Cutaneous histology Flashcards
1
Q
What are the main characteristics of the epidermis?
A
- stratified squamous epithelium
- 4 layers (+ lucidum on acral skin)
- corneum
- granulosum
- spinosum
- basale
- mainly composed of keratinocytes
- typically 0.05-0.1 mm thick
2
Q
Describe the stratum corneum
A
- cornified/keratin layer
- comprised of anucleated corneocytes
- primary barrier of the epidermis
- thicker at acral sites
- NO stratum corneum at mucosal sites
3
Q
Describe the stratum lucidum
A
- “clear” layer; thin eosinophilic band beneath the stratum corneum
- ONLY on acral skin
- 3-5 cell layers thick
- may function to reduce friction
4
Q
Describe the stratum granulosum
A
- flat cells filled with basophilic granules (keratohyaline and lamellar/odland bodies)
- barrier, cell cohesion, hydrolyltic enzymes
5
Q
Describe the stratum spinosum
A
- “prickle”/spinous layer
- polygonal cells (progressively flatter towards surface)
- abundant eosinophilic cytoplasm
- oval vesicular nuclei
- conspicuous nucleoli
- 5-10 cell layers thick
- contains differentiating keratinocytes
6
Q
Describe the stratum basale
A
- cuboidal or columnar cells (single layer)
- perpendicular to dermis
- more basophilic cytoplasm; dark large nuclei
- periapical cap of melanin
- connected by desmosomes (connected to basement membrane by hemidesmosomes)
- **Most mitotic activity
7
Q
What are the major characteristics of melanocytes?
A
- found sparsely in the basal layer of the epidermis (1 melanocyte/10 keratinocytes… 1/4 in cheek… less with skin damage)
- neural crest origin
- no desmosomal attachments
- pale cytoplasm
- transfer pigment to keratinocytes
8
Q
What are the major characteristics of langerhans cells?
A
- bone marrow derived
- dendritic antigen presenting cells
- normally in epidermis in concentration similar to melanocytes
**found at different layers (UNLIKE melanocytes which are only found in the basal layer unless there is pathology)
9
Q
What are the major characteristics of merkel cells?
A
- Found in:
- basal layer of epidermis
- bulge of hair follicle
- oral mucosa
- not easily identified on H&E
- closely associated with sensory nerves
- tough receptors
10
Q
What are the two layers of the dermis? What separates them?
A
- papillary dermis
- directly beneath epidermis (connects via dermal papillae containing capillaries)
- fine vertically oriented collagen
- reticular dermis
- coarse thicker collagen fibers parallel to surface epithelium
- contains sweat glands, lymph vessels, hair, and blood vessels
**separated by superficial vascular plexus
11
Q
Describe meissner’s corpuscles
A
- at dermal papilla of palms, soles, and lips
- thick lamellated capsule surrounding core of cells and nerve fibers
- sensory light touch receptors
12
Q
Describe fibroblasts
A
- thin, spindle shaped cells with elongated ovoid nuclei interspersed between collagen bundles
- synthesize collagen and elastin fibers and ground substance
13
Q
Describe elastic fibers
A
- not easily visible without special stains
- horizontally oriented thicker fibers in reticular dermis
- vertically oriented and more fine fibrils in papillary dermis
14
Q
Describe pacinian corpuscles
A
- at dermal-subcutaneous interface
- palms, soles, digits, genitalia, ligaments, joints
- ovoid ~1mm in length
- lamellated in cross section
- encapsulated sensory receptors for deep pressure and vibration
15
Q
What are the three parts of a hair follicle?
A
- infundibulum
*follicular orfice to entrance of sebaceous gland
*normal keratinization - isthmus
*sebaceous duct to insertion of arrector pili muscle
*trichilemmal keratinization (no granular layer)
*no inner root sheath - lower portion
*dermal papillae
*matrix
16
Q
Describe a hair follicle in cross section (parts outer to inner)
A
- fibrous sheath
- basemement membrane
- outer root sheath **continuous with the epidermis
- inner root sheath **supports hair fiber, degenerates at the level of sebaceous gland (aka no IRS higher than isthmus)
- henle’s layer
- huxley’s layer
- cuticle
- central cortex
17
Q
Describe a sebaceous gland
A
- lobular; lined with thin outer layer of basophilic germinative cells
- central bubbly clear cells filled with lipid and “scalloped” nuclei
- duct lined with stratified squamous epithelium
- holocrine secretion (completely degenerates to secrete sebum)
18
Q
Describe an apocrine gland
A
- single layer of columnar secretory cells with round nuclei
- coiled secretory portion (in lower reticular dermis or subcutaneous fat)
- straight duct opens into hair follicle above the level of the sebaceous gland (rarely opens to epidermal surface)
- found in axillae, anogenital area, external ear canal, eyelid, areola (inactive until puberty)
- decapitation secretion
**lumen may be larger than in eccrine tissue
19
Q
Describe an eccrine gland
A
- present everywhere except vermillion of lips, glans, labia minora, nail beds, inner prepuce **greatest on palms, soles, axillae, forehead
- Three parts:
- spiraled intraepidermal portion (acrosyringium)
- intradermal duct (straight and coiled portions)
- coiled secretory portion
20
Q
Describe the outermost portion of an eccrine gland
A
**the intraepidermal spiraled portion:
- also called acrosyringium or epidermal sweat duct unit
- empties directly onto epidermal surface
21
Q
Describe the middle portion of an eccrine gland
A
**the intradermal straight portion
(two layers of small cuboidal cells)
22
Q
Describe the innermost portion of an eccrine gland
A
**the coiled secretory portion
- one distinct layer of secretory cells surrounded by a layer of myoepithelial cells (similar to apocrine gland but smoother inner border and smaller lumen)
- lies in the lower reticular dermis
- surrounded by thick basement membrane
23
Q
Describe how lymphatics look on histology
A
- thin walled vessels lined by attenuated epithelium
- have multiple valves
- usually collapsed and difficult to detect in the dermis… see with obstruction
24
Q
Describe how subcutaneous fat looks on histology
A
“Hypodermis”:
- arranged in lobules, separated by vascular fibrous septa
- fat is dissolved by routine processing
- large single globule of lipid that displaces nucleus and cytoplasm
25
What regional anatomy is depicted by this histology?
