Skin: Histology Flashcards
2 junctions that connect keratinocytes
Desmosomes and adherens junctions
Cells of the stratum germinativum are connected to the basement membrane by these
Hemidesmosomes
Cells of this are connected to the basement membrane by hemidesmosomes
Stratum germinativum
Is the epidermis vascularized?
No
Is the epidermis keratinized?
Yes
What is the main cell morphology of the epidermis?
Stratified squamous epithelium
Name the 5 layers of the epidermis from superficial to deep
Stratum corneum
Stratum lucidum
Stratum granulosum
Stratum spinosum
Stratum basale
Component of the corneocyte layer that is found only in thicker skin
Are densely packed with keratin filaments
Stratum lucidum
Component of the corneocyte layer where nucleus and cytoplasmic organelles become disrupted and disappear as the cell gradually fills with keratin
Stratum lucidum
Layer of the epidermis that is made up of anucleate, dead cells that are cornified or filled with keratin in place of the cytoplasm
Stratum corneum
The most superficial cells of this epidermis layer undergo desquamation (shedding)
Stratum corneum
Layer of the epidermis where keratinocytes take on more keratin and contain basophilic, keratohyalin granules
Stratum granulosum
Two proteins contained in keratohyalin granules in the granular epidermis layer
Profilaggrin and involucrin
Filaggrin plays a role in this function of the skin
Barrier function
Genetic deficiency of this is characterized by lack of water retention in the skin, dryness, eczema, and reduction of protection to external substances
Filaggrin
Granules in the epidermis granular layer that contain polysacchardies, glycoproteins, and lipids that extrude into the intercellular space help hold together the stratum corneum cells
Lamellar granules
Lamellar granules are found in this epidermis layer
Stratum granulosum
Epidermis layer that receives maturing cells that proliferate from the stratum basale
Stratum spinosum
Epidermis layer made up of large polyhedral keratinocytes
Stratum spinosum
Keratinocytes in the stratum spinosum synthesize cytoplasmic intermediate filaments called
Cytokeratins
Cytoplasmic intermediate filaments synthesized by keratinocytes in the stratum spinosum that form tonofilaments
Cytokeratins
Keratinocytes in the stratum spinosum synthesize cytoplasmic intermediate filaments called cytokeratins that form these
Tonofilaments
These condensate and form desmosomes, which form strong contacts between adjacent keratinocytes in the stratum spinosum
Tonofilaments
In the stratum spinosum, tonofilaments condensate and form these
Desmosomes
Other name for macula adherens
Desmosome
Other name for desmosome
Macula adherens
2 members of the cadherin family that provide the linkage between the plasma membrane and adjacent cells in a desmosome
Desmogleins and Desmocollins
Deepest layer in the epidermis
Stratum basale
Morphology of the stratum basale
Single layer of cuboidal to low columnar epithelial cells
Layer of the epidermis that consists of a single layer of cuboidal to low columnar epithelial cells
Stratum basale
Keratinocytes in this layer proliferate so mitotic figures would be expected
Stratum basale
Keratinocytes are anchored to the dermis via these in the stratum basale
Hemidesmosomes
These belong to the integrin class of matrix receptors and occur in epithelia that require strong, stable adhesion to the connective tissue
Hemidesmosomes
Two types of cells that are dispersed among the keratinocytes of the stratum basale
Melanocytes and Merkel cells
Melanocytes and Merkel cells are dispersed among the keratinocytes of this layer of the epidermis
Stratum basale
Skin layer that supports the epidermis and consists of fibrous materials, and neurovascular structures
Dermis
Skin layer that consists of adipose tissue and neurovascular structures
Subcutis (aka Hypodermis or Panniculus)
Cells that separate and protect organisms from the external environment and make up approximately 85% of the epidermal cells
Keratinocytes
Cytokeratins are synthesized in this epidermis layer
Stratum spinosum
During keratinization, cytokeratins form tonofilaments and bundle to becomes these that fill the cytoplasm
Tonofibrils
Distinctive feature in the stratum granulosum and contain cysteine as well as involucrin
Keratohyalin granules
Keratohyalin granules are the distinctive feature of this layer of the epidermis
Stratum granulosum
Keratohyalin granules in the stratum granulosum contains this molecule which binds filaments together
Cysteine
Cysteine is contained in these and binds filaments together
Keratohyalin granules in the stratum granulosum
Keratin synthesis begins in the keratinocytes in this layer of the epidermis
Stratum basale
During keratinization, keratinocytes in the stratum spinosum superficially start to synthesize these
Keratohyalin granules
Molecule contained in keratohyalin granules that is associated with formation of the cell membrane and protein-lipid envelope
Involucrin
2 proteins in keratohylain granules that are affiliated with intermediate filaments and the formation of tonofibrils, which initiates the conversion of granules cells into cornified cells
