what is the skin
- Integument = skin.
- Largest organ in the body.
- Thin, flat, cutaneous membrane.
- Main layers are: epidermis, dermis and hypodermis.
- Integumentary system = Skin and appendages (hair, nail, glands)
what are the functions of the skin
*Protection - barrier + immunological.
* Sensation.
* Movement and growth without injury.
* Exocrine - water, urea, ammonia, uric acid.
* Endocrine -vitamin D production.
* Immunity.
* Homeostasis - thermoregulation, water conservation, gas exchange, excretion.
SKIN STRUCTUR the 3 layers
EPIDERMIS
* Outermost layer of skin.
* SSK epithelium.
* Provides waterproof barrier and creates skin tone.
* SSK
DERMIS
* Beneath the epidermis.
* Contains connective tissue, hair follicles and sweat glands.
* LOCT
* DICT
HYPODERMIS (SUBCUTIS)
* Deep subcutaneous layer.
* Made of adipose and connective tissue
* Adipose CT
how is skin classified
THICK SKIN
* Palms of hands, soles of feet.
* Thick epidermis.
* 5 strata (layers) of epidermis. the extra layer is Stratum lucidum. Other layers are thicker than in thin skin as well
* Sweat glands present.
* Hair and sebaceous glands absent
THIN SKIN
* Covering of the entire body.
* Thin epidermis.
* 4 strata (layers) of epidermis.
* Sweat glands present.
* Hair and sebaceous glands present
what is the epidermis
- Contact with exterior environment.
- Contains keratinocytes that produce keratin
- Keratinization → Desquamation.
- Self generating (50-60 days).
- Maintains thickness by desquamation.
- Avascular.
- Vitamin D synthesis.
- Thickness determines the skin category.
- Morphology: Stratified Squamous Keratinizing (SSK).
what are KERATINOCYTES
- Epidermal cell
- Majority cell type in the epidermis.
- 90% of skin cells.
- Arranged in layers (strata).
- Found in all layers – arise from
basal layer (stratum basale). - Held together by desmosomes.
- Becomes filled with keratin.
- Production of lamellar bodies.
- Life span: 50 – 60 days.
- Bound to dermis by:
- Basement membrane
- Friction (Rete) ridges
MELANOCYTES
Cells located in the epidermis
* 5% of skin cells
* No desmosomes – dendritic cells.
* Melanin pigment producing cells.
* Gives colour to skin.
* Protect skin from damaging effectsof ultraviolet radiation (UV).
* Slow replication.
* Number is constant in all races; degree of activity is variable.
* Found between stratum basale and stratum spinosum.
LANGERHANS CELLS
Cells located in the epidermis
* Aka. Dendritic cells.
* Cytoplasmic processes.
* Macrophages of the skin, antigen presenting cells.
* Has a role in immunity; antigen presenting cells to T-cells of the immune system.
* Found mainly in the stratum spinosum
MERKEL CELLS
- Aka. Tactile cell.
- Mechanoreceptors.
- Cutaneous sensation.
- Presence of keratin and neurosecretory granules in the cell.
- Associated with nerve endings.
- Found in stratum basale.
- Cells are held together by desmosomes
need a special stain cannot be seen with regular H&E stain
MORPHOLOGICAL LAYERS
OF THE EPIDERMIS
- Stratum corneum -“corny”
- Stratum lucidum -“clear”
- Stratum granulosum -“granular”
- Stratum spinosum -“spiny” or “prickly”
- Stratum basale -“base”
superficial to deep
old to young
Can’t Let Good Skin Burn
STRATUM BASALE
- Basal layer.
- One layer of cuboidal or low columnar cells.
- Repeated mitosis.
- Majority keratinocytes - contain intermediate keratin filaments that eventually become keratin.
- Attached to other basale cellsand to cells of the stratum spinosum by desmosomes.
- Attached to basement membrane by hemidesmosomes
STRATUM SPINOSUM
- Spiny or prickly layer.
- 8-10 layers of polyhedral keratinocytes with large nuclei.
- Very prominent desmosomes -
filled with tonofilaments. - Equipped to produce keratin
and form tonofilaments.
STRATUM GRANULOSUM
Granular layer.
