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Y2S2-RENAL/REPRO-PHYSIOLOGY > Glomerular function > Flashcards

Glomerular function Flashcards

1
Q

What are the different control mechanisms of the glomerular filtration and the renal blood flow?

A

1) Sympathetic nervous system

2) Catecholamines (norepinephrine)

3) Angiotensin-2

  • Most of the factors that affect GFR will affect RBF

4) Prostaglandins

5) Endothelial-derived nitric oxide

6) Endothelin

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2
Q

What is the sympathic nervous effect on the GFR?

A
  • In a strong sympathetic nervous system activation, there will be vasoconstriction of the afferent and efferent arterioles, which will collectively decrease the GFR
  • This occurs in cases of severe hemorrhage, for example
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2
Q

How do the catecholamines (norepinephrine) affect the GFR and the RBF?

A
  • The norepinephrine and epinephrine are released from the adrenal medulla; they will constrict the afferent and efferent arterioles, decreasing the GFR and RBF
  • Levels of these hormones are parallel to the activity of the sympathetic nervous system, pronouncing the effect of the sympathetic nervous system in certain conditions
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3
Q

What is the effect of angiotensin-2 on the GFR and the RBF?

A
  • It prevents the decrease of the GFR
  • It vasoconstricts the efferent arterioles only, they are released in response to the release of the vasodilators (like NO and PGs)
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4
Q

How does the renal system respond to severe hemorrhage?

A

It decreases the GFR and the RBF by activating the sympathetic nervous system and, thus, vasoconstricting the afferent and efferent arterioles of the kidney, releasing the catecholamines

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5
Q

What is the effect of PG on the GFR?

A
  • It vasodilates the renal vessels, increasing the GFR
  • They are not important in normal conditions, however, they are important during stressful conditions (surgery, volume depletion, etc)
  • In case the person was on NSAIDs, then the synthesis of the PGs might decrease, leading to a reduction in the GFR
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6
Q

What is the effect of the endothelial-derived nitric oxide on the GFR?

A
  • They vasodilate the renal vessels and thus increase the GFR; this vasodilation requires a basal level of NO for the vasodilation of the kidneys
  • In HTN patients and patients with atherosclerosis, there is a lower production of NO, leading to an increased vasoconstriction of the renal vessels and thus increased BP
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7
Q

What is the effect of endothelin on the GFR?

A
  • They are produced by the damaged vascular endothelial cells
  • The levels of plasma endothelin increase in certain diseases that are associated with vascular injury (like chronic uremia, renal failure, etc), which will collectively lead to vasoconstriction and decreased GFR
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8
Q

What produces endothelin?

A

The damaged vascular endothelial cells

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9
Q

What is the effect of the sympathetic nervous system on the resistance of the afferent arterioles?

A

They vasoconstrict it, leading to increased resistance

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10
Q

What is the effect of the sympathetic nervous system on the resistance of the efferent arterioles?

A

They increase the resistance leading to vasoconstriction

  • Therefore collectively the sympathetic nervous system decreases the GFR and the RBF
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11
Q

What is the effect of the catecholamines on the resistance of the afferent arterioles?

A

They increase the resistance of the afferent arterioles (leading to vasoconstriction)

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12
Q

What is the effect of catecholamines on the resistance of the efferent arterioles?

A

The increase it, and thus they lead to vasoconstriction

  • Therefore collectively the catecholamines leads to the vasoconstriction of the afferent and efferent arterioles which will decrease the GFR
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13
Q

What is the effect of angiotensin-2 on the resistance of the efferent arterioles?

A
  • They do not have an effect on the afferent arterioles
  • They increase the resistance in the efferent arterioles (thus leading to vasoconstriction)
  • However, this will keep the GFR at the same rate but the RBF will decrease
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14
Q

What is the effect of prostaglandins on the afferent arterioles?

A

They decrease their resistance, which will lead to vasodilation

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15
Q

What is the effect of PG on the resistance of the efferent arterioles?

A

They decrease it, inducing vasodilation

  • This will collectively lead to an increase in the GFR and RBF
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16
Q

What is the effect of the endothelial-derived nitric oxide on the resistance of the afferent arterioles?

A
  • They decrease the resistance of the afferent arterioles, leading to vasodilation
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17
Q

What is the effect of the endothelial-derived nitric oxide on the efferent arterioles?

A

They will decrease it resistance, leading to vasodilation

  • This will collectively increase the GFR and RBF
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18
Q

What is the effect of endothelin on the resistance of the afferent arterioles?

A

They increase the resistance of the afferent arterioles, inducing vasoconstriction

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19
Q

What is the effect of endothelin on the resistance of the efferent arterioles?

A

They increase it, inducing vasoconstriction

  • This will collectively lead to the decreased GFR and RBF
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20
Q

What are the different mechanisms that regulate the GFR?

