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RENAL PHYSIOLOGY > Reabsorption and Secretion > Flashcards

Reabsorption and Secretion Flashcards

1
Q

Filtration without resorption takes place in which regions of the nephron?

A

Glomerular capillaries

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2
Q

Why is pressure in the peritubular capillaries low?

A

Hydrostatic pressure overcoming frictional resistance in the efferent arterioles

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3
Q

Why is the oncotic pressure high in the peritubular capillaries?

A

Loss of 20% of plasma concentration causing a relative increase in concentration of plasma proteins

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4
Q

Starling forces in the peritubular capillaries favour what?

A

Reabsorption

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5
Q

What % of urea filtered at the glomerulus is reabsorbed in the tubule?

A

50%

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6
Q

What % of glucose filtered at the glomerulus is reabsorbed in the tubule?

A

100% (normally)

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7
Q

What % of water filtered at the glomerulus is reabsorbed in the tubule?

A

99%

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8
Q

What % of Na+ filtered at the glomerulus is reabsorbed in the tubule?

A

99.5%

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9
Q

What are the mechanisms of resorption?

A

Carrier mediated transport systems

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10
Q

What determines the maximum transport capacity of a substrate?

A

Level of Saturation of the carriers

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11
Q

If carriers are saturated, what happens to excess substrates?

A

The excess enters the urine

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12
Q

What happens when a substrate binds with a carrier protein?

A

The carrier protein changes shape and the substrate leaves

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13
Q

What is the renal threshold?

A

Plasma threshold at which saturation occurs

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14
Q

All glucose will be reabsorbed with glucose levels up to what?

A

<10mmoles/l

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15
Q

What happens when plasma glucose >10mmoles/l?

A

Excess over 10 appears in the urine

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16
Q

How much glucose will be secreted if [glucose] is 17.5mmoles/l?

A

7.5mmoles

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17
Q

What is normal plasma [glucose]?

A

5mmoles/l

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18
Q

Glycosuria is due to a failure in what?

A

INSULIN

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19
Q

What is the maximum transport capacity (Tm) of amino acids?

A

High - regulated by insulin

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20
Q

Why is the maximum transport capacity (Tm) of glucose so high?

A

Because non-diabetic patients should never exceed 10mmoles/l

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21
Q

What is the maximum transport capacity (Tm) of glucose?

A

10mmoles/l

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22
Q

How does maximum transport capacity (Tm) function to regulate substance concentrations?

A

Tm is set at a level where normal [plasma] causes saturation

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23
Q

What proportion of Na+ reabsorption occurs in the proximal tubule?

A

65-75%

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24
Q

How is Na+ reabsorbed?

A

Active transport

ATP pumps

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25
Q

Na+ ATP pumps are located where?

A

Basolateral surfaces of the tubule

26
Q

How do Na+ ions enter the tubule cell from the lumen?

A

Passively down the concentration gradient

27
Q

How do Na+ ions interstitial fluid from the tubule cell?

A

Na+K+ ATP pumps

Up the concentration gradient

28
Q

Why is Na+ able to penetrate the brush border membrane of the PCT so easily?

A

Microvilli on the surface and large number of Na+ ion channels

29
Q

How do negative ions cross the proximal tubular membrane?

A

Follow the electrical gradient established by the active transport of Na+

30
Q

What is the net effect of Na+ and Cl- leaving the tubule?

A

Osmotic force - water follows the ions out

31
Q

What is the net effect of water following ions out of the tubule?

A

Concentration of the substances left in the tubule

32
Q

How is Na+ reabsorbed?

A

Active transport

33
Q

How is H2O reabsorbed?

A

Osmosis

34
Q

How are permeable solutes reabsorbed?

A

Diffusion

35
Q

The rate of reabsorption of non-actively reabsorbed solutes depends on what?

A

Amount of H2O removed - determines extent of concentration gdt
Permeability of the membrane to the solute

36
Q

How permeable to urea is the tubule membrane?

A

Moderately

37
Q

What process establishes the gradient for reabsorption?

A

Active transport of Sodium in the basolateral membrane

38
Q

Other than the generation of an osmotic gradient, why is the active transport of Na+ in the tubules important?

A

Na+ is essential for carrier mediated transport systems

39
Q

What is the effect of high tubule [Na+] on glucose?

A

Facilitated glucose reabsorption

40
Q

What is the effect of low tubule [Na+] on glucose?

A

Inhibition of glucose reabsorption

41
Q

Na+ reabsorption is linked to the reabsorption of what?

A

HCO3-
Glucose
Amino acids

42
Q

What transporter is used to take glucose from lumen → cell?

A

Sodium dependent glucose transporter

43
Q

What transporter is used to take glucose from cell → ISF?

A

GLUT facilitated diffusion

44
Q

What transporter is used to take Na+ from cell → ISF?

A

Na+/K+ ATPase

45
Q

How do protein-bound substances enter the lumen?

A

Peritubular capillaries → lumen

Tm-limited carrier mediated secretory mechanisms

46
Q

The Organic Acid mechanism is used to excrete what?

A

Lactic/uric acid
Penicillin
Aspirin
Para-amino-hippuric acid

47
Q

Why are carrier mechanisms able to excrete exogenous substances?

A

They are not specific

48
Q

The Organic base mechanism is used to excrete what?

A

Choline, Creatinine
Morphine
Atropine

49
Q

Protein-bound substances are secreted where?

A

Proximal convoluted tubule

50
Q

What is the normal ECF [K+]?

A

4mmoles

51
Q

Hyperkalemia is defined as what?

A

> 5.5mmoles/l

52
Q

Hypokalemia is defined as what?

A

<3.5mmoles/l

53
Q

How does hyperkalaemia cause injury?

A

Decrease in resting membrane potential –> ventricular fibrillation

54
Q

How does hypokalemia cause injury?

A

Increased resting membrane potential
Hyperpolarised muscle
Cardiac arrhythmia

55
Q

Where is the majority of K+ reabsorbed?

A

Proximal tubule

56
Q

Changes in K+ excretion are due to what?

A

Changes in secretion in the distal parts of the tubule

57
Q

Increased renal tubule cell [K+] will cause what?

A

Increased K+ secretion

58
Q

K+ secretion is regulated by what?

A 
Adrenal cortex (Zona glomerulosa)
ALDOSTERONE
59
Q

Increased Aldosterone causes what?

A

Stimulation to increase renal tubule cell K+ secretion

Na+ reabsorption at distal tubule

60
Q

H+ ions are secreted by what?

A

Actively secreted into the lumen by TUBULE CELLS

61
Q

Increased K+ causes what?

A

Increased plasma [K+]
Increased aldosterone
Increased K+ secretion
Decreased [K+]

RENAL PHYSIOLOGY (10 decks)

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