Week 1 Downing - Histology of Skin/Integument Flashcards
What are the three components of the Integument?
- Epidermis
- Dermis
- Hypodermis
What are the four epidermal layers in order from bottom to top?
- Stratum germinativum (basale)
- Stratum spinosum
- Stratum granulosum
- Stratum corneum
What epidermal layers are mitotically active?
- Stratum germinativum
- Stratum spinosum
Where is the Stratum germinativum (basale) located?
- Deepest layer of epidermis
- Adjacent to the basal lamina
Where is the Stratum spinosum located?
Immediately above the Stratum germinativum (basale)
What is the structure of the Stratum germinativum (basale)?
- Single layer of cuboidal or columnar cells
- Hemidesmosomes along cell membrane that attach to basement membrane
- Contain many polyribosomes and intermediate filaments due to mitotic activity
What is the structure of the Stratum spinosum?
Prickle cell layer
- Several cell layers deep
- Polygonally shaped cells
- numerous desmosomes
- bundles of intermediate filaments (tonofibrils)
- membrane-bound lamellar bodies containing lipids
What is the structure of the Stratum granulosum?
- 3-5 cell layers thick
- flattened polygonally-shaped cells
- keratohyalin granules in cytoplasm
- nucleus pyknotic (dying)
What is the structure of the Stratum corneum?
- Variable number of cell layers
- Clear, dead, flattened, and fused cells
- Cytoplasm is keritinized
Where is the Stratum granulosum located?
- above stratum spinosum
- below stratum corneum
Where is the Stratum corneum located?
- Outermost layer of epidermis
What are the two phases of Keritinization?
- Synthetic phase
- Degradative phase
What happens during the Synthetic phase of Keritinization?
Form:
- Intermediate filaments
- Membrane coating granules
- Keratohyaline granules (filaggrin & trichohyalin)
What occurs during the Degradative phase of Keritinization?
- Membrane coating granule discharge
- form lipid layer
- Lysosomal degradation of organelles
- Consolidation of filaments and keratohyalin into a fibrous amorphous mass = KERATIN!
What are the three layers of the dermis?
- Papillary layer (vascular/nervous papillae)
- Reticular layer
- Langer’s lines
Where is the papillary dermis located?
- uppermost layer of the dermis
- primary ridges and secondary ridges extend into epidermis forming dermal papillae
- increase surface area between dermis & epidermis
- makes secure adherence between layers
What is the structure of the papillary dermis?
- Loose connective tissue
- collagen, some reticular/elastic fibers
- Vascular papillae
- capillary loop projections
- Nervous papillae
- Meissner’s corpuscles
- Pacinian corpuscles
Where is the reticular dermis located?
- the lower layer of the dermis
- found under the papillary dermis
What is the structure of the reticular dermis?
- composed of dense irregular connective tissue with densely packed collagen fibers
- type I collagen
- some reticular fibers
- primary location of dermal elastic fibers
How are secondary dermal ridges formed?
- Downward projection of epidermis in primary ridge
- projection of epidermis = rete peg
What are Langer lines?
- Direction of fibers in reticular dermiscreates lines of skin tension
- Differ in different regions of the body
- Surgical incisions gape less when parallel to these lines (less scarring
What is the hypodermis?
- Superficial fascia
- Not considered part of the skin
- Frequently large accumulations of fat cells
Where is the hypodermis located?
Below the dermis
What is the structure of the hypodermis?
- Loose connective tissue
- Fat cells
(Fat cells absen in hypodermis of eyelids, penis, and scrotum)
How is thick skin differentiated from thin skin?
- Based on epidermal thickness
- dermis is thin in both types
Where is thick skin present in the human body?
Palms of hands & Soles of feet
Where is thick dermis present in the human body?
Skin of back
How is melanin formed?
- Rough ER produces tyrosinase
- Golgi packages tyrosinase enzymes in a membrane-bound vesicle = pre-melanosome
- Tyrosine + Tyrosinase → DOPA
- DOPA + Tyrosinase → Melanin
Where are melanocytes found?
Usually present in the Stratum germinativum (basale) layer of the epidermis.
What happens to melanin granules after tyrosinase activity is halted?
- Melanosomes create branches/processes off of melanocyte
- Processes of melanocytes are insinuated between other epidermal cells
- Melanosomes are eventually donated to adjacent epidermal cells
What is skin pigmentation based on?
- Color of skin itself (carotenes) = yellow
- Blood capillaries = red/pink
- Varying amounts of melanin = brown
What are the three layers of vascular supply in the dermis called?
- Subcutaneous arteries & veins (deep)
- Rete cutaneum (cutaneous plexus)
- Rete subpapillare (subpapillary plexus)
Where are the Rete cutaneum (cutaneous plexus) blood vessels located?
- Between reticular layer of dermis and subcutaneous tissue
- dermal-hypodermal junction
Where are the Rete subpapillare vessels located?
In papillary layer of the dermis
(supply blood to papillary loops)
