Biol 203 - Topic 8: The Integumentary System

Components and Functions of the Integumentary System

• The integumentary system consists of:

  • The skin (cutaneous membrane)

  • Its derivatives: hair, nails, glands, receptors, etc.

• Functions of the Integumentary System:

  1. Protection:

  • Mechanical barrier: highly stratified epithelium with keratinized superficial cells.

  • Chemical barrier:

    • Melanin in epithelial cells blocks UV light.

    • Antibacterial/antifungal agents in sebum.

    • Acids in sweat (antibacterial).

  • Biological barrier:

    • Langerhans cells in the epidermis and macrophages engulf antigens and present them to the immune system.

  1. Excretion:

  • Water, some nitrogenous wastes (urea, uric acid, ammonia), and salts are eliminated in sweat.

  1. Sensation:

  • Specialized exteroreceptors detect stimuli such as temperature changes, pain, touch, pressure, vibration, etc.

  1. Blood Reservoir:

  • Approximately 5% of the total blood volume is found in cutaneous vessels.

  1. Synthesis of Vitamin D:

  • Vitamin D is needed for the intestinal absorption of calcium, magnesium, and phosphorus.

  • Deficiency can lead to rickets.

  1. Body Temperature Regulation:

  • Sweating enables heat loss through evaporation.

  • Cutaneous vasoconstriction and vasodilation control the amount of heat lost via radiation.

    • Cutaneous Vasoconstriction: heat conservation.

    • Cutaneous Vasodilation: heat loss.

Primary Skin Layers

• Two primary skin layers:

  • Epidermis:

  • Superficial layer.

  • Made of keratinized stratified squamous epithelium.

  • Dermis:

  • Deeper layer.

  • Outer areolar tissue.

  • Inner dense irregular connective tissue.

  • Hypodermis:

  • Attaches skin to underlying structures.

  • Made of areolar tissue and variable amounts of adipose.

Cells of the Epidermis

• Keratinocytes:

  • Most abundant.

  • Produce keratin (waterproofing protein).

• Melanocytes:

  • Synthesize and secrete melanin (dark pigment).

• Langerhans cells:

  • Arise in bone marrow.

  • Engulf foreign antigens and activate the immune system.

• Merkel cells:

  • Associated with dermal nerve endings.

  • Act as a sensory receptor for touch.

Production of Melanin

• Melanin Synthesis: $phenylalanine \rightarrow tyrosine \rightarrow dopa \rightarrow melanin$

  • Enzymes involved:

  • Tyrosinase: found in vesicles called melanosomes.

  • Phenylalanine hydroxylase.

• Types of Melanin:

  • Eumelanin: brown to black pigment synthesized in ellipsoidal melanosomes.

  • Pheomelanin: yellow-red pigment synthesized in spherical melanosomes.

• Human Albinos lack tyrosinase.

• Melanosomes are taken up by neighboring keratinocytes, which spreads dark color over the skin.

Layers of the Epidermis

• Stratum basale:

  • Structure: Single layer of young keratinocytes; a smaller number of melanocytes; touch and Merkel cells.

  • Function: Mitosis to replace cells lost superficially; melanin production.

• Stratum Spinosum:

  • Structure: 8-10 rows of flatter, irregular keratinocytes, Langerhans cells and melanosomes; connected by desmosomes.

  • Function: Keratin production begins; some mitosis occurs.

• Stratum granulosum:

  • Structure: 3-5 rows of flattened keratinocytes, keratohyalin granules with disintegrating organelles and lamellated granules.

• Stratum Lucidum:

  • Structure: 2-3 rows of flat, dead keratinocytes.

  • Function: Present only in thick skin (palms, soles).

• Stratum corneum:

  • Structure: 20-30 rows of dead keratinocytes filled with keratin and connected by glycoproteins.

  • Function: Waterproofing.

The Dermis

• General Features:

  • Deep to the epidermis.

  • Composed of connective tissue.

  • Vascular.

  • Contains sensory receptors and nerve fibers, glands, and hair follicles.

Regions of the Dermis

• Papillary region:

  • Structure: Areolar connective tissue with many blood vessels; dermal papillae indent the epidermis.

  • Function: Capillaries nourish the epidermis and are involved with thermoregulation; Meissner’s corpuscles (touch) and free nerve endings (pain) detect stimuli; papillae help to create large ridges in the fingers and feet for gripping.

• Reticular region:

  • Structure: Dense irregular connective tissue; collagen binds water.

  • Function: Strength, elasticity.

• Black tattoo pigment is seen in the dermis of the skin with H&E stain.