* 2-4 layers of keratinocytes filled with basophilic keratohyalin granules in the
cytoplasm.
* Keratinocytes mature and start to degenerate.
* Increase lysosomal activity
* Very thin in thin skin.
STRATUM LUCIDUM
- Clear layer.
- Flat, closely packed, clear cells.
- +/- nuclei.
- Cells are filled with eleidin.
- Absent in thin skin; prominent in thick skin
STRATUM CORNEUM
- “Corny layer”
- 20-30 cell layers if thin, flat cells - dead and continually being replaced – barrier
area. - Cell cytoplasm replaced by keratin fiber coated with:
- Glycophospholipid + keratin fibers = waterproof barrier.
- Glycophospholipid + keratin
fibers + desmosones = prevent wear and tear.
KERATINIZATION
Process by which cells from stratum basale transform into cells filled with keratin filaments in the stratum corneum.
* Keratinocyte → keratin.
when this goes wrong you can get Epidermolysis bullosa or Lamellar ichthyosis
DERMAL EPIDERMAL JUNCTION
- Scalloped margin at the interface of the epidermis and dermis.
- Formed by interdigitation of
1. INTERPAPILLARY PEGS – downward projections of the epidermis
2. DERMAL PAPILLAE – upward projection of the connective tissue from the dermis. - DEJ is more apparent in thick skin (hands and palms) where there is a lot of friction – friction rete ridges.
- Rete ridges enhances the gripping ability of our fingers
DERMIS
- Provides mechanical strength.
- Protection from mechanical injury and compression.
- Provide nourishment to the epidermis.
- Plays important role in wound healing.
- Vascular – thermoregulation.
- Somatic sensory nerve receptors:
- Pain, pressure, touch, temperature.
- Composed of: connective tissue, hair follicles, sweat and sebaceous glands.
Two sublayers:
1. Papillary dermis – LOCT.
* Superficial dermis..
2. Reticular dermis – DICT.
* Deep dermis
PAPILLARY DERMIS
- Superficial thin layer of the dermis.
- Forms the dermal papillae.
- Interdigitates with the interpapillary peg (epidermis).
- Forms dermal papillary junction
(DEJ) - Pronounced in thick skin (palms
and soles). - Morphology: LOCT
- Fine collagen fibers + elastin fibers
RETICULAR DERMIS
- Deep thick layer of the dermis.
- Attachment points:
- Skeletal muscles (face and scalp)
- Smooth muscle (arrector pili muscle, scrotum, areolae surrounding nipples, anus).
- Contains sweat glands, +/- hair follicles and sebaceous glands.
- Morphology: DICT
- Thick bundles of collagen fibers + elastin fibers (irregular pattern).
EPIDERMAL DERIVATIVES
IN THE DERMIS
- Hair follicles.
Associated with sebaceous glands; serves as the duct of sebaceous glands. - Surface epithelium morphology:
Stratified squamous - Sebaceous glands.
Associated with:
1. Arrector pili muscle – smooth muscle.
2. Hair follicle.
both make up the pilosebaceous unit - Secretion – sebum.
- Morphology: Simple branched acinar.
- Sweat glands (eccrine).
- Apocrine glands
SWEAT GLAND (ECCRINE)
- Palms, soles, forehead.
- Secretion - sweat
- Evaporation lowers body temperature.
- Excretes Na+, Cl-, urea, ammonia, uric acid.
- Morphology: Simple coiled tubular
- Secretory portion - simple cuboidal
- Excretory portion -stratified cuboidal
- Presence of myoepithelial cells in the secretory portion
- Contractile smooth-muscle like cells that contract and stimulate secretions of exocrine glands.
APOCRINE GLANDS
- Axillary, areolae of the breast,
genital regions. - Secretion - Viscid, milky secretion.
- Morphology: Simple coiled tubular
- Secretory portion - simple cuboidal
(budding on the apex) - Excretory portion -stratified cuboidal
- Presence of myoepithelial cells in
the secretory portion. - Functional at puberty
DERMIS VASCULATURE
- Numerous blood vessels, lymph vessels and nerves.
- Glomus bodies-
- Controls blood flow and thermal regulation in the skin.
- Blood gets shunted from different areas and flows between small arteries and small veins.
