Urinary Session 3- GFR, Blood Flow And Pharmacology Flashcards
Starting from renal artery what path will blood entering the kidney follow?
Renal artery 5 segmental arteries Interlobar arteries Arcuate arteries Interlobular arteries Afferent arterioles
What is the renal lobe?
Renal pyramid and cortex immediately above
How do the diameters of afferent and efferent arterioles affect hydrostatic pressure of blood in glomerulus?
Diameter of afferent arteriole is slightly greater than the diameter of the efferent arteriole so hydrostatic pressure of blood in the glomerulus is increased
What is forced out of the blood at the glomerular capillaries?
Most of the water
Most/all of the salts
Most/all of the glucose
Most/all of the urea
Why are blood cells and plasma proteins not filtered out?
Too large
What are water and solutes forced out of the glomerular capillaries called once in the Bowman’s capsule?
Ultrafiltrate
What is the rate of production of glomerular filtrate?
125ml per minute
Of the volume that reaches the glomerulus, what percentage is filtered out?
About 20%
What percentage of glomerular filtrate produced leaves the body?
About 1%
What are the 3 mechanisms of tubular reabsorption?
Osmosis, diffusion and active transport
Where is most of the volume of the glomerular filtrate reabsorbed?
PCT
What is most of the energy used by the kidneys used for?
Reabsorption of sodium ions
How does sodium more from the glomerular filtrate into the cells of the PCT?
Symporters on apical membrane- also facilitate passage of other substances through the membrane
What substances can be reabsorbed with Na?
Glucose, amino acids, water soluble vitamins, lactate, acetate, ketones and krebs cycle intermediates
What creates the Na gradient used for symporters?
NaKATPase on the basolateral membrane
How is water reabsorbed?
Osmosis following solutes
What is tubular secretion?
Substances added to glomerular filtrate in the nephron tubule to remove excessive quantities of certain dissolved substances
Which substances are secreted into the glomerular filtrate to be removed from the body?
K, H, ammonium ions, creatinine, urea, some hormones and some drugs
Where does tubular secretion occur?
From the epithelial cells that line the renal tubules and collecting ducts into the glomerular filtrate
How is continuous glomerular filtration maintained across a wide range of systemic blood pressures?
Selective vasoconstriction or dilation to maintain renal blood flow at a constant rate
What mechanisms are believed to mediate renal autoregulation?
Faster myogenic and slower tubuloglomerular feedback system
What is the purpose of autoregulation of renal blood flow?
To maintain GFR
Define clearance
The volume of plasma from which substance X can be completely cleared to the urine per unit time
What is the equation to calculate clearance?
C=UV/P
C= clearance, U= amount in urine, V= urine flow rate, P= arterial plasma conc
What are the units for clearance?
L/hr or ml/min
Why is calculating clearance important?
It allows you to calculate GFR which is used clinically as a measure of kidney function
What properties must a substance have to be used to measure GFR?
It must be freely filtered across the glomerulus, not be reabsorbed, secreted or metabolised by cells of the nephron and pass directly into the urine
What substance is usually measured for GFR?
Creatinine
What is the equation for creatinine clearance?
GFR = UV/P
Same as clearance equation
Why does progressive overestimation of GFR occur with severe disease?
Tubular secretion by organic cation secretory pathways in the proximal tubule accounts for 10-20% of urinary creatine and a progressively higher percentage as GFR falls
Define fractional excretion
Proportion of filtered solute that remains un-reabsorbed by the nephron
How can you calculate FE (hint: 3 step equation)
1. Calculate filtered load of substance ([P]z x [U]cr x V) / [P]cr = A [P]=plasma conc [U]=urinary conc V=urinary volume 2. Calculate amount of substance excreted. [U]z x V = B 3. Calculate percentage! Bx100/A = FE
