Where does the majority of reabsorption occur?
What is a normal healthy GFR?
Why is reabsorption specific?
Specific transport proteins
What is the osmolarity of the fluid at the start of the proximal tubules compared to that at the end?
no change in osmolarity
Which process mainly occurs in the proximal tubule?
Does secretion occur in the proximal tubule?
By which two means can substances be reabsorbed into peritubular capillaries?
Transcellular (through cell membranes)
Paracellular (through tight junctions)
What is primary active transport?
Energy used to transport a substance against its concentration gradient using a carrier
What is secondary active transport?
Active transport of a substance by carriers COUPLED to the concentration gradient of another ion
Secondary active transport usually occurs using the concentration gradient of which ion?
What is facilitated diffusion?
Passive transport WITH A CARRIER
Where is 2/3rds of filtered sodium reabsorbed?
Where are NaKATPases found on the tubular cells of the proximal tubules?
empties into capillaries
What is the function of NaKATPases on the basolateral membrane of the tubular cells?
What does this achieve?
Active transport of 3 Na OUT and 2 K IN
Maintains concentration gradient of sodium
So it can diffuse in (be reabsorbed) at the apical membrane
Where do sodium ions go once they have been secreted OUT of tubular cells by NaKATPase?
leaving conc gradient from filtrate to tubular cells
The transport of sodium from the filtrate to the capillaries sets up which types of gradient?
CONCENTRATION GRADIENT FOR SODIUM (so more is reabsorbed from proximal tubules)
OSMOTIC GRADIENT FOR WATER (following sodium)
ELECTROCHEMICAL GRADIENT FOR CHLORINE (so it's reabsorbed by the PARACELLULAR route)
By which routes are sodium and chlorine reabsorbed?
Sodium - transcellular
Chlorine - paracellular
Why doesn't the osmolarity of the proximal tubules decrease as you go along?
Water and salt reabsorbed equally
By which means does glucose leave proximal tubules?
Co-transport with sodium (SGLT2)
How does glucose leave the tubular cells by the basolateral membrane?
FACILITATED DIFFUSION down its concentration gradient
How does water follow sodium and glucose into the peritubular capillaries?
Which two substances are reabsorbed via the paracellular route?
What proportion of glucose is reabsorbed in the proximal tubules?
What is the equation for rate of filtration?
Rate of filtration = [substance]plasma x GFR
Does the rate of reabsorption of glucose increase in proportion with its rate of filtration?
Yes, up to the point where all the carriers are saturated
Which transporter is saturated when the rate of filtration of glucose is too high?
Which rate starts to increase if you pass the maximum rate of reabsorption of glucose?
Rate of excretion
What is the TM of glucose?
Transport maximum of glucose
RATE OF FILTRATION AFTER WHICH YOU START TO EXCRETE GLUCOSE
What is the
a) rate of filtration
b) plasma concentration
of glucose after which you start to get glycosuria?
a) 2 mmol/min, transport maximum
b) Around 12 mmol/L
After you reach the transport maximum for glucose, glucose is excreted by the kidneys, producing which sign?