Integumentary System

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Integumentary System

• Chapter 5

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Overview

• Composed of skin and its derivatives (sweat
  oil glands, hairs and nails)
• Primary function is protection

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The Skin I

• Two distinct regions
• Epidermis
• - outermost protective shield
• - composed of epithelial cells
• - avascularized, obtains nutrients by diffusing
  through tissue fluid from blood vessels in the
  dermis
• Dermis
• - makes up bulk of skin
• - tough, leathery layer fibrous connective
  tissue
• - vascularized

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The Skin II

• The dermis and epidermis rest on subcutaneous
  hypodermis, (superficial fascia)
• Not technically part of skin, but shares many of
  its functions
• Mostly adipose tissue w/ some areolar connective
• Stores fat
• Anchors skin to underlying structures (usually
  muscle), but allows free sliding
• Shock absorber and insulator

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Epidermis

• Avascular, keratinized stratified squamous
  epithelium
• Cells
• Keratinocytes (majority)
• Melanocytes
• Langerhans cells
• (a.k.a. epidermal dendritic cells)
• Merkel cells
• Layers/strata (from deep to superficial)
• Stratum basale (basal layer)
• Stratum spinosum (prickly layer)
• Stratum granulosum (granular layer)
• Stratum lucidum (clear layer) not found in
  thin skin
• Stratum corneum (horny layer)

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Dermis - Overview

• Dense, irregular connective tissue Well-supplied
  with blood vessels, lymphatic vessels nerves
• Cells typical of connective tissue proper
  fibroblasts, macrophages, occasional mast cells
  WBCs
• Semi-fluid matrix heavily embedded with collagen,
  elastin and reticular fibers
• Contains cutaneous receptors, glands hair
  follicles

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Layers of the Dermis

• Papillary superficial relatively thin
• Areolar connective tissue
• Dermal papillae that protrude into epidermis
• Epidermal ridges that produce fingerprints
• Reticular deep, 80 of dermal thickness
• Connective fibers more densely interwoven
• Less dense regions between collagen bundles
  produce cleavage (tension) lines in skin
• Points of tight dermal attachment to hypodermis
  produce dermal folds or flexure lines

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Skin Color

• Skin color reflects the amount of pigments
  (melanin carotene) oxygenation level of
  hemoglobin in the blood
• Melanin production is stimulated by exposure to
  UV light
• Melanin is produced by melanocytes transferred
  to keratinocytes where it protects keratinocyte
  nuclei from damaging effects of UV radiation
• Skin color can be affected by emotional state
• Alterations in skin color may indicate certain
  diseases/condition
• Ex) Cyanosis, Erythema, Pallor, Jaundice,
  Bronzing Bruising

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Sensory Receptors of the Skin I

• Free Nerve Endings Pain Temp cold receptors
  are more numerous than warm, but there is not
  obvious structural difference
• Hair end plexus Around base of hair follicle,
  fires when hair is touched
• Meissners corpuscle rapidly adapting
  mechanoreceptor perceive light touch primarily
  just below epidermis, concentrated in fingertips,
  palms, lips, tongue, nipples genitalia
• Merkels discs sense pressure texture where
  epidermis meets dermis

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Sensory Receptors of the Skin II

• Ruffinis organ slowly adapting mechanoreceptor
  senses pressure temperature deep in dermis
  perceives strecth touch monitors slippage
  helps gripping mechanism encapsulated by sheaths
  of connective tissue, networks of nerve fibers
• Pacinian corpuscle pain pressure relatively
  large, but fewer in number onion shaped, deep in
  dermis
• Krauses bulb (bulboid corpuscle) touch
  conjuctiva of eye, lips, tongue, genitalia
  encapsulated by sheaths of connective tissue,
  network of nerve fibers

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Appendages of the Skin Sweat Glands

• a.k.a suduriferous glands
• 2 sub-categories
• Eccrine (merocrine) sweat glands
• Distributed over entire body surface, primary
  function is thermoregulation
• Simple, coiled tubular glands that secrete a salt
  solution with a few other solutes
• Ducts usually empty to skin surface via pores
• Apocrine sweat glands
• May function as scent glands
• Primarily in axillary and anogenital areas
• Secretion similar to that of eccrine secretion,
  but also contains proteins fatty substances on
  which bacteria thrive

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Appendages of the Skin Sebaceous (oil) Glands

• All over body surface, except hands and soles
• Simple, aveolar glands, ducts usually empty into
  hair follicles
• Oily secretion, called sebum, lubricates the skin
  and hair, and acts as a bactericidal agent.
• Activated (at puberty) and controlled by
  androgens

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Hair

• Hair consists of dead, heavily keratinized cells
• Hair color reflects amount and kind of melanin
  present
• 2 regions
• Root (embedded in skin)
• Shaft (projects from the skin)
• Hair structure
• Central medulla (core)
• Cortex
• Outer cuticle

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Hair Follicles

• Extend from epidermal surface into the dermis,
  deep end expands forming a bulb
• Richly vascularized
• Sensory nerve endings, root hair plexus, wraps
  around each hair bulb. Bending hair stimulates
  these endings, hair act as sensitive touch
  receptors
• Arrector pili muscles pull follicles into an
  upright position, producing goose bumps
• Components

