Anatomy: Integumentary System - Chapter 5

• Chapter 5 focuses on the Integumentary System
• Copyright © 2019, 2017, 2015 Pearson Education, Inc. All Rights Reserved

Integumentary System

• Consists of the skin and derivatives, including hair, nails, sweat glands, and sebaceous glands.
• Integument refers to the skin covering the body.
• Also known as the cutaneous membrane, providing a barrier to the outside world.
• Acts as a visual indicator of physiology and health studied in dermatology.

Composition of the Integument

• The integument is the body's largest organ.
• It protects internal body structures.
• Accounts for 7-8% of body weight.
• Surface area ranges between 1.5-2.0 m².
• Thickness ranges from 1.5 mm to 4.0 mm.
• Composed of epithelium (surface covering).
• Consists of an underlying connective tissue, providing strength and resilience.
• Contains smooth muscle associated with hair follicles.
• Includes nervous tissue for sensory information about touch, pressure, temperature, and pain.

Layers of the Integument

• Includes the Epidermis, which consists of stratified squamous epithelium and is avascular.
• Includes the Dermis, which is the deeper layer composed of dense irregular connective tissue and is vascular.
• Includes the Hypodermis a subcutaneous layer, deep to the dermis.
• It consists of areolar connective tissue and adipose tissue.
• Functions to insulate and absorb shock, not part of the integumentary system.
• Closely involved in structure and skin function.

Epidermis

• Considered the epithelium of the integument that is keratinized and stratified squamous epithelium
• Composed of specific layers called "strata"
• There are 5 layers from deep to superficial: stratum basale → stratum spinosum → stratum granulosum → stratum lucidum → stratum corneum
• First three layers from deep, contain living keratinocytes
• The most superficial two layers contain dead keratinocytes.

Epidermis, stratum basale

• Deepest epidermal layer.
• Also known as stratum germinativum or basal layer.
• Consists of a single layer of cuboidal to low columnar cells that is attached to the underlying basement membrane.
• This layer is occupied by 3 cell types: Keratinocytes, Melanocytes, and Tactile cells.

Epidermis, stratum basale cells

• Keratinocytes: most abundant cells in epidermis, found in all layers.
• Keratinocyte stem cells replicate via mitosis to regenerate cells that replace old cells shed at the surface.
• Name derived from keratin synthesis, a protein that strengthens the epidermis.
• Melanocytes: Scattered among keratinocytes and produces pigment, melanin that scatters among the keratinocytes.
• Produce and store pigment, melanin in response to ultraviolet light.
• They transfer pigment granules called melanosomes into keratinocytes.
• Melanosomes accumulate around the nucleus of keratinocytes and protect nuclear DNA from UV radiation and are responsible for darker tones of skin.

Epidermis, Tactile and Dendritic cells

• Tactile Cells: Also known as Merkel cells, are few in number and responsive to touch.
• Tactile cells release chemicals to stimulate sensory nerve endings in response to compression.
• Dendritic Cells: Also known as Langerhans cells which are antigen presenting cells, APCs.
• Dendritic cells "patrol" deep epidermis and are responsive to pathogens/epidermal cancer cells.
• They are often present in stratum spinosum and granulosum and are immune cells that will help initiate an immune response (part of innate immune response => non-specific).

Cutaneous Mechanoreceptors

• Mechanical interactions result from physical interaction, including pressure and vibration.
• Categorization by morphology, kind of sensation perceived, and adaptation rate
• Slowly Adapting type 1 (SA1) mechanoreceptors, with the Merkel corpuscle end-organ, underlies skin's form and roughness perception.
• They have a small receptive field and responses to prolonged static stimulation.
• Slowly Adapting type 2 (SA2) mechanoreceptors, with the Ruffini corpuscle end-organ, respond to skin stretch but are loosely linked to proprioceptive or mechanoreceptive roles.
• They produce sustained responses to static stimulation but have large receptive fields.
• Rapidly Adapting (RA) mechnoreceptors end organ = the Meissner corpuscle which underlies the perception of flutter and slip on the skin.
• They exhibit small receptive fields and give transient responses to the initiation and termination of stimulation.
• The receptors or Lamellar corpuscles underlie the perception of high frequency vibration and produce transient responses, but have large receptive fields.