Cutaneous Receptors

• Exteroreceptor: A receptor that detects stimuli external to the body.

• Cutaneous receptors are general sensory receptors.

• Tactile receptors: Respond to a mixture of touch, pressure, stretch, and vibration.

• Temperature: Heat, cold.

• Pain.

• General sensory receptors are structurally “encapsulated” or “unencapsulated” nerve endings.

Unencapsulated Nerve Endings

• Free (naked) dendritic nerve ending:

  • Location: Most body tissues – dermis, cornea, joint capsules, ligaments, tendons.

  • Function: Nociceptors detect pain, thermoreceptors detect heat and cold, Proprioceptors detect stretch.

• Root hair Plexus:

  • Location: In and around hairs.

  • Function: Detect movement of hair.

Encapsulated Nerve Endings

• Meissner’s Corpuscle:

  • Structure: Dermal papillae especially in hairless skin (nipples, fingertips, soles of feet).

  • Function: Light touch (tactile).

• Ruffini’s Corpuscle:

  • Structure: Dermis, subcutaneous tissue, and joints.

  • Function: Stretching and deep & continuous pressure.

• Pacinian Corpuscle:

  • Structure: Dermis, subcutaneous tissue.

  • Function: Deep pressure, vibration.

• Krause's End Bulbs:

  • Location: Mucous membranes.

  • Function: Light touch.

Epidermal Derivatives of the Skin: Hair and Hair Follicles

• Location:

  • Everywhere except for palms, soles, lips, nipples, and portions of the external genitalia.

• Structure:

  • Hair is made of dead cells filled with hard keratin.

• Function:

  • Sensation, warmth, protection.

• Portions of the hair include:

  • Hair shaft.

  • Hair root.

  • Hair papilla.

• Layers of the hair include:

  • Central medulla.

  • Pigmented cortex.

  • Heavily keratinized cuticle.

Hair Follicles

• Hair follicles surround hairs.

• Hair follicles have three components:

  • External root sheath: derived from the dermis.

  • Glassy (basement) membrane.

  • Internal root sheath: derived from the epidermis.

• Hair papillae: an indentation at the base of the hair follicle that contains a capillary.

• Hair matrix cells: epithelial cells at the base of a hair follicle that divide to produce new hair.

• Arrector Pili Muscle (Pilomotor Muscle): smooth muscle that attaches to a hair follicle and pulls the follicle into an upright position.

• Phases of hair growth: The amount of time the follicle stays in the growth phase determines the maximum length of the hair.

• Normally, a cycle of activity/inactivity continues for the duration of life, but there are several factors which can interfere with hair follicles:

  • Adverse reactions to drugs and cosmetics, or as a result of scarring, tumors, radiation, the genetics of the individual, hormones and/or their immune system.

• Alopecia: hair loss.

• Hirsutism: superfluous hair.

• Alopecia Areata: autoimmune condition in which antibodies attack hair matrix cells.

• Androgenic alopecia: caused by hair follicles increased sensitivity to hormones which cause the follicles to become very small and underactive

• Polycystic ovarian syndrome and hyperandrogenemia Secondary to cyclosporin treatment

Nails

• Location: Distal dorsal segments of the fingers and toes.

• Structure: Nails are made of hard keratin.

• Function: Protection, Tools.

• Regions:

  • Free edge, body, and root.

• Nail bed: The epidermis below the nail body.

• Matrix: Proximal portion used for nail growth.

• Lunula: Whitish area superficial to the nail matrix.

• Cuticle: Eponychium; area where the proximal nail fold extends onto the nail body.

Sebaceous Glands

• Location: All areas of the body except the palms and soles.

• Structure: Simple alveolar glands usually, but not always, attached to hair follicles.

• Holocrine: Secrete sebum, which softens the skin and hair, reduces water loss and is antibacterial.

• Sebum is an oily acidic mixture of cholesterol, fats, and lysozyme.

Suderiferous (Sweat) Glands

• Eccrine:

  • Location: Everywhere except the nipples and portions of the external genitalia; concentrated on the palms, soles, forehead.

  • Structure: Simple coiled tubular gland with a duct that extends to the surface of the skin.

  • Merocrine: Produce hypotonic sweat.

  • Composition of sweat:

  • 99% water.

  • 1% solute (salts, antibodies, wastes, vitamin C, lactic acid).

  • Sweating is used for thermoregulation.

• Apocrine:

  • Location: Axillary, anogenital regions.

  • Structure: Simple coiled tubular gland with a duct that opens into a hair follicle.

  • Merocrine: Produce an eccrine-type sweat that also has large amounts of fats and proteins.

