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Renal System > Glomerular Filtration > Flashcards

Glomerular Filtration Flashcards

1
Q

What is the renal function?

A

Process the plasma portion of the blood by removing substances from it and, in a few cases, by adding substances to it

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2
Q

What are the functions of the kidneys?

A

Regulation of water, inorganic ion balance, and acid-base balance
Removal of metabolic waste products from the blood and their excretion in the urine
Removal of foreign chemicals from the blood and their excretion in the urine
Gluconeogenesis

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3
Q

Which hormones and enzymes are produced by the kidneys?

A

Erythropoietin
Renin
Conversion of 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D

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4
Q

What is the purpose of erythropoietin?

A

Controls erythrocyte production

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5
Q

What is the function of renin?

A

Controls formation of angiotensin, which influences blood pressure and sodium balance

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6
Q

What is the function of 1,25-dihydroxyvitamin D?

A

Influences calcium balance

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7
Q

What are the three basic renal processes?

A

Glomerular filtration, tubular reabsorption and tubular secretion
Synthesis and catbolism of certain substances

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8
Q

What does the excretion of a substance equal to?

A

The amount filtered plus the amount secreted minus the amount reabsorbed

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9
Q

What % of the plasma enters the glomerulus and is filtered?

A

20%

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10
Q

What happebs ti the remaining 80% of the plasma?

A

Enters the glomerulus but is NOT filtered and leaves through the efferent arterioles and into the peritubular capillaries

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11
Q

What is secretion?

A

The movement of substances from peritubular to tubular or epithelial cells into the lumen of the tubule

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12
Q

What is the pathway of the plasma once entering the renal artery?

A

Renal artery, afferent arteriole, glomerulus, efferent arteriole, peritubular capillaries

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13
Q

What is glomerular filtration?

A

Nondiscriminant filtration of protein-free plasms from the glomerulus into Bowman’s capsule

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14
Q

What is excretion?

A

Removal of substances in the urine

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15
Q

What is reabsorption?

A

Selective movement of filtered substances from the tubular lumen into the peritubular capillaries

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16
Q

Where does glomerular filtration occur?

A

From the glomerular capillary into the Bowman’s capsule

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17
Q

Where does tubular secretion occur?

A

From the peritubular capillary to Bowman’s capsule

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18
Q

Where does tubular reabsorption occur?

A

From the Bowman’s space into the vein

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19
Q

What is the equation for the amount excreted?

A

Amount filtered + amount secreted - amount reabsorbed

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20
Q

Do the renal processes apply to all substances?

A

No, for instance, 100% of glucose and amino acids are reabsorbed because they are needed in the body

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21
Q

What happens to the toxins in the kidneys?

A

Secreted and not reabsorbed, excreted from the body

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22
Q

What are the three layers that make up the glomerular membrane?

A

The glomerular capillary wall
The basement membrane (acellular membrane)
The inner layer of Bowman’s capsule

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23
Q

What is the function of the three layers ?

A

A fine molecular sieve that retains the blood cells and plasma proteins but permits H2O and solutes of small molecular dimension to filter through

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24
Q

What is the space between the podocytes?

A

Filtration slit

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25
Q

What does the glomerular filtarte contain?

A

All plasma substances other than protein (and substances bound to proteins) in virtually the same concentration as in plasma

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26
Q

What is the force that drives the glomerular filtration?

A

Hydrostatic pressue in glomerular capillaries

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27
Q

What are the forces that oppose the glomerular filtration?

A

Hydrostatic pressure in Bowman’s space and the osmotic force due to the proteins in the glomerular capillary plasma

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28
Q

What is the net difference favoring filtration?

A

Net glomerular filtration pressure

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29
Q

Why the osmotic pressure in Bowman’s capsule not considered?

A

It is 0, thus it does not count. The reason for that is the fact that osmotic pressure is determined by proteins and proteins are NOT filtered

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30
Q

What is the glomerular filtration rate? (GFR)

A

The volume of fluid filtered from the glomeruli into Bowman’s space per unit time

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31
Q

Why are the glomeruli of the kidney much more efficient than the other capillary beds in the body?

A

Filtration membrane is a large surface area and very permeable to water and solutes

Glomerular pressure is higher so they produce 180L/day vs 3 to 4L/day formed by other capillaries

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32
Q

What are the forces that favour filtration?

A

Glomerular capillary blood pressure
Net foltration pressure

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32
Q

What is the pressure inside the kidney glomeruli?

A

About 55mmHg

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33
Q

What are the forces that oppose filtration?

A

Plasma colloid osmotic pressure
Bowmanm’s hydrostatic pressure

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34
Q

Which forces normally do not vary much and also cannot be regulated?

A

Plasma colloid osmotic pressure and Bowman’s capsule hydrostatic pressire

35
Q

Which pressure can be controlled to adjust the GFR to suit the body’s needs?

A

Glomerular capillary hydrostatic pressure, more blood, higher pressure, imncreased GFR

36
Q

What are the two major control mechanisms that regulate GFR?

A

Autoregulation
Extrinsic sympathetic control

37
Q

What is the aim of the autoregulation mechanism?

A

Aims to prevent spontaneous changes in GFR

38
Q

WHat is the purpsoe of extrinsic sympathetic control?

A

AIms to have long-term regulation of arterial blood pressure

39
Q

What are the two mechanisms that contribute to autoregulation of the GFR?

A

Myogenic
Tubuloglomerular

40
Q

What is the myogenic mechanism like?

A

Respondes to changes in pressure within the nephron’s vascular component, myogenic will contract or relax depending on the blood flow

41
Q

What is the tubuloglomerular mechanism like?

