Unit 1: Epithelium + Integument Flashcards
What are tissues?
aggregates or groups of cells organized to perform one or more specific functions
All organs are made up of only four basic tissue types, but vary in
appearance, structural organization and physiological properties
What are the tissue classifications based on general morphological and functional characteristics?
Epithelial, connective, nerve, muscle
What is epithelium?
Avascular tissue that covers the exterior body surface, line internal closed cavities, and body tubes that communicate with the exterior
What does epithelium form with glands?
The secretory portion and their ducts
What does epithelium provide?
A selective permeable barrier between the external environment and underlying
connective tissue
What are the 3 principle characteristics of epithelium?
- Closely apposed to each other by cell-to-cell adhesions via cell junctions.
- Exhibit functional and morphologic polarity (apical domain, lateral domain, and basal domain).
- Basal surfaces attach to an underlying basement membrane (via cell junctions).
What is the basement membrane/basal membrane?
Extracellular structure separating epithelium from C.T.
What is the basal lamina?
structural attachment site for over-lying epithelial cells and underlying CT
(Use electron microscopy to see)
What is the basal lamina composed of?
network of delicate filaments which resembles a felt-like web. It is composed, principally of collagen types IV, XV, XVIII, proteoglycans, laminin and glycoproteins. PAS positive stain
What is the basement membrane?
The basal lamina and the underlying contributions of the connective tissue constitute the basement membrane. All epithelia rest upon a basement membrane
(Use light microscopy to see)
Are the basal laminate and basement membrane synonymous?
No
What is the classification of epithelium based on?
Number of cell layers and shape of the surface cells
What are the different shapes of epithelium?
Squamous, cubiodal, columnar
What is the shape of squamous epithelium?
Width of cell is greater than the height of
What is the shape of cuboidal epithelium?
width, depth and height are about the same
What is the shape of columnar epithelium?
The height exceeds the width of
What are the types of thickness of epithelium?
Simple, stratified
What is the thickness of simple epithelium?
One cell layer thick
What is the thickness of stratified epithelium
Two or more cell layers
How does simple squamous epithelium appear?
In the form of flat plates which are usually joined by intercellular junctions and resting on the basement membrane
What does the nucleus look like in simple squamous epithelium?
Nucleus often creates a bulge and is located in the widest part of each cell
What does simple squamous epithelium provide?
permits diffusion and bidirectional movement of gases, fluids, and nutrients from the free surface to underlying tissue
Where can simple squamous epithelium be found?
lining Bowman’s capsule in the kidney, parenchyma of lung, lining blood and lymphatic vessels, lining the pleural and abdominal cavities (mesothelium)
How does simple cuboidal epithelium appear?
Square in section, height and width are approx equal
What does the nucleus look like in simple cuboidal epithelium?
Nuclei appear round in cross section and centrally placed
What does simple cuboidal epithelium provide?
protection, forms conduits for gland ducts, and may be specialized for active secretion and absorption
What does simple cuboidal epithelium contain?
more organelles such as mitochondria and endoplasmic reticulum- evidence of high metabolic and functional activities
May have microvilli or cilia
Where is simple cuboidal epithelium found?
glands such as the thyroid, salivary ducts, pancreas and kidney
How does simple columnar epithelium appear?
Cells are taller than they are wide
Elongated oval appearance. The bases of cells rest on the basement membrane; apical surfaces contact a lumen.
What does the nucleus look like in simple columnar epithelium?
Ovoid in shape and located centrally or near basal surface
Where is simple columnar epithelium found?
areas engaged in protection of wet surfaces, nutrient absorption, and secretion
What does simple columnar epithelium contain?
Free surfaces often have microvilli
Lateral cell borders have junctional complexes, including an apical tight junction, adherens junctions, and desmosomes.
How does stratified squamous epithelium appear?
More than one cell layer thick, tissue is composed of a germinal layer (often cuboidal in shape)
What happens during the maturation of stratified squamous epithelium?
Undergoes mitosis and produces new cells which migrate toward the apical surface as they mature, lose contact with basal layer, producing multiple layers
May harden or keratinize
Where is stratified squamous epithelium found?
