostly in the stratum basale.

• Amount of melanin produced depends upon genes and exposure to sunlight.

Clinical Connection: Albinism and Vitiligo

• Albinism is the inherited inability to produce melanin which results in complete or partial absence of pigment in the skin, hair, and eyes.

• Vitiligo is a chronic disorder characterized by partial or complete loss of melanocytes from patches of skin producing irregular white spots. The loss of melanocytes is related to an immune system malfunction where antibodies attack melanocytes.

Accessory Structures of the Skin

Hair

• Found almost everywhere on the body except the palms of hands, soles of feet, sides of fingers and toes, lips, parts of external genitalia.

• Body has about 2.5 million hairs (75 percent on general body surface, not the head).

• Nonliving structures, and each hair is produced by a hair follicle.

Two types of hair

1. Terminal hairs: large, coarse, darkly pigmented (e.g., hairs found on the scalp or in the armpit).

2. Vellus hairs: smaller, shorter, delicate, and found on the general body surface; present on most body surfaces except the nipples, the palms, palmar surfaces of fingers, the soles, plantar surfaces of the toes, labia minora, and prepuce of penis.

• Composed of dead, keratinized epidermal cells bonded by extracellular proteins.

• Genetic and hormonal influences determine the thickness and distribution of our hair.

Structure of Hair

• The parts of a hair include:

  • The shaft (above the skin surface).

  • The follicle (below the level of the skin).

  • A root that penetrates into the dermis.

    • Epithelial root sheath.

    • Dermal root sheath.

• Hair Anatomy:

  • Central medulla.

  • Cortex surrounds medulla.

  • Cuticle on the outside of the cortex (heavily keratinized).

Structure of Hair

• Produced by hair bulb and consists of hard keratinized epithelial cells.

• Melanocytes provide pigment for hair color.

Hair Growth

• Hair growth stages are:

  • Growth stage – cells of matrix divide

  • Regression stage – hair moves away from blood supply in papillary and follicle atrophies

  • Resting stage – old hair root falls out; new growth begins

Associated Hair Structures

• Hair follicle: dermal and epidermal sheath surround hair root.

• Arrector pili: smooth muscle.

• Sebaceous gland.

• Sweat gland.

Hair Color

• Hair color is primarily due to the amount and type of melanin present in the keratinized cells of the hair.

  • Dark-colored hair: mostly eumelanin.

  • Blond and red hair: variants of phenomelanin.

  • Gray hair: progressive decline in melanin production.

  • White hair: lack of melanin; accumulation of air bubbles in shaft.

Appendages of the Skin: Nails

• Scale-like modifications of the epidermis.

• Heavily keratinized.

• Stratum basale extends beneath the nail bed and is responsible for growth.

• Lack of pigment makes them colorless.

• The cuticle is also called the eponychium; it fuses the nail plate and the skin of the finger together to form a waterproof barrier.

• The hyponychium is under the free edge of the nail.

• It also creates a waterproof barrier, fusing the skin of the finger to the underside of the nail plate.

Structure of Nails

• Nails are made of keratinized epidermal cells.

Nail Structures

• Fingernails and toenails are hard keratin structures that protect the ends of the fingers and toes.

• The nail root, also called the germinal matrix or nailbed, begins several millimeters into the finger and extends to the edge of the white, crescent-shaped lunula.

• This is where the growth occurs… approximately 1 mm per week.

Appendages of the Skin

Sebaceous glands

• Produce oil (lubricant for skin; kills bacteria).

• Most with ducts that empty into hair follicles.

• Glands are activated at puberty.

Sweat glands

• Widely distributed in skin.

• Two types:

  • Eccrine

  • Apocrine

Skin Glands

The skin contains 3 types of glands.

• Sebaceous (oil) glands are connected to hair follicles.

• Sudoriferous glands are sweat glands

  • Eccrine are the most numerous

  • Apocrine are located mainly in hairy skin areas

• Ceruminous glands are modified sweat glands located in the ear canal

Sweat Glands

Eccrine

• Eccrine gland secretions, commonly called sweat.

• Sweat is hypotonic and composed mostly of water, with some salt, antibodies, traces of metabolic waste, and dermicidin, an antimicrobial peptide.

• Normal pH of sweat is between 4 and 6.

• Once released, the sweat travels via a duct to the surface of the skin where it opens into a funnel-shaped pore.

• Eccrine glands are a primary component of thermoregulation in humans and thus help to maintain homeostasis.

Apocrine

• Larger than eccrine sweat glands, lie deeper in the dermis, and release their secretions into hair follicles.

• The secretions produced are similar to sweat but they also contain fatty substances and proteins make the sweat thicker and subject to bacterial decomposition and subsequent smell.

• Apocrine glands begin functioning at puberty.

• The release of this sweat is under both nervous and hormonal control and plays a role in the poorly understood human pheromone response.

Skin Glands Comparison

Types of Skin

Thin and Thick Skin Comparison

Wound Healing ( Lecture video 3)

• Skin injuries set off a healing process that occurs in several overlapping stages.

• The first step to repairing damaged skin is the formation of a blood clot that helps stop the flow of blood and scabs over with time.

• Many different types of cells are involved in wound repair, especially if the surface area that needs repair is extensive.

• Before the basal stem cells of the stratum basale can recreate the epidermis, fibroblasts mobilize and divide rapidly to repair the damaged tissue by collagen deposition, forming granulation tissue.

• Blood capillaries follow the fibroblasts and help increase blood circulation and oxygen supply to the area. Immune cells, such as macrophages, roam the area and engulf any foreign matter to reduce the chance of infection.