A
  • Despite marked changes in BP, feedback mechanisms inside the kidney keep GFR at a nearly constant level called autoregulation

1) Myogenic mechanism

2) Macula densa feedback (tubuloglomerular feedback)

3) Angiotensin-2

  • The significance of autoregulation is to maintain a relatively constant GFR for the precise control of renal excretion of water and solute
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21
Q

Describe the myogenic mechanism that regulates the GFR

A
  • The resistance of stretching by the blood vessels when the BP increases
  • The vessels respond to an increase in the wall tension by contracting the vascular smooth muscle, this contraction prevents the excessive stretch of the vessels and helps in preventing the increase in RBF and GFR

1) Increased arterial pressure

2) Increased stretch of the BV

3) Increased permeability of the cell to the calcium

4) Increased intracellular calcium

5) Increased vascular resistance (myogenic mechanism)

6) Decreased blood flow

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22
Q

So, briefly, what is the effect of the myogenic mechanism?

A

It decreases the RBF/GFR by increasing the vascular resistance when the arterial pressure increases (tension on the BV increases)

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23
Q

Describe the macula densa feedback mechanism and its role in regulating the GFR

A
  • It has two components that act together to control the GFR:
  1. Afferent arteriolar feedback mechanism
  2. Efferent arteriolar feedback mechanism

The mechanism is:

1) Decreased arterial pressure

2) Decreased glomerular hydrostatic pressure

3) Decreased GFR

4) Decreased sensing of NaCl by the macula densa and increased reabsorption of the NACl by the proximal tubule

