Structure and function of Skin Flashcards
What is the role of the epidermis?
Establishing and maintaining a selective barrier at all stages of life.
What is the composition of the embryonic epidermis?
A single layer of basal cells overlaid by periderm cells that are in direct contact with the amnionic fluid
What happens to the epidermis at eight weeks gestation?
Basal epidermal cells differentiate into keratinocytes and undergo stratification to form multiple cell layers that remian covered by the periderm
What happens to keratinocytes by the end of the second trimester of gestation?
Periderm cells are shed and replaced by stratified keratinocytes that undergo further differentiation to form the four distinct layers of the epidermis
What are the four layers of the epidermis?
Stratum corneum (outermost), granular layer, spinous layer, basal layer (innermost)
What cells make up the majority of the epidermis?
Keratinocytes
What is the role of keratin in the epidermis?
They are intermediate filament cytoskeletal proteins to impart strength and structure to individual keratinocytes and the tissue
What is the cause of epidermolysis bullosa simplex?
An epidermal blistering disease where epidermal keratin genes are mutated, which collapses the keratinocyte cytoskeleton
What is keratinization?
A progressive series of signaling and transcriptional changes to keratinocytes that results in spatiotemporal cellular changes to form the epidermis
What is the structure of the stratum corneum?
Lipid bilayers, cross-linked cornified envelope, keratin filament cables, filaggrin
What is the structure of the granular layer of the epidermis?
Tight junctions, lamellar granules, keratohyalin granules, keratin filament bundles, profilaggrin, loricrin, lipids
What is the structure of the spinous layer of the epidermis?
Bundles of keratin filaments, intercellular junctions, rich in desmosomes
What is the structure of the basal layer of the epidermis?
Intercellular junctions, rich in adherens junctions
How is the basal layer of the epidermis attached to the basement membrane?
Hemidesmosomes, focal adhesions
What is the structure of the basement membrane?
Laminin V, fibronectin, collagen IV
What is the role of the basal layer of the epidermis in wound healing?
Stem cells in the basal compartment
What type of cancer occurs in the basal layer of the epidermis?
Basal cell carcinoma
What is found at cell-cell junctions in the spinous layer of the epidermis?
Desmosomes
What conditions result from antibodies against desmosomal proteins in the spinous layer of the epidermis?
Pemphigus vulgaris, pemphigus foliaceous
What is the mechanism of scalded skin syndrome and bullous impetigo?
Staph aureus bacterial toxins proteolytically cleave desmosomes
What is produced by keratinocytes in the granular layer of the epidermis?
Keratohyalin granules that contain filament aggregating proteins (profillagrin)
What is the cause of icthyosis vulgaris?
Fillagrin mutations in the granular layer of the epidermis
What junctions are present in the granular layer (stratum granulosum) of the epidermis?
Tight junctions - they complement the lipid barrier to be semi-permeable, limit water loss, and keep noxious agents/pathogens out
What cells are in the cornified layer of the epidermis?
Highly resilient, keratinized, and anucleate cells called corneocytes that are surrounded by the cornified envelope ebedded into the lamellar membrane
What is the cause of lamellar ichthyosis?
It is a recessive disorder that causes disfiguring scaling due to stratum corneum defects
What are the lipid contents of the lamellar membranes?
Modified ceramides, cholesterol, fatty acids, and cholesterol esters
What is the cause of harlequin ichthyosis?
A mutation in a lipid transporter gene in the cornified layer of the stratum corneum
What is desquamination?
The process of corneocyte shedding via a series of proteolytic enzymes
What are melanocytes?
Neural crest derived, pigment producing cells mostly in the basal layer of the epidermis
What are melanosomes?
Products of melanocytes that are secreted directly into keratinocytes
What type of cancer occurs in melanocytes?
Melanomas
What are langerhans cells?
Bone marrow-derived cells primarily in the suprabasal layers that are critical for proccessing and presenting antigens to T cells and play a key role in immunological responsiveness of the skin.
What are merkel cells?
Mechanoreceptors in the epidermis that contribute to our sense of light touch through synaptic contacts with nerve endings in the basal layer
What is the cause of bullous pemphigoid?
It is an autoimmune disease where auto-antibodies target hemidesmosome proteins and cause blistering through basal keratinocyte detachment from the basement membrane
What are the main components of the dermis?
Collagen, elastic fibers, ground substances
What is the role of collagen in the dermis?
Type I and type III collagen provide robust tensile strength to the skin
What is the composition and purpose of elastic fibers in the dermis?
They are comprised of elastin and microfibrils (built from fibrillin proteins) and function to stretch/recoil and provide pliability to the skin
What are the ground substances in the dermis?
