Case 1: Histology of the skin Flashcards
Functions of skin
- protection from external influences (incl. dehydration, radiation, pathogens)
- sensation
- endocrine functions
- heat regulation
- immunity
Three main layers of the skin
- epidermis
- dermis
- hypodermis
What is the epidermis comprised of
- multiple layers of cells
- glands
- receptors
- vessels and veins
4 main cell types present in the epidermis
- Keratinocytes
- Melanocytes
- Langerhans cells
- Merkel cells
List the layers of the epidermis
- Stratum corneum (keratinised stratified squamous epithelium)
- Stratum lucidum
- Stratum granulosum
- Stratum spinosum
- Stratum basale
Difference between thick and thin skin
- thin skin: covers majority of the body, contains hair
- thick skin: 6x thicker than thin skin & hairless. palms of hands, finger times and soles of feet.
- thick & thin refers to thickness of epidermal region alone
Outline the structure of stratum corneum
- 10 to 20 cell layers
- comprises of layers of corneocytes (dead keratinocytes that lack nuclei and organelles)
- cells contain keratin and have a hard protein envelope
Define Desquamation
shedding of dead cells from skin surface
Outline the structure of stratum lucidum
- clear layer
- visible in thick skin
- 3 to 5 flattened layers of corneocytes, cells filled with eleidin (intermediate of keratin)
Outline the structure of stratum granulosum
- granular layer
- cells contain keratohyalin granules (precursor to keratin)
- keratohyalin promotes hydration and cross linking of keratin
Outline the structure of stratum spinosum
- 8 - 10 layers thick, polyhedral keratinocytes with large pale staining nuclei
- desmosomes
- langerhans cells mainly found here
Outline the structure of stratum basale
- stratum germinativum
- one cell layer throughout body except hairless skin
- made of basal keratinocytes (stem cells of epidermis), melanocytes, merkel cells
Outline the function of keratinocytes
- filled with keratin
- functions as waterproof barrier, protective against environment damage (UV, heat, waterloss, pathogen) and responsible for would healing (able to migrate)
Outline the structure and function of melanocytes
- neural crest origin
- sits on basement membrane of stratum basale
- melanogenesis: production of melanin.
- Gives colour to skin, hair and eyes. Melanin is passed onto keratinocytes. Skin colour dependant on the amounts of melanin)
Outline the morphology and function of Langerhans cells
- dendritic immune cells mainly found in stratum spinosum
- large granules (Birbeck granules)
- recognise and present antigens to the immune system, phagocytosis, play a role in allergy and chronic skin inflammation
Outline the morphology and function of Merkel cells
- oval shaped receptor cells
- synaptic contact with somatosensory afferents
- detect light touch sensations
- found in stratum basale
Outline the structure of the dermis
- flexible, supports the epidermis
- NB for thermoregulation
- rich vascular supply
- 2 layers:
1) Papillary layer: loose areolar connective tissue, small blood vessels, lymph and nerves. Fine collagen fibres and elastic fibres
2) Reticular layer: denser irregular connective tissue, vascular plexus, lymph, nerves and appendages. Compact irregular collagen fibres and thick elastic fibres
Structure of the dermo-epidermal junction
- uneven boundary
- Dermal papillae: projections from the dermis into the epidermis
- Epidermal ridges/ epidermal peg: projections of epidermis into dermis
- Provides mechanical strength due to the folds
- give rise to fingerprints
Outline the structure of the hypodermis
- subcutaneous, mainly for storage of fat (energy & insulation)
- consists of loose connective tissue and adipose tissue
- sweat glands
- hair follicles
- contains large blood vessels and nerves
Sebaceous glands
- some can have ducts that lead into hair follicle, some open directly onto skin surface
- produces sebum for skin lubrication, prevents brittle hair, slightly acidic thus bactericidal
- holocrine secretion
- active at puberty
Merocrine/eccrine glands
- most abundant
- open via duct to pore on skin
- stratified cuboidal epithelial cells
- myoepithelial cells assist with secretion
- produces sweat (water, vitC, salts, wastes) NB for thermoregulation
- associated odour from bacteria
Apocrine glands
- found in the axillae, breast areolae, genital areas
- larger than merocrine sweat glands
- simple cuboidal to columnar shaped cells
- myoepithelial cells
- secretes fatty acids and proteins
- exact function unknown
Skin nerve supply - outline the receptors found in the skin
- thermoreceptors - senses heat and cold
- meissner’s corpuscles - senses light touch
- nociceptor & ruffini endings - senses pain
- pacinian corpuscle - senses pressure and vibration