  • Function is unclear.

Hyperhydrosis

• Excessive sweating.

• No single cause:

  • Increased SNS activity

  • Idiopathic

  • Hyperthyroidism

  • Diabetes (nerve damage)

  • Spinal cord injuries

  • Panic disorders

  • Hot flashes

  • Some medications

Cutaneous horns

• Are made up of keratin and resulted from excessive keratin production by the keratocytes.

• They can occur in both benign and malignant condition.

• For an accurate microscopic diagnosis, the base of the horn should be sent for histology.

Body Temperature/Metabolism

• Metabolic Rate:

  • Rate of energy release from the body (usually reported in kcal/hour).

  • Assessed by measuring heat production or oxygen consumption.

• Basal Metabolic Rate (BMR)

  • Metabolic rate measured under standard conditions:

  • Subject hasn’t eaten for 12-14 hours

  • Subject is reclining

  • Subject is physically and mentally relaxed

  • Air temperature is $20-25$ oC ($68-77$o F)

  • Subject has not exercised for 30 minutes or more

The Harris-Benedict Equation

• Males: $BMR = 66 + (13.7 \, X \, W) + (5 \, X \, H) - (6.8 \, X \, A)$

• Females: $BMR = 655 + (9.6 \, X \, W) + (1.7 \, X \, H) – (4.7 \, X \, A)$

  • Where:

  • $W$ = actual weight in kg

  • $H$ = height in cm

  • $A$ = age in years

• Note that BMR is determined by:

  • Size:

  • Surface area is determined by height and weight; the greater the surface area, the greater the BMR; therefore, large people have greater BMRs than smaller people.

  • Gender:

  • Men have more muscle than women and less fat; muscle tissue has a higher BMR.

  • Age:

  • Younger people have higher BMRs than older people.

Other factors that increase the metabolic rate:

• Exercise

• Pregnancy, lactation

• Increased body temperature

• Hormones: thyroid hormone, epinephrine, norepinephinre

• Stress (sympathetic nervous system)

• Nutrients (food induced thermogenesis)

Thyroid hormone

• Anatomy

  • Secreted by the thyroid gland, which is located in the anterior neck.

  • Secretion is regulated by the hypothalamic-pituitary axis.

• Effects- increases metabolic rate

  • Stimulates oxygen consumption in most cells

  • Increases mitochondrial activity and enzymes

  • Stimulates metabolism of all food sources (carbs, proteins, fats)

Body Temperature/Heat Loss

• 80% of the heat that our body generates though metabolism is lost through the skin. The remainder is lost through mucous membranes.

• Radiation: Heat transfer in the form of infrared radiation; objects not touching.

• Conduction: Heat is transferred between objects that are in direct contact.

• Convection: Moving air currents enhance heat loss.

• Evaporation: Heat is lost when surface water is converted from a liquid to a vapor.

Temperature Zones

• The body can be divided into two temperature zones:

  • Core: Organs in the axis of the body (skull, thoracic and abdominopelvic cavities).

  • Shell: Heat loss surfaces; primarily the skin blood carries heat between the core and the shell.

  • When body core temperature rises, cutaneous vasodilation will deliver blood to the shell.

  • When body core temperature falls, cutaneous vasoconstriction will shift blood to the core.

Thermoregulation

• The regulation of body temperature is a balance of heat gain and heat loss mechanisms:

  • Heat Gain:

  • Metabolism

  • Shivering

  • Vasoconstriction

  • Behavioral mechanisms

  • Heat Loss

  • Radiation

  • Conduction/Convection

  • Evaporation (sweating)

  • Vasodilation

  • Behavioral Mechanisms

• Regulation Body temperature is regulated by a negative feedback mechanism

  • Receptors: peripheral thermoreceptors in the skin and central thermoreceptors in the core (respond to blood temperature)

  • Control : preotic center of the hypothalamus Center Hypothalamus Thalamus

Body Temperature and Response

• When body temperature is too high:

  • Cutaneous vessels dilate

  • Sweating is activated

  • Decreased metabolic rate

  • Behavioral heat loss mechanisms

• When body temperature is too low:

  • Cutaneous vessels constrict

  • Shivering is activated

  • Increased metabolic rate

  • Behavioral heat gain mechanisms

• Hyperthermia: Body temperature over $100$oF

• Hypothermia: Body temperature below $95$oF

• Frostbite tissue freezes when exposed to extreme cold temperatures

Heat Stroke/Heat Exhaustion

Heat Stroke

• Cause(s): Overexposure to extreme heat/humidity resulting in an inability to regulate body temperature.

