Lecture 6 Skin Layers Flashcards
Function of skin
Protection - UV chemicals microbes mechanical damage and water loss
Sensation- temp. Pressure touch pain
Thermoreg - insulation/ evaporation
Metabolic - fat storage and vit D
Sexual attractant
Varying structures of skin
Thickness - soles of feet
Hair - scalp
Nails- fingers and toes
Sensory nerves - finger tips
Glands - sweating and lactation
Basic structure of skin
Epidermis - keratinocytes, melanocytes, Langerhans cells, merkell cells.
Dermis
Hypodermis or subcutis
muscle
Appendages/sensory structures/physiology
Appendages:
hairs and sweat glands
Sensory Structures
Detect touch, temp., Pressure, pain
Physiology
Temp reg, appearance and immunity
Epidermis
Layer in contact with external environment
Down-growth produces epidermal appendages - hairs and sweat glands
Contains various cell types: keratinocytes (main cell type), melanocytes, Langerhans cells and Merkel cells
Forms a series of rete ridges to protect from shearing stress
Has 4 major cell layers
Epidermis 4 layers
Cornified layer (stratum corneum)
Granular layer (stratum granulosum)
Spinous (prickle) layer (stratum spinosum)
Basal layer ( stratum basale/germinativum)
Keratinocytes
Main cell type in epidermis, stratified squamous epithelium
Contain keratin intermediate fibres
Go through various changes as they move from basal to surface layer
Epidermal differentiation
All cell division in epidermis confined to basal stem cell layer no cell division in higher layers ( in healthy tissue)
Basal keratinocytes (base layer)
Site of production of keratinocytes
Cuboidal or low columnar epithelium
Mitosis
Keratinokytes in spinous layer (second layer)
Normally no mitosis, cells move here upwards from basement layer
Cells tightly bound to each other by desmosomes
Darkly staining - cells rich in keratohyalin granules and keratin filaments
Change in gene expression pattern can be distinguished from basal cells by immunostaining of diff markers e.g. type 1/10 keratin
Keratinocytes in granular layer (3rd layer)
Cells flatten and lose their nuclei and other organelles
Contain many keratohyalin granules and keratin bundles
Cells secrete lipids (stored and formed in their ‘lamellar bodies’) and change composition of cell membrane
Granular cells produce surface keratins and non- wettable substances
Mechanism by which nuclei are lost unknown (2022)
Stratum corneum/ cornified layer (top layer)
Tightly packed flattened dead remains of cells
Cornified envelope: cross-linked protein layer under the membrane of cornified cells
Cornified envelope+ lipids = epidermal barrier
Epidermis : thin skin - found all over body
Thin epidermis especially cornified layer
Thick dermis:
Poorly developed rete ridged system
Hair present
Sebaceous glands present
Few eccrine/merocrine sweat glands
Epidermis: thick skin - found on palms of hands and soles of feet
Thick cornified layer
Thin dermis
Well developed rete ridge system
No hairs
No sebaceous glands
Many sweat glands
Many sensory organs
Melanocytes
Produce melanin (skin colour/protection from UV)
Found in basal layer of epithelium bound to basement membrane
Derived from neuroectoderm
Numbers are relatively constant but degree of activity is genetically variable
Pale staining in H+E. Can be detected histochemically (DOPA)
Contain premelanosomes and melanosomes
Melanoprotein complexes: pass through processes into keratinocytes
Cells have many cytoplasmic processes extending into basal and spinous layers
Melanoma
Melignant melanocytes caused by repeated UV exposure. Digest the basement membrane
Masson Fontana: stains melanin and is used for detection of malignant melanoma
A-asymmetric
B-boundaries
C-colour (multi)
D-dimensions (increasing)
E- evolution (growth
Langerhans cells
Able to leave epidermis and enter dermis.
Components of the immune system - recognise antigens and present them to T Cells
Found in all layers of epidermis but mostly spinous cell layer
Have cytoplasmic processes extending between cells
Pale staining in H+E can be detected using metal impregnation techniques or immunocytochemistry (CD1)
Merkel cells
Sensory receptors in the epidermis - sense light touch
Found in basal layer of epithelium
Cells form synaptic junctions with peripheral nerve endings - Merkel’s disc or tactile corpuscle
Occur singly or in groups - many in fingertips
Pale staining in H+E detected by metal impregnation techniques
Dermis
Layer of supporting tissue on which epidermis sits
Contains various cell types - nerves, blood vessels, fibroblasts and fibrocytes, macrophages, lymphocytes and mast cells
ECM- collagen, elastin, glycosaminoglycans
Contains epidermal appendages- hairs and sweat glands
Contains sensory cells
Divided into 2 layers
Dermis: papillary/reticular
Papillary- upper layer - less collagen and elastic fibrils, more glycosaminoglycans and small capillaries
Collagen and elastic fibres thin and vertical
Reticular - lower layer dense collagen and thick elastic fibres major blood vessels and lymphatics
Collagen and elastic fibres thick and horizontal
Papillary dermis lighter stained
Hypodermis or subcutis
Deepest layer of skin
Mainly adipose tissue and collagen fibres
Contains some epidermal appendages
Contains major blood supply and nerves
Acts as insulator, shock absorber and food store.
Epidermal appendages
Hair and sebaceous gland- pilosebaceous unit
Eccrine sweat glands
Apocrine sweat glands
Downgrowths of epidermis
Sebaceous glands
outgrowth from external root sheath. Branched acinar gland produces sebum ( lipids+wax that coat skin)
Holocrine secretion used (cells die and release their contents into ducts)
Arrector pili muscle (bundle of smooth muscle) aids in secretion+ makes hair stand on end
Skin physiology summary
Protection:
Barrier (keratins)
Waterproof (kerans+sebum)
Against UV melanin (in melanocytes)
Thermal insulation (adipose in hypodermis)
Absorption
Transdermal drug administration e.g. nicotine, nitroglycerine - patches
Injury response
Keratinocytes produce cytokines that induce inflammation
Sensory organ
Senses environment e.g. temp.
Thermoreg
Sweat glands
Immunity
Langerhans cells - antigen presentation and immune response
Endocrine function
Production of vitamin D (inactive precursor, converts to vit d in kidneys/liver)
Appearance
Camouflage, sexual selection (melanocytes)
