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):
–
–
–
–
–
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
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”
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
Homeostatic Imbalances – Skin Cancer
– Most common cause is UV exposure
– Basal cell carcinoma and squamous cell carcinoma are cured if
removed before metastasis
– Melanoma (cancer of melanocytes), is less common but more
deadly
Basal Cell Carcinoma
Squamous Cell Carcinoma
Melanoma
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, seconddegree 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.