Epithelial Glands Flashcards
(34 cards)
Give the general characteristics of epithelium
Avascular
- No blood vessels in epithelium
- Oxygen & nutrients by diffusion from underlying connective tissue
Covers exterior body surfaces
-skin
Lines internal closed cavities
-endothelium of blood vessels of cardiovascular system
Lines body tubes
- gastrointestinal tract
- respiratory tract
- genitourinary tracts
Forms secretory portion (parenchyma) & ducts of glands
Specialized cells function as receptors for special senses
-smell, taste, vision
What are the 3 principle characteristics of epithelium ?
- Cells are closely apposed & adhere to each other
- Specialized cell to cell junctions
2. Exhibit functional & morphological polarity
3 surface domains
1. Free surface/ apical domain
2. Lateral domain
3. Basal domain
- Basal surface attached to underlying basement membrane
- cell to matrix junctions
What are the lateral specializations of cells ?
Lateral surface/domain
- Occluding junctions.
- tight junction (zonula occludens)
- Anchoring junctions
- Adhering junctions (zonula adherens)
- Desmosomes (macula adherens)
- Communicating junctions
- Gap junctions
Describe Zonula Occludens
Occluding junctions complex (cell to cell)
- Zonular occludens = tight junctions
- Localised sealing of the plasma membrane of adjacent cells
- Network of anastomosing strands that completely surround the apical cell borders
- Transmembrane proteins= Claudins & occludins
- Interaction with action cytoskeleton via ZO-1
What are the major proteins included in the zonula occludens junctions?
- Occluding
- Claudin
- JAM
- ZO-1
- ZO-2
- ZO-3
What are the associated protein partners and function of Occludin?
Occludin, ZO-1,ZO-2, ZO- 3, Vapp33, actin
Function: is present in most occluding junctions: maintains barrier between apical and lateral cell surface
What are the associated protein partners and function of Claudin?
Claudin, ZO-1, JAM
forms backbone of zonula occludens strands: forms and regulates aqueous channels used for paracellular diffusion
What are the associated proteins and function of JAM?
JAM, ZO-1, Claudin
Function: present in endothelial cells; mediates interactions between endothelial cells and monocytes adhesions
What are the associated proteins and function of ZO-1?
Associated proteins: ZO-3,ZO-2, Occludin, Claudin, JAM, cingulin, actin, ZONAB, ASIP, AF-6
Function: important link in transduction of signals from all transmembrane protein; interacts with actin filaments, has tumor suppressor actin
What are the associated proteins and function of ZO-2?
ZO-1, Occludin, cingulin, 4.1R
Function: Required in the epidermal growth factor-receptor signaling mechanism
What are the associated proteins and function of ZO-3?
Associated proteins: ZO-1, Occludin, actin
Function: interacts with ZO-1, Occludin, and actin filaments of cell cytoskeleton
In detail, explain the function of zonula occludens
Zonula occludens separates the luminal space from the intracellular space and connective tissue compartment
Paracellular pathway: across the zonula occludens between two cells
Transcellular pathway: across the plasma membrane of the epithelial cell
Establishes functional domains in the plasma membrane
- Apical
- Basolateral
Explain detail the function of the zonula adherens
Anchoring Junctional Complex(Cell to Cell)
-Lateral adhesion between epithelial cells
-Continuous band or belt that surrounds the entire cell, found just beneath the tight junction
- Transmembrane protein = E cadherin
- calcium dependent - Helps to attach adjacent cells (15-20nm apart)
- Interaction with actin cytoskeleton
What are the functions of macula adherens in detail?
Anchoring junctional complex
-macula adherens= desmosome
- lateral, localised, spot adhesion between epithelial cells about 30nm apart
- Focal dense spots (macula)
-Found beneath the zonula adherens of cells
- Transmembrane protein= desmocolin & desmoglein
- Cadherin family, calcium dependent - Intracellular plaque=plakoglobins & desmoplakins
- Interaction with intermediate filaments of cytoskeleton
What are gap junctions, where are they found?
Communicating junctional complex (cell to cell)
- present in a variety of tissues
- epithelium
- smooth & cardiac muscle
- nerve
-help coordinate activity of adjacent cells
Differentiate between connexins and con exons for gap junctions
Connexin- Transmembrane protein subunits
Connexons -half channel formed by 6 connexins
Connexons align to form a communicating channel connecting the cytoplasm of adjacent cells
Explain the lateral morphological specialization of lateral cell surface
Lateral interdigitations
-in foldings (plicae) of cytoplasmic processes of adjoining cells
-increased lateral cell surface area
- common in cells engaged in fluid and electrolyte transport
- Ex. Gall bladder, small intestine
- Sodium ions are pumped out of cytoplasm by Na+/K+ -ATPases
-Fluid accumulates in the intracellular space until driven into underlying connective tissue
Tight junctions prevent fluid escape in apical direction
Explain focal adhesion
Anchoring junctional complex
- cell to extracellular matrix junctions
- helps to anchor epithelial cells to basement membrane
Transmembrane proteins= integrins
- Link between actin microfilaments of cytoskeleton and extracellular matrix
- Important role during cell migration
Explain the function of the hemidesmosomes
Anchoring junctional complex
- cell to extracellular matrix junctions
- helps to another epithelial cells to basement membrane
- Half the component of a desmosome
- Transmembrane proteins= integrins
- Interaction with intermediate filaments of cytoskeleton
What is Bollus pemphigod?
Disease characterized by blister formation at epithelium attachment to basement membrane
-Antibodies directed against BP320 & type XVII collagen
Describe basal in folding s as a morphological modification
- Significantly increase the surface area of the basal domain
- Allow for more transport proteins and channels to be present
- Well developed in cells performing active transport of molecules
- kidney tubule
- striated ducts of exocrine glands
- Mitochondria arranged vertically in these folds
- Light microscopy- “striated” appearance
Explain the function of the basal membrane
- Can be visualized with light microscope
- Amorphus layer at basal surface of epithelia
- Found between epithelial cells and underlying connective tissue
- Especially thick in respiratory epithelium
- H&E x450
The basal lamina is called __________ in noneoithelial cells
External lamina
How can the basal lamina be visualized?
By electron microscopy
