Skin IA%% (+ Flashcards
Skin as an Organ
- Combination of the 4 primary tissues: epithelium, connective tissue, muscle, nerve.
- Epidermal cells are termed keratinocytes
- Largest organ in the body
- Has its own pathological conditions:
eg. sunburn, acne, eczema, psoriasis (red,crusty patches of skin), melanoma
•Provides important external evidence of underlying systemic conditions: eg. liver disease, systemic sclerosis (autoimmune disease of the connective tissue), mitral stenosis (a narrowing of the mitral valve opening that blocks blood flow from the left atrium to the left ventricle), urticaria (rash)
2 layers: Structure
1.Epidermis
- Epithelium
- Forms boundary between internal and external compartments
2.Dermis
- Connective tissue
- Gives structural strength
Note: Hypodermis
- Adipose (fatty) CT layer beneath skin = subcutaneous tissue, anchors skin to underlying structures - not part of skin
4 types of epidermal cells
Keratinocytes:
- Most frequent, contain keratin (contains sulphur), hard and resistance to abrasion.
- Extrude (force out) lipids – waterproofing.
- Constantly dividing – self regeneration protecting from trauma and other damage.
Melanocytes:
- pigment formation
Langerhans cells:
- immune surveillance
Merkel cells:
- touch receptors
Keratinisation
- Organic process whereby keratin is deposited in cells and these become horny as in dead skin, nails, hair
Epidermis
- Outer layer of skin (consisting itself of 5 strata = layers)
- Epithelial = Stratified squamous keratinising epithelium
- Ectodermal origin
- Prevents water loss by evaporation
- 5 layers formed by maturing keratinocytes
5 layers (superficial to deep):
- Statum corneum
- Stratum lucidum
- Statum granulosum
- Statum spinosum
- Statum basale
Stratum corneum (Stratum lucidum)
- Stratum lucidum difficult to distinguish from stratum corneum
- Conversion of keratohyalin ⇒ keratin
- Lots disulphide linkages give strength
- Stratum corneum has no organelles
- Desmosomes bind cells
- 15-30 day turnover
Stratum granulosum
- Presence of granules defines the layer
- Keratohyalin (possible precursors of keratin) are in Granules
Stratum spinosum
- Spinous layer
- Created post-mortem: Cells shrink but desmosome junctions “create” spines
- Little structural evidence of activity
- Preparative layer for keratinisation
Stratum basale (germinativum)
- Tall columnar cells interspersed with melanocytes and Merkel cells
- Cells bound to BM by hemidesmosomes
- Irregular interface with dermis - dermal papillae
- Continuous cell proliferation - are stem cells (undifferentiated)
Dermis:2 layers
Papillary layer
–Loose connective tissue
–Cellular
Reticular layer
–Dense irregular connective tissue
–Fibrous
Dermis: papillary layer
–Loose connective tissue
–Irregular interface with epidermis - “papillae”
–Cellular eg macrophages
–Protective against pathogens
–Blood vessels: Thermoregulation, Nutrition
–Nerve endings: Sense organ
Dermis: Reticular layer
–Dense irregular connective tissue
–Collagen bundles in 3 planes
–Elastic fibres
–Loss of elasticity is normal in old age
Skin- sense and repair
- Meissner’s corpuscles - light touch - fingertips
- Paccinian corpuscles - vibration & pressure
- Pain receptors
- Thermoreceptors
4 stages
- Blood clot
- Scab
- Granulation tissue
- Scar
Skin colour
- Blood
- Carotene (Carotenes are photosynthetic pigments important for photosynthesis)
- Melanin –Protects against UV
- Melanocytes (melanin-producing neural-crest derived cells located in the bottom layer, the stratum basale,of the skin’s epidermis)
Features
Waterproofing
- Function of epidermis
- Keratin in cells “waterproof”
UV
- Melanin –Protects against UV
Thermoregulation
- Eccrine sweat glands
- Blood vessels dialation: absorption/radiation
- Hair (polar bears, not humans)
Repair
- Hair
Eccrine sweat glands
- Simple tubular glands
- Located in dermis
- Coiled secretory portion
- Coiled and straight duct in dermis
- Spiral channel in epidermis
- Watery secretion
- Thermoregulatory
Hair 1
•Derived from epithelial layer
Origin of hair follicles
- From epidermis in utero
- Downgrowth of epithelial cells
- Invasion of knot of blood vessels
- Growth of hair
- Continuity with layers of epidermis
Hair 2
- Hair + sheath(s)
- Arrector pili muscles
–Attached to follicle root and base epidermis
–Follicle at angle
–Hair straightens when muscle contracts
•Sebaceous glands
–Between follicle and arrector pili muscle
–Secretes sebum (oily, waxy substance called sebum that is made of triglycerides, wax esters. Sebum waterproofs and lubricates the skin and hair of mammals)
–Function uncertain
Nail
- The distal end of each digit is protected by a strong plate of hard keratin, called a nail or nail plate, which grows out from a nail bed.
- The nail bed, is a specialised form of skin epithelium, and has the same 4 layers of the epidermis of skin, with the nail plate being analogous to the stratum corneum layer.
Skin glands
- Sebaceous glands: secretes a lubricating oily matter, sebum, into the hair follicles
- Eccrine glands: the major sweat glands of the human body
- Apocrine: sweat glands
–Axilla
–Protein rich - B.O.!
