Traffic across cells and glucose absorption Flashcards
What is the structure of epithelial tissues?
Consist of cell arrange din continuous sheets in either single or multiple layers
What are epithelial tissue on top of?
A basement membrane
What are epithelial tissues the boundaries between?
The body organs or between the body and the external environment
What is the rate of epithelial cell renewal? Why is this?
Very high Subject to physical breakdown and injury constantly
What are the two types of epithelium? Where are they found?
Covering and lining - epidermis of skin, lining of blood vessels and ducts Glandular - endocrine glands, sweat glands etc.
What are the classifications of their arrangements? Describe them
Simple - one cell layers stratified - many cell layers pseudo stratified - single layer of cells which look striated but is single layer
What are the classifications of the shape? Describe them
Squamous - flat Cuboidal - cube shape Columnar - tall Transitional - shape changes due to stretching
How are epithelial cell separated from each other? What keeps them connected then?
Separated by lateral intercellular space Held together by tight junctions
What are tight junctions composed of? What how do they allow adjacent cells to maintain cellular contact?
Thin bands that encircle the cell make contact with thin bands from adjacent cells
How does the number of contact points between neighbouring cells impact the tight junctions functions?
More contact points makes it harder for substances to move between adjacent cells so becomes ‘tighter’ junction
What are the functions of tight junctions? Explain what this function does?
A barrier - restrict the movement of substance throughout intercellular space between cells A fence - prevent membrane protein from moving all over the cell membrane as it controls their free movement
What kind of materials are epithelial cells a barrier to? How does it restrict these?
Larger molecules/cells their movement is stopped as they can’t physically fit through gaps
What does the fencing function of tight junctions create? What are they?
Apical membrane - membrane that is on top facing the external enviro (e.g. lumen, top layer of skin FYI) Basolateral membrane - membrane that adheres to the basement membrane and interfaces with blood
What are the two transport methods created by the apical and basolateral membrane?
Paracellular transport and transcellular transport
Explain where paracellular transport takes place
It occurs between the tight junctions down the intercellular space
What controls paracellular transport?
The laws of diffusion and the tightness of the tight junctions
How does more tight junctions affect paracellular transport?
More tight junctions/tighter junctions creates a stronger resistance to ion flow
How does tight junction resistance vary in the GI (gastrointestinal) tract and kidney?
It is leakiest at the proximal end (near the stomach) and tightest at the distal end At the start of the digestion are large molecules which need to be absorbed therefore leaky, at the end it is mainly just ions and non-digestible food therefore need to be more selective = tighter junctions
Explain where transcellular transport takes place
Through the apical membrane and basolateral membrane
What controls transcellular transport?
Passive diffusion combined with ion channels
What kind of processes can transcellular transport be involved in? What are the relative directions of each process?
Absorption (lumen to blood) and secretion (blood to lumen)
How can epithelial transport occur?
Either via paracellular, transcellular or both
What is the relationship between paracellular and transcellular transport? Explain the cause of this relationship?
They are interdependent The movement of ions through the transcellular pathway almost always results in the movement of water and other molecules through the paracellular pathway in order to maintain an osmotic equilibrium