Epithelial tissue Flashcards
four basic tissue types
epithelial, connective, muscular, and nervous tissues
what are connective, muscle and nervous tissue characterized by
connective- abundant ECM
muscle- elongated cells for contraction/movement
nervous- cells with long fine processes specialized to receive, generate and transmit impulses
stroma is always connective tissue except where?
brain and spinal cord
what are epithelial cells composed of
aggregated polyhedral cells adhering to each other and thin layer of ECM, forming sheets lining organs
which tissues line all external and internal surfaces of the body and all substances that enter or leave an organ must cross this type of tissue
epithelia
what are the principal functions of epithelia
- Covering, lining, and protecting surfaces (eg, epidermis)
- Absorption (eg, the intestinal lining)
- Secretion (eg, parenchymal cells of salivary glands)
give examples of epithelia that may be specialized sensory cells
taste buds or the olfactory epithelium
true or false, Most epithelia are adjacent to connective tissue containing blood vessels from which the epithelial cells receive nutrients and O2
true, even thick epithelia
how are epithelial cells organized
polar, organelles and membrane proteins distributed unevenly
what is the basal and apical pole
basal- region of the cell contacting the ECM and connective tissue
apical- opposite end, usually facing a space
what do the basal surface of all epithelia rest on
a thin extracellular, a semipermeable filter for substances reaching epithelial cells from below
what two parts of the basement membrane can be seen with a TEM
Nearest the epithelial cells is the basal lamina, a thin, electron dense, sheet-like layer of fine fibrils, and beneath this layer is a more diffuse and fibrous reticular lamina
what do the ECM components of the of the basal lamina include
- Type IV collagen
- Laminin
- Nidogen and perlecan
how is laminin organized in the ECM
large glycoproteins that attach to integrins and project through the mesh formed by the type IV collagen
how are Nidogen(rod-like protein) and perlecan (proteoglycan) organized in the ECM
cross-link laminins to the type IV collagen network–3D structure to bind epithelium to the surface and determine porosity and size of molecules filtered
what does the more diffuse meshwork of the reticular lamina contain
type III collagen and is bound to the basal lamina by anchoring fibrils of type VII collagen, both prod by connective tissue cells
functions of the basement membrane
- filters
- support for epithelia
- components organize integrins, maintaining polarity and localize endocytosis, signal transduction
- cell to cell interactions
- scaffold–repair and regeneration
what junctions are present in epithelia
- Tight or occluding junctions form a seal
- Adherent or anchoring junctions–adhesion
- Gap junctions–communication
what are tight junctions also known as and how do they work
zonulae occludentes (zonula occludens is the singular form) most apically located junction and form belt around circumferance of cell
what causes seal
due to tight interactions between the transmembrane proteins: claudin, occludin, nectins, and junctional adhesive molecules [JAMs]
these bind to actin and provide stability
• Occludin interacts with four major _____________ proteins: _________________.
• Nectins are connected to ___________ through the protein _____.
• Claudin (Latin claudere, to close), a family of 24 proteins forming __________ in the tight junctions, form a water channel for ________________.
• Junctional ______________ [JAMs]
these bind to actin and provide stability
• Occludin interacts with four major zonula occludin (ZO) proteins: 1, ZO-2, ZO-3, and afadin.
• Nectins are connected to actin filaments through the protein afadin.
• Claudin (Latin claudere, to close), a family of 24 proteins forming linear fibrils in the tight junctions, form a water channel for paracellular absorption.
• Junctional adhesive molecules [JAMs]
what bacteria binds to claudin (Zonula occludens proteins) molecules in intestinal cells preventing tight junctions–cell death
Clostridium perfringens secreting Enterotoxin causing food poisoning.
loss of tissue especially along intestinal lumen
what does Helicobacter pylori do to tight junction proteins
binds to tight junction proteins in stomach cells, and disrupts the connection by introducing a protein that targets ZO-1
what is a form of adherens junction also called
zonula adherens, anchoring cell to its neighbors
