Physiology - The Proximal Tubule Flashcards
how much fluid and salt are reabsorbed in the kidneys?
99%
how much glucose and amino acids are reabsorbed in the kidneys?
100%
how much urea is reabsorbed in the kidneys?
50%
how much creatinine is reabsorbed in the kidneys?
0%
what is the initial segment of the nephron?
the proximal tubule
how much fluid/min is reabsorbed in the proximal tubule?
around 80ml/min
what is the osmolarity of the fluid reabsorbed in the proximal tubule?
300 mosmol/l
iso-osmotic with the filtrate
what five things are reabsorbed in the proximal tubule?
sugar amino acids phosphate sulphate lactate
what is secreted in the proximal tubule? (6)
hydrogen hippurates neurotransmitters bile pigments uric acid drugs and toxins
what are the two methods of reabsorption in the tubules?
transcellular
paracellular
what is transcellular reabsorption?
reabsorption into the interstitial fluid by passing through the tubular epithelial cell
what is paracellular reabsorption?
reabsorption into the interstitial fluid by passing through the tight junctions of the tubular cells
what is primary active transport?
transport that requires energy to operate the carrier
substrate moved against its concentration gradient
what is secondary active transport?
carrier molecule is transported coupled to the concentration gradient of an ion
usually sodium
what is facilitated diffusion?
passive carrier mediated transport of a substance down its concentration gradient
where in the nephron are sodium ions reabsorbed?
all regions except the descending limb of the loop of henle
what drives net sodium ion reabsorption in the nephron?
the basolateral sodium potassium pump
how does sodium exit the tubular epithelial cell?
sodium potassium pump
how does sodium enter the tubular epithelial cell?
sodium dependent glucose transporter
sodium dependent AA transporter
sodium hydrogen counter transporters
what is the net movement of sodium in the proximal tubule and what does this mean for water?
from filtrate to blood
water moves in this direction
how is water reabsorbed in the proximal tubule?
via the paracellular route
how does glucose enter the tubular epithelial cell?
via the sodium glucose transporter
how does glucose leave the tubular epithelial cell?
via facilitated diffusion
what is the net movement of glucose in the proximal tubule?
from tubular fluid to blood
what is the transport maximum?
the max rate at which a substance can be reabsorbed
what is the renal threshold?
the concentration at which reabsorption of a substance plateaus
what is the renal threshold of glucose?
10-12 mmol/l
