Histology: Skin Flashcards
what are the physiological functions of skin? - (protect from? provides?)
- protec from: physical trauma, infection, uv radiation, penetration of drugs,
- provides: insulation, vit D synthesis, sensory information
what does thickness of skin depend on?
what does colour of skin depend on?
- *anatomical location:** thinnest on eyelids / thickets on palm / soles
- *colour:** amount of intraepidermal melanin pigment
what are the two layers of skin?
- *- 2 major layers:
- **dermis
- epidermis (outer layer)
describe layout of cells (e.g. stat / simple etc)
what are the 4 major layers of epidermis? whats the 5th one - where found?
derived from?
- *-** keratinised stratified squamous epithelium
- derived from ectoderm
4 layers:
- *- stratum basale
- stratum spinosum
- stratum granulosum
- stratum corneum
- **stratum lucidum: only in thick skin (palm and sole)
label this pls
describe statrum basale stucture
what happens
- single layer of cells rested on basal lamina
- **stem cells
- small cuboidal to low columnar
- less cytoplasm
- **brown pigment found in them: secreted by melanocytes.
what happens at the stem cells in stratum basale?
stratum germitativum: new keritonocytes form from the stem cells found in stratum basale by mitotic division
describe the structure of stratum spinosum
what happens when cells mature in stratum spinsoum?
- *- several cell thick
- **larger keratinocytes: numerous cytoplasmic processes or spines (attached by desmosomes)
- cells mature: increase in size, move upwards and become squamous, paralell to surface
describe the movement of immature -> mature keratinocytes
. Mature, differentiated keratinocytes are pushed towards the surface of the skin through these layers by the proliferative action of immature keratinocytes in the underlying layers. While being moved through the stratum granulosum and into the stratum corneum, keratinocyte nuclei dissolve and bioactive lipids are squeezed into the extracellular space. The cells are fully differentiated at the stratum corneum, where they are eventually shed into the environment.
describe structure of stratum granulosum
what are the granules found in this layer made from?
- *- top layer of non-k** part of epi
- **1-3 cell thick
- **k with keratohyalin granules: cystine and histidine protein granules, which are precurosrs of fillagrin, which aggregates the keratin filaments
- flattened form
which is the top layer of the non-keratinized part of epidermis?
stratum granulosum
describe structure of stratum corneum
- flat and **empty cells in skin
- loss of nucleus and cytoplasmic organelles: filled with keratin filaments**
- coated extracellularly with thick lipid layer: waterproof
- looks like a net
- thickness varies (eyelids v palms)
what is keratin?
in which places is the most abundant protein?
- *- intermediate filament: **components of cytoskeleton
- most abundant in: stratum corneum, hair and nails
what is structure like of keratins?
what keratin expression pattern is specific to?
- *- alpha keratin:** secondary structure of **alpha helix - longer chains = more flexible (hair)
- **beta-keratin: secondary structure of beta sheet - more rigid (nails)
- whether is alpha / beta determines softnes of skin
- exist as acidic / basic pair
- expression pattern: specific to epidermal layer (switches in the different layers)
where do u find alpha / beta keratin ?
alpha: hair
beta: nails
basal cells of epidermis cells are attached to what?
what do adherens and desmosomes, tight junctions and gap junctions do in epidermis basal lamina?
- basal cells adhere to ECM rich basement membrane: consists of Laminin 332, Collagen IV and Collagen VII)
- *- adherens and desmosomes:** attach cells extra- and intracellularly, mech support and integrity of epi
- *- tight junctions:** seal up intercellular space - prevent bacteria passing through
- *- gap junctions:** communication, nutrients
what are melanocytes? role? where?
melanocytes:
- function: produce and distribute melanin.
- location: scattered among stratum basale, also get long processes between the keratinocytes of the **stratum spinosum
- appearance:** have granules
how do you differentiate betweeen melanocytes and keratinocytes?
- *melanocytes**: smaller nucleus, cytoplasm looks like halo
- *keratinocytes**: brown looking
what do merkel cells do ? found? appearance?
- *merkel cells:**
- location: **stratum basale
- appearance:lobed nucleusanddenser cytoplasm.** looks like a bean. (hard to differentiate with melanocytes)
- function: underlying sensory nerve endings - light touch sensory. aso possess antigenic markers
explain how is the dermis divided?
- *papillary layer:
- ** loose CT.
- think collagen fibresL predom Collagen I and III
- contains BV and nerves that dont enter epidermis
- scattered lymphocytes
- meissner corpuscles present in acral skin
- *reticular layer:
- ** denser CT
- deep to the papillary layer.
- thicker and less cellular
- irregular bundles of collagen 1 and elastic fibres
- small and medium BV & nerves
- pacinian corpsucles: pressure receptors in acral skin
- pilar muscles - small muscle bundles associated with hair follicles
- smooth muscle bundles present in gentilia and areala
what is the pilosebaceous unit?
pilosebaceous unit: hair shaft, the hair follicle, the sebaceous gland, and the erector pili muscle
whats inside a hair shaft?
shaft (hair), external root sheath, internal root sheath, cuticle, cortex and medulla
hair bulb & dermal papilla
what do sebaceous glands do? look like?
function: produce sebum: oily substance. secreted by holocrine secretion. sebum and cell debris are secreted by pilosebaceous canal in hair
appearance: big cytoplasm
what are eccrine sweat glands? role ? function?
- function: secrete sweat: regulating body temp.
- location: everywhere
- cell structure: stratified cuboidal epithelium - directly connected to epidermis
secretory part contains:
- clear cells: cytoplams contains glycogen, producing watery component
- dark cells: darker cytoplasm - secrete protein rich secretion
- myoepthilial cells: in the basal segment. contractile, excretion of sweat
apocrine sweat glands?
function: sweat glands - associated with hair follicles
appearance: simple epithelium ducts (identical to eccrine)
cells found: large eosinophilic epithelial cells, with bleb like protrusions. eosinophilic epithelial cells produce a protein rich secretion containing pheromones
what are skin receptors?
- *1. meissner’s corpsucles:** respond to fine touch and pressure & low vibration frequency. encapsulated nerve endings (axon surroundered by schwann cells)
2. pacinian corpuscles: look like onions. myelinated nerve ending in the centre. deep in dermis. sensitive to vibration and pressure - *3. ruffini endings:** _deeper i_n base of epidermis - detect skin stretch, joint activity and warmth. finger position and movement
label this