Areas that need protection from abrasion, such as skin
How does stratified cuboidal/columnar epithelium appear?
Contains two or more layers of cells
What is the function of stratified cuboidal/columnar epithelium?
Protective in function (mainly)
Where is stratified cuboidal/columnar epithelium found?
Lining ducts of sweat glands and endocrine glands
Located in pharynx, larynx, conjunctiva of the eyelids, major ducts of the exocrine glands, anorectal junction, and parts of the male urethra.
What are the special classifications of epithelium?
Pseudostratified, transitional
What is pseudostratified epithelium?
Appears stratified, although some of the cells do not reach the free surface, all rest on the basement membrane
Where is pseudostratified epithelium found?
tracheal bronchial tree, ductus deferens, and efferent ductules of epididymis
What is transitional epithelium?
Stratified epithelium with special characteristics that allow it to distend
Where is transitional epithelium found?
Epithelium lining the lower urinary tract
Extends from the minor calyces of the kidney to the proximal part of the urethra
What do apical domain modifications do?
Allow cells to carry out specific functions
What are the structural surface modifications?
Microvilli, stereocilia, cilia
May also contain enzymes (hydrolases), ion channels, and carrier proteins
What are microvilli?
cytoplasmic (finger-like) projections that vary in appearance on the apical surface of epithelial cells
What is the appearance of microvilli?
Can be tall and closely packed or appear as blebs
The number and shape of microvilli correlate with
The cell’s absorptive capacity (increase cell surface area for nutrient absorption)
What is the structure/composition of microvilli?
Core = actin filaments linked by actin-bundling proteins
Filaments anchored to villin at tip of microvillus
As they extend down to cytoplasm, actin filaments interact with terminal web (horizontal network of actin filaments)
What does the terminal web in a microvilli do?
Anchors actin filaments stabilized by spectrin, to the apical cell membrane
What are stereocilia?
microvilli of unusual length (looks like a paintbrush)
Where are stereocilia usually found?
reproductive tract, ear
What are stereocilia in the reproductive tract like?
Unusually long, immotile microvilli
Where are stereocilia in the reproductive tract found?
epididymis, ductus deferens
What is the function of stereocilia in the reproductive tract?
Facilitate absorption
What is the structure of stereocilia in the reproductive tract?
Contain internal bundles of actin filaments that are cross-linked by fibrin. Organization is similar to microvilli but longer and the anchored by ezrin to the plasma membrane. They do not contain villin at the tip.
What is the function of stereocilia in the ear?
Sensory epithelium that are sensitive to mechanical vibration and serve as sensory mechanoreceptors
What is the appearance of stereocilia in the ear?
Uniform in diameter and organized into ridged bundles of increasing heights
What is the composition of stereocilia in the ear?
High density of actin filaments cross-linked by espin
What are cilia?
Hair-like extensions of the apical plasma membrane containing organized microtubules
What is the composition of cilia?
axoneme, which is a microtubule-based internal structure. It extends from the basal body, a centriole-derived, microtubules-organizing center (MTOC)
What are the classifications of cilia?
Motile, primary, or nodal
What is the structure of motile cilia?
Possess a typical 9+2 axonemal organization with microtubule-associated motor proteins needed for motility.
How do motile cilia move?
Movement originates from the sliding of microtubule doublets, which is generated by the ATPase activity of dynein arms
What is the structure of primary cilia?
Comprised of 9+0 microtubule pattern
What is the function of primary cilia?
signal receptors that sense the flow of fluid in organs- mechanoreceptors.
Mutations can affect the development of primary cilia, what happens if this occurs?
leads to various diseases such as polycystic kidney disease
What is the structure of nodal cilia?
9+0 pattern of microtubules that establish the left-right asymmetry of internal organs
Incorrect flow of nodal cilia during development can result in
Sinus inversus, dextrocardia, and other conditions
What kinds of salivary glands are there?
Unicellular, multicellular
Exocrine, endocrine
What are unicellular salivary glands?
