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Physiology > Renal Function: glomerular filtration and renal blood flow > Flashcards

Renal Function: glomerular filtration and renal blood flow Flashcards

1
Q

6 functions of the kidney

A
  • excretion of metabolic waste products (urea, creatinine)
  • regulation of acid-base balance (eliminate H, acids/base, conserve bicarb)
  • control of arterial pressure
  • secretion, metabolism, and excretion of hormones
  • excretion of foreign chemicals
  • gluconeogenesis
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2
Q

What are 2 markers that are routine on all serum chemistry analyses?

A

Urea and creatinine

- are metabolic waste products that need to be eliminated

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3
Q

Kidney is responsible for long term maintenance of ____

A

pH

- H+ is more tightly regulated than anything else in the body

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4
Q

What is the precursor for angiotensin 2?

A

Renin

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5
Q

Angiotensin 2 functions as a ______

A

Vasoconstrictor

- helps maintain bp during hypovolemia and reabsorbs Na and H2O to maintain circulating volume

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6
Q

What 2 hormones are critical to calcium homeostasis and maintaining proper bone metabolism and density?

A

Vitamin D (can only be activated in the kidney) and parathyroid hormone

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7
Q

What organ is responsible for maintaining blood glucose?

A

Liver, but kidney can convert AA and precursors to glucose during prolong fasting or liver disease

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8
Q

What is the main reservoir of rapidly available high energy phosphate bonds in muscle?

A

Phosphocreatinine

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9
Q

Creatinine

A
  • Cr production is proportional to muscle mass normally
  • may be increased in acute muscle diseases or decreased in chronic muscle wasting
  • 1-2% of muscle creatine turns over daily to creatinine
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10
Q

Why is creatinine an accurate estimate of glomerular filtration rate?

A

Cr is strictly filtered by the glomerulus with little or no secretion or reabsorption by the renal tubules

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11
Q

Renal damage is ____ over the life of the animal

A

Cumulative, nephrons don’t regenerate

- Serum Cr will increase over time

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12
Q

Does the kidney alter it’s function in response to changes in creatinine?

A

No, a change in Cr does not cause a change in GFR for compensation
- use serum Cr as an indicator of a changing GFR (as a result of something else)

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13
Q

GFR primarily responds to changes in ____

A

Sodium

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14
Q

Excessive protein intake leads to ____

A

Greater urea production and elimination

- could be due to increased intake, or increased body protein catabolism or degradation (seen in starvation)

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15
Q

Must eliminate _____ as urea, or ____ will accumulate

A

NH2, NH3 (ammonia)

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16
Q

Changes in urea results in _____

A

Significant changes in water excretion or retention

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17
Q

_____ follows urea!!!

A

Water

- urea is a potent osmotic particle

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18
Q

In excessive urea production and elimination, GFR will ______ and urine volume will _______

A

Increase, increase

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19
Q

During dehydration, the kidney will _____

A

Actively reabsorb urea to retain water or reduce water excretion

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20
Q

____ and ____ are indicators of loss of function

A

BUN and Cr (are late indicators)

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21
Q

The kidney is the most important organ for getting rid of ____

A

H+

- H ion concentration is tightly controlled (to the 0.00004 meq/L

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22
Q

What are the 3 mechanisms of H control?

A
  • buffers: act in seconds
    • -> proteins to act as temporary H+ sink
    • -> weak acid anion: bicarb, phosphate, etc
  • respiration: act in minutes
    • -> eliminates CO2, leaving water instead of carbonic acid (bicarb loss)
  • kidney: slow, but most important
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23
Q

Every time a CO2 is excreted, a ______ ion is lost

A

Bicarb (1:1 ratio)

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24
Q

Rates at which different substances are excreted in the urine represent sum of 3 different renal processes

A
  • glomerular filtration
  • reabsorption of substances from renal tubules into the blood
  • secretion of substances from blood into renal tubules
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25
Q

If intake of water/electrolytes exceeds excretion, the amount of that substance in the body will ____

A

Increase

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26
Q

Urine formation begins with fluid that is virtually free of ____

A

Protein
- most substances in plasma are freely filtered, so their concentration in the glomerular filtrate in Bowman’s capsule is the same as in the plasma

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27
Q

What happens to a substance that is freely filtered by glomerular capillaries but is neither reabsorbed or secreted?

