Flow, GFR And Pharmacology Flashcards by Maya White

What is the average renal blood flow?

1.1 L/min

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What is the renal plasma flow?

Renal blood flow minus the haematocrit (erythrocyte volume fraction - usually 45%)
RPF = 0.55 x RBF

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Generally, how many segmental arteries are there per kidney?

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What are the 2 types of nephron?

Cortical

Juxtamedullary

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Give some features of cortical nephrons

Small glomerulus
Afferent arteriole has large diameter than efferent
Sympathetic rich
High concentration of renin

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Give some features of the juxtamedullary nephrons

Big glomerulus
Diameter of afferent close to diameter of efferent
Sympathetic poor
Almost no concentration of renin

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How much of the blood from a renal artery is filtered at any one time?

20%

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What are the 3 layers of the glomerular filter?

Capillary endothelium
Basement membrane
Podocyte layer

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Which molecule do we think is the biggest molecule that can pass through glomerular filtration?

Inulin

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Which charge is repelled more at the glomerulus?

Negative charges

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What are the 3 forces acting at the filter?

Hydrostatic pressure in capillary
Hydrostatic pressure in Bowman’s capsule
Oncotic pressure in capillary

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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

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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
Decreased GFR

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Why doesn’t the flow rate change?

Because change is resistance is proportional to change in pressure

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Which organs have the best autoregulation?

Heart
Brain
Kidneys

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What is the role of autoregulation?

To keep GFR within the normal ranges

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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

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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

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Describe glucose cotransport in the PCT

Via SGLUT
2 Na+ ions plus 1 glucose molecule
Secondary active transport

What substances do we secrete into the kidney tubules?

Protons (H+)
Potassium
Organic anions and cations (a lot of the drugs that we prescribe)

Give examples of endogenous cations

ACH
Dopamine
Adrenaline
Histamine
Serotonin

Give examples of drugs that are cations

Sulfonamides
Morphine
Atropine

Give examples of endogenous anions

Urate
Bile salts
Fatty acids

Give examples of drugs that are anions

Penicillin
Salicylate
NSAIDs

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?

Age Sex Mass Ethnicity

What does xenobiotic mean?

Not belonging in the body

What processes contribute to pharmacokinetics?

Absorption Distribution Metabolism Excretion

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 | Linear properties

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 ...

Lipophilic

Does a large volume of distribution increase or decrease the half life?

Increase

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 Less lipophilic More drug excreted

What happens when weak bases are in more alkaline urine?

More likely to be electrically neutral More lipophilic Can diffuse out of nephron Less excreted

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

``` Inert Only filtered (not secreted or reabsorbed) ```

What molecules can be used to estimate GFR?

Creatinine | Inulin

What are the downsides of using inulin?

Expensive | Has to be injected