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Physiology > Glomerular filtration and tubular reabsorption > Flashcards

Glomerular filtration and tubular reabsorption Flashcards

1
Q

What is Glomerular Filtration?

A

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

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2
Q

What are freely filtered substances? Examples (6)?

A

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

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

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3
Q

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?

A

hydrostatic pressure is much higher than in other capillaries

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4
Q

Is there any reabsorption in the glomerulus?

A

No

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5
Q

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

A

Endothelial cell layer
BM
Podocytes

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6
Q

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

A

Spaces between the cells are larger than in a normal capillary

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7
Q

What are the three basic nephron mechanisms?

A

Filtration
Reabsorption
Secretion

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8
Q

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

A
  1. Small size of endothelial pores

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

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9
Q

What is nephrotic syndrome? How is it caused?

A

Increased permeability of the glomerular capillaries to protein

Disruption of structure of podocytes via mutation in Nephrin gene

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10
Q

What is the function of mesangial cells in the glomerulus?

A

Contract and change the surface area of the capillary

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11
Q

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

A

Podocin gene

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12
Q

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

A

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

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13
Q

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

A

0

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14
Q

What is the filtration fraction?

A

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

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15
Q

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

A

Increased

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16
Q

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

A

Decreases

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17
Q

What happens during severe sweating to the GFR? How?

A

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

18
Q

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

A

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

19
Q

What happens to the GFR during renal stones? How?

A

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

20
Q

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

A
  1. Filtration only
  2. Filtration, partial reabsorption
  3. Filtration, complete reabsorption
  4. Filtration, secretion
21
Q

Why do we filter 100% of plasma so often?

A

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

22
Q

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

A

Coupled endocytosis and exocytosis through a cell

Brings in proteins lost from filtration and brings out Ig

23
Q

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

A
  1. Through transcytosis

2. Breakdown into AA by attached enzymes, then reuptaken

24
Q

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

A

Easily, thus proteinuria

25
Q

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

A

Because they are the major place peptide hormones are broken down

26
Q

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

A

Filtered so many times

27
Q

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

A

Brush border

28
Q

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

A

Establishes low intracellular [Na], allowing to easy reuptake

29
Q

How is glucose brought back in from the tubule lumen?

A

Via SLGT (Na symporter)

30
Q

How are AAs brought back in from the tubule lumen?

A

Via AA/Na symporter

31
Q

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

A

Brings Na into the cell,

Pushes H out into the lumen

32
Q

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

A

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.

33
Q

What are the two forces acting to pull in Na?

A

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

34
Q

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

A

Aquaporins on both sides, and Na gradient

isosmotic reabsorption

35
Q

How is Cl maintained in the cell?

A

Cl/anion antiporters on the apical side of the cell

Cl/K symporters (goes out to capillaries) on the basal surface

36
Q

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

A

Cl is being taken up with Na

37
Q

What is secretion?

A

The active process or pumping out chemicals from the capillaries

38
Q

Why does glucose appear in the urine of DM pts?

A

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.

39
Q

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

A

Decreases b/c there is more water taken by glucose in the urine

This causes the polyuria/polydipsia seen in DM

40
Q

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)?

A

Some nephrons are worse at handling the loads than others.

Physiology (75 decks)

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