Goblet cells
What are multicellular salivary glands?
secretory portion & duct, classified by morphology of secretory units and branching of ducts
What are the types of multicellular salivary glands?
Simple, compound
What are simple multicellular salivary glands?
Single unbranched duct
What are the types of simple multicellular salivary glands?
Tubular, Coiled tubular, Branched tubular, Acinar
What are compound multicellular salivary glands?
Branching ducts
What are the types of compound multicellular salivary glands?
Tubular, Acinar, Tubuloacinar
What do exocrine salivary glands do?
release their secretory product into a duct or lumen of a hollow organ
What do endocrine salivary glands do?
release their secretion into the circulation which distributes it to the target organs.
The secretory unit of acinar glands has what shape? Where does it lead?
Flask-like shape, cells often pyramidal
Duct leads from each acinus and usually empties into larger duct
Exocrine glands may have what kinds of elements?
Tubular, acinar, compound branching of ducts
What are the classifications of exocrine glands?
simple tubular or acinar, compound tubular or acinar, and compound tubulo-acinar glands.
What are the types of cell junctional complexes?
Occluding junctions (zonula occludens/ tight junctions)
Anchoring junctions
Communicating junctions (gap junctions)
The structural integrity of epithelium is maintained by
adhesion of the constituent cells both to each other and to structural extracellular matrix
Adhesions are maintained by two main systems:
Cell membrane proteins that act as adhesion molecules.
Specialized areas of cell membranes are incorporated in cell junctions.
What is a junctional complex? ***
A series of junctions found together (adjacent cells are joined by physical and functional cell junctions)
What is the function of occluding junctions (tight junctions)? ***
establish a barrier between different compartments of the body and allow epithelial cells to function as a selective barrier. Limiting the movement of ions, water, and other macromolecules through the intercellular space and maintaining cell polarity.
Where are occluding junctions (tight junctions) located?
Most apical component in the junctional complex between epithelial cells.
What do Occluding Junctions (tight junction) provide?
Provide limited strength of attachment.
What are the groups of transmembrane proteins in Occluding Junctions (tight junction)?
- Claudins
- Occludin
- Junctional adhesion molecule (JAM)
- Tricellulin
What is the function of anchoring junctions? ***
mechanical stability, through anchoring the cytoskeleton of one cell to the cytoskeleton of an adjacent cell.
• Fasten cells into strong sheets
What do anchoring junctions play a role in? ***
cell-to-cell recognition, morphogenesis and differentiation
What do anchoring junctions provide?
lateral adhesions between epithelial cells. Cell-to-Cell adhesion
Anchoring cells to connective tissue. Cell-to- CT adhesion.
What are the types of cell-to-cell adhesions?
Zonula adherens, macula adherens
What are zonula adherens?
interacts with network of actin filaments inside the cell that provide lateral adhesion between epithelial cells
What are macula adherens?
desmosome which interacts with intermediate filaments. Provides a localized spot-like junction between cells.
What are the types of cell-to-connective tissue adhesions?
Focal adhesions, hemidesmosomes
What are the types of zonula adherens?
Cadherins, nectins
What part of the macula adherens provides linkage between cell-to-cell membranes?
Desmogleins and desmocollins
Where are hemidesmosomes found?
where cells anchor to extracellular materials such as the basal lamina
What do cell adhesion molecules (CAMs) do?
form an essential part of the anchoring junction on both the lateral and basal surfaces.
What do transmembrane proteins do?
Extracellular domains interact with similar domains of neighboring CAMs.
Cytoplasmic domains link to various cytoplasmic proteins to components of the cytoskeleton.
What intra/intercellular processes do CAMs help to regulate?
Cell adhesion
Cell proliferation
Cell migration
Cell communication
Cell recognition
Immune response
What is the function of gap junctions?
allow for the movement of molecules as large as 1.2nm in diameter such as Calcium and cyclic adenosine monophosphate (cAMP) between cells.
• Allow for chemical and electrical coupling between adjacent cells.
Gap junctions are the only known cellular structure that permits
The direct passage signaling molecules from one cell to another
In what tissues are gap junctions found?
