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Renal and Endocrine Biology > REB 20. Control of Renal Circulation, Glomerular Filtration > Flashcards

REB 20. Control of Renal Circulation, Glomerular Filtration Flashcards

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1
Q

What is the filtration rate in the glomerulus dependent on?

A

Glomerular Blood Flow

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2
Q

Is there any extrinsic regulation to control the renal circulation?

A

No - only autoregulation (self-regulation)

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3
Q

How does autoregulation of the renal circulation work? What are the basic mechanisms involved?

A

within NORMAL blood pressure ranges, there are variations in AFFERENT ARTERIOLAR RESISTANCE to ensure CONSTANT blood flow

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4
Q

What is the main goal of autoregulation of the renal circulation?

A

to ensure CONSTANT blood supply to the afferent arterioles and glomerular capillaries

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5
Q

What is autoregulation (definition)?

A

It is the term for LOCAL ARTERIOLAR MECHANISMS that keep blood flow CONSTANT despite wider variations in mean arterial (systemic) blood pressure

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6
Q

Different tissues have different autoregulatory abilities. How is the autoregulatory abilities in:
Brain?
Kidney?
Skeletal Muscle?

A

Brain - excellent

Kidney - good

Skeletal Muscle - poor

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7
Q

What range of blood pressures does autoregulation of the renal circulation occur at?

A

Mean Arterial Pressure: 80 to 180 mmHg

  • this is the autoregulatory range
  • it does not occur outside of this range
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8
Q

What is the autoregulatory range?

A

Mean Arterial Pressure: 80 to 180 mmHg

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9
Q

List the 2 mechanisms of the autoregulation.

A

[1] Myogenic Response

[2] Tubuloglomerular Feedback

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10
Q

Explain the general overview the myogenic response.

A
  • “muscle-produced”
  • increase in pressure in afferent arteriole
  • stretch in the wall of the vessel
  • causes reflex contraction of its smooth muscle
  • increases resistance of the vessel
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11
Q

What are the steps involved in myogenic response to increased pressure?

A

[1] increased arterial pressure

[2] pressure in afferent arteriole increases

[3] stretch of afferent arteriolar wall

[4] reflex contraction of muscle in wall of afferent arteriole

[5] afferent arteriole resistance increases

[6] renal blood flow kept constant

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12
Q

How does the stretch of the wall of the afferent arteriole cause reflex contraction?

A

[1] stretch of afferent arteriolar wall

[2] activates stretch-activated non-selective cation channels in smooth muscle

[3] depolarizes cell, Ca2+ influx

[4] muscle contraction

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13
Q

What is the Macula Densa? Where are the Macula Densa cells located?

A
  • region of specialized epithelial cells at point where the thick ascending limb loop of Henle meets distal convoluted tubule
  • at the junction of the ascending limb of the loop of Henle and the distal convoluted tubule
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14
Q

Explain the general overview the tubuloglomerular feedback response.

A
  • change in (a) renal blood flow and (b) glomerular filtration rate leads to the change in rate of fluid flow through the tubules
  • a signal from the macula densa cells causes a change in the afferent arteriolar tone
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15
Q

What are the steps involved in the tubuloglomerular feedback response to increased pressure?

A

[1] pressure in the afferent arteriole increases

[2] the glomerular filtration rate increases

[3] the tubular flow rate increases

[4] increased delivery of Na+/Cl- to macula densa

[5] increased NaCl reabsorption by macula densa cells

[6] Na/Cl uptake activates a non-selective cation channel which gates calcium entry that causes macula densa cells to release a PARACRINE AGENT (such as adenosine or ATP)

[7] Adenosine diffuses to afferent arteriole

[8] Afferent ateriolar constriction (renin release is also reduced)

[9] (a) Renal Blood Flow and (b) Glomerular Flow Rate returns to normal

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16
Q

If the tubular flow/salt content is LOW, what happens in the tubuloglomerular feedback response?

A

Other mediators (PGE2 and NP) are released which stimulate renin and vasodilation

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17
Q

What is the reason for maintaining RBF constant within the MAP range of 80 to 180 mmHg?

A
  • glomerular filtration rate (GFR) is dependent on the glomerular blood flow (GBF)
  • the glomerular blood flow (GBF) is dependent on the renal blood flow (RBF)
  • therefore, by maintaining RBF you are keeping GFR constant
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18
Q

What are the advantages of autoregulating GFR and RBF over the range of 80 to 180 mmHg? [2]

A

[1] ensures that small fluctuations in blood pressure which normally occur do not result in corresponding fluctuations in RBF (renal blood flow) and GFR (glomerular filtration rate) [!!]
— e.g. changes in posture, light to moderate exercise

[2] protects fragile glomerular capillaries against increases in perfusion pressure

19
Q

Does the RBF (renal blood flow) and GFR (glomerular filtration rate) ever change?

A

They do change under certain conditions - brought about by extrinsic control mechanisms mediated by NERVES and HORMONES

20
Q

What are the 2 categories of extrinsic control that may lead to changes in the RBF and GFR?

A

[1] Nervous Control

[2] Hormonal Control

21
Q

Explain the role of the nervous extrinsic control in the control of RBF and GFR.