A

Excretion of all that is filtered

  • excretion rate is equal to the rate at which it was filtered
  • is a good estimate of GFR
  • example of creatinine
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28
Q

What happens to a substance that is freely filtered but is partly reabsorbed from the tubules back into the blood?

A

Rate of urinary excretion is less than the rate of filtration at the glomerular capillaries
- typical for electrolytes (Na, Ca, K)

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29
Q

What happens to a substance that is freely filtered at the glomerular capillaries but is not excreted into the urine?

A

All the filtered substance is reabsorbed from the tubules back into the blood
- amino acids and glucose

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30
Q

What type of substance is freely filtered at the glomerular capillaries and is not reabsorbed, and additional quantities of this substance are secreted from the peritubular capillary blood into the renal tubules?

A

Organic acids

- allows them to be rapidly cleared from the blod and excreted in olarge amounts in the urine

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31
Q

What percent of cardiac output does the kidney recieve?

A

20%

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32
Q

Does albumin get filtered thru the glomerular capillaries?

A

No, due to its negative charge

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33
Q

What is the functional unit of the kidney?

A

Nephron

- consists of the glomerulus and its capillary tuft and the tubules

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34
Q

What contributes to increased glomerular filtration rate?

A

High hydrostatic pressure (60 mm Hg) and endothelial cell fenestrations
- allows for 20% of fluid and smaller solutes out of capillary and into Bowman’s capsule

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35
Q

Proximal convoluted tubules

A

Site of resorption of 65% of filtrate

  • high solute and water resorption
  • extremely metabolically active (unregulated absorption)
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36
Q

Loop of Henle

A

Absorbs 25% of renal filtrate

  • high water and electrolyte resorption
  • distal end passes by original glomerulus
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37
Q

Distal tubule

A

Water and Na reabsorption

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38
Q

Collecting duct

A

Site of final and variable water and sodium resorption under control of hormones (aldosterone and ADH)

  • K excretion
  • only place in the kidney where fine tuning of filtrate occurs (everywhere else reabsorption occurs at a fixed pace)
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39
Q

Past the _____ is where reabsorption is regulated

A

Macula densa

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40
Q

The kidney has _______ being fed from the same arterial input

A

2 capillary beds in series

  • each bed has its own control valve to control the path of least resistance
  • most capillaries return to venous outflow without going thru the inner medulla
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41
Q

The _____ determines whether fluid is filtered to become urine or not

A

Path of least resistance

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42
Q

The glomerular capillary bed is under ____ pressure, while the peritubular capillary bed is under _____ pressure

A

Very high; low

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43
Q

What percent of renal blood flow goes to the medulla?

A

1-2%

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44
Q

Cortical nephrons

A

Make up 70-75% of nephrons

  • located in the cortex with short loops of Henle that do not penetrate far into the medulla
  • extensive peritubular capillary network to reabsorb nutrients without concern for regulating bodily fluid composition
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45
Q

Juxtamedullary nephrons

A

Make up 25-30% of nephrons

  • located deep in the renal cortex near the medulla
  • have long loop of Henle with tubule and vasculature penetrating deep into the medulla
  • inner medulla hypertonic
  • counter current flow
  • more limited capillary network with a capillary running parallel to the tubule (vasa recta)
  • primarily responsible for regulating fluid retention and majory electrolytes
46
Q

Both nephrons differ in their ability to ______

A

Regulate reabsorption

- both filter equally well for elimination of waste products

47
Q

Kidney uses ____ oxygen as the brain per gram

A

2X

- oxygen consumed by kidneys is related to high rate of active sodium reabsorption by renal tubules

48
Q

Inner medulla oxygen tension is as low as _______

A

10 mm Hg

- makes this area highly susceptible to hypoxia

49
Q

What 2 things determine GFR?

