M&R 2 - Permeability Barriers Flashcards
What is the relationship between the rate of passive transport and increasing concentration gradient.
The rate of passive transport increases linearly with increasing conc gradient.
How do non polar molecules travel across bilayers?
They diffuse across the hydrophobic domain
How does water travel across the membrane?
Water diffuses passively down the osmotic gradient
In some cells the moment of water is also facilities by aquaporins
Why is the movement of ions and hydrophilic molecules important?
Maintains intracellular pH
Maintains ionic composition
Regulates cell volume
What are the two thermodynamically viable mechanisms of facilitated diffusion?
Carrier molecules (ping pong) Protein channels (pores)
What is the difference between active and passive transport?
Active needs energy passive is spontaneous.
What are the three ‘currencies’ of free energy used for active transport?
ATP
electron transport
Light
What is a co-transporter?
This is when the transport of one substance is linked to concentration of another.
What is a uni port?
One solute molecule from one side -> the other side
What is co transport in the same direction called? And what is different?
Same - symport
Different - anti port
What are the features of a Na+/K+ ATPase pump?
Plasma membrane pump that uses ATP to pump 3 sodium out and 2 potassium in.
Necessary for electrical excitability
Drives secondary active transport that leads to -
The control of pH, regulation of cell volume etc
Why do calcium levels need to be controlled in cells?
Ca2+ is toxic to cells. (See MoD)
What are the features of the PMCA pump?
Expels Ca2+ from the cell in exchange for H+ (anti port)
Uses ATP.
It has a high affinity for calcium but a low capacity
What are the features of the SERCA pump?
Accumulates Ca2+ in the ER in exchange for H+ (antiport)
Uses ATP, also has a high affinity low capacity
What are the features of the NCX pump?
Uses the Na+ gradient set il by the sodium potassium pump
(Secondary active transport)
Removes most Ca2+
Electrogenic - as current flows in direction of sodium gradient
What are the features of the Na+ glucose co transport
In the SI and the kidney the entry of sodium privies energy for the entry of glucose. (Symport)
When are ions used in pH regulation?
When buffering capacity is exceeded.
What are the features of the NHE pump?
Sodium in H+ out.
One to one exchange that raises cell pH and regulates cell volume.
What are the features of the NBC transporter?
This is the sodium bicarbonate transporter
Pumps sodium and bicarbonate in
And H+ and Cl- out.
Acid out - base in
What is the band 3 anion exchange?
This acidifies the cell by moving chloride ions inwards and pumping bicarbonate out.
How to cells respond to swelling?
They then extrude the osmotic ally active ions (sodium, potassium and chloride) via transporters.
How do cells respond to shrinkage?
This causes an influx of osmotically active ions
What is the normal bicarbonate reabsorption mechanism by the proximal tube?
The sodium potassium pump drives other channels by keeping intracellular Na+ concentrations low.
NHE can pump H+ ions into the lumen
H+ goes to ‘pick up’ bicarbonate and bring it back into the cell.
What is renal hypertensive therapy?
These are drugs which in it sodium transporters which in turn reduces the reuptake of Na+ so less water is reabsorbed.
Less water = less BV = less BP
What do loop diuretics do?
These act on the thick ascending limb
They block the NKCC2 transporter preventing sodium reuptake into the proximal cells
What do the thiazides do?
These act on the distal convoluted tube
They block NCCT transporters.
What do amilorides do?
These block ENaC transporters to prevent sodium uptake.
In the cortical collecting duct.
What do spironolactones do?
These are glucocorticoid receptor antagonists used to reduce the effect of raised aldosterone. Also in the cortical collecting duct .
Decreases blood pressure.
