Clearance and RPF
What percent of the theoretical RPF does ERPF represent?
90%
Some blood flows through areas such as capsule or medulla without being processed by nephrons.
Approximately 0
Is urea reabsorption via active or passive means?
Passive
What is the normal GFR for males?
125 mL/min
Which apical transporter for glucose is abundant in the early proximal tubule?
Sodium-Glucose Linked Transporter 2 (SGLT2).
SGLT1 dominates in later segments of the proximal tubule.
What does this equation describe
RPFv * Pvx + Ux * V̇
Amount of substance leaving the kidney (ideal)
Is the majority of sodium that is filtered by the kidneys reabsorbed or excreted?
Reabsorbed.
Only 150 mmol of the 25200 mmol filtered per day is excreted in urine.
Explain the difference between primary and secondary active transport
Primary active: Directly uses energy from ATP hydrolysis to move a substance against its concentration gradient.
Secondary active: Uses an electrochemical gradient (established by primary transport) to drive the movement of a substance.
What is the best calculation method clinically for GFR?
CKD-EPI
What two surfaces are present on tubular cells in the kidney?
Apical, basolateral
Name a substance that is assumed to yield a renal venous blood concentration of zero
Para-amino hippuric acid (PAH).
Assumed to be completely cleared by the kidney.
What is the normal pH range of urine?
4.4-8.4
Where is most of glucose reabsorbed, and what percentage of all glucose reabsorbed does this represent?
Proximal convoluted tubule - 90%
Name 5 criteria for a substance that is suitable for use in determining GFR
Freely filtered at glomerulus.
Not reabsorbed
Not excreted.
Not protein bound.
Not metabolised.
Not toxic.
Not stored in the kidney
At least what fraction of Na+, Cl-, and water are reabsorbed in the proximal tubule?
2/3
What does it mean when the clearance of a substance is less than the GFR?
Amount excreted in urine is less than amount that is filtered out at glomerulus --> there is reabsorption of the substance.
What percentage of water filtered by the kidneys is reabsorbed?
99%
What is the term referring to the plasma concentration at which the solute starts to appear in urine, and the name of the phenomenon that explains the discrepancy between the theoretical and practical values?
Renal threshold.
SPLAY
Describe the process where angiotensinogen becomes angiotensin II, and briefly explain the effects of angiotensin II.
Angiotensinogen is converted to angiotensin I by renin from the kidneys, then to angiotensin II by ACE1 in the lungs, which raises blood pressure and promotes sodium and water retention.
Name the two major types of transport in the proximal tubule and what happens to their effectiveness as you move along the proximal tubule.
From early to later segments;
- Transcellular transport slows down
- Paracellular pathways are tighter (less leaky)
Give the definition and equation for renal clearance.
The minimal volume of plasma which could have supplied the amount of the substance which is excreted in the urine per unit time.
Clearance = CA = UA * V̇ / PA
Differentiate molarity, osmolarity and osmolality and give the osmolality range of normal urine?
Molarity is moles of solute per liter of solution, osmolarity is osmoles of solute particles per liter of solution, and osmolality is osmoles of solute particles per kilogram of solvent.
Normal osmolality of urine is 50-1200 mosm/kg.
Name and describe the two limiting factors for reabsorption, and an example of a substance affected for each?
Tm limited reabsorption. E.g. glucose, phosphate, Vit C, amino acids.
Saturation of a carrier.
Active gradient-time limited mechanisms. E.g. sodium
Rate of transport is limited by the concentration gradient that can be established across the tubular wall within the short span of time where the fluid is in contact with the epithelium
Describe the pathway of blood flow through the kidney.
Renal artery → Segmental arteries → Interlobar arteries → Arcuate arteries → Interlobular (cortical radiate) arteries → Afferent arterioles → Glomerular capillaries → Efferent arterioles → Peritubular capillaries (and/or vasa recta in juxtamedullary nephrons) → Interlobular veins → Arcuate veins → Interlobar veins → Renal vein → Inferior vena cava
Name each segment of the proximal tubule
S1 – early proximal convoluted tubule
S2 – remaining cortical proximal tubule
S3 – medullary/straight proximal tubule