Trichohyalin and Filaggrin
Trichohyalin and filaggrin are intermediate filament associated proteins that are contained in these
Keratohyalin granules
Changes from stratum granulosum to stratum corneum occur with these 3 things
Decrease in pH
Breakdown of nucleus and other organelles
Thickening of plasma membrane
Desquamation at the cornified surface is regulated by proteolytic degradation of these
Desmosomes
Membrane coating granules produced by the stratum spinosum
Lamellar bodies
Granules produced by the stratum spinosum that contain pro-barrier lipids and processing enzymes that are secreted by exocytosis into the intracellular spaces and form the epidermal water barrier
Lamellar bodies
Type of melanin that is a brownish black pigment
Eumelanin
Type of melanin that is a reddish yellow pigment
Pheomelanin
Color of eumelanin
Brownish black
Color of pheomelanin
Reddish yellow
Melanin is produced by oxidation of tyrosine by this
Tyrosinase
Melanin is produced by oxidation of this by tyrosinase
Tyrosine
This is produced by oxidation of tyrosine by tyrosinase
Melanin
This is transferred to neighboring keratinocytes by pigment donation, which involves the phagocytosis of the tips of the melanocyte processes by keratinocytes
Melanin
APCs that originate from bone marrow, migrate to the skin via blood, and make up only 2-8% of the cells in the epidermis
Langerhans’ cells
Langerhans cells are located mostly in this layer of the epidermis
Stratum spinosum
Molecules that structurally expressed on Langerhans cell surface and used as a clinical marker
CD1a
CD1a molecules are a clinical marker for this
Langerhans cells
Cells with an indented nucleus and possess tennis racquet-shaped Birbeck granules
Langerhans cells
Morphology of the nucleus of Langerhans cells
Indented nucleus
In Langerhans cells, these represent relatively small vesicles, which appear as rods with a bulbous expansion at their end
Birbeck granules
Birbeck granules are found in this type of cell
Langerhans cells
APCs in the epidermis that have lobulated nuclei and almost clear cytoplasm
Langerhans cells
Mechanoreceptors that are also called epithelial tactile cells and are located in the stratum basale
Merkel’s cells
Merkels cell are located in this layer of the epidermis
Stratum basale
Cells that are characterized by dense neurosecretory granules containing peptides
Merkel’s cells
Cells that are closely related to terminal, unmyelinated bulb of afferent sensory fibers that are penetrating the basal lamina
Merkel’s cells
Rete ridges are another name for this
Epidermal downgrowths
Two types of cell adhesion junctions that contribute to the anchoring of the epidermis basal lamina to the dermal layer
Hemidesmosomes and focal adhesions
2 layers of the dermis
Papillary layer
Reticular layer
Layer of the dermis:
Loose areolar connective tissue
Papillary layer
Layer of the dermis:
Finger-like dermal papillae projecting into the stratum basale
Papillary layer
The dermis papillary layer has finger-like dermal papillae projecting into this layer of the epidermis
Stratum basale
Layer of the dermis:
Adipocytes, fibroblasts, phagocytes
Papillary layers
Layer of the dermis:
Contains less dense collagen fibers (type I and III)
Papillary layer
The papillary layer of the dermis contains these fibers
Less dense collagen fibers (type I and III)
Layer of the dermis:
Lymphatics, nerve fibers, and touch receptors called Meissner corpuscles
Papillary layer
Layer of the dermis:
Thicker layer
Reticular layer
Layer of the dermis:
Dense irregular connective tissue (elastin)
Reticular layer
Layer of the dermis:
Rich sensory and sympathetic nerve supply
Reticular layer
The reticular layer of the dermis contains these fibers
Elastin
Collagen fibers (mostly type I) extend into the papillary layer and the hypodermis
Collagen fibers (mostly type I) of the reticular layer of the dermis extend into these
Papillary layer and hypodermis
Creams that help restore skin turgor by stimulating blood flow and repair of the dermis
Retin-A cream
Langer lines are based on these
The orientation of collagen and elastic fivers in the reticular layer of the dermis
These are based on the orientation of collagen and elastic fiber orientation in the reticular layer of the dermis
Langer lines
Langer lines are based on the orientation of collagen and elastic fiber orientation in this skin layer
Reticular layer of the dermis
Form regular lines of tension in the skin and skin incisions that are made parallel to these lines heal with the least amount of scarring
Langer lines
Skin layer that is richly vascularized, which aids to the contribution of nutrients to the skin, as well as plays a role in thermoregulation
Dermis
A subpapillary plexus sits just inferior to this skin layer, and branches extend into the dermal papillae
Epidermis
This sits just inferior to the epidermis, and branches extend into the dermal papillae
Subpapillary plexus
This structure with larger blood vessels and lymphatic vessels is located where the dermis ends and the subcutis begins
Deep plexus
Where is the subpapillary plexus located in the skin?
