Lecture 2- Filtration And Clearance

Question 1

Characteristics of filtrate

Answer 1

Protein-free
Solute concentrations are the same as plasma
Formed as a result of hydrostatic and oncotic pressure differences across the glomerular membrane

Question 2

What is the filtration barrier composed of

Answer 2

Glomerular capillary endothelium
Basement membrane
Podocytes of bowman’s capsule

Question 3

How are molecules excluded from the barrier

Answer 3

Size and charge

Barrier favors smaller molecules and positively charged molecules

Question 4

Glomerular filtration rate (GFR)

Answer 4

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

In dogs, 80 mL/min

GFR= net filtration pressure (NFP) x filtration coefficient (kf)

Question 5

Net filtration pressure

Answer 5

Equals the glomerular capillary hydraulic pressure (Pgc) plus the Bowman’s capsule oncotic pressure minus glomerular capillary oncotic pressure and bowman’s capsule hydraulic pressure

*bowman’s capsule oncotic pressure is usually negligible

Question 6

How to control/ change GFR

Answer 6

Change Pgc (glomerular capillary hydraulic pressure)

Change filtration coefficient

Change plasma oncotic pressure

Renal tubular obstruction

Question 7

Ways to change glomerular capillary hydraulic pressure (Pgc)

Answer 7

Blood pressure
Efferent and afferent arteriole resistance
Sympathetic nervous system
Hormonal control
Obstruction

*Increased Pgc = increased GFR and decreased Pcg = decreased GFR

Question 8

Ways to change filtration coefficient

Answer 8

Permeability of membrane
Surface area for filtration

**as kf increases, GFR increases in a sigmoid fashion. Once kf passes a certain point, no further increase will result in increased GFR

Question 9

Ways to change plasma oncotic pressure

Answer 9

Starvation

*increases in plasma oncotic pressure= decreased GFR

Question 10

Clearancee

Answer 10

Imaginary volume of plasma from which a substance is removed per unit of time aka flow of plasma that is completely free of the substance

Cx (clearance) = (Ux * V) / Px

Ux= concentration in urine
V= urine flow rate
Px= concentration in plasma

Question 11

Inulin

Answer 11

Filtration marker used to study renal clearance

Freely filtered
Not resorbed
Not secreted
Not produced or metabolized by the kidney and does not alter GFR

GFR= Clearance of inulin

Question 12

Other filtration markers

Answer 12

Creatinine and blood urea nitrogen

Serum creatinine levels will rise when GFR decreases

BUN- not very reliable because it is dependent on diet