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Renal Physiology > Glomerular Filtration, Reabsorption, Secretion and Loop of Henle > Flashcards

Glomerular Filtration, Reabsorption, Secretion and Loop of Henle Flashcards

1
Q

How much blood flow does the kidneys receive? And how much of the CO?

A

1200mls/min

20-25% total CO

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2
Q

Normal GFR value

A

125mls/min

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3
Q

Factors affecting glomerular filtration

A

Balance between hydrostatic forces favouring filtration and

Oncotic pressure forces favouring reabsorption (starlings forces)

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4
Q

What determines the filterability of solutes across the glomerular filtration barrier?

A

Molecular size
Electrical charge
Shape

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5
Q

Layers of the glomerular barrier

A
  1. Fenerstrations/pores of glomerular endothelial cell; prevents filtration of blood cells but allows all components of blood plasma to pass through
  2. Basal lamina of glomerulus; prevents filtration of larger proteins
  3. Sit membrane between pedicles; prevents filtration of medium sized proteins
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6
Q

Why is the glomerular capillary pressure higher than in most capillaries of the body?

A

Because the afferent arteriole is short and wide and therefore offers little resistance to flow

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7
Q

How does the efferent arteriole of the glomerular capillaries have a high post capillary resistance?

A

Unique arrangement - Long and narrow

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8
Q

What is the golden rule of the circulation?

A

If you have high resistance, hydrostatic pressure upstream is increased, while the pressure downstream is decreased

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9
Q

Which from the afferent and efferent arterioles contribute to the very high glomerular capillary pressure?

A

Both

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10
Q

At the glomerular capillaries, hydrostatic pressure vs oncotic pressure

A

Hydrostatic - favouring filtration always exceeds the oncotic pressure

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11
Q

What is the only thing that occurs at the glomerular capillaries?

A

Filtration

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12
Q

What is responsible for reabsorption?

A

Peritubular capillaries

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13
Q

How much is filtered through the glomerulus into the renal tubule? How much of this is excreted as urine?

A

180 L/day

1 - 2L is excreted as urine

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14
Q

Why is only 1 - 2L of 180L / day excreted as urine?

A

An enormous amount of fluid must be reabsorbed back into the peritubular capillaries

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15
Q

What arteriole has important effects on starlings forces in the peritubular capillaries?

A

Efferent arteriole

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16
Q

Hydrostatic pressure in efferent arteriole

A

Very low

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17
Q

IIp and concentration of plasma proteins in the efferent afteriole and peritubular capillaries

A

Increased

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18
Q

The balance of pressures in the peritubular capillaries are entirely favour of what?

A

Reabsorption

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19
Q

How much of H20 filtered at the glomerulus is reabsorbed within the tubule?

A

99%

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20
Q

How much of glucose filtered at glomerulus is reabsorbed within the tubule?

A

100%

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21
Q

How much of Na+ filtered at the glomerulus is reabsorbed within the tubule?

A

99.5%

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22
Q

How much of urea filtered at the glomerulus is reabsorbed within the tubule?

A

50%

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23
Q

Where in the tubule are substances mostly reabsorbed?

A

Proximal convoluted tubule

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24
Q

Which occurs at the glomerular capillaries?

A

Filtration

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25
Q

Mechanisms of reabsorption

A
  1. Carrier mediated transport systems
  2. Reabsorption of Na+ ions
  3. Tubular secretion
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26
Q

What substances are reabsorbed by carrier mediated transport systems?

A 
Glucose
Amino acids
Organic acids
Sulphate ions
Phosphate ions
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27
Q

How do carrier mediated transport systems work to reabsorb substances?

A

Carriers have a maximum transport capacity Tm which is due to saturation of carriers
If Tm is exceeded, then the excess substrate enters the urine

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28
Q

What is the renal threshold?

A

The plasma threshold at which saturation occurs

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29
Q

Filtrationn of glucose

A

Freely filtered

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30
Q

What is the renal plasma glucose threshold?

A

10mmoles/l

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31
Q

What is responsible for glucose regulation?