Epidermis, stratum spinosum

• Several layers of polygonal keratinocytes are daughter cells pushed into this layer from stratum basale.
• It is also known as spiny layer due to appearance under microscopy.
• In this layer they begin to develop into specialized, or non-dividing keratinocytes.
• Non-dividing keratinocytes are attached by intercellular junctions called desmosomes that resist tension and pulling
• Presence of epidermal dendritic cells (Langerhans cells).

Epidermis, stratum granulosum

• There are 3-5 layers made of keratinocytes in this layer which is also referred to as the granular layer.
• It is superficial to the stratum spinosum.
• Keratinization first happens here, where keratinocytes fill with keratin and causes nucleus and organelles to disintegrate.
• The keratinized cells are fully dead butstructurally sound at this point.

Epidermis, stratum lucidum

• Contains 2-3 layers of keratinocytes known as a translucent layer that is also known as the clear layer.
• Superficial to the stratum granulosum.
• Found only on thick skin within the palms and soles
• Filled with a translucent protein, eleidin that is intermediate in keratin maturation

Epidermis, stratum corneum

• Consists of 20 to 30 layers of dead, interlocking keratinized cells.
• The cells anucleate (without a nucleus) and tightly packed with plasma membrane enclosing keratin protein
• also known as the hornlike layer
• It is the most superficial layer of epidermis
• Is a surface unsuitable for the growth of many microorganisms
• Secretions of exocrine glands helping prevent growth
• antimicrobial peptides (bacteria, virus, fungus)
  • defensins
  • cathelicidins

Epidermis, keratinocyte migration

• Keratinocytes originate from stem cells in stratum basale, migrate through strata to stratum corneum over two weeks, in which structural changes occur
• These remain in stratum corneum for another two weeks, where they shed.
• The cells change by undergoing apoptosis which is programmed controlled cell death.
• As cells die, they slough off as dandruff and dander and humans can shed ~50,000 cells/minute.

Epidermis, variations

• Variations exist between different body regions and individuals.
• variations also exist in thickness, color, and skin markings.

Thick versus Thin Skin

• Thick skin:
  • On palms of hands, soles of feet, and surfaces of fingers and toes.
  • Has all five layers of epidermal strata.
  • Has sweat glands but no hair follicles and no sebaceous glands.
  • Thickness from 0.4 to 0.6 mm thick.
• Thin skin:
  • Covers most of the body.
  • Locks a stratum lucidum but has sweat glands, has hair follicles and sebaceous glands.
  • Ranges from 0.075 to 0.150 mm thick.

Epidermis, skin color

• Coloring from melanin: pigment produced and stored in melanocytes where it occurs in brownish black to reddish yellow shades.
• It is transferred to keratinocytes in stratum basale
• UV light stimulates melanin production and amount in skin varies according to heredity and light exposure.
• All people have the same number of melanocytes with the activity and color varying among individuals.
• Darker skinned individuals produce more and darker colored melanin.

Epidermis, skin color II

• Coloring from hemoglobin: Oxygen binding compound present in red blood cells that has a bright red color upon binding oxygen.
• Gives blood vessels in dermis a reddish tint
• Seen easily in fair skinned individuals that becomes more visible if blood vessels dilate.
• Coloring from carotene: yellow-orange pigment acquired from yellow-orange vegetables
• It is most obvious in palms and soles and accumulates inside subcutaneous fat and keratinocytes of stratum corneum
• Is converted to vitamin A within the body, an important factor in vision, reducing free radicals and immune function.