Found in a wide variety of tissues including epithelium, smooth muscle, cardiac muscle and nerves.
What are gap junctions formed by?
Connexin proteins that are tightly packed
What is a connexon?
Six connexins form this
A hollow cylindrical structure that spans the plasma membrane
What is a gap junction plaque?
An accumulation of connexons
What does the Integument consist of?
Includes the skin and skin appendages- nails, hair, sweat glands and sebaceous glands.
What is the function of the Integument?
Serves as a protective barrier against injury, infectious pathogens, and ultraviolet radiation.
Helps maintain homeostasis body temperature, assists with vitamin D synthesis (endocrine function), ion excretion and sensory reception.
What are the layers of the skin?
Epidermis, dermis, hypodermis
What is the epidermis? What is it derived from?
Most superficial layer of skin and varies in thickness by location
ectodermal covering
What is the dermis? What is it derived from?
Dense CT the provides mechanical support,
strength, and thickness to skin.
Mesodermal derivative
Underlying epidermis
What is the hypodermis?
Variable amounts of adipose tissue
Referred to as subcutaneous tissue as well
What are the categorizations/classifications of skin?
Thick or thin
Differ in thickness of layers, presence of appendages, and glands
What are rete ridges?
form evagination of epidermis into the underlying dermis
What kind of tissue does the epidermis consist of?
Stratified squamous keratinizing epithelium in which the cells will be converted into plates of keratin. Composed of multiple layers of epithelial cells containing keratin (keratinocytes)
What are keratinocytes?
Multiple layers of epithelial cells containing keratin
What are the other cell types of the epidermis?
Melanocytes, merkel cells, langerhans cells
What is the function of the epidermis?
Fluid and electrolyte balance
Protection from UV
Immune surveillance
Sensory
What are the 5 layers of the epidermis?
- Stratum Basale (stratum germinativum)- deepest
- Stratum spinosum (spinous layer or prickle cell layer)
- Stratum granulosum
- Stratum lucidum (only found in thick skin)
- Stratum corneum- most superficial
What is the stratum basale?
A single layer of cells that rests on the basal lamina
Have extensive cell junctions (desmosomes + hemidesmosomes)
What is the function of the stratum basale?
Continuously divide to replace cell that move outward through the epidermis. Stem cells give rise to new cells termed keratinocytes through mitosis
What is the shape of stratum basale?
Basophilic, cuboidal to columnar shape, oval nuclei
What is present in the stratum basale?
Melanin (transferred from neighboring melanocytes found in this layer)
Desmosomes
Hemidesmosomes
Which layers of the epidermis contain keratinocytes?
Stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum
What is the shape/structure of keratinocytes in stratum spinosum?
Cuboidal, polyhedral or slightly flattened shaped cells with intercellular bridges and centrally located nucleus.
Several layers thick with some mitotic cells
Cytoplasmic processes or spines are apparent.
Keratinocytes appear larger than those of the stratum basale
What is the function of the stratum spinosum?
Resistance to abrasion and shearing forces
Many desmosomes connect cytoplasmic processes
What happens with keratin in the stratum spinosum?
Increased keratin is produced in this cell layer and assembled into keratin filaments (tonofilaments) making the cytoplasm eosinophilic.
How are keratin filaments organized?
into larger bundles called tonofibrils that project into and fill the spines/prickles
Where do tonofibrils that project into spines connect?
to desmosomes at the tip and link to the spine of a neighboring cell
What is the shape/structure of keratinocytes in stratum granulosum?
Most superficial layer of nonkeratinized portion of the epidermis. Stratified layer 2-5 cells thick.
Flattened polygonal cells with a central nucleus.
Cytoplasm contain non-membrane bound granules (keratohyalin granules) that are strongly basophilic.
What other components (besides the keratinocytes) make up the stratum granulosum?
Keratohyalin granules, lamellar bodies
What are keratohyalin granules?
cystine-rich and histidine rich proteins, which are precursors of the protein filaggrin
What does filaggrin do?
promotes tonofibril formation and keratinization (cornification), process by which cytoplasm fills with keratin
What are lamellar bodies?
are cytoplasmic secretory granules whose lipid-rich contents form extracellular sheets that act as intercellular cement and creates a barrier that is impermeable to water (lipid envelope)
Cells undergo apoptosis as they exit which layer
Stratum granulosum
What is the shape/structure of keratinocytes in stratum lucidum?