A
  • balance of hydrostatic and colloid osmotic pressures

- capillary filtration coefficient: product of permeability and filtering surface area of the capillaries

50
Q

Where does the glomerulus receive its blood supply from?

A

Afferent arteriole of renal circulation

- drains into an efferent arteriole instead of a venule

51
Q

What is the basic filtration unit of the kidney?

A

Renal corpuscle

- a glomerulus and its surrounding Bowman’s capsule

52
Q

What 3 components make up a glomerular capillary membrane?

A
  • endothelium
  • basement membrane
  • epithelial cells (podocytes)
    = filtration barrier
53
Q

Capillary endothelium

A

Perforated by fenestrae

- endowed with fixed negative charges that hinder passage of plasma proteins

54
Q

Basement membrane

A

Meshwork of collagen and proteoglycan fibrillae

  • large spaces allow for movement of water and small solutes
  • proteoglycans have strong negative charges which prevent plasma protein filtration
55
Q

Epithelial cells

A

Lining of Bowman’s capsule that surrounds the outer surface of the glomerulus

  • not continuous
  • podocytes encircle the capillaries
  • slit pores allow movement of glomerular filtrate
  • also have negative charges
56
Q

Molecular size

A
  • small molecules increase filterability

- large molecules decrease filterability

57
Q

Ionic charge

A
  • cations increase filterability

- anions decrease filterability

58
Q

Neutral dextrans are _____ than negatively charged dextrans of equal molecular weight

A

Filtered more readily

59
Q

What is the reason for differences in filterability?

A

Negative charges of BM and podocytes provide means for restricting large, negatively charged molecules

60
Q

How does albumin end up being filtered during minimal change nephrotic syndrome?

A

Due to loss of negative charge

- compromised by inflammation, or acid/base imbalance –> if a hydrogen ion is attached to an albumin it can be filtered

61
Q

When does albuminuria/proteinuria occur?

A

When more albumin is filtered than can be reabsorbed

62
Q

____ movement is paralleled by an equivalent _____ movement

A

Cation; anion

- if small cations (Na, K) become filtered, then small anions (Cl, bicarb) will also become filtered

63
Q

Net filtration pressure

A

Sum of hydrostatic and colloid osmotic forces across the glomerular membrane

64
Q

GFR formula

A

Filtration coefficient (Kf) x net filtration pressure

65
Q

Why is colloidal pressure within Bowman’s capsule negligible?

A

Protein should not be filtered

- only changes in disease states, which could cause fluid to cross the filtration barrier and into Bowman’s capsule

66
Q

What is the main factor used to control GFR?

A

Changes in blood pressure within the glomerulus

- accomplished by varying the afferent and efferent arteriolar sphincters

67
Q

Capillary filtration coefficient

A

Hydraulic conductivity x surface area

  • 400x increased permeability than most other capillary beds
  • not under physiologic control
  • affected in some disease states
68
Q

Capillary hydrostatic pressure

A

Primary means of physiologic regulation of GFR

  • under physiologic control
  • promotes filtration
69
Q

Capillary colloidal pressure

A

Does exert influence normally

  • not under physiologic control
  • opposes filtration
70
Q

Bowman’s hydrostatic pressure

A

Affected in some disease states

  • not under physiologic control
  • opposes filtration
71
Q

Bowman’s colloidal pressure

A

Essentially zero

  • not under physiologic control
  • affected in some disease states
72
Q

Changes (decreases) in filtration coefficient result in

A

Thickening of glomerular basement membrane = thicker diffusion barrier opposing blood flow

  • occurs with chronic hypertension, obesity, diabetes mellitus, glomerulonephritis
  • leads to impedment of glomerular filtration and retained waste products
73
Q

What are the 3 factors that influence glomerular hydrostatic pressure?

A
  • arterial pressure
  • afferent arteriolar resistance
  • efferent arteriolar resistance
74
Q

What happens if systemic arterial pressure and/or blood flow increases and there are no changes in glomerular resistance?