A

Senses changes in salt levels in the fluid flowing through the nephrons tubular component, will send signals through adenosine to contract or relax afferent arterioles

42
Q

What is the MAP range in which autoregulation of GFR occurs in?

A

80 to 180mmHg

43
Q

Why is at
autoregulation important?

A

Unintentional shifts in GFR could lead to dangerous imbalances of fluid, electrolytes, and wastes

44
Q

What do dramatic changes in MAP cause?

A

Glomerular capillary pressure and GFR to decrease if less than 80mmHg or increase if greater than 180mmHg

45
Q

What is the tubuloglomerular feedback mechanism like?

A

Afferent or efferent will contract or dilate based on the volumes of salt

46
Q

Which mechanism can override the autoregulation mechanism?

A

Strong sympathetic nervous system activation

For example: severe hemorrhage

47
Q

What will happen to MAP in the case of a severe hemorrhage?

A

It will be reduced, activated the sympathetic nervous system via the baroreceptor reflex –> renal sympathetic nerves constrict the afferent arteriole, decreasing GFR

48
Q

Does the parasympathetic nervous system exert any influence on the kidneys?

A

NO

49
Q

What happens to afferent/efferent to decrease the GFR?

A

Constriction of afferent or dilation of efferent, decrease in blood flow, decrease in hydrostatic pressure –> decrease in GFR

50
Q

What happens to afferent/efferent to increase the GFR?

A

Dilation of afferent and constriction of efferent, increase in blood flow, increase in hydrostatic pressure –> increase in GFR

51
Q

What is the effect of simultaneous constriction and dilation of both sets of arterioles?

A

Levels of GFR remain unchanged because of opposing effects

52
Q

What other factor can influence the GFR?

A

Changes in the filtration coefficient (permeability)

53
Q

What kind of input do the mesangial cells that surround the glomerular capillaries receive?

A

Neural and humoral

54
Q

What happens if there is contraction of the mesangial cells by sympathetic stimulation?

A

Decreases the surface area of the capillaries, which causes decrease in GFR

55
Q

What do podocytes also possess?

A

Actinlike filaments

56
Q

What is the effect of contraction/relaxation of the actinlike filaments?

A

Contraction –> decrease
Relaxation –> inrease the number of filtration slits open in the inner membrane of the Bowman’s capsule by changing shapes and proximities of the secondary foot processes

57
Q

What is the relation between the number of slits and permeability?

A

More slits –> greater permeability

58
Q

At the average net filtration pressure and permeability, what % of plasma is filtered?

A

20% of plasma that enters the kidney is converted into glomerular filtrate

59
Q

What is the average GFR and total renal plasma flow?

A

125mL/min –> GFR
625mL/min –> renal plasma flow

60
Q

What is the percentage of plasma in the blood?

A

55% of blood is plasma

61
Q

So, what is the total blood flow through the kidneys?

A

1140mL/min

62
Q

What percentage of the cardiac output is supplied to the kidneys?

A

22%

63
Q

What is the total cardiac output volume, if 1140 mL/min is 22%?

A

5000mL/min

64
Q

What is the purpose of the majority of blood supply to the kidneys?

A

It does not supply the renal tissue, but it is adjusted and purified by the kidneys, kidneys perform regulatory and excretory function on huge volumes of plasma

65
Q

What is the reason kidneys perform regulatory and excretory functions on plasma?

A

To maintain internal fluid environment stability

66
Q

How do you calculate the total amount of any protein or non-protein-bound substance filtered into Bowman’s capsule?

A

By multiplying the GFR by the plasma concentration of the substance –> known as filtered load

67
Q

What is the purpose of comparing filtered load to the amount of substance excreted?

A

Detect whether the substance undergoes net tubular reabsorption or net secretion

68
Q

What is the indication that tubular reabsorption of a substance has occurred?

A

The filtered load is greater than the amount excreted

69
Q

What does filtered load < amount excreted mean?

A

Net secretion of a substance has taken place

70
Q

What is renal clearance?

A

The volume of plasma from which that substance is completely removed by the kidneys per unit time

71
Q

Why is renal clearance important?

A

A useful way of qualifying renal functions in terms of clearance

72
Q

How do you calculate the renal clearance?

A

Divide the mass of the substance excreted in the urine per unit of time by the plasma concentration of the substance itself

73
Q

What is the formula of renal clearance?

A

C = UV/P
C –> clearance rate of substance
U –> urine concentration of substance
V –> urine volume per unit time
P –> plasma concentration of substance

74
Q

What is the unit for clearance rate of substance?

A

mL/min

75
Q

What is the unit for urine concentration of substance?

A

Quantity/mL urine

76
Q

What is the unit for urine volume per unit time?

A

mL/min

77
Q

What is the unit for plasma concentration of the substance?

A

Quantity/mL plasma

78
Q

How can GFR be MEASURED?

A

Means of inulin clearance

79
Q

Why can GFR be measured by inulin clearance?

A

Inulin is freely filtred and neither absorbed nor secreted

80
Q

How can GFR be ESTIMATED?

A

Creatinine clearance

81
Q

Why can GFR be estimated by creatinine clearance?

A

Creatinine is freely filtered but also secreted in small amounts

82
Q

What is creatinine?

A

Metabolite of muscle creatine

83
Q

What is the effect of slightly secreted amounts of creatinine on GFR?

A

Slightly overestimated GFR

84
Q

When is the creatinine clearance test used?

A

In clinical practice, there is a specific formula that accounts for age, weight and gender

85
Q
A

Renal System (13 decks)

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