\*\*Scalp;
* many large terminal hairs
* hair bulbs extend into subcutaneous fat
26
What regional anatomy is depicted by this histology?
\*\*Trunk;
* dermis is very thick
* broad parallel fascicles of collagen in reticular dermis
27
What regional anatomy is depicted by this histology?
\*\*eyelid;
* skeletal muscle bundles (instead of fat)
* hair follicels (small)
* stratumcorneum
28
What regional anatomy is depicted by this histology?
\*\*nose;
\*conspicuous sebaceous glands (often drain directly onto the skin surface)
29
What regional anatomy is depicted by this histology?
\*\*ear
* thin dermis
* cartilage in the center
30
What regional anatomy is depicted by this histology?
\*\*acral skin
* thick, compact stratum corneum
* prominent rete ridge pattern
* stratum lucidum present
31
What regional anatomy is depicted by this histology?
\*\*mucosa
* no granular or cornified layers
* keratinocytes pale due to glycogen content
32
What are the layers of the basement membrane zone (BMZ)?
1. Hemidesmosomes (BP 230, BP 180)
2. Lamina lucida (BP 180)
3. Lamina densa (laminin 332, collagen IV)
4. Sublamina densa (collagen VII)
33
What are the two major proteins of a hemidesmosome?
1. _BP 230_ (bullous pemphigoid antigen 1)
* belongs to the plakin family of proteins
* cytoplasmic localization
* organization of the cytoskeletal architecture
2. _BP 180_ (bullous pemphigoid antigen 2)
* AKA type XVII collagen
* transmembrane protein connecting basal keratingocytes via _BP 230_ to cytoskeleton
* connecting to dermal collagen VII via _laminin 332_
34
What is the major component of the lamina lucida?
BP180
35
What is the key BMZ laminin?
\*\*laminin 332;
* binds to hemidesmosomal protein integrin a6B4 on the basal keratinocytes
* also binds type VII collagen in the dermis
* provides adhesion between these two structures
36
What are the major components of the lamina densa?
* composed mostly of type IV collagen ("4 is the floor") and laminins (e.g. 332)
* type IV collagen is one of the most abundant collagenous glycoproteins of the BMZ
37
What makes up the sublamina densa?
\*\*_type VII collagen_
* large protein composed of three identical alpha chains
* form _anchoring fibrils_
* necessary to maintain epidermal-dermal cohesion (binds both type I and type IV vollagens)
38
What are the important proteins of the basement membrane zone (BMZ)?
* BP230
* BP180
* a6B4 integrin
* Laminin 332
* type VII collagen
39
What are the laboratory tests used for autoimmune bullous disorders?
1. direct immunofluorescence (DIF)
* directly tests skin sample (from perilesional skin)
* detects immunoglobulins and complement (C3)
2. indirect immunofluorescence (IIF)
* tests circulating antibodies in patient serum
* circulating Abs from patient serum bind BMZ antigens in the substrate (normal human skin)
* antigen-Ab complext detected by fluorescence
3. ELISA
* antibody-antibody interaction allows for easy visualization of results and can be completed in a short period of time
40
Describe bullous pemphigoid (BP)
* most common autoimmune bullous dermatosis (better prognosis than pemphigus vulgaris)
* primarily seen in the elderly
* tense blisters with serous or rarely even hemorrhagic content appear in phases
* antibodies to BP antigen 1 (BP230) and BP antigen 2 (BP180) cause subepidermal blisters
* treat with steroids/immunosuppressants
41
What would direct immunofluorescence show for a BP diagnosis?
DIF shows linear deposits of IgG and C3 along BMZ
42
What are the specific names for sebaceous glands in different areas of the body?
* Eyelid – Meibomian and Wolf glands
* Oral muscosa/lips - Fordyce
* Penis – Tyson
* Nipple - Montgomery
