Glomerular filtration and tubular reabsorption

Question 1

What is Glomerular Filtration?

Answer 1

the bulk flow of fluid from the glomerular capillaries into Bowman’s capsule

Question 2

What are freely filtered substances? Examples (6)?

Answer 2

Substances that are at the same concentration in the plasma and the filtrate

e.g. Na, K, Cl, HCO3, glucose, urea

Question 3

Glomerular capillaries are like other capillaries in that filtration depends on Starling forces. What is the major difference in these forces in the kidney compared to other capillaries?

Answer 3

hydrostatic pressure is much higher than in other capillaries

Question 4

Is there any reabsorption in the glomerulus?

Answer 4

No

Question 5

What are the layers that a substance must pass through to be filtered from the glomerulus? (3)

Answer 5

Endothelial cell layer
BM
Podocytes

Question 6

What are the characteristics of the endothelial cell layer in Bowman’s capsule?

Answer 6

Spaces between the cells are larger than in a normal capillary

Question 7

What are the three basic nephron mechanisms?

Answer 7

Filtration
Reabsorption
Secretion

Question 8

What are the two barriers to protein filtration through the endothelial cell membrane in the glomerulus?

Answer 8

1. Small size of endothelial pores

2. Negative charges on endothelium and podocytes (proteins usually negatively charged)

Question 9

What is nephrotic syndrome? How is it caused?

Answer 9

Increased permeability of the glomerular capillaries to protein

Disruption of structure of podocytes via mutation in Nephrin gene

Question 10

What is the function of mesangial cells in the glomerulus?

Answer 10

Contract and change the surface area of the capillary

Question 11

A mutation in what gene leads to a steroid resistant nephrotic syndrome?

Answer 11

Podocin gene

Question 12

What happens to the net filtration pressure as you move along the capillary? Why?

Answer 12

Oncotic pressure rises and net filtration pressure decreases. However, NFP >0

Question 13

What is the oncotic pressure in Bowman’s capsule (normally)?

Answer 13

0

Question 14

What is the filtration fraction?

Answer 14

the percent of the renal plasma flow (RPF) that is filtered at the glomerulus

Question 15

If the FF is increased then when will happen to the oncotic pressure at the efferent end of the glomerular capillaries?

Answer 15

Increased

Question 16

If the FF is lowered then the oncotic pressure at the efferent end of the glomerular capillaries does what?

Answer 16

Decreases

Question 17

What happens during severe sweating to the GFR? How?

Answer 17

Colloid osmotic pressure in the blood increases since sweat has no proteins, leading to lower GFR

Question 18

What happens during severe diarrhea, emesis to the GFR? How?

Answer 18

Colloid osmotic pressure in the blood increases since diarrhea/emesis has no proteins, leading to lower GFR

Question 19

What happens to the GFR during renal stones? How?

Answer 19

Decreases, since there is a higher osmotic pressure in the glomerulus

Question 20

What are the four possible outcomes of Filtration/reabsorption in the kidney tubule?

Answer 20

1. Filtration only
2. Filtration, partial reabsorption
3. Filtration, complete reabsorption
4. Filtration, secretion

Question 21

Why do we filter 100% of plasma so often?

Answer 21

Difficult to control plasma volume and composition if only filtered once a week or even once a day

Question 22

What is transcytosis? Why is this important for renal tubule function?

Answer 22

Coupled endocytosis and exocytosis through a cell

Brings in proteins lost from filtration and brings out Ig

Question 23

What are the two ways in which proteins lost in the urine are reabsorbed?

Answer 23

1. Through transcytosis

2. Breakdown into AA by attached enzymes, then reuptaken

Question 24

How easily can the processes the take back in protein be saturated? What is the consequence of this?

Answer 24

Easily, thus proteinuria

Question 25

Why can renal disease result in increased levels of peptide hormones?

Answer 25

Because they are the major place peptide hormones are broken down

Question 26

Why can only a small change in Na excretion/reabsorption have a large effect?

Answer 26

Filtered so many times

Question 27

What specialization do the cells that face the renal lumen have to aid in reuptake?

Answer 27

Brush border

Question 28

What is the function of the Na/K pump on the lumen cells?

Answer 28

Establishes low intracellular [Na], allowing to easy reuptake

Question 29

How is glucose brought back in from the tubule lumen?

Answer 29

Via SLGT (Na symporter)

Question 30

How are AAs brought back in from the tubule lumen?

Answer 30

Via AA/Na symporter

Question 31

What is the effect of the NHE (Na, H exchanger)?

Answer 31

Brings Na into the cell, Pushes H out into the lumen

Question 32

Because the tight junctions of the proximal tubule are permeable to Na+, Na+ transport is a gradient limited system. What does this mean?

Answer 32

If the concentration of Na+ became higher in the interstitial fluid than it is in the tubular lumen, the Na+ would back-leak into the tubule.

Question 33

What are the two forces acting to pull in Na?

Answer 33

Chemical and electric gradient (note these are in the same direction--into the cell)

Question 34

What allows for water to move so freely from the nephron tubules to the capillaries? What is this called?

Answer 34

Aquaporins on both sides, and Na gradient isosmotic reabsorption

Question 35

How is Cl maintained in the cell?

Answer 35

Cl/anion antiporters on the apical side of the cell Cl/K symporters (goes out to capillaries) on the basal surface

Question 36

What prevents a negative charge from building up in the tubule lumen (since Na is being brought out)?

Answer 36

Cl is being taken up with Na

Question 37

What is secretion?

Answer 37

The active process or pumping out chemicals from the capillaries

Question 38

Why does glucose appear in the urine of DM pts?

Answer 38

The plasma concentration of glucose is higher than the transport maximum of a nephron. Thus the filtered glucose that cannot be reabsorbed in the proximal tubule passes through the rest of the nephron into the urine.

Question 39

What happens to water reabsorption in DM? What symptom does this cause?

Answer 39

Decreases b/c there is more water taken by glucose in the urine This causes the polyuria/polydipsia seen in DM

Question 40

What causes the "Splay" of nephrons, (referring to the amount of glucose that is lost in the urine prior to reaching the maximum threshold of reabsorption)?

Answer 40

Some nephrons are worse at handling the loads than others.