Only a few cell layers thick
Considered a subdivision of the stratum corneum
Where is the stratum lucidum found?
Only in thick skin
What is the purpose of the stratum lucidum?
Highly refractive layer containing eosinophilic cells in which the process of keratinization is well advanced.
Nucleus and cytoplasmic organelles disappear as the cell fills with keratin
What is the shape/structure of keratinocytes in stratum corneum?
15-30 layers thick (varies, thickest thick skin in palms/feet)
Dead, flattened, desiccated, anucleate cells filled almost entirely with keratin filaments.
Keratinocytes in this layer are keratinized/cornified plates
Inner surface of plasma membrane coated with “cell envelope” which is a thick layer of insoluble proteins that provide mechanical strength to cells
What is the purpose of the stratum corneum?
Major contributor to protection/barrier function of epidermis
What forms lateral attachments in the stratum corneum?
Desmosomes
What happens to the most superficial cells in the stratum corneum?
They are shed in a process known as desquamation
What are the cells of the epidermis?
Keratinocyte, melanocyte, merkel, langerhans cells
What are the keratinocytes of the epidermis?
Predominant cell type, maturation (25-50) days
What are the melanocytes of the epidermis?
Pale-staining cells
Melanin granules determine skin color
Distributed to keratinocytes by phagocytosis
What are the merkel cells of the epidermis?
Ovoid cells with dense cytoplasmic granules
What is a Merkel disc?
Merkel cell + associated sensory nerve ending
= Merkel disc, a sensory mechanoreceptor
(light touch)
What are langerhans cells of the epidermis?
Clear cells in all layers of epidermis but primarily found in the stratum spinosum.
Star shaped cells containing cytoplasmic inclusions balled Birbeck granules (ingested material)
Dendritic type cell (antigen presenting cell)
What is the purpose of langerhans cells of the epidermis?
Activation by antigens or other stimuli trigger migration via lymphatics to draining lymph node.
Process and present cutaneous antigens to lymphoid cells
What kind of cell is essential for immune surveillance function in the skin?
Langerhans cells of the epidermis
What are the layers of the dermis?
Papillary layer, reticular layer
What does the epidermal-dermal junction contain?
Dermal papillae, epidermal (rete) ridges
What are dermal papillae?
Project into the underside of the dermis in epidermal-dermal junction
What are epidermal (rete) ridges?
Epidermal protrusions that project into the dermis
What is the shape/structure of the papillary layer of the dermis?
More superficial layer consisting of loose CT, less abundant collagen fibers (type I and III), fibroblasts, abundant mast cells and macrophages, some lymphocytes and nerves.
Dermal papillae projections interdigitate with the rete ridges from the epidermis to reinforce the dermal-epidermal junction
Are blood vessels found in the papillary layer of the dermis?
Yes, but do not enter the epidermal layer
What is the shape/structure of the reticular layer of the dermis?
Thicker and less cellular than the papillary layer.
Dense irregular CT with abundant blood vessels and nerve fibers. Thick irregular bundles of type I collagen and course elastic fibers.
What is the structure of the hypodermis?
Loose CT often with abundant adipose tissue.
what does the hypodermis contain?
Large blood vessels and nerve fibers are observed in this layer.
What is the purpose of the hypodermis?
Loosely binds skin to underlying organs and structures, allowing skin to slide over adjacent structures.
What provides the nerve supply to the skin?
Free nerve endings, encapsulated nerve terminals
What is the structure/composition of free nerve endings?
Terminate in stratum granulosum but often reach the stratum corneum
Lack CT or Schwann cell
What sensory information do the free nerve endings supply?
Fine touch, heat, cold, and pain
What is the most common route of nerve supply to the skin?
Free nerve endings
What is the shape/structure of encapsulated nerve terminals?
