Control of Plasma Volume Flashcards
What is the most osmotically effective solute in the extracellular fluid?
Sodium (Na+)
What is the effective circulating volume?
Volume of arterial blood effectively perfusing organs
How is sodium balance maintained?
Kidney excretion rates vary to match excretion with ingestion
Where is most of sodium filtered out of the nephron?
PCT
What effects change in renal sodium excretion?
Changes in osmotic + hydrostatic pressure - alter PCT reabsorption
RAAS - stimulates PCT reabsorption
Aldosterone - targets DCT + CD
WHat is pressure natriuresis/diuresis?
Increased sodium/water excretion when blood pressure increases
What happens when renal artery BP increases?
Reduced number of Na-H antiporter + Na-K ATPase activity in PCT
Less resorption of sodium - therefore less water resorption
Increased sodium + water excretion
What is transcellular reabsorption?
Reabsorption through cells
What is paracellular reabsorption?
Reabsorption between cells
What is the purpose of tight junctions?
Ensure apical and basolateral transporters stay on the right side
Where on the nephron can aquaporins be found?
PCT
CD
What aquaporins can be found on the PCT?
AQP1
AQP7
What aquaporins can be found on the collecting duct?
AQP2
AQP3
AQP4
Is sodium reabsorption mainly active or passive?
Active
What is the main mechanism of sodium reabsorption?
Transcellular process driven by 3Na-2K-ATPase pumps on basolateral membrane
How many parts is the PCT divided into?
3
What transporters are present in S1?
Basolateral 3Na-2K-ATPase
NaHCO3- cotransporter
Apical
- glucose co transport
- AA co transport
- NaH exchange
What transporters are present in S2-3?
Basolateral 3Na-2K-ATPase
Apical Na-H exchanger
What happens in the descending limb of the loop of Henle?
Increase in intercellular concentrations of sodium - allows paracellular reuptake of water
Concentrates sodium and chloride ions in lumen
What happens in the thin ascending limb of the loop of Henle?
Passive sodium reabsorption (paracellular) - due to gradient created in descending limb
What happens in the thick ascending limb of the loop of Henle?
Na moves from lumen to cells - NKCl2 transporter
Na moves from cell to interstitium - 3Na-2K-ATPase
K+ diffuses via ROMK back into lumen - maintain gradient
Cl- move into interstitium
Which part of the loop of Henle reabsorbs water?
Descending limb
Which part of the loop of Henle reabsorbs NaCl?
Ascending limb
What happens in the DCT?
Hypoosmotic fluid enters
DCT 1 - active transport of Na
- NCC transporter - apical
- 3Na-2K-ATPase - basolateral
DCT 2 - active transport of Na
- NCC transporter - apical
- ENa - apical
- 3Na-2K-ATPase - basolateral
Fluid is more hypo-osmotic at the end
How is calcium transported in the DCT?
Calcium enters cell
Binds to calbindin
Transported out of cell by sodium-calcium exchanger
What regulates calcium transport in the DCT?
Parathyroid hormone
1,25-dihydroxyvitamin D
How is the collecting duct divided?
Cortical region
Medullary region
What are the main cell types found in the cortical region of the CD?
Principal cells
Intercalated cells
What occurs in principal cells?
Reabsorption of sodium
- ENaC - apical
- 3Na-2K-ATPase - basolateral
What are the types of intercalated cells?
A-IC = acid secreting type
B-IC = bicarbonate secreting type