Renal Clearance

Question 1

What is the functional unit of the kidney?

Answer 1

Nephron

Question 2

What are the main parts of the nephron?

Answer 2

Glomerulus (filters blood)

Tubules (reabsorbs water and filtered solutes and tubular secretion)

Question 3

What are the two forms of reabsorption that occurs in the tubules?

Answer 3

1. Active reabsorption (transporters)
2. Passive reabsorption

Question 4

What are the excretory role of the kidney?

Answer 4

1. Regulates fluid, electrolyte, and acid-base balance
2. Removes metabolic waste products & foreign chemicals from blood for urinary excretion

Question 5

How does blood move in the glomerulus?

Answer 5

Blood from afferent arteriole brings blood to glomerulus and fluids and electrolytes (filtrate) are pushed into glomerulus (proteins and cells do not leave the blood)

10% of afferent flow is pushed into the glomerulus, the remainer leaves in the efferent arteriole

Question 6

What is reabsorption?

Answer 6

Movement of susbstances out of the renal tubules and back into the blood capillaries

Question 7

What is Secretion?

Answer 7

Movememt of substances out of the blood and into the renal tubules

Question 8

Can protein bound drug be excreted by the kidneys?

Answer 8

No, drug bound to protein cannot be excreted by the kidneys

Question 9

Are lipophillic drugs easily excreted by the kidneys?

Answer 9

No, they are usually eliminated by the liver

Polar drugs are usually excreted by the kidneys

Question 10

Review slide 11 for renal clearance equation

Question 11

What factors affect glomerular filtration?

Answer 11

1. Molecular size (smaller drugs have greater glomerular filtration)
2. Plasma protein binding (more binding = less glomerular filtration)
3. Glomerular integrity and total number of functioning nephrons

Question 12

What is the most common marker for GFR?

Answer 12

Serum creatinine

Creatinine is a byproduct of Creatine (accumulation of Creatinine is indicative of reduced GFR)

Question 13

What nephron model allows Creatinine clearance to be a marker of GFR?

Answer 13

Intact Nephron Hypothesis

1. Loss of either glomerular or tubular function means loss of whole nephron function
2. All-or-nothing
   a. All renal excretory processes decline in parallel
   b. So loss of a functional nephron is reflected in GFR

ex. If GFR is 20% or normal, then renal clearance is 20%

Question 14

What drugs tend to be secreted into the tubules?

Answer 14

Drugs that are charged, neutral, or lipophillic can be secreted into the tubules

Transporters are located on both apical and basolateral membranes (can be saturated or inhibited)

Question 15

What types of drugs are reabsorbed by the kidneys?

Answer 15

Transporter mediated:
Endogenous compunds like amino acids, fatty acids, glucose, lactose, vitamins, minerals

Passive reabsorption:
Filtered lipophillic drugs

Question 16

What physiological factors affect tubular reabsorption?

Answer 16

1. Urine concentration (water reabsorption increases drug concentration in remaining volume, improving concenetration gradient)
2. Urine Flow (applies to drugs that undergo significant reabsorption): higher urine flow = less drug reabsorbed
3. Urine pH (ionized drug is more likely to escape reabsorption, unionized drug is more likely to be reabsorbed)