A

Insulin

Counter regulatory hormones

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32
Q

Normal plasma glucose concentration

A

5 mmoles/l

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33
Q

What is the name for the presence of glucose in the urine?

A

Glycosuria

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34
Q

What is the most abundant ion in the ECF?

A

Na+

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35
Q

What % of Na+ ion reabsorption occurs in the proximal tubule?

A

65 - 75%

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36
Q

How are Na+ ions reabsorbed?

A

Active transport

- Na+ pumps

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37
Q

Active transport of Na+ ions

A

Active Na+ pumps are located on the basolateral surfaces where there is a high density of mitochondria
This decreases Na+ in the epithelial cells, increasing the gradient (a secondary gradient) for Na+ ions to move into the cells passively across the luminel membrane.
So links the passive transport on the tubule lumen to the active transport on the intralumineal membrane

38
Q

Are Na+ ions permeable at cell membranes?

39
Q

Why does the brush border of the proximal tubule cells have a higher permeability to Na+ ions than most other membranes in the body?

A

Enourmous surface area offered by the microvilli and the large number of Na+ ions channels, which facilitate this passive diffusion of Na+

40
Q

What is the reabsorption of Na+ ions key to?

A

The reabsorption of the other components of the fitrate

41
Q

How do negative ions diffuse across the proximal tubule membrane?

A

Passively across the proximal tubular membrane down the electrical gradient established and maintained by the active transport of Na+

42
Q

What does the active transport of Na+ out of the tubule followed by Cl- create?

A

An osmotic force, drawing H20 out of the tubules

43
Q

What does H20 removed by osmosis from the tubule fluid result in?

A

It concentrates all the substances left in the tubule (e.g. glucose, urea) creating outgoing concentration gradients

44
Q

What does the rate of reabsorption of these non actively reabsorbed solutes depend on?

A

Amount of H20 removed (which will determine the extent of the concentration gradient for other substances). More concentrated = easier to transport substances
The permeability of the membrane to any particular solute

45
Q

Permeability of the tubule membrane to urea

A

Moderately permeable to urea so that only about 50% is reabsorbed, the remainder stays in the tubule

46
Q

Permeability of the tublar membrane to insulin and mannitol

A

Impermeable

47
Q

What establishes the gradients down which other ions, H20 and solutes pass passively?

A

Active transport of Na+

48
Q

Anything which decreases active transport of Na e.g. decreased blood flow results in what?

A

Disruption of renal function

49
Q

Importance of Na+ transport

A
  1. Active transport of Na+ establishes the gradient down which other ions, H20 and solutes pass passively
  2. Carrier mediated transport systems - substances such as glucose, amino acids etc share the same carrier molecule as Na+ (symport)
  3. Na+ reabsorption is linked to HCO3- ion reabsorption
50
Q

Effects of [Na] concentration in the tubule on glucose transport

A

High [Na+] = facilitates glucose transport

Low [Na+] = inhibits glucose transport

51
Q

What drives the co transport of sodium and glucose?

A

ATP hydrolysis

52
Q

How does tubular secretion work?

A

Secretory mechanisms transport substances FROM the peritubular capillaries INTO the tubule lumen and therefore provides a second route into the tubule

53
Q

What molecules are tubular secretion important for?

A

Those that are protein bound

e.g. drugs

54
Q

Where are all of the substances in tubular secretion secreted?

A

In the proximal tubule

55
Q

What are the 3 basic renal processes?

A

Filtration
Reabsorption
Secretion

56
Q

Factor affecting GFR

A

Pressure in the glomerular capillaries

57
Q

What is the pressure in the glomerular capillaries dependent on?

A

The afferent and efferent arteriolar diameter and therefore the balance of resistance between them

58
Q

Extrinsic control of pressure in the glomerular capillaries

A

Sympathetic VC nerves
- afferent and efferent constriction
- Greater sensitivity of afferent arteriole
Circulating catecholamines
- constrict primary afferent
Angiotensin II
- constriction of efferent at [low], both afferent and efferent at [high]

59
Q

What is autoregulation independent of?

