Tubular Transport of NaCl and Water Flashcards
Total excretion is determined by:
Filtration-Reabsorption+Secretion.
How many L of fluid may be excreted in a single day?
15L of 180L filtered
How much salt excreted in a single day?
Up to 30 grams of 1500g filtered
Which of the following is false?
- Renal Tubules are lined by polarized epithelial cells
- The two general means of transport in a tubule are Transcellular and Paracellular
- Paracellular transport is from apical to basolateral membrane.
Paracellular transport is from apical to basolateral membrane.
FALSE:
It flows between cells (mainly through tight junctions)
What are the driving forces of simple diffusion?
- Electrical Gradient (charge difference)
- Chemical gradient (concentration difference)
How does facilitated diffusion differ from simple diffusion?
Facilitated diffusion requires carrier proteins to transfer ions/molecules.
The Kidney is 2nd only to heart in O2 consumption (QO2) per gram of tissue. Why?
There is a large amount of active transport going on.
What 4 important ions/molecules are reabsorbed in the Proximal Tubule?
- Na+
- Cl-
- Glucose
- H20
What are the main jobs of:
- Proximal Convoluted Tubule
- Loop of Henle
- Distal Convoluted Tubule
- Collecting Duct
- Proximal Convoluted Tubule
- Bulk Reabsorption (65% of NaCl and H2O and 100% of Glucose and Amino Acids– and pretty much everything else)
- Loop of Henle
- Urine Dilution
- Distal Convoluted Tubule
- Fine-tuning Na Balance
- Collecting Duct
- Fine tuning of K, Na, H+/HCO3-, H2O
True or False:
In the Loop of Henle, dilution of the filtrate occurs because H2O is secreted.
FALSE
Dilution occurs because the thick ascending limb of the LOH is impermiable to water but permiable to ions
True or False: NaCl cotransporters in the DCT (distal convoluted tubule) are thiazide sensitive.
True.
Remember Hydrachlorothiazide? This is where its MOA is.
In the collecting duct, there are 2 types of cells. Name them and their funcions. And for kicks and giggles, what is the fxn of hte collecting duct again?
Principal cells – fine tune:
- Sodium reabsorption and Potassium secretion (via Aldoserone mediated channels)
- Water reabsorption (via vasopressin or ADH mediated aquaporins)
Intercalated cells (alpha and beta)
- Acid-base balance
Collecting duct does “Fine tuning”
What are the molecular effects of Aldosterone and ADH?
Insert more channels:
ADH: Inserts aquaporins (H2O channel) on the luminal side of cells
Aldosterone: Inserts ENaC more channels (which absorb Na)
What is the relationship (>,<,=) between H2O and NaCl permiability in the Descending and Ascending Loop of Henle?
Descending: H2O > NaCl
Ascending: NaCl >>>> H2O (impermeable
Note, the deeper you go in the kidney, the more concentrated the peritubular tissue becomes.
What is the role of the vasa recta?
Maintain the osmotic gradient in the medula by allowing flow of H2O and Ions.
Look at the picture and ask yourself what is going on. Its a good one to understand.
Okay that was a lot… How about a summary? Here ya go…
yup
Fic=K’ (Pint - Pcap+piint - picap)
WTF does this mean?
This is an important CONCEPT that basically tells us that the net Hydrostatic(P) and oncotic (pi) pressures are greater in the interstitum of the kidney and therefore will cause reabsorption of H2O and ions into the blood.
The main driver is oncotic pressure because cells and protiens are left in the blood and not filtered into the nephron.
If GFR increases by 30 L, why doesnt urine output increase by 30L as well?
Glomerulo-tubular Feedback (2/3 H2O reabsorbed):
Inc GFR results in a inc [blood], and an inc peritubular capillary oncotic pressure. This leads to an inc in REABSORPTION of fluid.
Tubulo-glomerular feedback:
Macula densa cells in the juxtaglomerular apparatus sense excess NaCl delivery in loop of henle. They then tell the afferent arteriole to constrict. This decreases GFR.
