Skin Flashcards
skin general main role:
tough, tensile strength, covers the whole body, protection from friction/impact, UV rays
skin functions:
external layer relatively impermeable to water, thermoregulation, immune function
- makes vit D3, secretes oil, sweat
- receptors: touch, heat, pressure and pain
main layers of skin and composition:
epidermis and dermis, btw is basement membrane
- epidermis: keratinised stratified squamous epithelium
- dermis: deep connective tissue
hypodermis/ subcutaneous layer: areolar and adipose tissue
layers of epidermis and cell types found:
stratum: corneum, lucidum, granulosum, spinosum, basale (from superficial-deep)
mainly keratinocytes, also melanocytes, intraepidermal macrophages (Langerhans cells) and tactile (Merkel’s cells)
stratum basale: cell type/ composition/ features/ function
LIVING: simple basal columnar or cuboidal cells -> dermal/epidermal junction
- frequent mitotic cells, constantly renewing keratinocytes
- every 15-30 days
stratum spinosum: cell type/ composition/ features/ function
LIVING: prickle cell/ spiny layer (8-10 layers)
- cuboidal/ polyhedral
- or slightly flattened keratinocytes w/ nucleus and cytoplasm filled with bundles of keratin (strength, resistance)
- thick in areas of friction and pressure
stratum granulosum: cell type/ composition/ features/ function
DEAD: 3-5 layers of flatterned polygonal keratinocytes, cytoplasm filled with coarse basophilic granules
- cells undergo apoptosis
- also has small lamellar granules, fuse with cell membrane-> discharging contents into intercellular spaces= lipid-rich sheets (seals skin, barrier)
stratum lucidem: cell type/ composition/ features/ function
DEAD: 3-5 layers of translucent flattened cells, no evident nuclei/ organelles
- densely packed keratin filaments, thick plasma membrane
stratum corneum: cell type/ composition/ features/ function
DEAD: cornified (keratinised)
- varies thickness (15-20, up to 50 layers)
- no nucleus, packed with keratin
- layers continuously shed
keratinisation: enzymes remove cell organelles, leave mainly keratin = closely packed plates, tough, waterproof layer
- callouses from mechanical pressure
melanocytes: location/ features/ function
in basal layer, abundant cytoplasm, large irregular shape with projections extend in btw. keratinocytes
- produce melanin, skin pigment, blocks UV radiation from deeper skin layers
cytoplasm of epidermis:
contains ovoid granules, which produce melanin -> passes along cytoplasmic processes to basal and prickle cell layer keratinocytes
what gives skin colour?
melanin, carotene (temporary yellow), haemoglobin (pink/ red)
albinism:
lack of melanin in skin, eyes and hair, susceptible to damage from UV
Vitiligo:
autoimmune disease, degradation of melanin pigment, due to somatic cells not recognising
intraepidermal macrophages:
Langerhans cells
- important part of immune system, present in small no. on healthy skin
- ovoid nucleus, cytoplasm and cytoplasmic processes extending btw. keratinocytes
- mainly in spinosum
- in hypersensitivity reactions
tactile cells:
Merkel’s cells
- found in basal layer
- resemble melanocytes, form synapses with peripheral nerve endings = touch receptors
Dermis: function/ composition/ features/ layers
supporting ct. of epidermis, binds to subcutaneous tissue
- has epidermal appendages: hair follicles, hair, sweat glands, sebaceous glands, nails, mammary glands
- vascularised: has blood vessels, nerves, and nerve endings
upper papillary layer, lower reticular layer
upper papillary layer: cell type/ composition/ features/ function
areolar ct.
- paler than reticular dermis, less collagen/ elastin, more matrix
- random collagen/ elastin
- fine blood vessels and nerve endings
lower reticular layer: cell type/ composition/ features/ function
most of dermis, DICT, broad bands of dense collagem, thick fibres of elastin, usually parallel to surface
- blood vessels, lymph, nerves
collagen and elastic fibres general function:
collagen: strength, no elastic
elastic: connect dermis -> basal lamina, stretch and return to og size
stretch marks: and eg
striae, from extensive stretching of skin fast, and collagen fibres break
- pregnancy, growth
- surgery can cut btw tension lines, minimise scarring
dermal/ epidermal junction:
irregular, dermal papillae interdigitate (like interconnect) with epidermal ridges
- creates fine ridges on hands and feet (thick skin)
- dermatoglyphics (finger print)
hair layers/ structure
derived from epithelium, shaft (above skin) + root (within skin)
- medulla (pigment granules, air cells)
- cortex (heavily keratinised, pigment granules)
- cuticle (cuboidal/ columnar, heavily keratinised)
- follicles surround root, deep into dermis/ hypodermis
- internal/ external root sheaths: ct. sheath
hair bulb, arrector pili:
dilation at base, specialised area of dermis -> germinative cells produce hair shaft = keratinised dermal papilla
- arrector pili: narrow band of smooth muscle, contracts- hair more erect
sebaceous glands: cell type/ composition/ features/ function
- sebaceous glands connected to hair follicle
- secretes sebum, coating hair and skin (waterproof, protects from drying out)
- most on body surface, esp face, forehead and scalp
- outgrowth of external root sheath (hair) in dermis
- simple branched acinar
- holocrine gland (whole cell ruptures), secretion = cell death
- basal cells in periphery of gland proliferate (multiply) to replace lost cells
sweat glands: cell type/ composition/ features/ function
sudiferous:
secrete: water, electrolytes
- temperature regulation
- merocrine (eccrine) (forming vesicles to move into cell) and apocrine (rupturing of vesicles to discharge from cell) NOT associated with hair follicles
- simple coiled tubular
sweat glands: secretory and duct portions
- secretory portion in dermis, sometimes hypodermis
- secretory segment: cuboidal/ low columnar epithelium
- duct segment: stratified cuboidal epithelium (2 layers) smaller/ darker than secretory cells
sweat glands: apocrine
located in axilla, nipple region, anus, external genitalia
- connected to hair follicles, secretes protein/ carb/ ammonia/ lipids
- interacts with skin bacteria= body odour (only from puberty)
- larger glands
- coiled, tubular gland
- secretory portion: dermis/ hypodermis, large lumen
- duct: stratified cuboidal epithelium
compare thin vs thick skin: distrubution
thin: all parts of body except palms, digits, soles
thick: palms, palmar surfaces, digits, soles
compare thin vs thick skin: epidermal strata
thin: lucidum lacking, thin spinosum/ corneum
thick: thick lucidum, spinosum, corneum
compare thin vs thick skin: epidermal ridges
thin: lacking due to undeveloped disorganised dermal papillae
thick: present as papillae in parallel rows
compare thin vs thick skin: hair follicles/ arrector pili
thin: present
thick: absent
compare thin vs thick skin: sebaceous glands
thin: present
thick: absent
compare thin vs thick skin: sudoriferous glands
thin: fewer
thick: more numerous
compare thin vs thick skin: sensory receptors
thin: sparser
thick: denser