Skin Flashcards
(13 cards)
Functions of skin
- protection
- control of evaporation
- sensation
- absorption
- manufacture of vitamin D
- thermoregulation
- storage and synthesis
- excretion
Layer of skin
- stratified squamous keratinising epithelium
- dense irregular connective tissue
- adipose tissue
Strata of epidermis
Stratum Corneum:
Surface stratum, cells have no
organelles – almost entirely
composed of keratin
Stratum Lucidum:
Thick skin only – not always
observed
Stratum Granulosum:
2-3 layers of flattening cells;
granules contain a lipid rich
secretion, which acts as a
water sealant.
Stratum Spinosum:
2-8 layers; ‘prickle cells’; desmosomes; tonofilaments
Stratum Basale:(Germinativum)
Deepest stratum; single layer of cuboidal cells; hemidesmosomes bond layer to basal lamina and dermis. It is here that new
cells are generated for the renewal of the epidermal layers of the skin
Cells of epidermis
Keratinocytes: make
up majority of cells
within epidermis –
they produce keratin
Melanocytes: synthesise the pigment melanin and are located in the basal layer. Skin colour is due to production and breakdown; protects
against UV - everyone has same number. Melanin is transferred from melanocytes to nearby keratinocytes in the basale and spinosum layers
Merkel cells: or epithelial tactile cells are sensitive mechanoreceptors essential for light touch sensation
Langerhans cells: Antigen presenting cells- are usually most clearly seen in the
spinous layer – they represent 2-8% of epidermal cells
Keratinocyte development
Cornification:
Cornified cell envelope, nuclear breakdown
Late differentiation:
Expression of late markers e.g.
filaggrin (bundles keratin filaments)
Intermediate differentiation:
Reinforcement of the
cytoskeleton
Early differentiation:
Growth arrest, exit from cell
cycle
Proliferation:
DNA synthesis and mitosis
Indistinct layer of dermis (2)
- Papillary layer - superficial
region that interdigitates with
epidermal ridges - Reticular layer- deeper region
that is attached to underlying
hypodermis
Thick vs Thin
Thick - palms and soles of feet
Thin - everywhere else
Sweat glands
- Merocrine (eccrine) – highest density in palms and soles
- Apocrine – axillary and anogenital regions
Hair Follicles
- Extend from epidermis to dermis
- Associated sebaceous glands
- Arrector pili – smooth muscle
Sebaceous Glands
- Secrete sebum (oily mixture of lipids)
- Usually secreted into base of hair follicle
- Sebum softens & lubricates hair and skin, prevents brittleness, slows
water loss and kills bacteria
Unencapsulated receptors
- Merkel cells, each associated with expanded nerve endings
which function as tonic receptors for sustained light touch and
for sensing an object’s texture. - Free nerve endings in the papillary dermis and extending into
lower epidermal layers, which respond primarily to high and
low temperatures, pain, and itching, but also function as tactile
receptors. - Root hair plexuses, a web of sensory fibres surrounding the
bases of hair follicles in the dermis that detects movements of
the hairs.
Encapsulated receptors
- Meissner (tactile) corpuscles are elliptical structures - they initiate
impulses when light touch or low-frequency stimuli against skin
temporarily deform their shape. They are numerous in the
fingertips, palms, and soles. - Pacinian (lamellar) corpuscles are large oval structures, found
deep in the dermis and hypodermis. They are specialized for
sensing coarse touch, pressure (sustained touch), and vibrations,
with distortion of the capsule amplifying a mechanical stimulus to
the axonal core where an impulse is initiated. - Krause end bulbs are simple encapsulated, ovoid structures, with
extremely thin, collagenous capsules penetrated by a sensory
fibre. They are found primarily in the skin of male and female
genitalia where they sense low frequency vibrations. - Ruffini corpuscles are stimulated by stretch (tension) or twisting
(torque) in the skin.
