Epithelia Flashcards
What is a tight junction?
connect two adjacent plasma membranes of two cells NOT the cytosols
Separates apical side to basolateral side
What is a gap junction?
Connects cytoplasm of cells - little tunnels between cells allowing small solutes to move between cells
Important for conductive cells like cardiomyocytes
What is a desmosome?
Strengthening connection of cells and epithelia
Connects cells by adherence by intracellular filaments via cadherines
Stabilise to withstand pressure and provide structure to cells like velcro
Why do we have epithelia?
- Functions (PASSF)
To separate and control homeostasis of the inside and outside environment
Protection (skin) Absorption (kidney, GIT) Secretion (glands) Sensation (skin, eye) Filtration (kidney)
What is the main goal of controlling water and solutes?
Maintaining blood pressure
Epithelia definition
Cells must be connected to create a barrier
Have a cell polarity to create an electrochemical gradient to facilitate a function
Different protein expression
Different behaviours and regulations
What is the basolateral membrane and what happens there?
Serosal interstitial meaning inside or facing the blood side
High water and K+ permeability
Contains Na+/K+ ATPase
What is the apical side of the cell and what does it do?
Mucosal lumenal facing lumen/ outside
Brush border membrane - extends surface area of membrane for absorption
Variable water permeability
DOES NOT contain Na+/K+ ATPase
Leaky junction
Allows water and sodium to go throuigh
Leaky junction
Allows water and sodium to go through
Highly water permeability
PCT type of tight junction
leaky oh no lets paracellular flow of water and solutes
CCT type of tight junction
tight tight doesnt let that water through
PCT type of tight junction
leaky oh no
high water permeability
lets paracellular flow of water and solutes
Transcellularly AQP1
CCT type of tight junction
tight tight barely lets that water through
ONLY transcellularly AQP2
Hormonally controlled by ADH, aquaporins are present depending on hydration levels
Tight junctions connect cytoplasmic compartments of cells
False
The exchange of ions between cells can facilitate the propagation of action potentials (T/F)
True
Tight junctions connect cytoplasmic compartments of cells (T/F)
False
Absorption is driven by ….. transport
Na+ transport
Secretion is driven by ….. transport
Cl- transport
Simple diffusion definition
If the membrane is permeable to the solute, it will move down its gradient
Dependant on concentration gradient
Facilitated diffusion definition
Requires a specific membrane protein channel
Still flows down its concentration gradient just cannot cross the membrane by itself
Active transport definition
Requires energy and a specific membrane protein
Solute is going against its concentration gradient
Secondary active transport definition
If the gradient generated by a primary active transporter is used by a second active transporter (uses the energy from one thing to drive another)
Simple diffusion example
Paracellular pathway
Facilitated diffusion examples
AQP
GLUTs
Primary active transport examples
Na+/K+
Secondary active transport examples
SGLT1, SGLT2
Channel vs transporter
Transporter: requires a conformational change to move the solute from one side of the cell to the other
CAN BE SATURATED
Channel: pore in membrane allowing flow of specific solute
Na absorption is initiated by?
Or
How is the electrochemical gradient created?
Na+/K+ ATPase on basolateral side generating a gradient of low Na inside the cell and high on lumenal side
Electrochemical gradient
Drive for different processes
SGLT1 and SGLT2 help get glucose in the cell how?
these secondary active proteins use the Na gradient and couple glucose influx
Electric gradient is generated by
Na+/K+ ATPase kicks out more Na than puts in K+
3Na+/2K+
creating a negative charge on the inside, further electrically attracting Na+ from the lumenal side into the cell
Why does Cl- move paracellularly from the lumen to interstitium?
The basolateral side has become more positive from movement of Na and K and therefore Cl- is pulled and creates the osmotic gradient which therefore pulls water transcellularly and paracellularly to move down osmotic gradient
