Integument I Flashcards
Epidermis (Epithelium + cells)
Keratinized stratifies squamous
epithelium
Derived from ectoderm
Dermis
Dense connective tissue
Derived from mesoderm
Hypodermis
-deep to (beneath) the dermis
-ariable amounts of adipose
tissue (panniculus adiposus) arranged
in lobules and separated by
connective tissue septa
-mechanoreceptors in this layer
largest cell population
▪ Keratinocytes
pigment producing cells
of the epidermis.
Melanocytes
• Langerhan’s cells
antigen presenting cells (APC’s) • plays a role in the immunological function of skin • accounts for 2%-5% of cells
Merkel cells
mechanoreceptors
• associated with sensory nerve endings
• constitutes 6%-10% of cells in the
epidermis
Keratinocytes-Functions:
Produces keratin (cytokeratin)– mainly the keratinocytes of stratum basale • Produce keratohyalin granules – cells in spinosum and granulosum layers • Contributes to the formation of the epidermal water barrier
Melanocytes
- Located in the basal layer (stratum basale)
- Originates from neural crest
Melanocytes-Functions:
-Produce melanin that is transferred to surrounding keratinocytes (Cytocrine secretion) -Skin color -Oxidation of tyrosine to 3,4- dihydroxyphenylalanine (DOPA) and subsequent transformation of DOPA into melanin
Melanin distribution
Light skinned persons - concentrated in stratum basale
• Dark sinned persons - dispersed throughout stratum basale and spinosum
Eumelanin
-Protection against UVR damage
-Scatter and absorb UV rays and eliminate UV-generated
free radicals
-Degrades faster in lighter skinned individuals
Pheomelanin
Allows UV
- Found more commonly in atypical nevi and melanomas
- Increased oxidative damage
Langerhan’s Cell: Structure
Originates from common lymphoid progenitor (CLP) • Present in all epidermal layers but most easily recognized in stratum spinosum
Langerhan’s Cell:Function
- Immunological role
-delayed type
hypersensitivity reactions
-• Express both MHC 1 and MHC II and
receptors for IgG
Merkel’s Cell: Structure
-Most abundant in skin where sensory
perception is acute
-Merkel’s corpuscle
Merkel’s Cell:Function
-Detect touch sensations
-• Have desmosomes and contain
keratin filaments
-Nucleus is lobed
-Cytoplasm contains neurosecretory
granules
-Possess antigenic markers of both
epidermal and neural type
Thick Skin
Found only in the palms and soles
• Usually hairless and much thicker
epidermis
• Carries a stratum lucidum
Thin Skin
Found everywhere else
• Thinner epidermis than thick skin
• Hair follicles are widespread except for
a few locations
Stratum basale
-Can differentiate
-• Single layer of cuboidal to low columnar
cells
-basophilic staining
-Rests on the basal lamina
• Attached by hemidesmosomes
Stratum Spinosum (S)
-Maturing and slowly dying cells
-Exhibit numerous cytoplasmic processes or
spines
-• Processes of neighboring cells are connected to each
other via desmosomes
-
Bullous pemphigoid
Clinical correlate –Stratum Basale
Pemphigus vulgaris
Clinical correlate-Stratum Spinosum
Stratum Granulosum
- conspicuous granules
- Keratinization (soft keratin)
- • Lamellar bodies • Epidermal water barrier
Stratum Lucidum
Stratum Lucidum
Stratum Corneum (SC)
-Several layers of dead keratinocytes
-• Lack organelles
• Thick plasma membranes covered with
lipid forming a barrier that is impermeable
to water (WATER BARRIER)
- Abrupt transition from granulosum
Pemphigoid vulgaris
Clinical correlates–Stratum Corneum (SC)
Formation of Epithelial Water Barrier-Cell envelope
• Insoluble proteins on inside of cell
membrane
• Mechanical part of barrier
Formation of Epithelial Water Barrier-Lipid envelope
Lipid layer on outer surface of the cell
membrane
• Lamellar bodies
Epidermal Turnover Time: Normal-Days 1-2
Keratinocytes in stratum
basale divide mitotically
and migrate to stratum
spinosum
Epidermal Turnover Time: Normal -Days 3-31
Duration of keratinocytes
stay in stratum spinosum
Later move to granulosum
Epidermal Turnover Time: Normal -Days 32-46
Keratinocytes become
keratinized and enter
stratum corneum