Epidermal Wound Healing

Occurs when superficial wounds affect only the epidermis.

Deep Wound Healing

Additional steps occur when an injury extends into the dermis and subcutaneous layer.

• Inflammatory Phase – clot forms

• Migratory Phase – clot becomes a scab

• Proliferative Phase – growth of epithelial cells beneath scab

• Maturation Phase – scab sloughs off once epidermis restored

Aging

Age-Associated Changes

• Wrinkles

• Dehydration and cracking

• Sweat production decreases

• The numbers of functional melanocytes decrease, which results in gray hair and atypical skin pigmentation

• Subcutaneous fat is lost, and skin thickness decreases

• Nails may become more brittle

Skin Homeostatic Imbalances

Infections

• Athlete’s foot: fungal infection

• Boils and carbuncles: bacterial infection

• Cold sores: virus

Infections and allergies

• Contact dermatitis: exposures cause allergic reaction

• Impetigo: caused by bacterial infection

• Psoriasis: cause is unknown; triggered by trauma, infection, stress

Eczema

• Eczema is a common skin disorder that presents as a red, flaky rash.

• It is an inflammatory condition that occurs in individuals of all ages.

• It is an allergic reaction that manifests as dry, itchy patches of skin that look like a rash. It may swell, flake, crack, and bleed and can be treated with corticosteroids and immunosuppressants.

Acne

• Acne is a result of over-productive sebaceous glands, which leads to the formation of blackheads and inflammation of the skin.

• It occurs from an over productive, blocked sebaceous gland.

Skin Homeostatic Imbalances: Burns

• A burn is tissue damage caused by excessive heat, electricity, radioactivity, or corrosive chemicals that denature (break down) the proteins in the skin cells.

• Burns are graded according to their severity- Associated dangers: Dehydration, Electrolyte imbalance and Circulatory shock

Rule of Nines

• Way to determine the extent of burns; body is divided into 11 areas for quick estimation, and each area represents about 9%.

Evaluating burns

1. Depth of burns

   • Assessed with a pin.

   • Absence of reaction to pinprick indicates third-degree burn (loss of sensation).

2. Percentage of skin that has been burned

   • Rule of nines: Method of estimating percentage of surface area affected by burns; modified for children (different body proportions).

Severity of Burns

• First-degree burns

  • Only the epidermis is damaged; skin is red and swollen.

• Second-degree burns

  • Epidermis and upper dermis are damaged; skin is red with blisters.

• Third-degree burns

  • Destroys the entire skin layer; burn is gray-white or black.

Critical Burns

Burns are considered critical if:

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

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

• There are third-degree burns of the face, hands, or feet.

Emergency Treatment of Burns

• Replacing lost fluids and electrolytes, providing sufficient nutrients.

• Increased metabolic demands for thermoregulation and healing, preventing infection.

• Cleaning and covering burn, administering antibiotics, assisting tissue repair with skin grafts.

Skin functions affected by burns

• Fluid and electrolyte balance: Skin loses effectiveness as a barrier; in full-thickness burns, the fluid loss rate increases up to five times the normal level.

• Thermoregulation: Increased fluid loss leads to increased evaporative cooling; it takes more energy to maintain body temperature.

• Protection from infection: Dampness (from fluid loss) encourages bacterial growth; if the skin is broken, infection is likely to occur.

• Sepsis: Widespread bacterial infection (leading cause of death in burn victims).

Skin Cancer

• Cancer – abnormal cell mass of cells

  • Benign: Does not spread (encapsulated).

  • Malignant: Metastasized (moves) to other parts of the body.

• Skin cancer is the most common type of cancer.

Clinical Connection: Skin Cancer

• Excessive exposure to ultraviolet light (from the sun or tanning salons) is the most common cause of skin cancer.

• The three major types are basal cell carcinoma (78%), squamous cell carcinoma (20%), and malignant melanoma (2%).

Skin Cancer Types

• Basal cell carcinoma

  • Least malignant and most common type; arises from the stratum basale.

• Squamous cell carcinoma

  • Arises from the stratum spinosum; metastasizes to lymph nodes.

  • Early removal allows a good chance of cure.

• Malignant melanoma

  • Most deadly of skin cancers; cancer of melanocytes.

  • Metastasizes rapidly to lymph and blood vessels.

ABCD Rule (for Melanoma Detection)

• A = Asymmetry: Two sides of pigmented mole do not match.

• B = Border Irregularity: Borders of mole are not smooth.

• C = Color: Different colors in pigmented area.

• D = Diameter: Spot is larger than 6 mm in diameter.

• E = Evolving: and changing in size and shape

Skin Cancer

• Basal cell carcinoma

  • Most common form of skin cancer.

  • Originates in the stratum basale due to mutations caused by overexposure to UV radiation.

  • Virtually no metastasis and most people survive.

• Squamous cell carcinoma

  • Effects the keratinocytes of the stratum spinosum and presents as lesions.

  • Presents here as a lesion on an individual’s nose.

  • Second most common skin cancer

    • ABCDE rule

      • Asymmetrical

      • Borders

      • Color

      • Diameter

      • Evolving

Skin Cancer - Malignant Melanoma

• Most serious form of skin cancer and is extremely dangerous.

• Cancerous melanocytes grow rapidly and metastasize through the lymphatic system.

• If detected early and removed surgically, the 5-year survival rate is 99 percent.

• If not detected until after metastasis, the 5-year survival rate drops to 14 percent.

Clinical Connection: Pressure Ulcers

• With age, there is an increased susceptibility to pressure ulcers (“bed sores”).

• When shedding of epithelium caused by a deficiency of blood flow to tissues occurs, pressure ulcers can develop.