Download Document

Skin
Department of Histology and Embryology
Li jinxin No.1020603
The following are emphasized
1.General structure of the skin.
2.The five layers of the epidermis.
3.Components of the cutaneous
appendages.
1. General characteristics
Skin is composed of two parts:
epidermis and dermis.Under the
dermis is the hypodermis or
subcutaneous tissue.
The skin appendages consist of
sweat glands,sebaceous glands,hair
and nails.Most of them are located
among the dermis.
epidermis
dermis
Sweat gland
Section of skin from fingertip
Function of skin
•
•
•
•
Protection
Sensory reception
Excretion and absorption
Thermoregulation
2. Epidermis
• The epidermis consists of stratified
squamous epithelium of keratinised type.
• Its cells are arranged in five layers:
stratum basale (basal layer)
stratum spinous (spinous layer)
stratum granulosum (granular layer)
stratum lucitum (clear layer)
stratum corneum (cornified layer)
cornified layer
clear layer
granular layer
spinous layer
basal layer
Section of skin from fingertip
Epidermis
• All the epidermis cells divide into two
types:
keratinocyte and non- keratinocyte
• Most of the cells are keratinsed cells .In
the deeper layer,cells are continuously
produced and in the superficial layer they
are keratinised and shed away.
2.1 layers of epidermis
2.2.1 Basal layer
• This is a layer of
columnar or
cuboidal cells.
• The cytoplasm is
basophilic.
•Large numbers of ribosomes,
tonofibrils and desmosomes.
2.2.2 Spinous layer
*It is composed of 4-10
layers of polygonal cells.
*Many spinous processes
are to be found on the
cell surface.
*The cytoplasm is
basophilic.
*Numerous ribosomes, desmosomes,
lamellar granules.
2.1.3 Granular layer
It is composed of 3-5 layer of flattened
cells.The cytoplasm contains abundant
keratohyalin granules.
2.2.4 Clear layer
It is made up of 3-4 layers of transparent
cells which are stained red by eosin. No
nucleus and organelles.
2.1.5 Cornified layer
The nuclei and organelles of which have
degenerated and become lost.The cytoplasm
has become keratin.Intercellular spaces are
filled by material derived in part from
discharged lamellated granules.
2.2 Non- keratinocyte
• 2.2.1 Melanocytes
• Melanocytes are large cells with long
branched processes. They are located
among the stratum basale cells.
•Numerous ribosomes,
rough endoplasmic reticulum and
Golgi complexes.
Melanocytes
•
•
•
•
Melanosome (It contains tyrosinase)
Melanin
Melanin granule
Melanin granules can absorb
ultraviolet light and protect the body
against ultraviolet irradiation.
2.2.2 Langerhans cells
2.2.3 Merkel cells
3 Dermis
It is composed of dense connective
tissue.The dermis is subdivided into two
layers:the papillary layer and the
reticular layer.
Dermis
• 3.1 Papillary layer
• Numerous dermal papillaes.It has a rich
blood capillary network,free nerve
ending,tactile corpuseles.
• 3.2 Reticular layer
• Dense connetive tissue.It has blood
vessels,lymphatics,nerves and skin
appendages.
4 Hypodermis
• This is a layer of loose connective
tissue between the skin and deeper
structures.
5 Skin appendages
Including hair,sweat glands,sebaceous
glands and nails.
epidermis
hair muscle
sebaceous
gland
hair follicle
sweat gland
5.1 Hair
hair shaft
hair root
hair bulb
hair papilla
hair follicle
hair muscle
5.2 Sweat glands
• There are two types:small sweat
glands and large sweat glands.
• A sweat gland is divided into two
parts:a secretory portion and a duct.
secretory portion
duct
5.3 Sebaceous glands
• The secretory portion consists of two
types of cells:the periphery cells and the
center cells.
duct
periphery cell
center cell
Sebaceous glands
• The periphery cells grow large toward
the center.
• As the cells become mature,the cytoplasm
is gradually filled with fatty droplets,the
nuclei shrink and even disappear.
• At last,the cells break down and turn into
sebum.
• The ducts open to the upper part of hair
follicles.
Exercise
• Statement the structure of
epidermis.
• Statement the structure and
function of Melanocyte.