Transcript A layer of loose connective tissue between the skin and deeper

Skin
General outline
 skin is the heaviest organ of the human body, it constitutes
about 16% of body weight
 is composed of epidermis , dermis and its appendages
 the function of the skin:
barrier and protection
sensory reception
excretion
body temperature regulation
absorbing some materials
Layers of skin
• Epidermis – outer layer composed of stratified
squamous epithelium.
• Dermis – layer mainly composed of dense and
loose irregular connective tissue with lots of
appendages in it.
*Hypodermis –Loose connective tissue between
skin and deeper structures, lots of adipose cells
form adipose tissue
epidermis
dermis
Epidermis: stratified squamous epithelium of keratinized type
Dermis: dense connective tissue
Epidermis
• Contains many layers of stratified squamous
epithelium.
• Depending on the thickness of the skin, it is
classified as thick or thin skin.
• The cells of thick skin are arranged in five
layers
• There are no blood vessels in the epidermis
• Abundant never ending
Layers of Thick Skin
From basal to surface:
•
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Stratum basale
Stratum spinosum
Stratum granulosum
Stratum lucidum
Stratum corneum
stratum corneum
stratum lucidum
stratum granulosum
stratum spinosum
stratum basale
Stratum basale
• A layer of cuboidal or columnar cells
• Cells are actively undergoing mitosis and push
previous cells outward. Keeps constant renewal
of EC.
• These cells receive nutrients from the blood
supply that is found in the dermis next to them.
stratum granulosum
stratum spinosum
stratum basale
Stratum spinosum
• Stratum spinosum are
polyhedral cells connected
to each other by
intercellular bridges
(called spinous cells)
• A few lamellated granules
are found in the
cytoplasm, containing
glycolipid and steroid
Stratum granulosum
•Relatively flattened cells,
the unclei are undergoing
disintegration
•Containing irregularly
keratohyalin granules
which fill the cell destroying
nuclei and other organelles.
Stratum lucidum
• is made up of several
layers of homogeneous and
translucent cells, the nuclei
and organelles of the cells
no longer exist.
Stratum corneum
• is the outermost or surface
layer.
• It constituted of a series of
tightly-connected, flattened,
cornified cells
• Cells are filled with keratin,
intercellular spaces are filled of
material discharged by
lamellated granules
•Thickness varies on different
parts of body
Cell Types in Epidermis
• Keratinocytes – responsible for production of
keratin- makes skin waterproof
• Non-keratinised cells
Melanocytes- responsible for the production of
melanin.
Langerhans cells – specialized cells believed to
process antigens and deliver to lymph nodes.
Merkel cells – function as mechanoreceptors
Melanocyte:
pigment-producing cell
• large cells with long branched processes, located among the
stratum basale cells
• derived from neural crest cell
• abundant melanosome, containing tyrosinase which turns
tyrosine into melanin
• The melanin granule content of the skin is responsible for skin
color
• Melanin granule absorb ultraviolet light, protect the body
against ultraviolet irradiation
Langerhans Cell:
dendritic type, located among the spinous cells, presents
antigens,
-take up antigens in the skin and transport to lymph nodes
-reservoir for the HIV virus
Merkel Cell:
- Have short processes, distributed in the basal cell layer
- Their functional significance is not clear
It is presumed that they are sensitive
Mechanoreceptor because they are in
close relation to nerve endings
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
Reticular layer
Sweat glands
Lamellated corpuscle
Tactile Corpuscle in papillary layer
Tactile
corpuscle
Meissner’s corpuscle
Hypodermis
(subcutaneous tissue)
•A layer of loose connective
tissue between the skin and
deeper structures
•the fat content is more
significant in the hypodermis
which not only serves as a
reservoir of fat but also
protects deeper tissue against
pressure or impact
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 root
Hair follicle
Hair follicle
Hair root
Hair papilla
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.
•Arrector pili – smooth
muscle of hair
this muscle contracts–
“goose pimple”
Sebaceous gland
Arrector pili
The secretory potions are round sacs, the cells at the
periphery are smaller, toward the centre the cells grow large
and become mature which fill with fatty droplet
Arrector pili
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