Introduction to Physiology and Histopathology of Skin
what type of hypersensitivity is atopic dermatitis?
type 1 (IgE mediated)
allergic contact dermatitis is a type ____ hypersensitivity reaction
type IV
Langerhans cells are important player in type ___ hypersensitivity reactions
type IV delayed type
what happens in Raynaud phenomenon?
vasospasm when exposed to stress or cold -> loss of heat/blood supply to fingers/toes -> then supply returns and they appear red
What is icthyosis vulgaris?
- autosomal dominant skin disorder characterized by diffuse dermal scaling. caused by loss of function mutations in the filaggrin gene - skin is dry, thick, scaly and resembles fish scales
what are keloids?
- benign overgrowth of dense fibrous tissue (abnormal scar proliferation via normal mechanisms) - dermis fibroblasts lay haphazard dense collagen bundles
what makes up a pilosebaceous unit?
- hair follicle - sebaceous (oil) gland - apocrine sweat gland (axillary, anogenital areas) - arrector pili muscle
how does acne vulgaris occur?
- hyperkeratinization causes obstruction of hair follicle - sebaceous glands produce more sebum - bacteria (propionibacterium acnes) thrives in this situation and causes inflammation - all results in acne or comedones
what is contained within granules of stratum granulosum?
- keratohyalin granules filled with proteins like fillagrin and profillagrin (these bind intermediate keratin filaments together) - at transition between this layer and stratum corneum, secrete lamellar bodies (lipids, proteins) that keep moisture in skin
what is erythema nodosum?
- type of panniculitis (subcutis inflammation) - appears as deep erythematous nodules typically on shins - can be from infection like mycobacteria or autoimmune disease like Crohn
4 stages of cutaneous wound healing
1. coagulation 2. inflammatory phase 3. proliferative-migratory phase (tissue formation) 4. remodeling
how long is cycle of keratinocyte before they shed off?
28 days
what immune cells are especially important in skin and recognize, uptake, process, and present antigens?
Langerhans cells (dendritic cells)
example of type IV hypersensitivity reaction
allergic contact dermatitis (urushiol oil in poison ivy)
mutations in fillagrin can result in ____
atopic dermatitis (dry, erythematous plaques)
MC skin cancer
basal cell carcinoma
which layer of epidermis is source of epidermal stem cells?
basal cell layer
benign collection of melanocytes: malignancy of melanocytes:
benign collection of melanocytes: nevi, mole malignancy of melanocytes: melanoma
where are adnexal structures in skin?
between dermis and subcutis
___ bridge cells in stratum spinosum layer while ___ bridge the basal cell layer to basement membrane
desmosomes - stratum spinosum hemidesmosomes - basal cells to basement membrane
what is in stratum corneum?
desquamating keratinocytes that lack nuclei and contain keratin and fillagrin protect against water loss, trauma, infection
there are mechanoreceptors in skin that allow us to sense things. when impaired, there can be insensitivity to injury which may occur in ____ (chronic illness)
diabetes peripheral neuropathy -> chronic foot ulcer
define spongiosis
edema in epidermis
layers of skin
epidermis, dermis, subcutis
what causes psoriasis?
excessive keratinocyte proliferation, 10x faster than normal
bullous pemphigoid results from autoimmune destruction of ____
hemidesmosomes (tense blister between epidermis and dermis -> not as prone to break)
define parakeratosis
hyperkeratosis with retained nuclei (normally stratum corneum cells are anuclei)
what cell is most responsible for type I hypersensitivity reactions?
mast cells
what chemical in skin protects from UV radiation?
melanin
melanocytes store melanin in ___ which they transfer to keratinocytes for pigmentation
melanosomes
two parts of dermis
papillary (upper) and reticular (lower)
how do basal cell carcinomas appear grossly?
pearly, erythematous papule or plaque with rolled borders and telangiectasias in sun exposed areas (face)
what is actinic keratosis?
precancerous rough, scaly, patch of skin due to sun exposure
define acantholysis
separation of epidermal cells
where are melanocytes in epidermis?
stratum basale
layers of epidermis top to bottom
stratum corneum, stratum granulosum, stratum spinosum, stratum basale
erythema nodosum is a disorder of the ____
subcutis
examples of adnexal structures within dermis
sweat glands, hair follicles
Raynaud phenomenon is a disorder of the skin's ____ regulation
temperature
what are Birbeck granules?
tennis racket/rod shaped intracytoplasmic organelles found in Langerhans cells
what are eccrine sweat glands?
they regulate body temperature by excreting sweat on skin ducts open in skin pore (throughout body)
define hyperkeratosis
thickened stratum corneum (top layer of skin)
define acanthosis
thickening of stratum spinosum, epidermal hyperplasia
