Flashcards in Epithelium Deck (35):
What are the characteristic features of epithelia?
1. have a free surface (outside, which contacts air, vs inner lumen--blood)
2. Rest on a basement membrane
3. Are polarized with basal, apical and lateral domains
4. are attached to each other by cell junctions
5. are avascular
describe the basement membrane
a narrow layer of ECM between epidermis and underlying connective tissue (CT)
functions of the basement membrane?
-Support of epithelial cells
-Anchor epithelial cells to CT
-Linkages through basement membrane
-Permeability barrier (+/- )(anionic/cationic filters)
-Most barrier functions is produced by cell-cell junctions
what is the basement membrane produced by epithelium composed of?
-Proteoglycans (heparin sulphate)
-Collagen IV (+ other collagens)
-Laminin and other minor proteins
what is the basement membrane produced by CT composed of?
Collagens III and VII and fibronectin
how can the BM be visualized?
stain for carbs or proteoglycans (pink or blue stain)
--H&E staining does not work
how can cells be classified, and describe th requirements of classification
1. Number of layers
-single (either called simple or pseudostratified epithelium)
-All cells contact the basal lamina
-multiple layers (stratified epithelium)
-Only basal (bottom) cells contact basal lamina
2. Shape of the cells in the layer next to the free surface
flat (squamous), square (cuboidal), tall (columnar)
Structural / functional specialization
what is the role of simple squamous epithelium?
-Rapid diffusion of metabolites, oxygen, CO2
-Movement of cells into CT (inflammation)
Taller cuboidal/columnar cells can be more active and/or carry on active transport of metabolites--height can dictate activity
what is the purpose of simple cuboidal cells?
where might you find simple columnar cells?
covers intestinal villi
describe pseudostratefied cells, their purpose, and give examples
All cells touch the basement membrane but not all reach the free surface. Nuclei are at different levels
Secretion and transport
parts of vas deferens (no cilia)
what is urothelium?
transitional epithelium that lines the bladder--the free surface cells change shape; They stretch by addition of membrane from vesicles when urine fills the lumen of the urethra or bladder.
what might make a cell polarized?
cilia, microvilli, stereocilia
what are basal infoldings?
Basal infoldings of the plasma membrane--specialized basal domains
Often associated with mitochondria.
Seen as little lines by light microscopy
Forms micro environment
Striated duct of the
what are exocrine glands classified by?
-Number of cells
-Duct structure (simple or compound)
-Shape of the secretory unit
-Tubular (tubular)/ flask shaped (alveolar)
-Simple or branched
-Branched--secreting into the same duct
-Rich in proteins
Mode of secretion
-Regular secretion, protein synth’d on
-RERpackaged in golgisecretory vesicle fuse
-with membranecontents of vesicle released to
-Whole cell breaks down and releases contents
-Blebbing of bits of a cell
what are the two types of embryonic tissue?
Tissue from which all other CT develops
Cells are stellate and interconnected
Mesenchymal cells often persist in mature CT
Abundant ground substance
Differentiated into fibroblasts (unipotent)
few fibers but more than embryonic
e.g. Whartons jelly in umbilical cord (fetal)
Full of water but can dry up quickly
Also prevents heavy bleeding when umbilical cord
is cut/dries up
pulp of developing tooth
vitreous body in eye
nucleus pulposus of intervertebral disk
Loose CT--lots of white space, like a packing material
where is dense irregular ct found?
Many collagen fibers interlacing
Found where tissues under mechanical stress
Encapsulating organs/ or muscles and nerves
Reticular layer of dermis of skin
Adventitia (outer layer) of large blood vessels
Inactive mammary gland
Loose CT near ducts
See lots of white-->know its loose
dense regular CT where is it found?
Bundled fibers oriented in one direction
Tendons – high tensile strength (collagenous fibers)
Connect muscle to bone
Stretch in one direction
Ligments – highly elastic (elastic fibers)
Connect bond to bone, must be elastic
Stretch in one direction
Fibers arranged in sheets (fascia)
where are fibroblasts found, what is tehre morphologyy, and functions?
Abundant RER - increases when active
more ribosomes = more basophilic cytoplasm
Prominent Golgi complex
Collagen and reticular and elastic fibers that assemble OUTSIDE of the cell.
They must secrete collagen/fibres etc so they can assemble
Fibroblasts in close association with epithelia
Respond to injury
Signal other cell
what are the steps in collagen synthesis?
1. Fibroblasts: alpha chains made on ribosomes bound to ER
2. Hydroxylation of lysine and proline (vitamin C)
3. Glycosylation (addition of sugar residues)
4. Formation of procollagen triple helix
5. Packaging in Golgi
procollagen to tropocollagen
Assembly of collagen fibers
how are collagenous fibres arranged in loose and dense CT?
fibers are arranged irregularly in loose and dense irregular CT
fibers are organized in a single direction in dense regular CT
what type of collagen is collagenous fibre?
what type of collagen is reticular fibre?
Type III collagen +
--tend to be highly glycosylated
what is ground substance?
Hyaluronic acid (the primary GAG in loose CT)
small, highly expanded
hydrophilic and negatively charged (binds lots of water and salt to form the extracellular fluid)
GAGs (condroitin-, dermatan-, heparin-,
Heparan-, keratan-sulfate) linked to proteins
what are the steps of wound healing?
refer to slides 40-42 lol 2much4me
Functions of CT?
Medium for exchange between tissue, blood and lymph
Must pass through CT
Metabolic (adipose, bone)
Highly metabolic tissues
what type of CT are macrophages normally found in?
loose CT; Rich in endocytic and phagocytic organelles
RER, golgi, mitochondria
Surface has projections and folds - engulf foreign matter
what type of CT are mast cells found in and what do they release?
found in loose CT; Degranulation releases:
Vasoactive, histamine, and serotonin (preformed small molecules)
Slow reacting substance of anaphylaxis (SRS-A) and prostaglandins (newly synthesized)
Matrix of granules contains peroxidase and SOD (scavenge peroxide and superoxide), heparin (anticoagulant), chymotrypsin (protease)
Granules important in immediate hypersensitivity reactions
Granules also act to Attract of eosinophils and neutrophils – enables extravasation
similarities to mast cells vs basophils?
Granules stain similarly
Granules rich in histamine and heparin
Common progenitor cell
Both have IgE receptors
Both present antigens
Complex immunomodulatory roles are similar
Both can settle in tissues (basophils recruited to lymph nodes)
Mast cells end up in CT
differences of mast cells vs basophils?
Circulating basophils have granules
mast cells make granules after settling in connective tissues
Go into CT as a progenitor
Mast cell granules are rich in enzymes and some of these enzymes break down snake and bee venom
MCs in CT right below epithelium, where you will be stung/bitten
Basophils enhance antibody production and have a particular role in acquired immunity to ticks and insects
what are the major collagen types?
I Bone, dentin, cementum, scar tissue
II Hyaline and elastic cartilage
III Reticular fibers (highly glycosylated)
—delicate, can barely see in loose CT
IV Basal lamina (non fibrous procollagen)
V Associates with type I, placenta
VIII Basement membrane
describe the structure of elastic fibres
Thin long fibers, bundles or fenestrated sheets of elastin surrounded by microfibrils (arrows) composed of fibrillin
(Marfan syndrome: fibrillin gene defect)