Renal Basics - Muster

Question 1

What are the functions of the kidney?

(Hint: 9 total)

Answer 1

1. Filtration & Clearance
2. Blood pressure maintenance
3. Na⁺ homeostasis
   
   1. Volume, NOT concentration
4. H₂O homeostasis
5. K⁺ homeostasis
6. Bone/mineral homeostasis
   
   1. Vitamin D, PO₄^-, Ca²⁺
7. Acid/Base homeostasis
8. RBC production/regulation
   
   1. EPO
9. Gluconeogenesis

Question 2

What are the components of the filtration barrier in the kidney?

Answer 2

• Size:
  
  • Capillary endothelium
  • Basement membrane
  • Podocytes
• Charge:
  
  • GMB and slit diaphragms = negative charge

Question 3

What are the limitations in size of particles that are capable of bing filtered?

Answer 3

• Freely filtered: <70,000 D
  
  • Na⁺ = 23 D
  • K⁺ = 39 D
  • Creatinine = 113 D
  • Urea 60 D
• Completely excluded: >70,000 D

(Albumin ~66,000 D so some gets through)

Question 4

What is the role of hydrostatic pressure and oncotic pressure on GFR?

Answer 4

• Hydrostatic pressure:
  
  • P_gc (inside) = supports filtration
  • P_bs (outside) = supports absorption
• Oncotic pressure:
  
  • π_gc (inside) = supports absorption
  • π_bs (outside) = supports filtration

Higher (more +) filtration => Increased GFR

GFR = k_f [(P_gc + π_bs) – (P_bs + π_gc)]

Question 5

What will happen to RPF, GFR, and hydrostatic pressure if the afferent arteriole is constricted?

Answer 5

• RPF = decreased
• GFR = decreased
• Hydrostatic pressure (P_gc) = decreased

Question 6

What will happen to RPF, GFR, and hydrostatic pressure if the afferent arteriole is dilated?

Answer 6

• RPF = increased
• GFR = increased
• Hydrostatic pressure (P_gc) = increased

Question 7

What will happen to RPF, GFR, and hydrostatic pressure if the efferent arteriole is constricted?

Answer 7

• RPF = same OR decreased
• GFR = same OR decreased
• Hydrostatic Pressure (P_gc) = increased
  
  • efferent constrictions causes pressure to back up to glomerulus

Question 8

What will happen to RPF, GFR, and hydrostatic pressure if the efferent arteriole is dilated?

Answer 8

• RPF = same OR increased
• GFR = decreased
• Hydrostatic Pressure (P_gc) = decreased

Question 9

How does the sympathetic nervous system activity effect RPF, hydrostatic pressure, and GFR?

Answer 9

• Sympathetic activity => release NE
  
  • constric afferent & efferent arterioles
    
    • RPF = decreases
    • Hydrostatic Pressure = no change
    • GFR = decreases

Question 10

How does Angiotensin II effect RPF, hydrostatic pressure, and GFR?

Answer 10

• Ang II => constriction of afferent and efferent arterioles
  
  • RPF = same OR decreased
  • Hydrostatic Pressure = increased
  • GFR = same OR increased

Question 11

How do Prostaglandins effect RPF, hydrostatic pressure, and GFR?

Answer 11

• Prostaglandins => vasodilate afferent arteriole
  
  • RPF = increased
  • Hydrostatic pressure = increased
  • GFR = increased

Question 12

What is filtration fraction?

Answer 12

The ratio of the glomerular filtration rate (GFR) to the renal plasma flow (RPF)

• Filtration Fraction, FF = GFR/RPF

Question 13

What is Excretion Rate?

Answer 13

urine flow rate x [solute_urine]

• should be whatever is required to keep you in balance

Question 14

What are the benefits of using creatinine to predict GFR?

Answer 14

• If you know:
  
  • the plasma concetnration
  • can measure the urinary concentration
  • know urine volume
• You can calculate GFR!

Question 15

What are the limitations of using creatinine to predict GFR?

Answer 15

• Assumes steady state
• Rarely collected appropriately when using measurement of a 24 hour urine
• Creatinine is secreted (10-40%)
  
  • secretion ramps up in the early phases of GFR decline
• Creatinine can have variable production based upon age, illness, etc.