Variations in the epidermis

• Nevus: Commonly called a mole that is a harmless overgrowth of melanin forming cells and rarely becomes malignant.
• Should be monitored for changes suggesting malignancy.
• Freckles: yellowish or brown spots representing localized areas of increased melanocyte activity with a degree of pigmentation based on sun exposure and heredity

Epidermis, UV Radiation, Sunscreens, and Sunless Tanners

• Ultraviolet radiation believed to cause skin cancer by altering DNA.
• Destroys folic acid (necessary for DNA synthesis) and the UVA is between 320 and 400 nm.
• The UVB is between 290 to 320 nm.
• Sunscreens block UVA and UVB rays and protects the skin if used correctly with enough SPF.
• Existing sunless tanners create tanned skin without UV light exposure, but offers no protection against UV rays.

Alterations in skin color

• Cyanosis: Blue skin color: Low oxygenation of hemoglobin
• Pallor: Blanching or pale color associated with anemia, low blood pressure, fear, and anger
• Erythema: Redness linked to fever, hypertension, inflammation, and allergy
• Jaundice: Yellow cast due to liver disorders with bilirubin accumulation.

More variations in the epidermis

• Hemangioma: skin discoloration due to benign blood vessel tumor
• Capillary hemangiomas: appear in skin as bright red to deep purple nodules, usually present at birth and disappear in childhood, called strawberry-colored birthmarks
• Cavernous hemangiomas: involve larger dermal blood vessels, may last a lifetime and known as port-wine stains

Ridge patterns

• Epidermis: Ridge patterns of the skin are present in small conical pegs in thin skin
• In 1823, 9 basic patters were described * complex arches and whorls on finger, palms, soles, and toes.
• These called friction ridges are formed from large folds and valleys of dermis and epidermis.
• Friction ridges help increase friction on contact and give a nearly unique pattern and helps with personal identification
• They are largely used in forensic science
• Only by 1880s-1890's begun to be used as fingerprints for law enforcement.

Dermis

• Is deep to the epidermis that ranges in thickness from 0.5 mm to 3.0 mm composed of strong flexible connective tissue
• Consists primarily of collagen and elastic and reticular fibers.
• It contains motile dendritic cells,(immune function), blood & lymphatic vessels
• It also contains sweat glands & sebaceous glands, hair follicles, nail roots, and sensory nerve endings, arrector pili muscle
• Is divided between the papillary layer & deeper reticular layer

Dermis, papillary layer

• Directly adjacent to the epidermis composed of areolar connective tissue.
• Consists of Loose, interlacing collagen & elastic fibers.
• derives name from projections of the dermis where termed dermal papillae * contain capillaries and sensory nerve endings
• Projections of epidermis interdigitating with papillae gives termed epidermal ridges, that interlock and increase the area of contact between layers

Dermis, reticular layer

• Deeper, major portion of the dermis (~80%) that extends from papillary layer to subcutaneous layer
• Consists primarily of dense irregular connective tissue
• Strength and resiliency is given by & elastic fibers
• Contains large bundles of collagen fibers that are interwoven into a meshwork surrounding structures in dermis
• In thick skin, they lie on top of dermal ridges, give rise to epidermal rigdes => friction ridges.

Dermis, ridges and flexure lines

• Friction ridges consist of epidermal ridges that lie on top of dermal ridges and sweat duct openings along the crests of friction ridges help make fingerprints.
• Flexure lines form where the dermis is closely attached to the underlying structures.

Dermis, lines of cleavage

• Collagen and elastic fibers are oriented in parallel bundles generated from tension lines in reticular layer.
• Alignment results from applied stress during routine movement where bundles functioning to resist stress is a consideration for surgery
• Incisions parallel to cleavage lines are more likely to heal quickly and incisions perpendicular to cleavage lines are more likely to open due to cut elastic fibers.

Stretch Marks & Wrinkles

• Fibers contribute to skin characteristics consisting of collagen fibers imparting tensile strength and elastic fibers allowing stretch and recoil
• "break down" and clump of collagen & elastic fibers results in wrinkles, which are sometimes caused by skin stretched beyond its capabilities
• Causing some collagen fibers to tear, or stretch marks that are termed striae that occur, the flexibility and thickness of dermis is diminished by UV light and aging may cause sagging or wrinkled skin.

