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Renal Physiology > Renal Blood Circulation and Glomerular Filtration > Flashcards

Renal Blood Circulation and Glomerular Filtration Flashcards

1
Q

What is glomerular filtration?

A

Process whereby a clear fluid from which blood cells and macromolecules (e.g. Proteins) are excluded, is produced from the blood perfusing the glomerulus at the beginning of each nephron

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2
Q

Of the renal plasma flow how much becomes glomerular filtrate?

A

20%

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3
Q

What is the filtration fraction?

A

glomerular filtration rate/renal plasma flow

- represents the proportion of the fluid reaching the kidneys that passes into the renal tubules

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4
Q

What is a normal filtration fraction?

A

Fraction of plasma filtered is 20% of plasma flowing through the kidney

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5
Q

What are the 3 layers of the glomerular capillary wall?

A
  1. endothelium
  2. basement membrane
    3, epithelium - podocytes
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6
Q

Describe the endothelium of the glomerular capillary wall?

A

has fenestrations - 70nm in diameter

- allow solutes and proteins through but not red blood cells

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7
Q

Describe the basement membrane of the glomerular capillary wall?

A
  1. has strong negative electrical charges
    - Charges associated with proteoglycans
    - negative charge repels plasma proteins
  2. has tiny pores
    - prevent plasma proteins from going through
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8
Q

Describe the epithelium of the glomerular capillaries?

A

interdigitated podocyte cells that encircle the outer surface of glomerulus
- filtration slits are found between these cells

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9
Q

Filtration depends on which molecular properties?

A
  1. size
  2. charge - positive ions are filtered more
  3. molecular weight
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10
Q

Filterability of substances by glomerular capillaries decreases with?

A

molecular weight

e.g. albumin

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11
Q

What is Dextran?

A

Polysaccharide that can be manufactured as neutral, -ve or +ve charge
- +ve charged molecules are filtered much more readily than –ve charged molecules

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12
Q

What is minimal change nephropathy?

A

a condition whereby there is loss of -ve charge in the basement membrane
- happens mostly in children

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13
Q

What is glomerular filtration rate?

A

The volume of fluid filtered in the glomerulus per unit time
- The sum of the filtration rates of all the
functioning nephrons

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14
Q

What is considered a normal filtration rate?

A
  1. 90-140 ml/min for males
  2. 80-125 ml/min for females
    - GFR is ≈ 180 L/day in average human (125
    ml/min)
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15
Q

Glomerular filtration rate is proportional to?

A

body surface area

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16
Q

Glomerular filtration rate can be calculated by?

A

measuring the excretion and plasma concentration of a substance that is freely filtered
e.g. inulin and creatinine

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17
Q

GFR declines with?

A
  1. age

2. renal disease

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18
Q

What are the determinants of GFR?

A

Starling forces

  1. Glomerular capillary hydrostatic pressure (Pgc)
  2. Colloid osmotic pressure (Pπ) in glomerular capillaries
  3. Bowman’s capsule hydrostatic pressure (Pbs)
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19
Q

What is glomerular capillary hydrostatic pressure?

A

the primary means for physiological regulation of GFR

  • promotes filtration : pushes solute + water in blood plasma through glomerular filter
  • Increase in glomerular hydrostatic pressure increases GFR, decrease in hydrostatic pressure reduces GFR
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20
Q

Hydrostatic pressure is determined by?

A
  1. arterial pressure
  2. afferent arteriolar resistance
  3. efferent arteriolar resistance
21
Q

Glomerular capillary hydrostatic pressure is estimated at?

A

55 mm Hg

22
Q

Describe how the resistance of afferent arteriole can affect GFR?

A
  1. Increased resistance of afferent arteriole reduces GFR
    - renal blood flow is reduced
  2. Dilation of afferent arteriole increases GFR
    - renal blood flow is increased
23
Q

Describe how the vasoconstriction of efferent arterioles affects the GFR?

A
  • there is a decrease in renal flow out of the glomerulus
  • there is more blood in the glomerulus which increases the hydrostatic pressure in the capillaries
  • the increase in hydrostatic pressure increases the GFR
24
Q

Describe how dilation of the efferent arterioles affects the GFR?

