Sodium and water transport along the nephron Flashcards
How many moles of sodium are filtered in the Bowman’s capsule a day?
2500 mmoles
How many moles of sodium are excreted a day?
150 mmol
How many litres of blood are filtered a day?
180 L
How many litres of urine are produced a day?
1.5 L
What happens to the sodium and water that are not excreted?
Reabsorbed in the tubules
What are the sites of reabsorption in the tubule?
PCT -> PST -> DTLLH -> TALLH -> DCT -> Collecting duct
What reabsorption happens in the PCT?
50% water and 50% sodium is reabsorbed Isotonic
What reabsorption happens in the PST?
20% water and 20% sodium Isotonic
What reabsorption happens in the DTLLH?
5% water
What reabsorption happens in the ATLLH?
20% sodium
What reabsorption happens in the DCT?
5% sodium
What reabsorption happens in the collecting duct?
4% sodium 19% water
In which parts of the tubule is reabsorption isotonic?
PCT and PST
Which parts of the tubule are impermeable to water?
TALLH and DCT
What separates the lumen and interstitial fluid in a renal epithelial cell?
Tight junction
What controls most reabsorption in the renal epithelial cells?
Sodium movement
What controls movement of sodium in and out of renal epithelial cells?
Sodium potassium pump
What does the lumen refer to?
The tubule
What does the interstitial milieu refer to?
The blood
What substances are reabsorbed in the PCT along with sodium?
Glucose Amino acids Phosphate Chlorine Protons Water
What type of transporters control the movement of these molecules along with sodium?
Most are symporters Protons - sodium - proton antiporter Chlorine - channel Water - aquaporins
What feature makes cells permeable to water?
Presence of aquaporins
What is the role of the TDLLH in controlling salt and water reabsorption?
Mainly control equilibration of sodium and water via channels and aquaporins
Is the process of reabsorption in the TALLH active?
Yes - requires lots of ATP
What type of cotransporter is uniquely present on epithelial cells of the TALLH?
2-chloride, potassium, sodium cotransporter
What does the potassium transporter on TALLH epithelial cells do?
Recycle potassium
Why is a positive transepithelial potential created in TALLH epithelial cells?
Chlorine is transported into the blood - 2 chlorines for every sodium Transporting more chlorine ions than sodium = positive transepithelial potential
What does this positive transepithelial potential do?
Transports additional chlorine, sodium, potassium and calcium through a paracellular shunt
Which cells of the collecting duct regulate water and sodium reabsorption?
ENaC - epithelial sodium channel ROMK - Renal Outer Medullary Potassium Channel
Is water and sodium permeability regulated in collecting duct epithelial cells?
Yes
What is the name of the cells in the colllecting duct that regulate sodium and water reabsorption?
Principal cells
How do ENaC and ROMK work to control sodium and potassium concentration?
Sodium reabsorption is paralleled by potassium excretion into the urine
How does the ability to regulate the expression of ROMK and ENaC affect the function of the collecting ducts?
Allows Potassium excretion to be regulated by the cells Sodium concentration in the urine to be regulated
What is Tmax?
Point at which increases in concentration of a molecule does not result in an increase in the movement of a substance across a membrane
What is the Tmax of glucose?
10 mmol/L
What happens if there is glucose in urine?
Osmotic diuresis Dehydration
What is glycosuria?
Glucose in the urine
What are two conditions that can lead to glycosuria?
Renal glycosuria - defective uptake in PCT due to mutation in SGLT2 (gene encoding for sodium glucose cotransporter) Diabetes mellitus - plasma glucose is very high, exceeds transport capacity of nephrons
What are names of diseases affecting salt handling?
Bartter’s syndrome EAST syndrome Pseudohypoaldosteronism Gitelman’s syndrome Liddle syndrome
What is Barterr’s syndrome?
Condition that affects the 2 major ion transporters of TALLH NKCC2 ROMK - recycling potassium pathway ClC-K
What is EAST syndrome?
Affects basolateral potassium channels in the DCT
What is Gitelman’s syndrome?
Affects NaCl cotransporters in the DCT
What is Pseudohypoaldosteronism?
Gain of function of ENaC in the collecting duct
What is Liddle syndrome?
Loss of function of ENaC in the collecting duct
What are diseases affecting water handling?
Nephrogenic
Central
Nephrogenic syndrome of innapropriate antidiuresis
Diabetes insipidus
What is the reason for central source affecting water handling?
Low secretion of ADH from pituitary
Due to pituitary tumours or due to post surgery effects
How does diabetes insipidus affect water handling?
Large amounts of severly diluted urine is produced
Due to impaired glucose metabolism
How does nephrogenic syndrome of innapropriate antidiuresis affect water handling?
Gain of function of V2 ADH receptors
How does nephrogenic syndrome affect water handling?
Collecting ducts do not respond to ADH
What does a generalised renal epithelial cell look like?
What does a PCT epithelial cell look like?
What does a TALLH epithelial cell look like?
What does a DCT epithelial cell look like?
What does a principal cell look like?
