Download 9. skin (1)

Integumentary system
General outline
 skin (Integument) is the largest organ of the human body, it constitutes about
16% of body weight, its total surface area is about 1.2-2.2 m2
Skin -- 2 layers: epidermis and dermis, attaching to underlying structure via
hypodermis.
Appendages -- hair, nails, sebaceous glands, sweat glands.
the function of the skin:
barrier and protection
sensory reception
excretion
body temperature regulation
absorbing some materials
remarkable regenertive capacity
skin
epidermis
(dermis)
hypodermis
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
 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 degeneratestained 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 flattened,
acidophilic and transparent cells.
Nuclei and organelles disappear
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:
---Location:--located among
stratum basale cells
---structure:
LM: -large cell with long branches
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
---Location:-among the spinous cell
---structure:
LM: -dark nucleus, light cytoplasms
-dendritic-typed processes
EM: -lysosome
-Birbeck granule:
/membrane-coated
/characteristic racket-shape
---function:
• antigen presenting cell in skin
• involve in immune reaction
c. Merkel’s cell
---Location:
located in basal layer
---structure
with short processes
contain many dense-core
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（tactile corpuscle）
---reticular layer:
1.Dense connective tissue
2.Contains blood vessels,
lymphatics, nerves and
lamellated
corpuscles
and appendages of skin.
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 follicle
Hair 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
Cell features:
in the central :
Large Polygonal shaped
cells with many droplets fat
in cytoplasm;
at periphery ： small
cuboidal shaped
cells ,dark staining .
Production: sebum
Arrector pili muscle
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