• Effects: Elevated body temperature ($>104$OF); mental confusion, elevated pulse (160-180/min); loss of consciousness, convulsions, decreased sweating; this is a life-threatening emergency.

• Treatment: Move the individual to a cooler place, loosening clothing and applying ice packs in the areas of greatest circulation (back, under arms, knees, groin); provide fluids and electrolytes.

Heat Exhaustion

• Cause(s): Overexposure to high temperatures; reduced fluid intake, failure to regulate body temperature.

• Effects: Excessive loss of fluids and electrolytes leads to dizziness, weakness, fainting, weak and rapid pulse, reduced blood volume, reduced blood pressure, normal or nearly normal body temperature.

• Treatment: Move individual into a cooler environment; place in a shock position; replace fluids and electrolytes.

Fever

• A fever is an abnormally high body temperature.

• Pyrogens are substances that cause fevers.

  • Exogenous pyrogens: sources are bacteria, viruses, fungi, protozoa, some medications.

  • Endogenous pyrogens: sources are white blood cells, injured body cells, macrophages; include interleukin (IL)-6, IL-1, and tumor necrosis factor.

Pathogenesis of a fever

$Exogenic \, pyrogen \rightarrow Endogenic \, pyrogen \rightarrow Prostaglandin \, produced \, in \, the \, hypothalamus \rightarrow Preoptic \, neurons \, rest \, to \, a \, higher \, “set \, point”$

Symptoms/Effects of a Fever

• Rising Stage

  • increased metabolic rate

  • shivering

  • cutaneous vasoconstriction

  • skin is warm, dry, pale

  • you “feel cold”

• Plateau

  • sustained increased in metabolic rate

  • reduced blood pressure (PNS)

  • dehydration/anorexia possible

  • skin is warm, moist , red

  • you “feel warm”

• Falling Stage

  • decreased metabolic rate

  • sweating

  • cutaneous vasodilation

Burns

• A skin injury attributed to any of the following causes:

  • Thermal injury (extreme heat/cold)

  • Corrosive chemicals

  • Electric currents

  • Steam

  • Ultraviolet radiation

• Most common causes of hospitalization for burns:

  • Flames 44%

  • Hot liquids 29%

  • Hot objects 8%

  • Electric 6%

  • Semi-liquids 5%

  • Steam 4%

  • Chemical 4%

Evaluation of Burns

• Burns are evaluated with respect to depth, amount of surface area covered, location, cause, age, and the presence of the disease.

Depth of Burns

• Superficial (First) Degree

  • Areas Destroyed: Superficial epidermis

  • Symptoms/Outcomes: Skin appears pink/red; blisters may form after a few days; painful; hyperesthesia; heals in 3-5 days

• Partial Thickness (Second Degree)

  • Can be superficial partial or deep partial thickness

  • Areas Destroyed: Epidermis and upper dermis

  • Symptoms/Outcomes: Skin appears red; blisters immediately; painful; hyperesthesia; heals in 10-21 days

• Full Thickness (Third Degree)

  • Areas Destroyed: Epidermis, dermis, possibly muscle, fat, bone

  • Symptoms/Outcomes: Skin appears white or charred; dry; no blisters; no pain or sensation

Extent – Surface Area Covered:

• Based on the body surface area (BSA) covered with second or third-degree burns.

• Rule of Nines for Adults and Children

Lund Browder Method

• Takes into account changing body proportions that occur during development

• Pediatric Burn Assessment

Skin Disorders

Basal Cell Carcinoma

• White tumor with rolled borders.

• Central ulceration.

Squamous Cell Carcinoma

• Invasive squamous cell carcinoma.

• Lesions are firm and may be skin colored, red or yellow and can be smooth, crusted, or ulcerated.

Malignant Melanoma

• Lesion is typically asymmetric with an irregular border, variations in color, and a diameter greater than 6 mm

• ABCD rule

Skin Cancer Deaths in the U.S

• Melanoma – 75%

• Squamous cell carcinoma 19%

Boils

• Furuncle: One deeply infected and inflamed hair follicles

• Carbuncle: A cluster of deeply infected and inflamed hair follicles

Fever Blister

• Fluid filled blisters that rupture and form painful lesions

Contact Dermatitis Reactions

• Betadine Reaction

• Reaction to Nickel

• Contact with a poison oak branch

Decubitus Ulcer

• Body weight

• Deep pressure necrosis

Epidermolysis Bullosa

Impetigo

• Round, fluid filled lesions that develop a honey colored crust

Psoriasis

Vitiligo

• Melanocyte destruction

Acne vulgaris

• Note the lesions – blackheads and whiteheads