Cutaneous Vessels (including diseases) Flashcards
What are the three intercommunicating plexuses of arteries and veins?
1) Deep plexus (interface of dermis and subcutis - some branches supply lower hair follicle and epitrichial sweat glands)
2) Middle plexus (level of the sebaceous gland and supplies arrector pili, middle hair follicle, and sebaceous glands)
3) Superficial plexus (capillary loops just below the epidermis - supplies upper hair follicle and epidermis)
Describe arterioles
endothelial cells surrounded by smooth muscle cells, most likely function as part of the resistance vessels in skin
How do capillaries differ from arterioles?
Smaller and lack surrounding smooth muscle cells
Describe venules
A majority of dermal vessels are post-capillary venules
Most physiologically reactive segment of the microcirculation, are where inflammatory cells migrate from the vasculature to the tissue and where endothelial cells develop gaps due to inflammation which increases vascular permeability
What are the three sections of the microcirculatory bed?
Arterioles, capillaries, and venules
What IHC stain is useful for diagnosis of vascular neoplasms and for identification of vascular invasion by neoplasms?
Factor VIII-related antigen
What happens to selectins and members of the immunoglobulin superfamily on endothelial cells with inflammation?
E- and P-selectin as well as ICAM-1/VCAM-1 are upregulated and mediate rolling, adhesion, and transmigration of leukocytes (ex. neutrophils) from the blood
What are the 3 main functions of the endothelium?
1) maintain homeostasis of the blood
2) separate blood from tissues
3) regulate blood flow
Name 3 signaling molecules that regulate dermal angiogenesis.
1) Mast cells (histamine)
2) Macrophages (TNF-α)
3) TGF-β
Describe pericytes
- Aligned parallel to the blood vessels and vary in appearance from club-like to fusiform
- Contractile cells that contain actin-like and myosin-like filaments and regulate capillary flow
- Unknown origin
- Integral part of vessel wall and enmeshed in mural basement membrane material
Describe veil cells
- Flat, advential, fibroblast-like cells that surround all dermal microvessels
- exact function and nature are undetermined
- entirely external to vessel wall and demarcates it from the surrounding dermis
- perivascular mast cells are usually present in the space between the walls and the veil cells
What IHC stain would you use to identify veil cells?
Factor XIIIa (indicates that it is part of the dermal dendrocyte system)
Describe arteriovenous anastomoses
Normal connections between arteries and veins that allow arterial blood to enter the veins and bypass the capillaries
- associated with thermoregulation (ex. waterbird feet)
- occur in all areas but more common in extremities
- occur at all layers of the dermis but especially the deep dermis
- vary in structure from simple to the glomus
- can be pathologic
What causes dilation of arteriovenous anastomoses?
Acetylcholine and histamine
What causes constriction of arteriovenous anastomoses?
Epinephrine and norepinephrine
What is a glomus?
- A special AV shunt located in the deep dermis
- Consists of an arterial section (Sucquet-Hoyer canal) which branches from an arteriole and a venous section that is thin-walled with a wide lumen
- Has a tunica media that is densley packed with 4-6 layers of golmus cells that are large and pump, have clear cytoplasm, and resemble epithelial cells
- the glomus cells are generally regard as modified smooth muscle cells
Describe pathologic AV anastomoses/fistulae
- Can be congenital or acquired through trauma
- Hard to treat, surgery is frequently recommended
- Frequently in legs/limbs
- Arteriography can visualize them
Where do the cutaneous lymphatics arise from?
Capillary networks in the superficial dermis (though not usually seen in routine histopath preparations above the mid-dermis)
What are the functions of the dermal lymphatics?
- Control movement of interstitial tissue fluid so are essential for nutrition and control the true microcirculation of the skin
- Drain and take away material that arises through daily wear and tear so are important for the recycling of protein and cellular debris as well as removing topical medications/toxins, injected medications, etc
- Link skin to lymph nodes for immune regulation
Describe lymph formation and the removal via contractions
- Initial collector system is non-contractile, have an attenuated endothelial layer, discontinuous BMZ, and non-continuous cell junctions
- Lymph formation depends on periodic expansion of the lymphatics and compression (caused muscle contractions and physical motion) which causes emptying of the initial lymphatics to contractile lymphatics that have smooth muscle and exhibit peristalsis
How do you distinguish lymphatics from capillaries on H&E?
- Lymphatics have a wider/more angular lumen, more attenuated and flattened endothelial cells, no pericytes, shouldn’t have blood (but might with injury or inflammation)
What are Voight lines?
Boundaries of areas of distribution of the main cutaneous nerve stems
What are Langers lines?
Reflect the course of blood vessels or lymphatics
What are Blaschko’s lines?
- Lines follow a V-shape over the spine, S-shape on the abdomen, axial distribution on limbs, wavy on the face
- Reflect a mosaic condition
What are cleavage lines?
Same as tension lines
What is the pathogenesis of cutaneous vasculitis?
- Non-immunopathic (endotoxins or hemodynamic factors)
- Immunopathic
- Type III hypersensitivity
- Infectious pathogens initiating specific immune response
- Secondary vasculitis from local bacteria or septicemia
- Immune-mediated to drugs or underlying diseases
- Auto-immune disease
What are some causes of vasculitis?
Immunologic response
Food hypersensitivity – eos vasculitis
Insect bites – eos vasculitis
Neoplasia
–> MCT – eos vasculitis
Lupus erythematosus (or other connective tissue disorders)
Drug induced – many drugs including dexamethasone, prednisone
–> Itraconazole (dose dependent at 10mg/kg/d but not 5)
Vaccines esp rabies
Other – bacteria, protozoa, viruses
Canine eosinophilic dermatitis – eos vasculitis
PF
Cryoglobulinemia
Idiopathic
What are the clinical features of acute vasculitis?
- Skin is typically only organ system affected but not always
–> may also have other signs of illness
–> systemic vasculitis may lead to shock and DIC - Usually dependent areas, pressure points, extremities
- Purpura, purpuric plaques, hemorrhagic bullae, eschar, crateriform ulcers, pitting edematous areas, occasional acrocyanosis, petechia, erythematous urticaria, plaques, papules, pustules
–> Does not blanch with diascopy
What is lupus vasculitis?
Form of lupus associated with systemic or cutaneous lupus erythematosus
What is cryoglobulinemia/cryofibrinogenemia?
Vasculitis associated with precipitation of cold reactive immunoglobulins or immune complexes which affects the distal extremities
What is vaccine-associated vasculitis?
Lesions develop 2-6 months following vaccination at the site
- the pinnal apex is most common non-injected site
What is the most common vaccine associated with vasculitis?
Rabies