5a) Increased renin

6) Increased angiotensin-2

7) Increased efferent arteriolar resistance

5b) Decreased afferent arteriolar resistance

  • This will collectively lead to an increase in GFR and blood volume (due to NaCl reabsorption)
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24
Do the myogenic mechanisms work in response to increased or decreased arterial pressure?
Increased
25
Does the macula densa mechanism work in response to increased or decreased arterial pressure?
Decreased
26
How does the Angiotensin-2 regulate the GFR?
- Released in response to the decreased GFR and thus the sensing of NaCl by the macula densa, which will increase the release of renin and thus angiotensin-2. then ang-2 will: 1) Increase the blood pressure 2) Increase the efferent arteriolar resistance
27
Angiotensin 2 responds to increased or decreased arterial pressure.
Decreased
28
Mnemonic for the role of the GFR regulators
1) Prostaglandins Dilates Afferent (PDA) 2) Angiotensin-2 Constricts Efferent (ACE)
29
What are the vasoconstrictors of the renal blood flow?
1) Sympathetic nerves (catecholamines) 2) Angiotensin-2 3) Endothelin
30
What are the vasodilators of the renal blood flow?
1) PGE2 2) PGI2 3) NO 4) Bradykinin 5) Dopamine 6) ANP
31
Describe the renal blood flow
The high amount of blood is sent to the kidneys to have a huge amount of GFR, a huge amount of filtration at a very high rate to get the waste products filtered out into the capsular fluid, they cannot be reabsorbed. It’s not easy for the waste products to be secreted out. 90% of the 20-25% of CO goes to the cortex; the other 10% goes to the medulla (you need to know). in the medulla, the blood is very slow
32
What will happen to the glomerular cap pressure, peritubular cap pressure, and the nephron plasma flow when we vasoconstrict the efferent arterioles?
1) Increased glomerular cap pressure 2) Decreased peritubular cap pressure 3) Decreased plasma flow to the nephron
33
What will happen to the glomerular cap pressure, peritubular cap pressure, and the nephron plasma flow when we vasodilate the efferent arterioles?
1) Decreased glomerular cap pressure 2) Increased peritubular cap pressure 3) Increased plasma flow to the nephron
34
What will happen to the glomerular cap pressure, peritubular cap pressure, and the nephron plasma flow when we vasoconstrict the afferent arterioles?
1) Decreased glomerular cap pressure 2) Decreased peritubular cap pressure 3) Decreased plasma flow to the nephron
35
What will happen to the glomerular cap pressure, peritubular cap pressure, and the nephron plasma flow when we vasodilate the afferent arterioles?
1) Increased glomerular cap pressure 2) Increased peritubular cap pressure 3) Increased plasma flow to the nephron
36
What is the main regulator of the renal blood flow?
The mean arterial pressure - MAP can vary from 80 to 200 mmHg but renal blood flow is constant because of the change in arteriolar diameter - Although regulated, the higher the mean arterial pressure the more the urine output
37
What are the other regulators of the RBF?
1) Myogenic hypothesis 2) Tubuloglomerular feed-back
38
What controls the urine output?
1) Pressure natriuresis 2) Pressure diuresis
39
What is meant by pressure natriuresis?
Pressure natriuresis is the process by which an increase in arterial blood pressure leads to increased sodium excretion by the kidneys. Mechanism: - Increased renal perfusion pressure → Enhances glomerular filtration rate (GFR) - Reduced sodium reabsorption → Less sodium is reabsorbed in the renal tubules, increasing sodium excretion - Water follows sodium → This helps regulate blood volume and long-term blood pressure
40
What is the importance of pressure natriuresis?
1) It plays a key role in blood pressure regulation 2) It helps counteract hypertension by promoting sodium loss 3) It works alongside the renin-angiotensin-aldosterone system (RAAS) and other renal mechanisms
41
What is meant by pressure diuresis?
Pressure diuresis is the process by which an increase in arterial blood pressure leads to increased urine output due to reduced water reabsorption by the kidneys. Mechanism: - Increased renal perfusion pressure → Increases glomerular filtration rate (GFR) - Reduced tubular reabsorption of water → More water is excreted in urine - Blood volume reduction → Helps lower blood pressure over time
42
What is the importance of pressure diuresis?
1. It works alongside pressure natriuresis to regulate blood pressure 2. It plays a role in long-term blood pressure control by adjusting fluid balance 3. Helps counteract hypertension by promoting water loss
43
What is meant by renal clearance
- Clearance is the volume of plasma from which a particular substance was completely cleared by the kidneys per unit time - Clearance (Cs ml/min) = Us (urine concentration mmol/ml) * V (Urine flow rate ml/min) / Ps (plasma concentration mmol/ml)
44
What is the significance of the clearance?
- GFR 1) To assess the glomerular function 2) GFR is the clearance of a substance that is freely filtered at the glomerulus but not reabsorbed or secreted in the tubules - Renal plasma/blood flow 1) It is not routinely performed 2) The clearance of a substance filtered at the glomerulus and completely secreted by the tubules
45
What is urine excretion?
Excretion = filtration (at the bowman's capsule) - Reabsorption + Secretion
46
What are the different ways by which the kidneys handle substances?
1) Filtration only (insulin) 2) Filtration with partial reabsorption (Sodium, urea, phosphate, and chloride) 3) Filtration with complete reabsorption (glucose) 4) Filtration with secretion (para-aminohippuric acid, creatinine)
47
What is the renal clearance of albumin?
Zero, as it is not filtered
48
What is the renal clearance of glucose?
Zero, although it is filtered but, it is completely reabsorbed
49
What substances are filtered and partially reabsorbed?
1) Sodium 2) Urea 3) Phosphate 4) Chloride
50
Describe the renal clearance of insulin
It is freely filtered but neither reabsorbed nor secreted, and thus it measures the glomerular filtration rate
51
Which substance has the highest renal clearance?
Para-aminohippuric acid, as it is both filtered and secreted
52
How can we use insulin to measure and estimate the GFR?
- Inulin is a fructose polymer that is: 1) Freely filtered at the glomerulus 2) Not reabsorbed, secreted, or metabolized in the nephron 3) Excreted only by filtration, making its clearance a direct measure of GFR GFR = Uinsulin * Urine velocity / Plasma concentration of urine This formula shows that GFR is equal to the clearance of inulin, meaning the volume of plasma completely cleared of inulin per unit time
53
What are the limitations of Inulin Clearance in Clinical Practice
1) Requires IV infusion of inulin for steady plasma levels 2) Requires timed urine collection and plasma sampling 3) Expensive and time-consuming, so it is rarely used outside research
54
What are the ideal properties of a substance used to measure the GFR?
1) Freely filtered at the glomerulus 2) Not reabsorbed by the tubules 3) Not secreted by the tubules 4) Not metabolised by the nephron 5) Not toxic to the body 6) Does not affect the renal function (glomerular function in particular) 7) It is easily measured in the plasma and urine 8) Found in the body
55
How is creatinine cleared, and how is it used to measure the GFR?
- Creatinine is a by-product of muscle metabolism cleared by the glomerular filtrate - It is not a perfect marker for the GFR as it is secreted by the tubules - If a urine sample collection is not doable, it can be measured by the plasma, and the GFR will be inversely proportional to it (if serum creatinine increases, then GFR is decreased by the same proportion)
56
What is the relationship between creatinine and GFR?
They are indirectly proportional (one increases by a fold, the other decreases by the same fold) For instance: - If GFR decreases to one-eighth – the plasma cr increases eight times - If GFR decreases to 1/4th – plasma cr increases four times
57
What is the renal perfusion flow?
- Fick's principle (amount of a substance entering organ equals amount leaving the organ) - If a substance is completely cleared from the plasma, its clearance rate will be equal to the renal plasma flow - Para-amino hippuric acid is used to measure the RPF as it is filtered and secreted by the kidney (90%) - Renal perfusion flow measures the amount of substance excreted from the entire plasma flowing through the kidney (filtered + secreted)
58
How to measure the renal clearance again for PAH?
- paraamino-hippuric acid is give exogenously 1) PRF = Urince concentration * Velocity of urine / Plasma concentration - And thus - PRF ml/min = Upah * urine velocity / (concentration of PAH in renal artery - concentration of PAH in renal vein)
59
How to use the PRF to calculate the renal blood flow?
- Renal blood flow = RPF/1-PCV (packed cell volume) - 1-PCV = Plasma - RBF (ml) = RPF/1-0.4
60
How do you calculate the total renal perfusion flow?
- We must use the extraction ratio, which is the (RA concentration of PAH - RV concentration of PAH / RA concentration of PAH = 0.9), then: - Total RPF = PAH clearance / PAH extraction ratio

Y2S2-RENAL/REPRO-PHYSIOLOGY (9 decks)

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