A

[1] afferent and efferent arterioles richly innervated by SYMPATHETIC fibres

[2] there is increased sympathetic nervous system activity

[3] NA causes contraction of the smooth muscle in vessel walls

[4] afferent + efferent arteriole vasoconstriction causes a reduction in RBF and GFR

22
Q

Explain the role of the hormonal extrinsic control in the control of RBF and GFR.

A

[1] vascular smooth muscle in the walls of interlobular arteries and afferent + efferent arterioles is sensitive to certain circulating compounds

[2] sensitive to (a) Adrenaline and (b) Angiotensin 2

[3] leads to vascular smooth muscle contraction

[4] leads to vessel constriction

23
Q

What is the function of the bradykinin?

A

it leads to the dilation of blood vessels

24
Q

Explain the role of nerves and hormones (extrinsic control) in:
a person at rest with normal circulating blood volume

A

[1] activity in sympathetic nervous system fibres supplying the renal vessels is ZERO

[2] RBF and GFR maintained CONSTANT by auto-regulation

25
Q

Explain the role of nerves and hormones (extrinsic control) in:
severe exercise, pain, severe emotional stimuli on RBF and GFR

A

[1] sympathetic nervous system activity in renal vessels

[2] adrenaline released from adrenal medulla

[3] vascular smooth muscle contraction

[4] vessel constriction

[5] GFR decreases

26
Q

Explain the role of nerves and hormones (extrinsic control) in:
effect of crisis situation (e.g. haemorrhage) on RBF and GFR

A

[1] high degree of sympathetic nervous system activity may be detected in renal vessels

[2] also, adrenaline is released and circulating levels of angiotensin 2 increase

[3] vessel constriction

[4] GFR decreases

27
Q

What is the benefit of reducing RBF (renal blood flow) during severe exercise?

A
  • helps direct more blood to muscles
28
Q

What is the benefit of reducing RBF (renal blood flow) during haemorrhage?

A
  • reduced urine production

- helps combat fluid loss

29
Q

Could a decrease in Renal Blood Flow (RBF) after haemorrhage result in renal ischaemia?

A
  • a severe decrease in RBF can lead to TUBULAR NECROSIS and RENAL FAILURE, but…
  • Prostaglandins (PGE2 and PGI2) dampen the vasoconstrictior effects on the afferent arterioles of sympathetic nervous system and angiotensin 2
  • are produced WITHIN the kidneys; synthesis stimulated by ischaemia, sympathetic nervous system and angiotensin 2
  • balance between PG activity and that of SNS and angiotensin 2 will determine the extent of decrease in RBF
30
Q

What is the major driving force for glomerular filtration?

A
  • glomerular capillary blood pressure

- large diameter of afferent vs. efferent arteriole generates pressure pushing out plasma through (leaky) capillaries

31
Q

What passes through the filtration barrier to form the tubular filtrate?

A
  • ALL components of plasma, except cells and proteins, pass through the barrier

Passage through the barrier is influenced by…

  • molecular size
  • charge (negatively charged molecules are restricted by barrier)
  • molecule shape - deformable molecules pass better than rigid ones
32
Q

What are the 3 factors that influence the passage through the tubular filtrate?

A

[1] Molecular Size

[2] Charge
- negatively charged molecules are restricted by barrier

[3] Molecule Shape
- deformable molecules pass better than rigid ones

33
Q

What is the normal Glomerular Filtration Rate (GFR) in males and females? (numerical values)

A

Males: GFR = 125 mL/min

Females: GFR = 115 mL/min

34
Q

GFR is normally constant but would decrease in what condition?

A

renal disease

35
Q

What does the Glomerular Capillary Blood Pressure have an effect on?

A

favours filtration

36
Q

What does the Plasma-Colloid Osmotic Pressure have an effect on?

A

opposes filtration

37
Q

What does the Bowman’s Capsule Hydrostatic Pressure have an effect on?

A

opposes filtration

38
Q

What does the Net Filtration Pressure have an effect on?

A

favours filtration

39
Q

What are 3 layers of the Glomerular Filtration Barrier?

A

[1] Endothelium of Glomerular Capillaries (very capillaries)

[2] Basement Membrane

  • colalgen, glycoproteins
  • provide structure and barrier to small proteins

[3] Epithelial Cells of Bownmans Capsulse

40
Q

What are some of the conditions that will change the GFR?

A

[1] Alterations in any of the Forces Underlying GFR affect GFR

[2] Physiological Mechanisms Regulating GFR (both act at level or arteriole calibre/resistance)

  • – autoregulation (inherent response to stretch of smooth muscle
  • – extrinsic sympathetic control (e.g. during haemorrhage)

[3] Other (Unregulated) Influence son GFR

  • – decrease in plasma protein reduces force opposing filtration so this increases GFR
  • – urinary tract blockage - increase pressure in Bowman’s capsule (decreases GFR
  • – plasma-colloid pressure increases in dehydrating diarrhoea so GFR is decreased
41
Q

How many litres of filtrate is formed per day?

A

180 L

42
Q

How many litres of urine (filtrate) is excreted?

A

1.5 L

43
Q

How much filtrate is reabsorbed per day?

A

178.5 L

Renal and Endocrine Biology (25 decks)

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