Physio 4 Flashcards
What does the reabsorption of a substance depend on?
specific membrane transport proteins
IS Glomerular filtration specific?
No
Is reabsorption of a substance-specific?
Yes
What is the reabsorption rate in the proximal tubule?
80 ml/min
Is there a change in the osmolarity of the fluid as it passes through the proximal tubule?
No
What is the osmolarity of the fluid as it enters the loop of henle?
300 ml (almost same)
Which substances are absorbed in the proximal tubule?
Sugars Amino acids Phosphate Sulphate Lactate
Which substances are secreted into the proximal tubule?
H+ Hippurates Neurotransmitters Bile pigments Uric acid Drugs (atropine, morphine, penicillin) Toxins
How is adrenaline and noradrenaline excreted?
Via the urine
What are the barriers which the substance must cross to get undergo transcellular tubular reabsorption?
- Luminal membrane of the epithelial membrane
- Cytoplasm
- Basolateral membrane
- Interstitial fluid space
Peritubular capillary
What
tight junctions at the apical junctions
What is the route of paracellular reabsorption?
Varies btw different segments of the nephron
some areas tighter and some areas of the nephron less thick - determines the reabsorption
What does transcellular reabsorption depend on?
Transport protein
one at the apical membrane and the other at the basolateral membrane
What are the primary active transporters?
Need energy from the hydrolysis of ATP to move something against the concentration gradient.
eg: Na/ K pump - pumps 3 Na out and brings 1 K in for each ATP molecule
What is the secondary active transport?
The carrier molecule is transported coupled to the down concentration gradient of an ion (usually Na+)
moves something either in the same(symporters) or opposite direction(antiporters)
What is facilitated diffusion?
Passive carrier-mediated transport of a substance down its concentration gradient
eg: moves glucose across the lipid bylayer via the protein, no energy
Where are the Na/K pumps present?
only at the basolateral membrane
What is the main function of the Na/ K pump?
To maintain the concentration gradient of Na across the cell membrane
Is the proximal tubule membrane leaky or not?
Yes it is
What are the transport proteins present in the apical membrane of the proximal tubule?
Na/ Glucose symporters
Na/ Amino symporters
Na/ H anteporters
What is the net movement of the Na in the proximal tubule?
From the filtrate to the peritubular capillaries = transcellular movement
Net reabsorption of the positively charged Na via this them
What is the net movement of the Cl in the proximal tubule?
sets up an electrical gradient and coupled to the reabsorptio nof Na, Reabsorption via the
paracellular route occurs for Cl
How does the osmolarity of the fluid change in the proximal tubule?
No change. Reabsorption of salt and water both occur in the proximal tubule hence the osmolarity remains the same
What is the net movement of the Cl in the proximal tubule?
Due to the osmotic drag of the NaCl and moves across from the tubule to the peritubular capillaries
What is the oncotic drag of the peritubular capillaries?
plasma protetins in the peritubular capillaries pulls the slat and water from the lateral space into the peritubular capillaries
How is glucose reabsorbed in the proximal tubule?
Via Na/ glucose symporters
concentration gradient across the basolateral membrane and it uses a facilitated transporter to move the glucose from inside the cell into the interstitial fluid
moved across the tubular cell via the transcellular route
water follows the glucose gradient via paracellular route and into the peritubular capillaries.
Which route does water take to cross the eipthelial cell in proximal tubule?
Paracellular route
How does glucose reabsorption in the proximal tubule change the osmolarity?
No change remains the same as the water is also absorbed with it
What force causes the movement of glucose and water across the membrane?
oncotic drag of the peritubular capillaries
What is the transport maximum (Tm)
max rate at which a substance can be reabsorbed by the kidney
dependent on the specifc membrane transport protein
Rate of filtration
Plasma concentration of A x GFR
What is the plasma concentration of the glucose?
4-5 mmol/ L
What happens if the plasma concetration of the glucose is > 10-12 mmol/L?
10-12 mmol/L
the transport mechanisms that reabsorb glucose is saturated
what happens if we filter lots of glucose?
lots og flucose in the tubular fluid, only can move a certain amount via the transporters and the rest gets peed out
What is the platea line in transport maximum?
kidney filtering higher than normal plasma glucose concetration - uncontrolled diabetes
What marker is used for finding the plasma renal flow?
Para-amino hippuric acid
What does the secretion of H+ depend on?
Membrane transport protein
Comment on the transporters in the proximal tubule with respect to saturation.
transport protein thats secrete and reabsorb substances can both be saturated
What is the osmotic concentration of the tubular fluid when it leaves the proximal tubule?
iso-osmotic - 300 mosmol/l