Large structures with distinct appearance
Composed of nerve terminal surrounded by multi-layered connective tissue sheath
Each structure is innervated by a single myelinated axon, which branches to supply multiple nerve termini of the same type.
What are the types of encapsulated sensory receptors?
Pacinian corpuscles, meissner’s corpuscles, ruffini’s corpuscles
Where are pacinian corpuscles found?
In the deep dermis and hypodermis
What type of information do pacinian corpuscles transmit?
Deep pressure receptors
What is the shape/structure of pacinian corpuscles?
Large, ovoid structures also found in CT associated with joints and internal organs.
Nerve ending surrounded by concentric layers of support cells
Where are meissner’s corpuscles found?
In the dermal papillae layer
What type of information do meissner’s corpuscles transmit?
Fine touch, pressure, and vibration
What is the shape/structure of meissner’s corpuscles?
Tapered cylinders with long axis perpendicular to surface of skin
Nerve endings spiral thru corpuscle surrounded by few support cells.
Where are ruffini’s corpuscles found?
In the reticular layer of the dermis
What type of information do ruffini’s corpuscles transmit?
Detective pressure, temperature, and stretching
What is the shape/structure of ruffini’s corpuscles?
Encapsulated mechanoreceptor
Where are sebaceous glands found?
Located between a hair follicle and its arrector
pili muscle in the dermis
What do sebaceous glands secrete?
Sebum - secretory product made of lipid rich decomposed cells
How are secretions emptied in a sebaceous gland?
By a duct into the upper part of the hair follicle
What is the shape/structure of sebaceous glands?
Pale staining and ovoid with a thin CT capsule.
Ducts are composed of stratified squamous epithelium 2/3 along the shaft.
What kind of tissue composes arrector pili muscles?
Smooth muscle
What do arrector pili muscles do?
Erection of hair and aids sebaceous gland secretion
What is the innervation of arrector pili muscles?
Sympathetic
What are the types of sweat glands?
Eccrine and apocrine
What is the etiology of eccrine sweat glands?
Independent structures that arise as down growth from the fetal epidermis
What is the shape/location of eccrine sweat glands?
Coiled secretory unit located deep in the dermis and straight duct that opens into the skin
What components make up eccrine sweat glands?
Secretory portion, ducts
How do secretory portions of eccrine sweat glands appear?
pale staining, larger diameter portions; lumens lined by pseudostratified epithelium containing dark cells and clear cells, surrounded by myoepithelial cells
How do ducts of eccrine sweat glands appear?
are dark staining, smaller in diameter; lumens lined by stratified cuboidal epithelium with 2 layers of small, darkly staining cuboidal cells
How are eccrine sweat glands controlled?
Autonomic control - heat and stress
What do eccrine sweat glands secrete?
Watery NaCl - thermoregulation
What is the etiology of apocrine sweat glands?
Develop from downgrowth of the epidermis; open into hair follicle
What is the shape/location of apocrine sweat glands?
Large lumen tubular glands associated with hair follicles
Concentrated around anus, genitalia, axilla, eyelids, nipple and ear.
How does the secretory portion/lumen of apocrine sweat glands appear?
Secretory unit of cuboidal cells covered by flattened cells, very large luminal diameter
lumen lined by simple epithelium and surrounded by myoepithelial cells
How do the ducts of apocrine sweat glands appear?
Dermal ducts like sweat glands lined by stratified cuboidal epithelium, no myoepithelial cells in ducts
What do apocrine sweat glands secrete?
Viscid, slightly milky secretion, function unknown
How can you tell eccrine and apocrine sweat glands apart by location?
Eccrine: deep in dermis with straight duct opening into skin
Apocrine: concentrated around anus, genitalia, axilla, eyelids, nipple, and ear
How can you tell eccrine and apocrine sweat glands apart by secretory portions?
Eccrine: narrower lumens lined by pseudostratified epithelium
Apocrine: very wide lumens lined by simple cuboidal epithelium
How can you tell eccrine and apocrine sweat glands apart by ducts?
Eccrine: more coiled, go to surface
Apocrine: quite straight, go to canal of the hair follicle
