Skin Flashcards
What is the function of skin?
-Physical protection and barrier to UV (melanocytes/melanin)
- Prevention of water loss
Sensory (pain, heat, touch etc- merkel cells mechanoreceptors)
-Manufacture of Vitamin D (cholestrol, converted to cholecalciferol or vit d in sunlight)
- Temperature regulation
- Excretion
What are the 3 main layers of skin? (2 true, 1 associated)
Epidermis (inc epidermal appendages- for example
-sweat glands
-sebaceous glands
- hair follicles
-nails (all epithelial tissue)
Epidermis lacks blood supply, blood diffuses from dermal layer into epidermis
Dermis (connective tissue- collagen/elastin), blood vessels
Hypodermis/ subcutaneous tissue/ superficial fascia- NOT STRICTLY SKIN
What type of epithelial tissue does the epidermis consist of?
Stratified Squamous Keratinising Epithelium- contains keratinocytes
keratinocytes main type of cell that make up epidermis, that are constantly sloughed off as new keratinocytes develop.
What type of connective tissue is the dermis made up of?
Dense Irregular CT- contains fibroblasts, collagen and elastin fibres
What type of gland is the sebaceous gland?
They are exocrine- simple, unbranched acinar glands
What are the characteristics of a sebaceous gland?
Consist of a single duct that secretes sebum- an oily secretion made up of triglycerides, protein, cholestrol and inorganic salts.
They are connected to hair follicles and are found in most parts of the skin, especially scalp and face.
They have round large cells with a centrally located nucleus, cloudy cytoplasm (lipid containing).
Sebocytes are epithelial cells responsible for production of sebum.
What are the functions of sebaceous glands?
Secrete sebum that coats the surface of hairs, lubricates skin, prevents excess evaporation and hinders the growth of some bacteria.
What is the difference between an exocrine and an endocrine gland?
Exocrine is ductal/ secretes its chemical substances into a duct
Endocrine secretes its chemical substances directly into the bloodstream
What similarities do eccrine and apocrine sweat glands have?
Both of these sweat glands have secretory units to make secretion, and a cut to release secretion onto surface.
What are the characteristics of an apocrine sweat gland?
Large lumen and epithelium cells lining
Apocrine secrete a substance made of protein, lipid and steroids in response to emotional stress
“Scent glands”- BO as bacteria feed on protonatious/ fatty product (genitalia/ armpits)
What are the characteristics of an eccrine sweat gland?
Secrete a substance that is mainly water
Found everywhere bar palms/ soles and important in thermoregulation and maintenance of homeostasis
What are the 5 strata of the epidermis?
- Stratum corneum- surface stratum, 15/20 cell layers (corneocytes) have no organelles- almost entirely keratin. Can be shed (thin) or worn off (thick).
- Stratum Lucidum- thin, clear layer of dead skin cells in the epidermis named for its translucent appearance under a microscope. It is readily visible by light microscopy only in areas of thick skin (palms of hands /soles of feet)
- Stratum Granulosum- 2-3 layers of flattening cells- keratohyalin granules that contain lipid rich secretion, undergo terminal differentiation into keratinocytes
secretion= water sealant+ prevents pathogen infiltration - Stratum spinosum- generally thickest layer (2-8 layers)
- “prickle cells”- mitotically active basally located keratinocytes
-rich in tonofilaments (thin bundles of intermediate filaments)
- Interdigitative between eo, forming intercellular bridges (DESMOSOMES)
- Langerhans cells- dendritic cells involved in adaptive immune response - Stratum Basale- supported by B.mem, immediately above dermis- large nuclei, producing/ proliferating cells worn off from SC. Active cell division
What are junctional complexes?
Molecular nuts/bolts responsible for anchoring cells together ( laterally or apically/ basally)
Desmosomes laterally anchor cells of SS: Hemidesmosomes basally attached to BM
How are keratinocytes developed?
During the process of keratinzation they migrate up from the basement membrane toward the stratum corneum [14].
Keratinocytes are derived from undifferentiated cells in the stratum basale of the epidermis. The process of keratinization occurs in two stages, a synthetic stage and a degradative stage. The synthetic stage begins after the basal stem cells divide. Half of the daughter cells remain in the basal cell layer, while the other half of the cells progress toward the surface and differentiate Keratinocytes have the capacity to increase their rate of replication during periods of inflammation, disease, or injury [15].
In the stratum spinosum the cells begin to change from columnar to polygonal. At this stage, keratinocytes begin to synthesize keratin, insoluble proteins that act as intermediate filaments and tether half desmosomes from one side of the cell to another tion to bind epidermal cells together [16].
Keratinocytes gradually travel to and through the stratum granulosum, where enzymes induce degradation of their nuclei and organelles but not their keratin. These terminally differentiating keratinocytes contain keratohyalin granules composed of profilaggrin, a precursor to filaggrin that causes keratin filament aggregation [8]. Conversion to filaggrin occurs in the granular layer, resulting in the formation of an electron dense interfilamentous protein matrix containing keratin and several other structural proteins including involucrin. Involucrin encases a group of keratin macrofibers that have been aggregated by filaggrin [8]. Keratohyalin is important in the formation of so-called soft flexible keratin. In the absence of keratohyalin, the keratin formed is hard and rigid, as seen in hair and nails. In the stratum granulosum, membrane-coating granules attach to the cell membrane and release a viscous lipid substance that contributes to cell adhesion, thus creating the permeability barrier [4].
The keratinocytes continue to travel up to their last stop, the stratum corneum. At this stage the cells have become flattened and dead, with thick cornified envelopes containing keratin, filaggrin, and involucrin [18]. Additionally, the disulfide bonds of keratin provide strength to the stratum corneum. As desmosomal intercellular adhesion and lamellated lipid are lost, the cells shed from the skin. This programmed maturation that ultimately results in cell death is called terminal differentiation [16].