Just inferior to the epidermis
branches extend into the dermal papillae
Where is the deep plexus with larger blood vessels and lymphatic vessels located in the skin?
Where the dermis ends and the subcutis begins
Skin layer that serves as an energy storage site
Subcutaneous layer (subcutis layer, hypodermis)
Skin layer deep to the dermis
Subcutaneous layer (subcutis layer, hypodermis)
Skin layer that contains adipose tissue that varies throughout region in the body, as well as fibrous bands (septa) that act as supportive structures
Subcutaneous layer (subcutis layer, hypodermis)
The vascular supply in this skin layer allows for efficient drug uptake when drugs are injected
Subcutaneous layer
Thin layer of striated muscle that lies deep to the subcutaneous fascia in many animals
In humans, it remains well defined in the skin of the neck, face and scalp
Panniculus carnosus
Where is the panniculus carnosus located in the skin layers?
Deep to the subcutaneous fascia
Afferent or efferent:
Sensory nerves
Afferent
Afferent or efferent:
Motor nerves
Efferent
Free nerve endings are the most abundant receptors in the epidermis and terminate largely in this layer
Stratum granulosum
These are the most abundant receptors in the epidermis and terminate largely in the stratum granulosum
Can be myelinated or unmyelinated
Detects pain, itch, and changes in temperature
Free nerve endings
Elliptical structures that are located mostly in the dermal papillae in hairless regions of skin like that of palms, fingertips, and soles
Meissner corpuscle
Meissner corpuscles have this shape
Elliptical
Meissner corpuscles are located in this location of skin layers
Dermal papillae
Meissner corpuscles are found in these regions of the body
Hairless regions of skin like that of palms, fingertips, and soles
Meissner corpuscle have sensitivity to this
Light touch
Structures where axons course through lamellae made up of flattened Schwann cells
Meissner corpuscle
Structures in the dermal papillae that are sensitive to light touch
Meissner corpuscles
Nervous structure of the skin:
Response to torque, stretch and the mechanical displacement of collagen fibers
Ruffini corpuscles
These are considered phasic receptors that generate short action potentials at the beginning and end of a stimulus
Ruffini corpuscles
Simple and encapsulated bulb structures that contain thin collagenous capsules
These are found in genitalia regions and sense low frequency vibrations
Krause end bulbs
Simple and encapsulated bulb structures that contain thin collagenous capsules
Krause end bulbs
Nervous structure of the skin that senses low frequency vibrations
Found in genitalia regions
Krause end bulbs
Pacinian corpuscles receive this type of nerve fiber
Myelinated
Nervous structure of the skin sensitive to deep pressure, course touch, and vibrations
Pacinian corpuscles
Encapsulated receptors found in deeper regions of the dermis (reticular) and subcutaneous tissue
Pacinian corpuscles
Type of hair that is short, soft and pale
Vellus
Type of hair that is long, coarse and dark
Terminal
Part of the hair follicle that’s located between the sebaceous duct opening and the bulge
Isthmus
Upper part of a hair follicle that extends from the skin’s surface to the opening of the sebaceous duct
Infundibulum
Hair follicles arise from invaginations of this
Epidermis
(protrudes into the dermis or further)
Area located within the outer root sheath of the hair follicle, where stem cells reside, positioned at the point where the arrector pili muscle attaches to the follicle
Follicular bulge
Is hair keratinized?
