Renal Flashcards
Normal glomerular filtration rate?
120 mL/min
Normal filtration fraction
20%
Filtration fraction equation
FF = GFR (glomerular filtration rate) / RPF (renal plasma flow)
120/600
The glomerulus is =
a ball of capillaries surrounded by the Bowman’s capsule
3 main layers of the filtration barrier
Glomerular capillary endothelium
Specialised capillary basement membrane
Modified epithelial lining of the Bowman’s capsule
How small do molecules need to be to fit through the filtration barrier?
<7000 Da
What other molecular characteristic reduces it’s ability to pass through the filtration barrier?
If it’s negatively charged
Clearance definition =
Equation =
volume of plasma that is cleared of a substance per unit time
Clearance = (Urine conc of a substance x urine flow rate) / plasma concentration
Why is creatinine used for estimate eGFR?
It is freely filtered and not reabsorbed
Primary vs secondary active transport
Primary - uses ATP directly as an energy source
or secondary which uses the concentration gradient created by primary
Facilitated diffusion =
Rate of diffusion of specific substances enhanced by ion channels and uniporters
Maximum tubular transport =
Limit to the rate at which any transporter can operate, therefore maximum rate of absorption / secretion can be reached
Renal threshold concentration =
level at which transporters start to saturate and glucose appears in the urine
(varies across nephrons)
11 mmol/L
Glucose tubular transport maximum
21 mmol/L
This is the level at which all the nephrons have become saturated
Difference between the threshold and transport maximum =
splay
Main function of the proximal tuble
Reabsorption
Glucose
Amino acids
Phosphate
Bicarb
Na+
K+
Ca2+
Cl-
Urea
Water
Movement of Na+ in the proximal tubule
Moving down electrochemical gradient into the tubule cell
Then actively transported into the interstitial space
Only 20% diffuses into the capillaries due to back flux via paracellular pathways
Movement of glucose in the proximal tubule e
Reabsorbed into the tuble cell by cotransport with Na2+
Diffuses out of the cells into the interstitium
Tubular fluid is WHAT compared to plasma when it enters the loop of henle
Isotonic
Tubular fluid is WHAT compared to plasma at the tip of the harpin
Hypertonic
Tubular fluid is WHAT compared to plasma as it enters the distal nephron
Hypotonic
Water and ion movements in the descending limb
Permeable to water so diffuses out of the lumen via passive transport (impermeable to solutes)
Water and ion movements in the thin ascending limb
Passive movement of urea and NaCl out of the lumen
(nil water movement as impermeable)
Water and ion movements in the thick ascending limb
Active reabsorption of NaCl out of the lumen
(nil water movement as impermeable)
Countercurrent multiplier role
Creation of concentration via active transport in the ascending limb, increases interstitial fluid osmolality, therefore causes more passive movement of water down the osmotic gradient in the descending limb.
Loop diuretics MOA
Inhibit the Na/Cl/K symporter on the apical membrane, preventing reabsorptin of NaCl and water
What cells do both the distal tubule and collecting ducts contain?
Principle cells - respond to ADH
Intercalated cells - secrete H+
Distal collecting system is WHAT to water?
Except in the presence of?
Impermeable
ADH
Importance of urea in the distal collecting system
Provides osmolality in the medulla
Action of aldosterone on K+ in the distal collecting system?
Increase K+ secretion, increased Na+ pump activity so more water retained
W
What regulated calcium reabsorption in the distal tubule?
PTH & activated Vit D
