Epithelia Flashcards
Covering epithelia is classified as being either…
1) Simple epithelia (1 layer of cells)
2) Stratified epithelia (>1 layer of cells)
What are 4 functions of epithelia?
1) Physical protection against abrasion, microbes, etc.
2) Controlled permeability across the body
3) Provides sensation (general and special [vision, hearing, balance, smell])
4) Produce specialized secretions via glandular epithelia
The function of epithelia is governed by…
Its structure
In order to enter the body, any substance must first cross…
Epithelium
The two main categories of epithelia are…
1) Covering
2) Glandular
The cellularity of epithelia can be described as…
Consisting of densely-packed cells with little material between them (unlike CT)
Polarity of epithelia describes…
Apical, lateral, and basal surface specializations, allowing each surface to perform special functions
What is a lumen?
Space inside any hollow structure in your body
Epithelia is attached to…
Basement membrane and underlying connective tissue
Is epithelial avascular or vascular?
Avascular - nourished by diffusion from underlying CT
Is epithelial innervated?
YES - avascular but innervated
Cells of the epithelia are frequently _____ via mitosis.
Regenerated
Specialized intercellular junctions connect cells both…
Physically and functionally
What are two examples of apical surface specializations?
1) Microvilli - found GI tract
2) Cilia - found in respiratory tract
What is an apical surface specialization of epithelia that increases surface area for absorption/secretion?
Microvilli
What are microvilli?
- Minimally motile, finger like projections of apical surface
- Have brush border
- Number of microvilli is associated with the rate of molecular transfer
- Cross-linked actin microfilaments make up the core
- Well developed in SI and kidney
Where would we find cilia?
- Epithelia specialized to move fluid along its luminal surface
- Respiratory tract
- Uterine tubes
What are cilia?
- Highly motile, synchronized, finger like extensions of apical cell membrane that move fluid along luminal surface of epithelia
- Core consists of microtubules with proteins such as dynein
- Taller than microvilli
What is the function of anchoring junctions?
Provide mechanical strength to connect the cytoskeleton of epithelial cells to each other and to underlying BM; helps epithelium to withstand shear forces
What are occluding junctions?
Block the intercellular space - control paracellular molecular movement
What are communicating junctions?
Control ionic/molecular movement between adjacent epithelial cells
Both covering and glandular epithelia develop from…
Simple sheets of epithelia in the embryo
What is the difference between exocrine and endrocrine glands?
Exocrine: Secrete outward onto epithelia surface via a duct
Endocrine: Lose connection to free surface, and secrete hormones inward, delivering products to target tissue via CV system
What are two types of protein fibres?
1) Collagen fibres - provide tensile strength
2) Elastic fibres - provide tissue resiliency
Connective tissue involves both ____ and ____.
Cells and ECM
What are proteoglycans responsible for?
- Gelatinous consistency of ECM
- Turgidity and ability of CT to resist compression
- Ability of the matrix to function as a molecular filter of varying pore size and charge distribution
- Ability of the matrix to control the diffusion of substances, cells, pathogens through interstitial fluid
What are adhesive glycoproteins?
- Proteins with bound carbohydrates
- Stabilize ECM by linking components to cell surfaces
- Have binding sites for protein fibres, proteoglycans, and integrins of cell membranes
Connective tissue develops from…
Embryonic mesenchyme
The external body surface is covered by an epithelium called ____.
Epidermis
What are mucous membranes?
Epithelia, combined with underlying CT (lamina propria), that line internal passages open to the exterior, including GI, GU, and respiratory tracts
Epithelia lining vessels are called ___.
Endothelium
What is mesothelium?
Epithelia lining internal body cavities that DO NOT open to the exterior
What are serous membranes?
Mesothelia, combined with underlying CT, which included pleura, pericardia, and peritoneum
Epithelial cells have ______ to allow for selective molecular movement, stability, and joining of cells.
Specialized intercellular junctions
What is the basement membrane?
An acellular layer made of molecules produced by cells, which provides structural support and an attachment site for overlying epithelial cells, and acts as a semipermeable filter and scaffold for epithelial repair
What is an example of unicellular exocrine glands?
