Flashcards in Flow, GFR And Pharmacology Deck (45):
What is the average renal blood flow?
What is the renal plasma flow?
Renal blood flow minus the haematocrit (erythrocyte volume fraction - usually 45%)
RPF = 0.55 x RBF
Generally, how many segmental arteries are there per kidney?
What are the 2 types of nephron?
Give some features of cortical nephrons
Afferent arteriole has large diameter than efferent
High concentration of renin
Give some features of the juxtamedullary nephrons
Diameter of afferent close to diameter of efferent
Almost no concentration of renin
How much of the blood from a renal artery is filtered at any one time?
What are the 3 layers of the glomerular filter?
Which molecule do we think is the biggest molecule that can pass through glomerular filtration?
Which charge is repelled more at the glomerulus?
What are the 3 forces acting at the filter?
Hydrostatic pressure in capillary
Hydrostatic pressure in Bowman's capsule
Oncotic pressure in capillary
What is the myogenic response?
The control over GFR by changing the tone of the arteriole walls
Controls GFR through day-to-day BP changes
Describe the effect on the GFR of an increase in tone in the afferent arteriole
Increased resistance leads to reduced blood flow
Decreased hydrostatic pressure
Why doesn't the flow rate change?
Because change is resistance is proportional to change in pressure
Which organs have the best autoregulation?
What is the role of autoregulation?
To keep GFR within the normal ranges
Describe tubular-glomerular feedback
Changes in tubular flow rate occur as a result of changes in GFR
This changes the amount of NaCl that reaches the DCT
Cl- ions detected in the macula densa
Stimulates juxtaglomerular apparatus to release appropriate chemicals
What chemicals can be released by the JGA and what are their effects?
Adenosine - vasodilator of the efferent arteriole - reduces GFR
Prostaglandins - vasodilator of afferent arteriole - increases GFR
Describe glucose cotransport in the PCT
2 Na+ ions plus 1 glucose molecule
Secondary active transport
What substances do we secrete into the kidney tubules?
Organic anions and cations (a lot of the drugs that we prescribe)
Give examples of endogenous cations
Give examples of drugs that are cations
Give examples of endogenous anions
Give examples of drugs that are anions
What is the normal GFR range for males and females?
Males = 115 - 125 ml/min
Females = 90 - 100
What is the formula for renal clearance?
RC = UV/P
U = urinary conc of substance
V = flow rate of urine formation
P = plasma conc of same substance
What factors does the complicated eGFR equation take into account?
What does xenobiotic mean?
Not belonging in the body
What processes contribute to pharmacokinetics?
What is drug clearance?
The rate of elimination by the kidney and the liver
How do we work out the half-life of a drug?
(0.693 x Vd) / CL
0.693 - constant
Vd - volume of distribution
CL - clearance rate of drug
Generally the rate of removal of a drug is proportional to...
The drug's free concentration in the plasma
If a drug is more lipophilic how does this affect its excretion?
Can diffuse more easily back out of the kidney tubule
(Across the plasma membrane)
How does plasma protein binding affect drug excretion?
Reduces the amount of drug available for glomerular filtration
(And/or removal by the anion/cation transporters in the tubules)
If the drug has a high volume of distribution then the drug is more likely to be ...
Does a large volume of distribution increase or decrease the half life?
Describe the 2 phases of liver metabolism
Phase I = reduction, oxidation, hydroxylation
Phase II = conjugation
(Both phases act to increase charge to make kidney excretion easier)
What occurs when weak acidic anions are present in acidic urine?
Will be protonated
Become electrically neutral
Diffuse out of the nephron
What happens when weak acidic anions are in more alkaline urine?
Less likely to be protonated
More will be excreted (as will be charged therefore less likely to be reabsorbed)
What happens when weak bases are in acidic urine?
Will become protonated
More drug excreted
What happens when weak bases are in more alkaline urine?
More likely to be electrically neutral
Can diffuse out of nephron
Define renal clearance
The virtual volume of plasma that would be totally cleared of a given solute per unit time.
Describe the features of inulin that make it good for measuring GFR
Only filtered (not secreted or reabsorbed)
What molecules can be used to estimate GFR?