A
  • there is an increase in renal blood flow
  • there is a decrease in resistance of blood leaving the glomerular capillaries and therefore a decrease in hydrostatic pressure
  • a decrease in hydrostatic pressure leads to a decrease in GFR
25
Q

What is colloid osmotic pressure in glomerular capillaries?

A

Generated as a result of increased plasma protein concentration after filtration

26
Q

Describe plasma protein concentration in the efferent arteriole?

A

increases by 20% after filtration

- depends on arterial pressure and filtration fraction

27
Q

How does colloid osmotic pressure affect GFR?

A
  1. increase in solute concentration increases osmotic pressure and decrease GFR
  2. decrease in solute concentration decreases osmotic pressure and increases GFR
    - water follows solutes
28
Q

What is considered a normal colloid osmotic pressure?

A

Pπ ≈ 30 mm Hg

29
Q

What is Bowmans capsule hydrostatic pressure?

A

pressure exerted by fluid on the walls of the glomerulus

30
Q

How does Bowmans capsule hydrostatic pressure affect GFR?

A

increase in hydrostatic pressure in Bowmans space decreases filtration rate

  • Can increase markedly in pathological states (e.g. obstruction of urinary tract)
  • water and solute cant move up a pressure gradient
31
Q

What is considered a normal Bowmans capsule hydrostatic pressure?

A

≈ 15 mm Hg

32
Q

How does Bowmans capsule hydrostatic pressure affect GFR?

A

increase in hydrostatic pressure in Bowmans space decreases filtration rate
- water and solute cant move up a pressure gradient

33
Q

What is net filtration pressure?

A

PGC – Pπ – PBS
= 55 - 30 - 15
= 10 mm Hg

34
Q

Afferent and efferent arterioles are innervated by?

A

sympathetic nervous system

- Strong activation of SNS causes constriction of renal arterioles

35
Q

What is the myogenic mechanism in autoregulation of renal blood flow?

A

Intrinsic capacity of afferent arteriole smooth muscles to increase state of contraction in response to increase in renal perfusion pressure

36
Q

The myogenic mechanism is mediated by?

A

vasoactive agents produced by endothelial cells acting on smooth muscle cells of afferent arteriole

37
Q

How does the myogenic mechanism work?

A

Increase in vessel diameter opens stretch-activated, non selective cation channels in vascular smooth muscles, depolarising the cell leading to influx of Ca2+ that stimulates contraction

38
Q

GFR in individual nephrons is regulated according to?

A

the rate of solute flow in that nephron

39
Q

Fluid ionic composition is sensed by?

A

macula densa

40
Q

Describe the tubuloglomerular feedback?

A
  1. macula densa senses increase in NaCl concentration
  2. macula densa secretes adenosine
  3. Adenosine acts on adenosine 1 receptor on afferent arteriole to mediate vasoconstriction
41
Q

Describe the macula densa feedback mechanism for autoregulation during decreased arterial pressure?

A
42
Q

Name the 3 hormones that constrict arterioles to decrease RBF and GFR?

A

Norepinephrine, epinephrine and endothelin

43
Q

When are the vasoconstricting hormones particularly critical?

A

during severe haemorrhage

44
Q

When is endothelin released in particular?

A

is released by damaged vascular endothelial cells of kidney and other tissues
- Endothelin levels increased during damage to blood vessel

45
Q

Angiotensin II acts as a?

A

vasoconstrictor

46
Q

Angiotensin II preferentially constricts?

A

efferent arterioles

47
Q

How does Angiotensin II work?

A
  1. Increases glomerular hydrostatic pressure (PGC), while reducing RBF
    - more blood enters the glomerulus and less blood leaves it
  2. Maintains excretion of waste substances (e.g. urea, creatinine)
48
Q

When are Angiotensin II levels increased?

A

in circumstances of reduced arterial pressure, or volume depletion, preventing decrease in GFR

49
Q

Name hormones that act as vasodilators?

A
  1. Endothelial-derived NO - decreases renal vascular resistance
  2. Prostaglandins (e.g. PGE2 and PGI2) and bradykinin - vasodilators that oppose vasoconstriction of afferent arteriole

Renal Physiology (8 decks)

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