Dermis, innervation and blood supply

• Dermis has extensive nerve fibers with nerve fibers detecting pressure, vibration, and temperature.
• Motor nerve fibers controlling blood flow and gland secretions
• Dermal blood vessels: supplies nutrients to epidermis and dermis with large vessels along reticular and subcutaneous border
• Smaller vessels branching into dermis and dermal papillae are play important roles in body temperature and blood pressure regulation.
• Body temperature is affected by vasoconstriction: blood vessel diameters reduced shunting blood to deeper structures conserving heat
• Body temperature is also affected by vasodilation: blood vessel diameter increased bring more blood closer to the body surface
• During this process heat is lost and that is why the body is flushed.

Subcutaneous layer

• The subcutaneous level is not considered part of integument.
• Consists of areolar and adipose connective tissue
• The region pads and protects the body and can act as an energy reservoir
• Acts to provide thermal insulation and can be injected with drugs
• Sexes develop different layer thicknesses and distribution with women exhibiting thicker layers while men exhibit thinner layers.
• Women tend to be exhibit more thickness around around the breasts, buttocks, hips, and thighs/
• Men thinner layer around the heck, upper arms, abdomen and lower back.

Integumentary Structures derived from Epidermis Nails

• Nails, hair, and exocrine glands are all derived from epidermal epithelium.
• This is otherwise noted as epidermal derivatives.
• These are created from portions of epidermis integrated into the dermis.
• Structure of scales come from scalelike modifications of the stratum corneum.
• These modifications form on the dorsal edges of fingers and toes and protect the distal tips of the digits.
• They assist in grasping objects.

Structure of nails

• Nails have a distal whitish free edge (no underlying capillaries)
• There is a pinkish nail body (underlying capillaries) a
• Part embedded in the skin is the nail root where three constitute the nail plate
• Active living part of the nail occurs in the nail bed covered by a layer of living epidermis
• The actively growing part of the nail occurs on the end called the nail matrix where folds of skin overlap the nail called the nail folds
• The narrow band of epidermis from margin of nail wall onto nail body is termed the eponychium (or cuticle)
• The free nail edge projecting over region of thickened stratum corneum is the hyponychium.

Hair, Hair composition, Hair Types

• Hair is found everywhere on the body except the hands, the sides and soles of the feet and toes, lips and portions of the external genitalia
• A) Hair is composed of a single hair, termed pilus which has the shape of a slender filament and is composed of keratinized cells that grows from hair follicles. -B) Hair type is divided into 3 main categories: -Lanugo: babies, fine, unpigmented, downy hair that appears in last trimester -Vellus: primarily human hair found on upper & lower limbs -Terminal hair: is coarser, pigmented, and longer and on scalp, eyebrows, and eyelashes as well as men's beards and during puberty replaces vellus hair in axillary and pubic regions.

Hair: Zones

• Hair is divided into 3 zones that runs along the the length of a hair
• These include the shaft which is a portion of hair beyond skin surface and the only region containing dead epithelial cells
• Hair has a root which is the portion of hair found deep to skin surface and consists of both root and bulb consisting of living epithelial cells
• There is also the hair bulb which contains swelling at the base where hair originates in the dermis
• The hair is surrounded by hair papilla, composed of connective tissue
• There are three more components that the hair is composed of including: the hair matrix, medulla, and cortex

Hair, Hair Components

• Hair components -Hair matrix -structure at the base of the hair bulb -epithelial cells dividing here -produces new cells gradually pushed toward surface -Medulla -remnant of matrix -contains flexible, soft keratin -Cortex -flattened cells closer to outer hair surface -relatively hard -Cuticle -single cell layer around cortex

