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