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Integument• Is composed of skin and its appendages, sweat
glands, sebaceous glands, hair and nails.• Skin is classified according to the thickness of the
epidermis into:
1.Thick skin (palms and soles) (400-600µm). It contains the 5 layers of cells but lacks hair follicles, arrector pili muscles and sebaceous glands.
2.Thin skin covers most of the reminder of the body (75-150µm), has thin stratum corneum and lacks stratum lucidum and granulosum. It has hair follicles, arrector pili muscles,, sebaceous glands and sweat glands.
Skin• Is composed of:
A- Epidermis (stratified squamous keratinized epithelium).
B- Dermis (dense irregular collagenous CT.).
The interface between them is formed by dermal ridges (papillae) that interdigitate with epidermal ridges. The two types of ridges are called rete apparatus.
The hypodermis (superficial fascia) (is not a part of skin), a loose CT. with fat.
Thick skin
Thin skin
Epidermis• It is 0.07-0.12mm in thickness (thicker in palms
and soles).• The stratified squamous keratinized epithelium
of skin is formed of 4 types of cells:
1.Keratinocytes.
2.Melanocytes.
3.Langerhans cells.
4.Merkel cells
keratinocytes• Are arranged into 5 layers, they are continually
renewed by mitotic activity of the basal layer of the epidermis. Toward the surface the cells accumulate keratin filaments.
• The 5 layers are:
1.Stratum basale (germinativum)
2.Stratum spinosum
3.Stratum granulosum
4.Stratum lucidum
5.Stratum corneum
Stratum basale (germinativum)
• It is the (deepest) germinal layer that undergoes mitosis, forms interdigitations with the dermis and is separated from it by basement membrane.
• It is formed of a single layer of cuboidal to columnar cells that have basophilic cytoplasm that has tonofilaments and large nucleus. They have desmosomes and hemidesmosomes.
Stratum spinosum• Is the thickest layer that is formed of several layers of
polyhedral to flattened cells. The most basal layer shows mitotic activity (together with the str. Basale are sometimes called malpighian layer).They are rich in tonofilaments (cytokeratin) than str.basalis.Tonofilament radiate outward through the processes toward adjacent cells forming inter-cellular bridges.
• The most superficial layers show more bundles of tonofilaments (tonofibrils) causing the cytoplasm to be eosinophilic.
• Their cytoplasm contain membrane-coating granules (lamellar granules) that contain lipid.
Stratum basale and spinosum
Stratum spinosum
Stratum granulosum• Is formed of 3-5 layers of
flattened keratinocytes
(the most superficial layer that
still possess nuclei).
Their cytoplasm is rich in coarse,
irregular basophilic
kratohyaline not
membrane bound granules, but
they have membrane bound
granules that release lipid-rich
substance.
Stratum lucidum• Is the clear, homogenous,
lightly staining thin layer
of cells above str.
Granulosum. • Is present only in thick
skin.• Its cells lack organelles
and nuclei but they contain
eleidin (packed keratin
filaments)
Stratum corneum
• Is the most superficial layer, formed of numerous layers of flattened, keratinized cells with thickened plasmalemma.
• Its cells lack nuclei and organelles but are filled with keratin filaments.
• The far cells from the skin surface display desmosomes, while those near to the surface (squames or horny cells) lose desmosomes.
Non-keratinocytes in the epidermis
• I-Langerhans (dendretic) cells, are antigen presenting cells located among the cells of str. Spinosum. They have multiple long processes, dense nucleus and pale cytoplasm. They have no intermediate filaments but contain lysosomes and membrane bound Birkeck granules.
• They are a part of
mononuclear phagocyte system.• They are immune cells
II-Merkel cells• Are scattered among str. Basale and serve as
mechanoreceptors but they extend their processes between keratinocytes to which they are attached by desmosomes.
• The nuclei are indented.• The basale lamina of the cells
have unmeylinated sensory
nerves to approximate the
Merkels cells forming
Merkel cell-neurite
complexes.
III-Melanocytes• Are derived from neural crest cells, located
among cells of str. Basale and the superficial portion of the dermis.
• They are round to columnar cells.
• Their long processes penetrate the intercellular spaces of str.spinosum.
• They contain melanosomes that leave melanocytes through the processes, penetrate the cytoplasm of str.spinosum cells. Melanosomes contain tyrosinase enzyme that change tyrosine into melanin.
Melanocyte
Dermis (corium)• Is formed of 2 layers:
1.Papillary layer, is composed of loose CT.that interdigitate with epidrmis forming dermal papillae or ridges. Its collagen type III and elastic fibers form network, while anchoring fibers (type VII)extends from the basal lamina into the papillary layer. It contains fibrobalsts, plasma cells, mast cells, and other CT.cells, capillary loops, and Meissner corpuscles.
2.Reticular layer, is continuous with papillary layer. It contains dense irregular T., thick type I collagen and elastic fibers. It contains sweat glands, sebaceous glands, hair follicles and smooth muscle cells and pacinian and Ruffini corpuscles
Epidermis-dermis interface• It presents parallel primary dermal ridges, on its
surface separated by primary grooves that house projections of the epidermis. Also in the center of each dermal ridge is a secondary groove which receive down growth of the epidermis (inter-papillary peg),
along these ridges are
dermal papillae
Glands of the skin• I-Eccrine sweat glands, are located in the skin
throughout most of the body. They are simple coiled tubular glands (merocrine), located deep in the dermis or hypodermis. The secretory unit is formed of cuboidal to columnar cells which are:
a.Dark cells, are mucus-secreting cells (contain granules).
b.Clear cells, are water-secreting cells and do not have granules.
*They have myoepithelial cells.
Their ducts are composed of
stratified cuboidal epithelium.
• II –Apocrine sweat glands, are found in certain regions as axilla, areola of the nipple and anal region. They are larger than eccrine glands. Their ducts open into canals of the hair follicles not into the surface of skin as eccrine glands. Their secretory cells are
cuboidal to columnar and
have myoepithelial cells.
The glands have wide
lumen. They are under
the influnce of sex
hormones so they appear after
puberty
• III-Sebaceous glands, are embedded in the dermis and hypodermis and secrete sebum. Their ducts open into the hair follicles. They are lobular with clusters of acini opening into single short ducts.
Each acinus is composed of
peripheral located small
basal cells, which surrounded
large round cells.
Their ducts are lined by
stratified squamous epithelium.
The hair follicle• Is formed of:
a.Hair root (Has matrix that acts as str.basale).
With the dermal papilla forms hair pulp
b. Mid-shaft that is formed of medulla, cortex, cuticle, internal root sheath, external root sheath and glassy membrane.
c. Shaft of the hair that
extends through the
surface.
Hair follicles
Finger nailIs formed of:
1.Nail plate (hard keratin)
2.Nail bed (epidermis under the nail plate).
3.Nail matrix (from the nail root) that proliferate to form
nail plate.
Thick skin
Thin skin
Practical slides