Structure of hair and follicles

• Hair follicle wall: is a oblique tube surrounding hair root with an extends into dermis and sometimes subcutaneous layer
• It has an outer connective tissue root sheath originating in dermis
• It also has an inner epithelial tissue root sheath originating from epidermis
• Hair has Arrector pili muscle: has thin ribbons of smooth muscle that extend from hair follicle to the dermal papillae an delevates hair with contraction, producing “goosebumps"

Hair functions

• Functions of hair: Protection from scalp, nostrils, ears, eyebrows, and eyelashes
• Functions of hair: Heat retention which prevents loss of hear from scalp to air and sensory reception has associated tactile receptors
• Functions of hair: Visual indentification (important factor in determining age, sex, general demographic)

Hair color and signaling

• Hair color: synthesis of melanin in the matrix adjusted to hair papillae, environmental and hormone factors come to play here. Hair will become lighter with age.
• Chem signals: pheromones chemical signals that attract partners and this is secreted throughout various portions of the body.

Hair, renewal and shedding/growth

• Hair Replacement: Hair growth occurs at a rate of ⅓ mm per day for two to five years
• Followed by a dormant stage of three to four months.
• Eventually, the hair is pushed out and replaced by a new hair.
• Hair also becomes “ingrown" if it cannot erupt from its pore.
• Hair loss begins with a rate of 10-100 hairs lost per day
• this be the result of drugs, dietary factors, radiation, or other stressors
• Alopecia defined by hair thinning and is generally cause by aging
• Hair can also become can undergo “diffuse hair loss," generally from the scalp and usually occur in women
• male pattern baldness occurs via hormones in males that inhibit the growth of hair.

Exocrine Glands of the Skin : Two most common include

• Sweat: the body has two primary forms of sweat glands that are merocrine and apocrine.
• General description is the secretory portion is tubular and coiled.
• Sweat is moved through the sweat glands by the sweat pores.
• The cells forming sweat glands can contract in order to discharge various liquids through sympathetic stimulation
• The General description of Merocrin: they are abundantly present and secrete directly on the epidermis.
• Major function of them is to regulate fluid and thermoregulation of the body. These are delivered by exocytosis
• Apocrine: Discharges onto hair follicles
• Produces a cloudy and viscous secretions that contains more lipids.
• Found around the nipples, axillae, in the pubic and anal region
• Mammary glands are basically a variant of apocrine sweat glands that is present in lactating
• Ceruminous glands make ear wax

Exocrine Glands of Skin, Sebaceous Glands

• Sebaceous glands produce sebum in hair and are stimulated by hormones and androgens
• They are very oily and bacteriocidal in effect and are activated during puberty

Functions of the Integument

• The Protection occurs generally through physical barriers and defense against physical trauma.
• Provides protection from chemicals toxins, microbes, and solar radiation.
• the system also prevents water loss by secreted necessary liquids for homeostasis
• Dehydration in areas such as the epidermis is the danger
• System also functions to supply metabolic production such as production of vitamin B

System Functions : II

• the immune system can functions and trigger the immune response
• Dendritic cells in epidermis as well as through absorption and waste
• the system is able to intake and excrete chemicals, solids , drugs etc.
• This is able to occur by various methods such as the movement of water and chemicals
• Dermis : sensory perception of the body, blood regulation for regulation

Integument repair

• Integument system can be respond to both repetitive movement and mechanical damage
• Repetitive movements such as walking and moving can cause mechanical damage is addressed by mitosis of epidermal tissue to create a thicker and more protective layer of skin
• Damage can generally be repaired through regeneration that the damaged cells with identical cells to create a protective layer
• If not possible or if there damage to a region of the integument system then Fibrosis can occur that provides collagen protection

Integument changes with age

• Aging comes due to UV light as well as thinning skin
• Aging comes as a reduction of the production of cells and damage to the DNA in dermal cells
• Reduced immune systems
• In hair causes thinner hair.

Skin cancer

• The majority on skin cancer stems from the epidermis.
• This is also most deadly within the cells.
• Most cancer comes from head and neck region and can be prevented by sunscreen.