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皮膚的構造與功能
高榮皮膚科主治醫師
陳雅惠
Look at your skin
More than a covering
 A vital organ, complex structure
 Develop from the same tissues as the
brain
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Skin facts
Surface area: about 2500 cm² in a
newborn baby, 18000 cm² in an adult.
 About 6-16% of body weight: average 3
kg in a woman, perhaps 5 kg in a man.
 thickness: varies on sites. thinnest on
the eyelids and thickest on the palms
and the soles.
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Three layers:
epidermis, dermis, subcutaneous fat
Epidermis
Thickness: 35-50m, only 20 m
around eye, thicker on the palm and
sole (mm)
 oxygen and nutrients from the dermis
 Translucent
 Basement membrane
 Rete ridges
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Epidermis-2
All keratinocytes originate from basal layer
 Move upward,change shape and loss
nucleus, produce
skin protein (keratin)
and fat (sphigolipid,
ceramide)
 Corneocytes: dead
 Resist to injury
keep water
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Epidermis-2
Desquamation (squames)
 Renew cycle: about 30 days
 Psoriasis: 4-7 times faster
 Speed up: sunburn, peel
 aging
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Epidermis-3
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A model of “bricks and mortar”
Corneocytes, desmosomes, natural fat
up to 15% of the stratum corneum consists
of water.
TEWL (transepidermal water loss)
Dermis
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3000 m thick, keep resilience and supple
Contain blood vessels, nerves, hair roots
and sweat glands
Fibroblasts make collagen and elastin
Ground substance: glycoprotein (hyaluronic
acid, chrondroitin sulfate), maintain water
Dermis-2
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Collagen: 75%
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Elastic fibers: Elastin, 5%
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Stretch marks
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Wound repair
– Across lines, deep, large
– Granulation tissue
– Hypertrophic scar
– Keloid
Subcutaneous fat layer
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Adipocytes, larger vessels and nerves
Depth differs from site and individual
Cushing, conserve body heat
store fat: women (buttocks and thighs),
men (abdominal wall)
cellulite
Sebaceous glands
Part of hair follicles
 in every part except palm and sole
 Sebum: pH= 4.2-5.6, protect skin and lubricate
hair shaft
 Mixture of sebum and sweat:
natural oil-in-water emulsion,
kill some fungi
 Influence by male hormone
most sensitive at puberty
on face and trunk

Eccrine glands
Empty directly on to the skin
 in every part except lips and glans penis
 Produce sweat: mixture of water and salts
 Regulate the
body temperature
 Remove waste
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Apocrine glands
In axillary and genital area, breast
 Decapitation secretion
 Dependent on sex hormone
 Germs grow in moist area
produce body odor
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Hairs
Vellus hairs: most skin, attached to tiny
muscles in the dermis, “goose bumps”
 Terminal hairs: scalp, eyelids, eyebrows,
 Beard, chest, arm and leg: due to male
hormone
 Cuticle, cortex, medulla
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Blood vessels
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Supply the skin and appendages
Regulate body temperature
Sympathetic nerve make it constriction;
parasym. nerve, dilatation.
Nerves
Autonomic nerves: vessels, sweat glands,
smooth muscles
 Sensory nerves
 Subepidermal plexus
 Merckel plexus
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Functions of the epidermis
protecting
the
body
from
the
environment, particularly the sun
 preventing excessive water loss from
the body
 protecting the body from infection.
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Functions of the epidermis-1
ultraviolet radiation create free radicals
 protecting the nuclei of the cells in the
epidermis and the collagen of the
dermis
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– Part is reflected by the stratum corneum at
the skin surface
– part is absorbed by the melanin in the
epidermal cells
– some is scattered within the skin
Functions of the epidermis-2
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Water: 70-75% of the weight of the basal layer,
but only 10-15% of the stratum corneum.
If below 10%, it becomes dry, less flexible and
prone to damage, breakdown and infection.
The epidermis as a whole is about 35m thick
when dry, swell to 48 m on full hydration.
Functions of the epidermis-3
Hydration components of Stratum component
1. Keratin
2. a cornified envelope of corneocytes
3. Lipids
– Linoleic acid (diet), ceramides
4. natural moisturising factors (NMF)
– Amino acids (40%), pyrrolidone carboxylic acid
(12%), lactic acid (12%), urea (8%), salts (18%),
unidetified compounds (10%)
5. desmosomes
6. enzymes
Functions of the epidermis-4
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Three level against invasion by
microorganism
– Natural layer of oil-in-water emulsion on skin
– Stratum corneum
– White blood cells in skin
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Defense concerns chemicals
– Langerhans cells
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semipermeable
Functions of the dermis
protection to the body from bumps and knocks
 provide oxygen and nutrients
 remove waste products of metabolism from the
epidermis, which are also carried away in the blood
 provide shape and form to the body, by holding all its
structures together
 contributing to skin color, particularly in people with little
melanin in the epidermis
Organs in the dermis have special functions of their own:
 regulation of body temperature through control of blood
flow and sweating
 skin sensations of touch, pain, heat and cold
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