A

Nerves

Hormones

60
Q

Autoregulatory range in men

A

60 - 130 mmHg

61
Q

In what situations would autoregulation be overriden and why?

A

Blood volume / BP face serious compromise e.g. in haemorrhage.
Liberates blood for more immediately important organs

62
Q

What is the renal threshold?

A

The plasma threshold at which saturation occurs

63
Q

What is the major cation in the cells of the body?

64
Q

Normal ECF [K+]

A

approx. 4 mmoles/l

65
Q

Hyperkalaemia value

A

5.5 mmoles/l

66
Q

Hypokalaemia value

A

< 3.5 mmoles/l

67
Q

What does hyperkalaemia result in?

A

Decrease resting membrane potential of excitable cells and eventually ventricular fibrillation and death

68
Q

What does hypokalaemia result in?

A

Increases resting membrane potential i.e. hyperpolarises muscle, cardiac cells -> cardiac arrythmias and eventually death

69
Q

Where is K+ reabsorbed?

A

Primarily at the proximal tubule

70
Q

What are changes in K+ excretion due to?

A

Its secretion in distal parts of the tubule

71
Q

K+ secretion is regulated by what?

A

Adrenal cortical hormone aldosterone

72
Q

An increase in [K+] in ECF bathing the aldosterone secreting cells does what?

A

Stimulates aldosterone release which circulates to the kidneys to stimulate increase in the renal tubule cell K+ secretion

73
Q

What does aldosterone also do?

A

Stimulates Na+ reabsorption at the distal tubule but by a different reflex pathway

74
Q

Where is the major site of reabsorption?

A

Proximal tubule

75
Q

Parts of the Loop of Henle

A

Ascending Limb

Descending Limb

76
Q

What is the maximum concentration of urine that can be produced by the human kidney?

A

1200 - 1400 mOsmoles/l

77
Q

What is the minimum obligatory H20 loss needed (even if we do not drink) and why is this?

A

500mls
Due to urea, sulphate, phosphate, other waste products and non waste ions (Na+ and K+) which must be excreted each day to approx. 600mOsmoles

78
Q

Minimum urine concentration a man can produce

A

30 - 50 mOsmoles/l

79
Q

What nephrons are the loops of Henle in?

A

Juxtamedullary nephrons

80
Q

How are kidneys able to produce urine of varying concentration?

A

Because of the loops of Henle acting as counter-current multipliers

81
Q

How does the counter current of Loop of Henle work?

A

Fluid flows down the descending limb and UP the ascending limb, in osmotic correlation to each other
Fluid enters at the proximal and leaves at the distal tubule - concentrated fluid in the descending limb rounds the bend and delivers a high conc to the ascending limb
- active NaCl removal
- further concentrates the interstitium
So concentrates fluid on the way down and promptly re-dilutes it on the way back up, NOT by adding H20 but by removing NaCl

82
Q

What is a counter current?

A

Something that flows passed itself

83
Q

What are the critical characteristics of the loops which makes them counter current multipliers?

A
  1. The ascending loop actively co transports Na+ and Cl- ions out of the tubule lumen and into the interstitium
  2. The descending limb is freely permeable to H20 but relatively impermeable to NaCl
84
Q

What is the ascending limb impermeable to?

85
Q

What is the overwhelming significance of the counter current multiplier?

A

It creates an increasingly concentrated gradient in the interstitium
Also deliverys hypotonic fluid to the distal tubule

86
Q

What are the vasa recta?

A

The specialised arrangement of the peritubular capillaries of the juxtamedullary nephrons acting as counter current exchangers

87
Q

Permeability of vasa recta

A

Permeable to H20 and solutes and therefore equilibrium with the medullary interstitial gradient

88
Q

Functions of the vasa recta

A

Providing O2 for medulla
In providing O2 must not disturb gradient
Removes volume from the interstitium, up to the 36l/day

89
Q

Where is the site of water regulation?

A

The collecting duct

90
Q

What is the collecting duct permeability under control of?

91
Q

What does ADH stand for?

A

Anti diuretic hormone

92
Q

Another name for ADH

A

Vasopressin

Renal Physiology (7 decks)

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