• inner epidermal root sheath, enclosing the matrix
  (region of hair bulb that produces hair)
• Outer connective tissue sheath derived from
  dermis

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Types Growth of Hair

• Two classifications
• Vellus body hair of children and adult females
• Terminal coarser, longer hair of eyebrows
  scalp
• Usually darker
• Appear in axillary and pubic regions during
  puberty
• Influences on hair growth and density
• Poor nutrition poor hair growth
• Conditions that increase blood (chronic physical
  irritation or inflammation) flow generally
  enhance local hair growth

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Hair Thinning and Baldness

• Hair grows fastest from teen years to 40s, then
  slows
• Hair thinning or alopecia results from hairs are
  not replaced as fast as they are shed
• True baldness (male-pattern baldness) is an
  x-linked genetic condition

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Nails

• Scale-like modification of the epidermis
• Correspond to hooves or claws or other animals
• Composed of keratin, like hair
• Normally appear pink because of bed of
  capillaries under nail bed, region over thick
  nail matix appears as a white crescent, lunula

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Homeostatic Imbalances Skin Cancer

• Most common cause is UV exposure
• Basal cell carcinoma is the most common and least
  deadly. It is slow growing and easily detected
  prior to metastasis.
• Squamous cell carcinoma is faster growing but
  still usually detected prior to metastasis.
• Melanoma (cancer of melanocytes), is the least
  common but most deadly. However, it is also
  curable when detected early!
• Actinic keratosis are pre-malignant thick, scaly
  or crusty patches of skin usually found on areas
  over-exposed to sun although not cancerous, may
  develop into a form of skin-cancer

Actinic keratosis
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Basal Cell Carcinoma

• Cells of the stratum basale invade the hypodermis
• Usually presents as lesions on sun-exposed areas
  dome-shaped with central pearly ulcer beaded
  edge
• Slow growing seldom metastasizes prior to being
  noticed
• Least malignant most common (estimated that gt
  30 of all Caucasians will have it)
• 99 of cases can be fully cured by surgical
  removal

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Squamous Cell Carcinoma

• Arises from keratinocytes of the stratum spinosum
• Lesion is a scaly, reddish papule most often on
  head or hands
• Tends to grow rapidly will metastasize if not
  removed
• High chance of complete cure, but most be caught
  early and removed by surgery or treated with
  radiation

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Melanoma

• Most dangerous accounts for only 5 of the
  cases, but number of cases is on the rise It is
  estimated 2 of people will be diagnosed with
  melanoma in their lifetime
• Although the least common, melanoma is
  responsible for 75 of all skin-cancer deaths
• 99 cure if detected early when gt4mm,
  probability of metastasis is high and will be at
  a very rapid rate, probability of cure drops to
  15
• Can occur wherever there is pigment
  Approximately 1/3 develop in pre-existing moles,
  the remaining 2/3 arise spontaneously

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Stages of Melanoma
Clark-Beslow System measurement of depth and
thickness T (thickness (1-4) a no
ulceration, b ulceration N node
involvement M metastasis

• Stage 0 have not grown below the epidermis
  surgical removal plus .5cm perimeter of normal
  skin
• Stage I surgical removal plus margin of normal
  skin based on thickness of melanoma (1cm per mm
  of melanoma stage 1 2mm of less
• Stage II wide excision, 2cm perimeter per mm if
  gt2mm usually lymph biopsy
• Stage III lymph node dissection, wide excision
  interferon therapy
• Stage IV metastasis is beyond lymph nodes
• Recurrent risk increases with size of primary
  melanoma often second is smaller than 1st
  survival varies greatly based on original case,
  but likelihood less than original

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ABCDE Rule
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Homeostatic Imbalances Burns

• Initial threat is loss of protein and electrolyte
  rich body fluids, which may lead to circulation
  collapse
• Bacterial infection is also a significant threat
• Rule of Nines to evaluate extent of burn
• Classified, in increasing severity, as
  first-degree, second-degree and third-degree.
  Third degree requires grafting for recovery

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Evaluating Burns
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Developmental Aspects

• Epidermis develops from embryonic ectoderm,
  dermis (and hypodermis) develop from mesoderm.
• Fetus exhibits a downy lanugo coat. Fetal
  sebaceous glands produce vernice caseosa, which
  helps protects fetal skin from watery
  environment.
• Newborns skin is thin. During childhood, skin
  thickens and more subcutaneous fat is deposited.
  During puberty, sebaceous glands are activated
  and terminal hairs appear in greater numbers.
• In old age, rate of epidermal declines and skin
  and hair thin. Skin glands become less active.
  Loss of collagen, elastin fibers and subcutaneous
  fat lead to wrinkling. Delayed action genes
  cause graying and balding. Photodamage is a
  major cause of skin aging.

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Functions of the Integumentary System

1. Protection chemical barrier (antibacterial
   sebum), physical barrier (hardened keratinized
   surface), and biological barrier (phagocytes)
2. Temperature regulation Skin vasculature sweat
   glands, regulated by nervous system
3. Cutaneous sensation sensory receptors respond to
   temperature, touch, pressure and pain
4. Metabolic functions Vitamin D synthesized from
   cholesterol in skin cells
5. Blood reservoir extensive vascular supply of
   dermis
6. Excretion sweat contains small amounts of
   nitrogen wastes