Glycosaminoglycans (hyaluronic acid and dermatan sulfate) and glycoproteins (fibronectin and vitronectin)
What are the two layers of the dermis?
Papillary dermis and reticulardermis
What is the papillary dermis?
A layer of the dermis that underlies the epidermis (separated by the basement membrane), and contains less dense connective tissue
What is the reticular dermis?
The layer of thedermis between the papillary dermis and the subcutaneous fat, contains more dense connective tissue
What are the fibroblasts in the dermis?
Mesenchymal cells that are more concentrated in the papillary layer
What is the role of mesenchymal cells?
Responsible for synthesis and remodeling of the connective tissue proteins found in the dermis
What are the macrophages in the dermis?
Phagocytic, bone marrow derived cells that contribute to the remodeling of the matrix and clear debris during wound healing
What are mast cells?
Bone marrow derived immune cells in the dermis that harbor heparin and histamine-containing granules that are involved in hypersensitivity skin reactions
What is the structure of a hair follicle?
The hair bulb surrounds a special region of the dermis called the dermal papilla
What are the growth cycle phases of a hair follicle?
Anagen, catagen, telogen
What is the anagen phase of hair growth?
Growth phase where hair germ cells proliferate rapidly in response to signals from the dermal papilla and give rise to more differentiated matrix keratinocytes
What is the catagen phase of hair growth?
Involution phase where matrix keratinocytes stop dividing, hair fibers thin, and follicles involute and regress
What is the telogen phase of hair growth?
The rest phase where bulge stem cells remail quiescent
What is the structure of sebaceous glands?
They are multilobulated structures composed of acini and ductal epithelial cells
What do acini cells do?
They produce lipids in sebaceous glands
What do ductal epithelial cells do?
Cells that transition from sebocytes to keratinocytes in the sebaceous gland and eventually open into the hair follicle canal
What is the sebum?
The nuclear and cytoplasmic content of sebaceous gland cells that are released into the sebaceous canal
What are eccrine sweat glands?
Glands with ducts that secrete their products directly at the surface of the skin
What are apocrine sweat glands?
Glands with ducts that are in direct communication with the hair follicle canal
What is eccrine gland sweat composed of?
Water, inorganic ions, lactate, urea, amino acids, proteins
The glands reabsorb sodium from the secretory coil, which makes the sweat hypotonic
What is the major function of eccrine sweat glands?
Thermoregulation and they are under cholinergic control
What is the structure of the hypodermis/subcutaneous tissue?
An adipose-enriched tissue compartment with nerve branches and vascular networks that integrate into the dermis
What are the major cell types of the hypodermis?
Adipocytes, fibroblasts, macrophages, blood vessels, and nerves
What are major functions of the skin?
1) resists physical trauma
2) repair wounds
3) prevent entry of noxious agents
4) protect against harmful UV irradiation of the sun
5) limit escape of essential body fluids
6) immune regulation
7) thermoregulation
8) insulation
9) absorption
10) sensation
What is the life cycle of an epidermal keratinocyte?
Keratinocytes are in proliferative and non-proliferative states in the basal layer, where they contact the basement membrane. Keratinocytes in the basal layer commit to a program of terminal differentiation up through the suprabasal layers. In the spinous layer, they have increased adhesive capacity and elaborate an insoluble keratin cytoskeletin. In the granular layer, cells gain tight junctionbarrier properties and process keratohyalin granules. Finally, they undergo special cell death and secrete lipids to form the lipid barrier
In which epidermal layers are keratinocytes most likely to be found proliferating?
a) basal
b) spinous
c) granular
d) cornified
a) basal
What are the phenotypic consequences of impaired dermal-epidermal junction? How does this compare and differ from conditions where desmosomes are targeted by auto-antibodies or bacterial toxins?
Impairment of proteins that anchor keratinocytes to the basement membrane causing sub-epidermal blistering at this site. Pathogenic targeting of desmosomal proteins also causes blistering in the suprabasal layers of epidermis.
The major protein component of the dermis is:
a) collagen
b) elastin
c) fibronectin
d) laminin
a) collagen
Which skin structures are in direct communication with the hair follicle?
a) sebaceous gland
b) eccrine sweat gland
c) epidermis
d) apocrine sweat gland
a) sebaceous gland
c) epidermis
d) apocrine sweat gland
What is 1?
Epidermis
What is 2?
Dermis
What is 3?
Hypodermis
What is a?
Hair
What is b?
Sebaceous glands
What is c?
Sweat glands
What is a?
Epidermis
What is b?
Dermis
What is c?
Blood vessel
What is a?
Cornified layer of epidermis
What is b?
Granular layer of epidermis
What is c?
Spinous layer of epidermis
What is d?
Basal layer of epidermis
