7 - skin Flashcards
functions of skin
- Protection - injury, uv radiation, pathogens
- Metabolism - production of vitamin D
- Sensation - receptors for touch, pressure, pain , temperature
- Thermoregulation - vascular network, sweat
- Waste removal
what is the epidermis epithelium
stratified squamous keratinised epithelium
layers of epidermis
- Basale - regeneration
- Spinosum - connected via desmosomes - typically form after shrinking
- Granulosum - contains granules w/ keratohyalin - involved in keratinisation
- Lucidum - thick skin - dense cells w/ NO nucleus or organelles
- Corneum - keratin - dead cells are shed - desquamation
melanocytes
- Produce melanin
- Determine colour of skin + hair
- Same amount in white + dark skin - higher synthetic activity in dark skin
- Contain melanosomes - the site for synthesis, storage and transport of melanin, the most common light-absorbing pigment found in the animal kingdom
langerhans cells
- Phagocytic + antigen-presenting and processing cells
- Present in all layers of epidermis
- Contain birbeck granules - function of Birbeck granules is debated, possibly migrate to periphery of Langerhans cells + release their contents into extracellular matrix -combine w/ vacuole - tennis racket
- Increased numbers in inflammatory skin diseases - contact allergen dermatitis
merkel’s cells
MERKEL’S CELLS
- Soles + palms - present in thick skin
- Sensory mechanoreceptors
- mechanoreceptor is a sensory receptor that responds to mechanical pressure
- membrane bound vesicles in slides
dermis
- connective tissue supporting epidermis + binding to subcutaneous tissue
- thickness varies according to body region
- surface consists of dermal - papillae - interdigitate w/ epidermal ridges
parts of dermis
PAPILLARY DERMIS - UPPERMOST
- loose connective tissue
- interlacing collagen + elastin fibres
- arterioles, capillary loops, venules, lymphatics
RETICULAR DERMIS - DEEPER
- dense irregular connective tissue
- blood vessels, nerves, skin appendages
- much larger collagen bundles, elastic fibres
SUBCUTIS
- loose connective + adipose tissue
specialised
meissners
-fine, discriminative touch - papillary
pacinian
- deep pressure + vibration - deep in subcutis
ruffini
- adapt slowly to pressure that results in stretching of the skin. They record the sustained presence of pressure on the skin eg. shopping bag holding
hair
- Skin appendages first develop in the second trimester of intrauterine development as simple downgrowths of the surface epithelium
- Hairs are long, thin, cylindrical shafts composed of keratin - Large hairs may have a central medulla
- hair shafts have a surface cuticle composed of a single layer of flattened keratin scales. This covers a cortex of keratin forming the bulk of the hair
nails
- Plates of keratinized epithelial cells (nail plate) on dorsal surfaces of tip of each finger/toe
- plate rests on a stratified squamous epithelium, the nail bed
- dermis beneath the nail plate is firmly attached to the periosteum of the distal phalanx
- nail matrix - epithelium under nail root - is thicker than the epithelium of the rest of the nail bed and exhibits pronounced epidermal ridges
- Nail root -part hidden in nail groove (invagination of skin)
- Stratum basale of nail bed is thickened - becomes nail matrix -site of active cell proliferation (seen as lunula - white circle - under nail)
- Dividing cells move outwards, become keratinized, and part of nail
The skin overlying the root of the nail is known as the nail fold and its highly keratinised free edge is known as the eponychium. The skin beneath the free end of the nail is known as the hyponychium.
sebaceous glands
- Attached to hair usually
- Embedded in papillary dermis
- 100 per cm2(more in face, forehead, scalp)
- Acinar (like sacs)
- holocrine secretion - rupture
Sebaceous glands secrete a mixture of lipids called sebum which may provide some waterproofing of the skin surface and hair shafts
pilosebaceous unit
each hair follicle + associated sebaceous gland
eccrine sweat glands
- merocrine - only secretion leaves - cell stays intact
- Coiled secretory gland in dermis
- Ducts open at skin surface
- Consist of cuboidal cells surrounding a small lumen
- Myoepithelial cells help to expel secretion - a thin layer above the basement membrane but generally beneath the luminal cells.
- Ducts have double layer of epithelial cell
apocrine sweat glands
- Present in axilla, areolar and genital regions
- Much larger than eccrine sweat glands
- Not functional until puberty
- Produce viscous secretion, initially odourless, but may acquire distinctive odour after bacterial decomposition
- Animals mainly possess apocrine sweat gland