Goblet cells - found in respiratory and GI tract; secrete mucous across apical aspect onto exposed surface of epithelial sheet to protect cells of the covering epithelia
What is an example of a unicellular endocrine gland?
Neuroendocrine cells - secrete their cell products across the basal aspect into tissue fluid of underlying CT
Example: enteroendocrine cells of the GI tract; such as those that secrete gastrin (paracrine signalling) and CCK (endocrine signalling)
Short, sparse microvilli are found in tissues with…
Low rates of molecular transfer
Tall, densely-packed microvilli are found in tissues with…
High rates of molecular transfer
Men with cilia dyskinesia may experience…
Infertility due to immotile sperm, since the tails of sperm are structurally similar to the core of cilia
What are three structures by which anchoring junctions are created?
1) Zonula Adherens
2) Desmosomes
3) Hemidesmosomes
What is Zonula Adherens?
- A structure that entirely surrounds cells like a “belt”, linking adjacent cells to each other in all directions
- They link the actin microfilament network of the cytoskeleton of adjacent cells, which distributes applied shear forces throughout the entire sheet
- Cadherins, which are transmembrane proteins, link across the intercellular space
How do desmosomes contribute to anchoring junctions?
- Arranged like rivets to join the intermediate filament network of the cytoskeleton of adjacent cells, linking the the lateral surfaces of the cells
- Like ZA, have transmembrane proteins called cadherins that link across the intercellular space
- The more there are, the more strongly cells are bound together
What are hemidesmosomes and how do they contribute to anchoring junctions?
- Like half a desmosome
- Link the the intermediate filament network of epithelial cytoskeleton across their basal surface to underlying BM
- Unlike ZA and desmosomes, their transmembrane proteins are integrins
- Integrin links BM molecules across the extracellular space
- Hemidesmosomes bind epithelium to underlying tissue, resisting their separation
Control of paracellular molecular movement occurs via ______ junctions.
Tight
What are tight junctions?
- Integral transmembrane glycoproteins arranged as branching, anastomosing strips
- Bind to similar proteins in the adjacent cell membranes
- Known as Zona Occludens; arranged in a belt like fashion around the cell
- Seal paracellular space around the circumference of cells, controlling molecular movement between cells
- Density determines barrier properties of the epithelium (tighter vs more leaky)
- Create functional tissue compartments such as the blood-brain barrier
- Prevents back-diffusion of molecules, and creates concentration gradients
Control of intercellular molecular movement occurs via ______ junctions.
Gap
What are gap junctions?
- A complex of transmembrane proteins in the lateral cell membrane that form a pore
- Joined across the intercellular space, connecting the cytoplasm of adjacent cells
- Permits passage of ions and small molecules cell to cell
- Coordinate cellular function; found in cilia, cardio myocytes, bones cells, SM cells
- Can open and close with conformational change
What are three questions to ask when classifying epithelia?
1) Does every cell touch the basement membrane (simple vs stratified)?
2) What is the shape of the cells at the EXPOSED surface (squamous vs cuboidal vs columnar)?
3) Are there any specializations of note (microvilli vs cilia vs goblet cells)?
Where are common areas for simple squamous epithelia?
- Found in areas where rapid molecular transfer is important
- Blood capillary luminal walls (endothelia)
- Alveoli luminal surfaces
Where is simple cuboidal epithelia commonly found?
- Areas where secretion and absorption are important
- Renal tubules, GI tract (can have microvilli)
 Where is simple columnar epithelium commonly found?
- Surfaces involved in high rates of secretion and absorption
- Small intestine, gall bladder
- Can have microvilli
- Often have many tight junctions to prevent back diffusion
Where are pseudostratified epithelia commonly found?
- Respiratory tract
- Usually ciliated
What type of epithelium would we likely find in areas such as: the lining of the mouth, throat, esophagus, vagina, anus, and cervix?
Stratified squamous nonkeritanized epithelium - lines internal surfaces requiring protection
________ epithelium is often found lining external surfaces, such as the skin, requiring protection.
Stratified squamous keratinized epithelium
What is transitional epithelium and where is it commonly found?
- A stratified epithelium with dome shaped surface cells when the organ is EMPTY, and flattened surface cells when the organ FILLS
- Lines surfaces which must allow stretch and recoil, such as the urinary bladder and ureter
