Cell Junctions and Epithelial Tissue Flashcards
What is the function of Gab Junctions (GJ)?
Mediates cell-to-cell communication through combined intercellular channels (H2O) that permit the transfer of ions and small molecules
What is the structure of GJ?
Composed of connexins which are hexamers of medium-sized families of integral proteins
GJ couple cells both _______ and _______
Electrically and mechanically
Where are GJs found?
Low resistance ion pathway joining excitable cells (nerve and muscle) and joining virtually all cells in solid tissues
What permits tissue-specific GJs?
Multiple isoforms of connexins
Ex: Informs have similar functions but in different tissues, cardiac and skeletal systems both contract
What do different combinations of connexins do?
Creates channels that differ in permeability and regulation
Ex: temperature, flow of H2O, open and closes
How is regulation mediated?
Changes in pH or Ca2+ or signals (neurotransmitters)
What is the difference between GJ and tight junctions (TJ)?
GJ is seen as an area of close plasma membrane apposition, TJ joins the cells together
What is the function of TJ?
TJ holds the cells closely together near the apex to prevent molecules from leaking across the epithelium
- Like a fence, traffic is controlled to go a certain way
What are the types of TJ?
Claudin (main transmembrane protein)
Occludin (second major transmembrane)
Zonula Occludens (large scaffold protein that provides a structural support)
What is the purpose of claudins?
A selectively permeable seal
How do claudins function?
There are over 20 claudin protein families in humans that express different combinations in different epithelia to confer particular permeability properties
Ex: Kidney-specific claudin permits Mg2+ to be reabsorbed from urine into the blood
Claudins are dysregulated in various ______
Cancer
Ex: IBD- claudin dysregulation correlates with an increased intestinal permeability, sustained activation of inflammation
What happens if there is impaired barrier function?
Luminal bacterial leakage inversely exacerbates inflammation
Epidermal growth factors influx contributes to tumorigenesis
What happens if there is a pathogenic breach?
Overactive inflammatory response which also changes claudin expression leading to impaired barrier function
___ influx contributes to tumorigenesis
Epidermal growth factor (EGF)
What recovers epithelial claudin expression and promotes mucosal healing?
Probiotics
What are anchoring junctions?
Complexes that adhere cells to other cells or the extracellular matrix
What is the structure of anchoring junctions?
Provides a strong membrane-spanning structure that is tethered inside the cell to the tension-bearing filaments of the cytoskeleton
What are the types of anchoring junctions?
Laterally attached to the site of cell: Adherens Junction & Desmosomes
The surface of cell, connects to the matrix: Hemidesmosomes & Focal adhesion
What is TJ plaque?
Internal attachment
What is TJ transmembrane?
External attachment
Ex: Claudins
What are Adheren Junctions?
Connected to the cytoskeleton by actin
What are Desmosomes?
Connected to the cytoskeleton by intermediate filaments
What are Hemidesmosomes?
Connected to the cytoskeleton by intermediate filaments
What are Focal Adhesions?
Connected to the cytoskeleton by actin
What Anchoring Junctions contain cadherins transmembrane proteins?
Adherens Junction and Desmosomes
What Anchoring Junctions contain integrins transmembrane proteins?
Hemidesmosomes and Focal Adhesions
Where are the AJs located?
AJs are located below the TJ, the formation of AJs is a prerequisite for TJ assembly
What is the structure of cadherins?
The structure is dependent on Ca2+ ions
What happens if mutation disrupts the production or function of E-cadherins?
Often found in cancer cells and thought to help make them malignant due to the gain of invasiveness and metastatic potential of cells
What role do Desmosomes play?
Play a critical role in tissues subjected to mechanical stress like the myocardium, bladder, and skin
What are hemidesmosomes and focal adhesion?
Aids in the interaction of a cell-extracellular matrix
What are the functions of cell junctions?
- Attachment- mechanical support, can move to other cells if stressed
- Separation- protection & traffic regulation
- Communication between cells-
mechanical, metabolic, etc - Cell polarity- Orientation of the cell to establish basal surfaces
What is Epithelial Tissue?
Sheets covering all the surfaces of the body exposed to the outside world and lining the outside of the organs
Classification of cells
The first name: denotes the number of cell layers present
Second name: Shape of the cell
What is the Simple Squamos?
The type of epithelium typically lines blood vessels and body cavities and regulates the passage of substances into underlying tissues
What is Simple Cuboidal?
This type of epithelium is typically found in glandular (secreting) tissue and kidney tubules
What is Simple Columnar?
This type of epithelium is often specialized for absorption and usually apical cilia or microvilli, these cells line your stomach and intestines
What is Stratified Squamos?
This type of epithelium usually has protective functions, including protection against microorganisms from invading underlying tissue and/or protection against water loss
- Makes up the outer layer of skin
What is Stratified Cuboidal?
This type of epithelium is not as common and is found in the excretory ducts of your salivary and sweat glands
What is a Stratified Columnar?
This type of epithelium is not as common and is seen in the mucous membrane lining of your eyelids, where it’s protective and mucus-secreting
What is a Pseudostratified Columnar?
This type of epithelium lines your upper respiratory tract and usually has a lot of cilia
What is Transitional Epithelium (Urothelium)?
This type of epithelium is made up of several layers of cells that become flattened when stretched
- It lines most urinary tract and allows the bladder to expand
Characteristics of Epithelial tissue
Specialized contacts, polarity, avascular, innervated, & regenerative
