Renal: Dynamics of Glomerular Filtration

Question 1

What does Glomerular filtrate consists of?

Answer 1

It’s very much like blood plasma, however, it contains very little total protein. Consists mainly of inorganic ions and low-molecular-weight organic solutes in virtually the same concentrations as in the plasma.

Question 2

What does “Freely Filtered” mean?

Answer 2

Substances that are present in the filtrate at the same concentration as in the plasma

Question 3

What components of blood are freely filtered?

Answer 3

Ions (Na, K, CL, HCO3)
Neutral organics (glucose and Urea)
Amino acids
Peptides (insulin and ADH)

Question 4

Volume of filtrate formed per unit time = Glomerular Filtration Rate. What is the normal GFR?

Answer 4

180L/day (125ml/min)

Question 5

What is the net filtration of fluid across all other capillaries (besides the Glomerulus) in the body ?

Answer 5

4L/day

Question 6

What is the average total volume of plasma in humans?

Answer 6

3L. ENTIRE plasma is filtered by the kidneys some 60 times a day.

Question 7

Where is the site of Plasma Filtration?

Answer 7

Glomerulus

Question 8

What determines barriers of Glomerular Filtration?

Answer 8

Cell Types

Question 9

Glomerulus Cell Types:

Answer 9

1. Podocytes
2. Endothelial
3. Mesangial

Question 10

What are the Glomerulus Cell Types’ functions?

Answer 10

Podocytes: help keep things out based on size
Fenestrated Epithelium: Filter things based on size
Mesangial: modified smooth muscle cells, lay down extra-cellular matrix proteins; Keep things out based on charge

Question 11

SUM of the Hydrostatic Pressures and the osmotic pressures resulting from protein SUBTRACTED by the oncotic or colloid osmotic pressures

Answer 11

Net Filtration Pressure (NFP)

Question 12

HPglo - ( ONCOTICglo + HPbowmanspace)

Answer 12

NFP Equation

Question 13

Hydrostatic pressure: Glomerulus and Bowman Space

Oncotic pressure of fluid: Glomerulus and Bowman Space

Answer 13

Filtration Pressures

Question 14

What is the Filtration Rate Equation?

Answer 14

Rate of Filtration= Kf x NFP

Question 15

Kf *(HydrostaticPressureGC - HydrostaticPressureBC - OncoticPressureGC)

= Kf * NFP

Answer 15

GFR

Question 16

Pressure that pushes fluid out blood into capsule; FAVOR filtration

Answer 16

Hydrostatic Pressure

Question 17

Pressure that pushes fluid into blood; OPPOSE filtration

Answer 17

Oncotic Pressure

Question 18

What is the net outward pressure if the Afferent arteriole has 45mmHg (HPglo), -10mmHg (HPbowspace), -25mmHg (ONCOTICglo)?

If Blood Pressure drops 10mmHg of HPglo, the net outward pressure/filtration pressure equals what then?

Answer 18

10mmHg. 0mmHg

Question 19

What portion of the NFP equation favors filtration?

Answer 19

HPglo

Question 20

What portion of the NFP equation opposes filtration?

Answer 20

ONCOTICglo , HPbowspace

Question 21

What is the relationship between Kf and GFR?

Answer 21

Decrease Kf, Decrease GFR

Question 22

What can change Kf?

Answer 22

Glomerular disease and drugs.

Mesangial contraction, reducing area available for filtration.

Question 23

Hydrostatic Pressure of the Glomerulus comes from what?

Answer 23

Blood Pressure

Question 24

True/False: Hydrostatic Pressure of the Bowman Space is very constant

Answer 24

True

Question 25

If you Dilate Afferents, is GFR increased or decreased?

Answer 25

Increased

Question 26

If you Dilate Afferents and Constrict Efferents, is GFR increased or decreased?

Answer 26

Increased

Question 27

What is the relationship between Hydrostatic Pressure of Bowman Space and GFR?

Answer 27

Decreased GFR, Increased Hydrostatic Pressure of Bowman Space

Question 28

What is the relationship between Oncotic Pressure of Glomerulus and GFR?

Answer 28

Decreased Oncotic Pressure of Glomerulus, Increase GFR

Question 29

Filtered Load

Answer 29

Amount of substance that is filtered per unit time and enters the nephron

Question 30

Filtered Load Equation? (only works for freely filtered substances)

Answer 30

GFR*Plasma concentration

Ex: Na
125 ml/min * 140 mEq/L = 17.5 mEq/min.

Question 31

What are the short and long-term affects from Autoregulation?

Answer 31

Myogenic response (short-term)
Tubuloglomerular Feedback (long-term)

Question 32

Concentraion of glucose in plasma is 100 mg/dL and the GFR is 125 ml/min. How much glucose is filtered per min?

Answer 32

125 mg/min

Question 33

A drug is noted to cause a decrease in GFR. Identify 4 possible actions of the drug that might decrease GFR.

Answer 33

1 Constrict glomerular mesangial cells, and decrease Kf.
2 Lower arterial pressure and hence HPglo
3 Constrict the afferent arteriole, and hence reduce HPglo
4. Dilated the efferent arteriole and reduce HPglo

Question 34

A drug is noted to cause an increase in GFR with no change in net filtration pressure. What might the drug by doing?

Answer 34

It might be increasing Kf

Question 35

If you Constrict Afferents, is GFR increased or decreased?

Answer 35

Decreased

Question 36

A person is given a drug that dilates the afferent arteriole and constricts the efferent arteriole by the same amounts. Assuming no other actions of the drug, what happens to this person’s GFR and RBF?

Answer 36

RBF will show no change because the drug has no effect on total renal vascular resistance.
GFR will increase because of the large increase in HPglo.