Session 4 Flashcards
What does the Proximal Convoluted Tubule reabsorb?
Electrolytes Glucose (100%) Urea Amino acids (100%) Water
What does the Distal Convoluted Tubule do?
Reabsorbs water, therefore concentrating the urine.
It reabsorbs water and Na+ as a result of aldosterone action
What effects the Collecting Duct’s permeability?
Anti Diuretic hormone
Why can’t plasma volume be changed by adding water to the plasma directly?
Because the osmolarity of the plasma would change. Also no active water pumps
How do you change plasma volume without effect osmolarity?
Add a isosmotic solution which would increase the volume without changing osmolarity.
What is the major osmotically active solute?
Na+ in the extra cellular fluid
What transporter in on the apical membrane of the macula densa cells?
NaK2Cl
What is Glomerulotubular balance?
Protects against Na+ secretion.
In balance with PCT
Prevents Na+ overload in the PCT and therefore loss of Na+
How does Cl- reabsorption occur?
Can be transcellular (Active)
Can be paracellular (Passive)
Coupled to Na+ reabsorption and Na/K ATPase
What are the Na+ transporters in the Proximal Convoluted Tubule?
Na+/H+ antiporter
Na+/Glucose symporter
What is the Na+ transporters in the Loop of Henle?
NaKCC2 symporter
What is the Na+ transporters in the early Distal Convoluted Tubule?
NaCl Symporter
What is the Na+ transporters in the late Distal Convoluted Tubule and Collecting ducts?
ENaC (Epitherlial Sodium channels)
What are the 2 segments of the Proximal Convoluted Tubule?
S1
S2 & S3
What is the transporter for Na+ in S1?
Basolateral Na/K ATPase
Basolateral Na/HCO3- co-transporter
Apical NHX (Co transports with Glucose)
Aquaporin
How is electroneutrality maintained in S1?
Urea and Cl- concentration remains high to compensate for loss of glucose.
The high Cl- creates a concentration gradient for chloride reabsorption in S2-S3
How is Na+ and water reabsorbed in S2-S3?
With a basolateral Na+/K+ ATPase
Apical Na+ reabsorbed via NHX, also has Cl- transport, aquaporin
What are some of the properties of the PCT in relation to water reabsorption?
Highly permeable to water
Obligatory water reabsorption
Driving force is the osmotic gradient established by solute absorption
What is the hydrostatic pressure of the interstitium in the PCT?
High
Why is the oncotic force in the peritubular capillaries high?
Due to the loss of 20% of the filtrate at the glomerulus, but cells and proteins are left in the blood. (Therefore water wants to be reabsorbed into the blood)
Which part of the Loop of Henle reabsorbs most of the water?
The descending limb
Which part of the Loop of Henle is impermeable to water and only reabsorbs solutes?
The ascending limb - Has no Aquaporin
What is the transporter in the Thick ascending limb of the Loop of Henle?
NaKCC2
What is the route of K+ at the Loop of Henle?
K+ diffuses into the lumen vis ROMK and Cl- move into the interstitium
Less K+ in the filtrate at this point so (to maintain activity of the NaKCC2 transporter) K+ diffuses back into the filtrate.
How does the actions of the ascending limb effect the descending limb?
The descending limb increases the intracellular concentration of solutes in the interstitium so that water moves out of the ascending limb.
Where, in the nephron, is the only place that has a variable water permeability?
The late Distal Convoluted Tubule & Collecting ducts
What is the composition of fluid that enters the Distal Convoluted tubule?
Hypo osmotic (Lower solute concentration)
What is the target for Thiazide?
The NCC transporter in the Distal Convoluted Tubule
What other cation enters in the Distal convoluted tubule?
Ca2+ through calcium channels which are sensitive to Parathyroid hormone
What are the 2 cell types in the Collecting duct?
Principle cells
Type B intercalated cells
What is the role of principle cells?
Reabsoption of Na+ ions via the ENac
Produce a negative charge in the lumen via the paracelluar route.
What is the role of Type B intercalated cells?
Active reabsorption of Cl-
Secretes H+ or HCO3- ions
How can Na+ reabsorption in the PCT be effected?
The RAAS system
What are principle cells a target for?
Aldosterone
