Transcript Structure of skin

Skin
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Zhong Jie Li （李仲杰）, Ph. D
School of Medicine,Zhejiang University
20131017
skin
epidermis
(dermis)
hypodermis
General outline
 skin is the largest organ of the human body, it constitutes
about 16% of body weight
 is composed of epidermis , dermis and its appendages
its total surface area is about 1.2-2.2 m2
 the function of the skin:
barrier and protection
sensory reception
excretion
body temperature regulation
absorbing some materials
remarkable regenertive capacity
•Thick skin
•Thin skin
1. Structure of skin
---epidermis
---dermis
1) Epidermis
---consist of keratinised cell and
non-keratinised cell
Keratinised stratified squamous epithelium
①keratinised cell:
---from basal to
surface, we can
classify the cells
into five layers
Epidermis
stratum corneum （C）
stratum lucidum （L）
stratum granulosum （G）
stratum spinosum（S）
stratum basale （B）
a. stratum basale
---structure:
LM: -a layer of cuboidal or low
columnar cell with a large,
pale nuclei
-basophilic cytoplasm
EM: -free ribosome
-keratin filament
- desmosome
---function:
mitotic activity and proliferation,
for constant renewal of
epidermal cells.
b. stratum spinosum
---structure:
LM: 4-10 layers polygonal cell
with large round nucleus
-spinous processes
-slight basophilic cytoplasm
EM: -tonofibrils
-lamellated granules:
/100-300nm membranecoated
/contain phospholipid
and steroid
-intercellular bridgesDesmosome
c. stratum granulosum
---structure:
LM: 3-5 layers flattened cell
-nuclei
begin
to
degenerate-stained slightly
-keratohyalin granules:
basophilic
EM: -keratohyalin granules:
with tonofilament
insert
into them
-lamellated
granules:
fused with cell membrane
* keratohyalin + tonofilament
= keratin
d. stratum lucidum
---structure:
LM:
-3-4 layers of cell appear
homogeneous and
transparent
-no nucleus and
organella
-eosinophilic-keratohyalin
-tonofilament embedded
in homogeneous matrix
lucidum
e. stratum corneum
---structure:
LM: 15~20 layers
horny cell
---died cell- no
nucleus and
organella
---eosinophilic
---keratin
* desquamation:
surface keratin will
shed from outer
surface due to
abrasion
corneum
lucidum
② non-keratinised cell:
a. melanocyte:
---structure:
LM: -large cell with long branches
-located among stratum basale
cells
EM: -risosome
-RER
-Golgi complexes
tyrosine
-melanosome(tyrosinase) →↓
melanin
↓
melanin granules
---function:
• responsible for skin color
• absorb ultraviolet light
• protect deep tissue
b. Langerhans cell
---structure:
LM: -dark nucleus, light cytoplasms
-among the spinous cell
-dendritic-typed processes
EM: -lysosome
-Birbeck granule:
/membrane-coated
/characteristic racket-shape
/15-30 nm long, 4 nm in D
---function:
• antigen presenting cell in skin
• involve in immune reaction
c. Merkel’s cell
located in basal layer
with short processes
contain many densecore granules
chemical synapse:
between Merkel’s
cell and afferent N
---function: not very clear,
may be
• sensory epithelial cell
• neuroendocrine cell
2) Dermis:
located beneath the epidermis
 Papillary layer:
•a thin layer of LCT which increase the total contact
surface between the dermis and epidermis, contain
capillary network and nerve ending (tactile corpuscle)
 Reticular layer:
•under the papillary layer; consists of irregular DCT;
contain large blood vessels, appendages of skin,
nerves (lamellated corpuscle). The elastic network is
responsible for the elasticity of the skin.
---papillary layer:
dermal papillaeincrease the
junction between
epi. and underlying
CT
papillary layer
reticular layer
Meissner’s corpuscle
---reticular layer:
DCT, contains rough
F ,CF, EF, RF
• large BV, LV
• lamellar corpuscle
• skin appendages:
including
sweat
gland,
sebaceous
gland and hair
2. hypodermis: LCT and fat tissue
Skin appendages
 hair
 sebaceous gland
 sweat gland
Skin appendages
Hair
• Hair is a thorny thread-like
structure.
• Hair shaft is the part that
extends above the surface and
hair root is part that is
embedded in the skin
• Hair resides in a hair follicle.
• Hairs differ in length,
thickness and color according
to their position on the body
hair follicle
hair root
hair bulb
papilla
Sturcture of Hair root
•Hair follicle
•Hair
root
•Hair follicle
•Hair
•Hair follicle
root
Sebaceous Glands
• Associated with the hair follicles
• Produce oily substance, which is act as a
lubricant to make the skin soft and protects
both skin and the hair from drying out.
• Oil released to outside via the hair follicle. If
passage becomes blocked, cause acne.
Sebaceous glands
Secretory portion:
in the central :
Large Polygonal shaped
cells with many droplets
fat in cytoplasm;
the basal layer : small
cuboidal shaped
cells ,dark staining .
Production: sebum
Arrector pili muscle
Arrector
pili
•Arrector pili – smooth
muscle of hair
this muscle contracts–
“goose pimple”
Sweat Glands
• Sweat glands are distributed over most of the body.
• Simple tubular glands that transverse from the dermis
to the surface of the epidermis.
• Merocrine sweat glands are found on most of the body
and produce a thin watery solution and function in
heat regulation.
• Apocrine sweat glands are found in axilla, mammary
areolae, and circumanal region produce much thicker
secretion that is odor producing. Often become
activated at puberty
A sweat gland is divided into two parts:
•Secretory portion: is composed of pyramidal secretory cells
•Duct: lined by two layers of cuboidal epithelial cells
Secretory
portion
duct