Integumentary System
Chapter 5
Overview
• Composed of skin and it’s derivatives (sweat & oil
glands, hairs and nails)
• Primary function is protection
The Skin I
Two distinct regions
1. Epidermis
-
outermost protective shield
composed of epithelial cells
avascularized, obtains
nutrients by diffusing
through tissue fluid from
blood vessels in the dermis
2. Dermis
- makes up bulk of skin
- tough, leathery layer; fibrous
connective tissue
- vascularized
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
Epidermis
• Avascular, keratinized stratified squamous epithelium
• Cells:
– Keratinocytes (majority)
– Melanocytes
– Langerhan’s cells
(a.k.a. epidermal dendritic cells)
– Merkel cells
• Layers/strata (from deep to superficial):
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–
–
–
–
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)
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
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
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
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
• Meissner’s corpuscle: rapidly adapting mechanoreceptor;
perceive light touch; primarily just below epidermis,
concentrated in fingertips, palms, lips, tongue, nipples &
genitalia
• Merkel’s discs: sense pressure & texture; where epidermis
meets dermis
Sensory Receptors of the Skin II
• Ruffini’s 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
• Krause’s bulb (bulboid corpuscle): touch; conjuctiva of
eye, lips, tongue, genitalia; encapsulated by sheath’s of
connective tissue, network of nerve fibers
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
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
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
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:
1. inner epidermal root sheath,
enclosing the matrix (region
of hair bulb that produces
hair)
2. Outer connective tissue
sheath derived from dermis
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
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
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”
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
Basal Cell Carcinoma
• Cells of the stratum basale invade the hypodermis
• Usually presents as lesions on sun-exposed areas; domeshaped with central pearly ulcer & beaded edge
• Slow growing; seldom metastasizes prior to being noticed
• Least malignant & most common; (estimated that > 30% of
all Caucasians will have it)
• 99% of cases can be fully cured by surgical removal
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
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 >4mm, 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”
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 >2mm; 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
“ABCDE” Rule
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
Evaluating Burns
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.
• Newborn’s 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.
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