Yes
During injury of the epidermis, the epidermal stem cells migrate from this part of the hair follicle toward the skin surface and participate in the initial resurfacing of damaged epidermis
Follicular bulge
Multilayered cellular covering that surrounds the deep part of the hair
Internal root sheath
These differentiate into keratin-producing cells and the internal root sheath of the hair follicle
Matrix cells (germinative)
Melanocytes located here transfer melanosomes into the epithelial cells that will later differentiate to form hair
Hair bulb matrix
Most superficial layer of the internal root sheath of hair
Henle’s layer
Deepest layer of the internal root sheath of hair
Internal root sheath cuticle
3 layers of the internal root sheath, from superficial to deep
Henle’s layer
Huxley’s layer
Internal root sheath cuticle
Layer of the internal root sheath that is in contact with the external root sheath and is made of cuboidal cells
Henle’s layer
Layer of the internal root sheath that is a single or double layer of flattened cells
Huxley’s layer
Layer of the internal root sheath that is composed of squamous cells that are in contact with the hair shaft
Internal root sheath cuticle
Multilayered section of the hair follicle that is composed of rapidly reproducing matrix cells and has the composition similar to epidermal cells
External root sheath
At the hair bulb, this takes on the composition of the stratum basale
External root sheath
At the hair bulb, the external root sheath takes on the composition of this
Stratum basale
The external root sheath takes on the composition of the stratum basale at this part of the hair follicle
At the hair bulb
A thick basal lamina that separates the external root sheath of the hair follicle from the dermis
Glassy membrane
The glassy membrane separates this part of the hair follicle from the dermis
External root sheath
The glassy membrane separates the external root sheath of the hair follicle from this
Dermis
Part of the hair proper that forms the central portion of the shaft and contains a column of loosely connected keratinized cells containing soft keratin (only present in thick hairs)
Medulla
Largest layer of the hair proper
Cortex
Structure of the hair proper that is composed of cortical cells filled with hard keratin intermediate filaments
These filaments are cross-linked which contribute to the rigidness of the hair shaft
Cortex
What contributes to the rigidness of the hair shaft?
Hard keratin intermediate filaments in the cortical cells of the cortex of the hair proper are cross-linked
Outermost layer of the hair shaft
Cuticle of hair shaft
Part of the hair shaft that consists of several layers of transparent, keratinized squamous cells
Said to resemble fish scales or roof tiles
Cuticle of hair shaft
What is the morphology of the cuticle of hair shaft?
Several layers of transparent, keratinized squamous cells
Said to resemble fish scales or roof tiles
The growth of hair is due to rapidly dividing, proliferating, and differentiating cells in this part
Hair matrix
Melanocytes in this part of the follicle transfer melanosomes into the epithelial cells that will later differentiate to form hair
Hair bulb matrix
Consists of smooth muscle fibers and elevates the hair shaft during contraction (goose bumps), as well as contributes to the expression of sebum from the sebaceous gland
Arrector pili muscle
Sebaceous glands release their contents (sebum) via this process
Holocrine secretion
Glands composed of lobules of large polyhedral pale-staining cells containing abundant lipids droplets and small dark-staining central nuclei
Sebaceous glands
Lobules from these structures are located about two-thirds up from the hair bulb and connect to the hair follicle through short sebaceous ducts
Sebaceous glands
Types of cells in eccrine sweat glands that are mainly contractile and help expel sweat into the lumen of an acinus
The duct lacks these cells
Myoepithelial cells
Cells that provide the protein component of sweat
Rough ER and secretory glands
Dark cells
Cells that produce the water component of sweat
Have abundant glyocgen
Clear cells
Structure composed of large, tubular branches, that are less coiled than eccrine sweat glands
Apocrine sweat gland
In many mammals, glands similar to this secrete pheromones
Apocrine sweat glands
Apocrine sweat glands start to function at this stage in life
Puberty
Are controlled by sex hormones
Type of sweat gland that starts to function at puberty and is controlled by sex hormones
Apocrine sweat gland
Nails are a modified extension of the epidermis, specifically this layer
Stratum corneum
The nail plate contains this morphological cell type
Squamous cells
with hard keratin (corneocytes)
The nail bed consists of these 2 skin layers
Stratum germinativum (nail matrix) and dermis
The edge of the skin fold covering the root of the nail
Eponychium (cuticle)
The skin beneath the free end of the nail
Hyponychium
Is this dermal or epidermal repair:
1. Blood clot formation
2. Removal of damaged collagen fibers (macrophages)
3. Formation of granulation tissue (new connective tissue)
4. Reepithelization of exposed surface. Proliferation and migration of fibroblasts (5-8 days)
5. Deposition and remodeling of ECM
Dermal
Is this dermal or epidermal repair:
1. Proliferation in stratum basale of surrounding undamaged sites
2. Increase in mitotic activity
3. Wound covered by scab that represents dehydrated blood clot (10-15 days)
4. The overlying scab is eventually shed due to proliferation of keratinocytes and desquamation
Epidermal
Does dermal or epidermal repair involve the formation of scab?
Epidermal
Does dermal or epidermal repair involve formation of granulation tissue?
Dermal
