L5) Tissues, Organs & Systems ✔ Flashcards
Define Tissue
A collection of cells that are adapted to perform a specific function
Define Organ
Two or more tissues combined to create a structural unit that has a particular function that are a sum of its parts.
How are cells held together?
Cell-Cell adhesion molecules
Extracellular-matrix proteins ( fibres)
Internal-external scaffolding
Close proximity ( pressure effects)
What is the cellular organisation of epithelial tissue?
1) Epithelial cell sheets line all the cavities and free surfaces of the body.
2) Epithelia almost always rest on a supporting bed of connective tissues - through basement membrane that contains many different proteins.
3) The supporting bed attaches the epithelial layer to other tissues.
4) The specialised junctions between epithelial cells help to form tissue barriers
What is the epithelial cell adherence system in the lateral surface ?
Tight junctions
Adhesion junction / Adhesion belt
Desmosome
Gap junctions
Cell adhesion molecules
What is the epithelial cell adherence system in the basal surface ?
Hemi-desmosome
Focal adhesions
Integrins
Proteoglycans
Cell adhesion molecules
Where are tight junctions found?
Very top of the cell nearest to lumen/apical surface in the lateral border.
What is the role of tight junctions?
To prevent movement of larger molecules through outer layer/lumen into the deeper tissue layers of the organ.
What is paracellular transport?
When the gut can transiently open to allow small molecules (sugars, water & Amino acids) to cross to the underlying tissues.
Happens via tight junctions
Where are adhesion junctions found ?
Found in pairs in the lateral surface .
Found in epithelial and endothelial cells only
Describe the structure of adhesion junction
Formed from intracellular actin filaments
Linked to E-cadherin proteins that cross the intercellular space
What is the function of adhesion junction?
Tissue stabilising factor
Transport barrier
What are desmosomes?
Strongest cell-to-cell adhesion molecule.
Found in tissues that experience intense mechanical stress (bladder tissue, cardiac tissue)
The only cell-to-cell adhesion found in the upper epidermal (skin) cells
What is the function of desmosome ?
To provide mechanical strength
To prevent muscle destruction
Describe the structure of desmosome?
Made up of cytokertain fibres intracellularly
and E-cadherins intercellularly (spring-like)
Where are Gap junctions found?
Close to the base of epithelial cells
In cardiac and smooth muscle cells
What is the function of Gap junctions?
To quickly communicate changes in intercellular molecular composition - electrolyte and energy changes
Allows free movement of small molecules from one cell to another.
Why are Gap junctions important in smooth muscle ?
Allows wave of electrical impulse
What is the structure of Gap Junctions?
consists of cylinders of proteins (connexins) arranged in a hexagonal pattern that open and close (ATP)
Where are Hemi-desmosome found?
Only found on basal surface of epithelial cells
What is the role of Hemi-desmosome?
To anchor epithelial cells to the basal lamina & prevent loss to external surface.
What is the structure of Hemi-desmosome?
Attach to a layer of extracellular matrix ( collagen & laminin fibres)
Intracellular intermediate filaments of cytokeratin attached to laminin through integrins.
How does basal lamina attach to connective tissue layer?
Through elastin, fibrillin and other collagens
What is the function of Focal adhesion?
Similar function to hemi-desomosomes - attachment to basal lamina
Compare Focal adhesion and Hemi-desmosomes?
Both use integrins
Focal adhesion uses intracellular actin filaments ( Hemi- desmosomes use cytokeratin)
Focal adhesion binds to fibronectin ( Hemi-desmosome use laminin)
What are integrins?
Integrins central to cohesive forces holding tissues together
Always works as alpha-beta dimer
What is part of basement membrane?
Basal lamina - clear and dense layer
Reticular lamina - even denser