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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
What does the glomerular filtarte contain?
All plasma substances other than protein (and substances bound to proteins) in virtually the same concentration as in plasma
26
What is the force that drives the glomerular filtration?
Hydrostatic pressue in glomerular capillaries
27
What are the forces that oppose the glomerular filtration?
Hydrostatic pressure in Bowman's space and the osmotic force due to the proteins in the glomerular capillary plasma
28
What is the net difference favoring filtration?
Net glomerular filtration pressure
29
Why the osmotic pressure in Bowman's capsule not considered?
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
30
What is the glomerular filtration rate? (GFR)
The volume of fluid filtered from the glomeruli into Bowman's space per unit time
31
Why are the glomeruli of the kidney much more efficient than the other capillary beds in the body?
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
32
What are the forces that favour filtration?
Glomerular capillary blood pressure Net foltration pressure
32
What is the pressure inside the kidney glomeruli?
About 55mmHg
33
What are the forces that oppose filtration?
Plasma colloid osmotic pressure Bowmanm's hydrostatic pressure
34
Which forces normally do not vary much and also cannot be regulated?
Plasma colloid osmotic pressure and Bowman's capsule hydrostatic pressire
35
Which pressure can be controlled to adjust the GFR to suit the body's needs?
Glomerular capillary hydrostatic pressure, more blood, higher pressure, imncreased GFR
36
What are the two major control mechanisms that regulate GFR?
Autoregulation Extrinsic sympathetic control
37
What is the aim of the autoregulation mechanism?
Aims to prevent spontaneous changes in GFR
38
WHat is the purpsoe of extrinsic sympathetic control?
AIms to have long-term regulation of arterial blood pressure
39
What are the two mechanisms that contribute to autoregulation of the GFR?
Myogenic Tubuloglomerular
40
What is the myogenic mechanism like?
Respondes to changes in pressure within the nephron's vascular component, myogenic will contract or relax depending on the blood flow
41
What is the tubuloglomerular mechanism like?
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
What is the MAP range in which autoregulation of GFR occurs in?
80 to 180mmHg
43
Why is at autoregulation important?
Unintentional shifts in GFR could lead to dangerous imbalances of fluid, electrolytes, and wastes
44
What do dramatic changes in MAP cause?
Glomerular capillary pressure and GFR to decrease if less than 80mmHg or increase if greater than 180mmHg
45
What is the tubuloglomerular feedback mechanism like?
Afferent or efferent will contract or dilate based on the volumes of salt
46
Which mechanism can override the autoregulation mechanism?
Strong sympathetic nervous system activation For example: severe hemorrhage
47
What will happen to MAP in the case of a severe hemorrhage?
It will be reduced, activated the sympathetic nervous system via the baroreceptor reflex --> renal sympathetic nerves constrict the afferent arteriole, decreasing GFR
48
Does the parasympathetic nervous system exert any influence on the kidneys?
NO
49
What happens to afferent/efferent to decrease the GFR?
Constriction of afferent or dilation of efferent, decrease in blood flow, decrease in hydrostatic pressure --> decrease in GFR
50
What happens to afferent/efferent to increase the GFR?
Dilation of afferent and constriction of efferent, increase in blood flow, increase in hydrostatic pressure --> increase in GFR
51
What is the effect of simultaneous constriction and dilation of both sets of arterioles?
Levels of GFR remain unchanged because of opposing effects
52
What other factor can influence the GFR?
Changes in the filtration coefficient (permeability)
53
What kind of input do the mesangial cells that surround the glomerular capillaries receive?
Neural and humoral
54
What happens if there is contraction of the mesangial cells by sympathetic stimulation?
Decreases the surface area of the capillaries, which causes decrease in GFR
55
What do podocytes also possess?
Actinlike filaments
56
What is the effect of contraction/relaxation of the actinlike filaments?
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
What is the relation between the number of slits and permeability?
More slits --> greater permeability
58
At the average net filtration pressure and permeability, what % of plasma is filtered?
20% of plasma that enters the kidney is converted into glomerular filtrate
59
What is the average GFR and total renal plasma flow?
125mL/min --> GFR 625mL/min --> renal plasma flow
60
What is the percentage of plasma in the blood?
55% of blood is plasma
61
So, what is the total blood flow through the kidneys?
1140mL/min
62
What percentage of the cardiac output is supplied to the kidneys?
22%
63
What is the total cardiac output volume, if 1140 mL/min is 22%?
5000mL/min
64
What is the purpose of the majority of blood supply to the kidneys?
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
What is the reason kidneys perform regulatory and excretory functions on plasma?
To maintain internal fluid environment stability
66
How do you calculate the total amount of any protein or non-protein-bound substance filtered into Bowman's capsule?
By multiplying the GFR by the plasma concentration of the substance --> known as filtered load
67
What is the purpose of comparing filtered load to the amount of substance excreted?
Detect whether the substance undergoes net tubular reabsorption or net secretion
68
What is the indication that tubular reabsorption of a substance has occurred?
The filtered load is greater than the amount excreted
69
What does filtered load < amount excreted mean?
Net secretion of a substance has taken place
70
What is renal clearance?
The volume of plasma from which that substance is completely removed by the kidneys per unit time
71
Why is renal clearance important?
A useful way of qualifying renal functions in terms of clearance
72
How do you calculate the renal clearance?
Divide the mass of the substance excreted in the urine per unit of time by the plasma concentration of the substance itself
73
What is the formula of renal clearance?
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
What is the unit for clearance rate of substance?
mL/min
75
What is the unit for urine concentration of substance?
Quantity/mL urine
76
What is the unit for urine volume per unit time?
mL/min
77
What is the unit for plasma concentration of the substance?
Quantity/mL plasma
78
How can GFR be MEASURED?
Means of inulin clearance
79
Why can GFR be measured by inulin clearance?
Inulin is freely filtred and neither absorbed nor secreted
80
How can GFR be ESTIMATED?
Creatinine clearance
81
Why can GFR be estimated by creatinine clearance?
Creatinine is freely filtered but also secreted in small amounts
82
What is creatinine?
Metabolite of muscle creatine
83
What is the effect of slightly secreted amounts of creatinine on GFR?
Slightly overestimated GFR
84
When is the creatinine clearance test used?
In clinical practice, there is a specific formula that accounts for age, weight and gender
85

Renal System (24 decks)

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