Dermatology Flashcards
What are the functions of the skin?
Protection (against damage, water loss, radiation, and disease)
Sensation (specialized nerve cells communicate stimuli)
Sexual signaling (Health communicated by appearance)
Metabolism (Synthesizes vitamin D3 which is importnat in proper bone formation)
Thermoregulation (Capillaries in the papillary dermis)
What are the features of the stratum basale?
Single layer of basophilic cuboidal cells
Attached to basement membrane (hemidesmosomes)
Attached to each other (desmosomes)
Intense mitotic activity (Progenitor cells for all layers)
Keratinocytes have keratin which increases in amount an crosslinking as cells move superficially
Friction blisters occur between S. Basale and basement
What are the features of the S. Spinosum?
Desmosomes between keratinocytes give a spiny appearance
Thickest layer
Typically the last mitotic layer
What are the features of the S. Grunulosum
Three to five layers of flattened highly basophilic cells
Basophilic masses are called keratohyaline granules
Also have golgi derived lamellar granules which are responsible for secreting lipid rich waterproof layer around cells
Keratinization in conjunction this layer help prevent water loss
What are features of the S. Lucidum
Only found in thick skin
Translucent layer of flattened keratinocytes held together by desmosomes
Cytoplasm consists almost exclusively of densely packed keratin
Features of the Stratum Corneum
15-20 layers of squamous cells filled with filamentous keratins
By this time tonofibrils have massed with filagrins and are just one mass with the keratohyaline granules
Amorphous proteinaceous cells are called squames and are continuously lost
What are melanocytes?
Derivatives of neural crest cells responsible for production of melanin and carotenes which color the skin
Tyrosine converted to DOPA which is converted to melanin
Affected in albinism or vitiligo
How does tanning occur?
Tanning is a two stage process that darkens the existing melanin and causes the melanocytes to produce more melanin which can then build up in the keratinocytes
What are langerhans cells?
The dendritic cells of the epidermis
Represent 2-8% of epidermal cells
What are Merkel Cells?
Epithelial tactile cells
Sensitive mechanoreceptors for light touch
Abundant in sensitive skin like that of the fingertips
Derive from basal layer stem cells
What is the dermis?
Layer of connective tissue beneath the epidermis
Connects epidermis to the hypodermis
Used to make leather
Thickest in the back at 4mm
Papillary layer and reticular layer
What is important about the subcutaneous layer?
Consists of loose connective tissue
Also called superficial fascia
Cotains adipocytes (good fat) which can be used in metabolism
Extensive vascular supply promotes rapic uptake of insulin or drugs injected into it
What are meissner’s corpuscles?
Phasic mechanoreceptors
present in the dermal papillae
light touch or low frequency stimuli
Numerous in fingertips but decline slowly with age
Pascinian Corpuscles
Large oval structures deep within reticular dermis
Specialized for course touch, pressure, and vibrations
Phasic receptors
Describe a hair follicle from inside to outside
Medulla (Highly Keratinized)
Cortex (Highly Keratinized)
Cuticle (continuous with internal root sheath at level of hair bulb)
Internal root sheath (disappears just above attached sebacous gland)
External root sheath (continuous with basal layer of surrounding epithelium)
Arrector pili muscle
Attached to hair follicle
Contraction causes hair to stand up on end
Contraction also cause sebum to be released from sebaceous glands
Nails
Keratinized epithelium
Nail root covered by a fold of stratum corneum called eponychium
Nail plate is bound to nail bed which consists of S. Spinosum and S. Basale layers
Continuous growth of nail matrix pushes nail plate out at 1mm/month in toes and 3mm in fingers
What are the common sources of skin infections?
Endogenous sources (normal flora taking advantage of immunosuppression) (P. Acnes)
Exogenous sources (Bacteria that is aquired from another source)
Toxins (superantigens secreted by bacteria)
What are the general characteristics of all streptococci?
Gram positive
Catalase negative
Appear in pairs or in chains
Obligate extracellular bacteria
What are the characteristics of Group A Strep?
Beta Hemolytic
Landsfield A antigen present (tested with rapid antigen test, kinda like pregnancy test)
Bacitracin sensitive
How does group A strep avoid being taken up by host neutrophils?
M proteins prevent complement fixation
Hyalunonic Acid capsule mimics normal human HA and therefore forces the body to recognize the bug as “self”
What are the common supporative GAS diseases?
Strep throat
Pyoderma (Impetigo, Erysipilis, Cellulitis, Necrotizing Fascitis)
What are common non-supporative sequelae caused by GAS?
Acute Rheumatic Fever (if patient develops this they must be put on prophylactic penicillin for the rest of their life to prevent additional cardiac antibodies)
ARF is caused because many M proteins mimic normal proteins in the body like tropomyosin
Glomerular Nephritis
How do superantigens from GAS work?
They cause bonding between MHC and T cells even when no antigen is present
Locking them together causes the T cells to release TNF-A and IFN y leading to fever
