Glomerular Filtration

Question 1

Glomerular filtrate

Answer 1

-large amounts of fluid and solutes are filtered through the glomerular capillaries into Bowman’s capsule

Question 2

What molecules are not filtered?

Answer 2

-all molecules are freely filtrated except: proteins, calcium (1/2 bound to proteins), and fatty acids (bound to proteins)

Question 3

Filtration fraction

Answer 3

-approx. 20% of renal plasma flow is filtered to the Bowman’s capsule, rest will leave the kidney

Question 4

Human glomerular filtration rate (GFR)

Answer 4

-125 ml/min or 180L/day

Question 5

What does filtration rate depend?

Answer 5

1.the glomerular capillary filtration coefficient (Kf)= constant
>indicator of membrane permeability and surface area
2.Filtration forces (hydrostatic and colloid osmotic forces)
>greater force will result in increased filtration

Question 6

Filtration barrier layers

Answer 6

1.Endothelium of glomerular capillaries
2.Basement membrane of capillaries
3.Epithelial cells of Bowman’s capsule (podocytes)

Question 7

Permeability of filtration barrier

Answer 7

1.Perfortated endothelium (fenestrae)
2.Permeable basement membrane of capillaries (proteoglycans)
3. Podocytes: Non-continuous epithelium with long foot-like processes with gaps in between (slit pores)

Question 8

Filtration fraction formula

Answer 8

Filtration fraction= GFR/Renal plasma flow
Ex. 0.2 (20%)=(180 L/day)/renal plasma flow
Renal plasma flow= 180/0.2= 900 L/day

Question 9

Filterability of molecules in the glomerulus

Answer 9

-associated with size and molecular charge
>smaller molecules pass through filtration layers more easily
>molecules of positive charge will have increased filterability due to the membrane filters negative charge (attracts)
>molecules with negative charge have less filterability due to electrostatic repulsion
**if molecule is small, but has negative charge then its filterability is less

Question 10

Layers electrical charge

Answer 10

-all 3 layers of the filtration barrier have a negative charge

Question 11

Filterability of water, Na, glucose, Inulin,

Answer 11

Filterability =100%

Question 12

What molecules have limited filterability?

Answer 12

-plasma proteins (myoglobin, albumin) have very limited filterability due to their larger size and negative molecular charge

Question 13

Dextrin filtration

Answer 13

-strongly based on molecular size and charge
>if positive, will be more easily filtered
>if negative, will be more difficult to filter

Question 14

In some kidney diseases, the negative charge of the basement membrane is reduced. What changes would you expect in composition of urine?

Answer 14

-Would expect to see proteins such as albumin within the urine (proteinuria) because they are positive charged by since there is less negative charge in the membrane, there will be less repulsion and more easy transport