Lecture 2: Filtration and Clearance (Bolsor)

Question 0

what is the filtration barrier between glomerular capillary and Bowman’s capsule composed of? (3 components)

Answer 0

glomerular capillary endothelium, basement membrane, and epithelial podocytes of Bowman’s capsule

Question 1

3 main characteristics of filtrate

Answer 1

1) virtually protein-free
2) solute concentrations are the same as plasma
3) formed as a result of hydrostatic and oncotic pressure differences across the glomerular membrane

Question 2

why does more blood enter the Bowman’s capsule through the afferent arterioles than leaves through the efferent arterioles?

Answer 2

some is filtered out through the capillaries inside the capsule

Question 3

Is it normal to have protein in urine?

Answer 3

NO

Question 4

increased molecular size –> ability to filtrate that molecule in Bowman’s capsule

Answer 4

decreases

Question 5

which molecule filters more easily in the kidney: myoglobin or hemoglobin?

Answer 5

myoglobin, because of its smaller size. Charge also has an effect to a lesser extent

Question 6

Effect of charge on filtration in kidney

Answer 6

+ charged molecules filter more easily than - charged molecules. However, molecular size has a larger effect on filterability, so after a certain large molecular size, changes in charge will have no effect on filterability.

Question 7

Index of filterability

Answer 7

ratio of the concentration of a given molecule in the filtrate (inside Bowman’s capsule) and in the plasma. Ratio of 1 indicates molecule passes through the filtration barrier easily

Question 8

Do albumin and Hb has high or low index of filterability?

Answer 8

low, because they do not pass filtration barrier easily and mainly remain in the plasma

Question 9

glomerular filtration rate (GFR)

Answer 9

volume of plasma filtered into Bowman’s capsule per unit time

Question 10

formula for GFR

Answer 10

GFR = net filtration pressue (NFP) X filtration coefficient (kf)

Question 11

equation for NFP

Answer 11

NFP = glomerular capillary hydraulic pressue (PGC) + Bowman’s capsule oncotic pressure (pieBC) - Bowman’s capsule hydraulic pressure (PBC) - glom. capillar oncotic pressure (pieGC)

Question 12

main force moving fluid into Bowman’s capsule

Answer 12

hydrostatic pressure in glomerular capillary

Question 13

5 factors that influence hydrostatic pressure of the glomerular capillary (PGC)

Answer 13

1) blood pressure
2) efferent and afferent arteriolar resistance
3) sympathetic nervous system
4) hormonal control
5) obstruction

Question 14

higher PGC –> GFR?

Answer 14

increases

Question 15

How does sympathetic system regulate GFR?

Answer 15

controls blood flow through the glomerular capillary bed and secondarily controls the hydrostatic pressure in glomerular capillaries

Question 16

increased afferent arteriolar resistance –> PGC? GFR?

Answer 16

decreases both

Question 17

increased efferent arteriolar resistance –> PGC and GFR?

Answer 17

increases both (pressure backs up in the system like a blocked hose)

Question 18

normal GFR for dogs

Answer 18

80ml/min

Question 19

what controls the filtration coefficient Kf? (2 main factors)

Answer 19

permeability and surface area for filtration

Question 20

What happens to GFR as filtration coefficient Kf continues to increase?

Answer 20

GFR will increase rapidly at first, then reach a plateau as additional increases in Kf don’t have any effect on GFR

Question 21

How can surface area for filtration be changed?

Answer 21

by controlling the number of glomerular capillaries that are perfused

Question 22

starvation –> oncotic pressure of glom. capillary? GFR?

Answer 22

oncotic pressure drops due to decreased plasma protein concentrations. GFR rises

Question 23

cellular debris in renal tubules –> GFR, urine flow?

Answer 23

both decrease. GFR decreases because high pressure in bladder raises pressure in ureters up to the kidney, causing resistance to filtration.

Question 24

clearance

Answer 24

volume of plasma from which a substance is completely removed per unit time. Used to assess overall renal function

Question 25

equation for renal clearance Cx

Answer 25

Cx = (Ux*V)/Px where Ux is conc. in urine, V is urine flow rate, and Px is conc. in plasma

Question 26

inulin and its important properties

Answer 26

synthetic substance used as a tool to study renal clearance. clearance of inulin is a marker for GFR

• freely filtered
• not reabsorbed, secreted, produced, or metabolized by the kidney
• doesn’t alter GFR itself

GFR = Cin = (Uin*V)/Pin
GFR

Question 27

clinical relevance of creatinine with respect to kidney

Answer 27

used as an indicator of GFR because plasma creatinine is inversely correlated with GFR