A

There will be an increase in blood pressure and/or flow to the glomerular capillary bed = GFR increased

75
Q

What serves as the primary means for physiologic regulation of GFR?

A

Changes in glomerular hydrostatic pressure

- controlled by afferent and efferent arterioles

76
Q

What happens when afferent arterioles are constricted?

A

Increased resistance leads to decreased renal blood flow, decreased glomerular hydrostatic pressure = decreased GFR
- helpful during emergency situations but will reduce removal of waste products

77
Q

What happens during vasodilation of afferent arterioles?

A

Increased glomerular hydrostatic pressure, increased glomerular flow rate, reducing the increase in colloidal pressure = increased GFR

78
Q

What happens when efferent arterioles are constricted?

A

Could still reduce renal blood flow, but increases glomerular hydrostatic pressure = increased GFR
- occurs during dehydration or sustained/moderate to heavy exercise

79
Q

What happens when efferent arteriole constriction is too severe?

A

Decreased GFR due to increased colloidal pressure

80
Q

What happens when efferent arterioles are dilated?

A

Decrease glomerular hydrostatic pressure = decreased GFR

81
Q

What happens during times of plentiful water supply?

A

We don’t need the sphincters

- increased arteriolar pressure and blood flow increases GFR = excess water and salt is filtered across the glomerulus

82
Q

What are 2 factors that influence glomerular colloid osmotic pressure?

A
  • arterial plasma colloid osmotic pressure

- fraction of plasma filtered by glomerular capillaries (filtration fraction)

83
Q

Where, within the capillary, does blood protein become more concentrated?

A

At the end of the glomerular capillary by 20% due to loss of fluid

84
Q

What provides the basis for reabsorption of water from the tubules?

A

Increased colloidal pressure leaving the glomerulus and entering the capillaries surrounding the tubules

85
Q

What happens to colloidal pressure during dehydration?

A

Leads to increased concentration of albumin in the plasma, which retains fluid in the capillary and diminishes urine filtrate

86
Q

Increases in blood flow with a constant glomerular pressure results in increased GFR due to ______ in colloidal pressure

A

Moderate increase

  • new blood flows in as fast as the amount of fluid that is being filtered out
  • leads to decrease in protein concentration in the tubular capillaries = less reabsorption of fluid from renal tubules, resulting in a greater rate of clearance when excess fluid is consumed
87
Q

Slower blood flow into the glomlerulus with a constant glomerular hydrostatic pressure results in ______ GFR

A

Decreased

  • colloidal pressure holding fluid in matches that of hydrostatic pressure pushing fluid out before the end of the glomerular capillary
  • protein concentration and colloidal pressure in the peritubular capillaries are as high as possible = maximal reabsorption of fluid from renal tubules
88
Q

Goal of renal blood flow control

A

Maintain constant GFR over a wide range of flow and pressure ranges for waste excretion without excess loss of fluid

89
Q

What could result from an increase in blood pressure by 25%?

A

Increase urine output if all other variables remained the same

  • transient: exercise, fear, etc
  • persistent: hypertension
90
Q

In hypovolemic states, it is necessary to ______ urine production, and maintain waste excretion

A

Minimize

91
Q

What results from strong activation of renal sympathetic nerves?

A

Constriction of renal arterioles and decrease in renal blood flow and GFR
- plays important role in reducing GFR during severe, acute disturbances

92
Q

Endothelin

A

Vasoconstrictor released by damaged vascular endothelial cells of kidneys
- may contribute to hemostasis during disease states

93
Q

Myogenic mechanism definition

A

Ability of individual blood vessels to resist stretching during increased arterial pressure
- helps maintain vascular resistance preventing increase in glomerular blood flow with increase in GFR

94
Q

Myogenic mechanism method

A

Smooth muscle in renal arteries and arterioles is stretched, Ca channels open allowing Ca in the cell and activation of myosin/actin contractile elements

95
Q

Angiotensin 2

A

Constricts efferent arteriole, increasing glomerular hydrostatic pressure preserving GFR while reducing renal blood flow

96
Q

How are afferent arterioles protected from angiotensin 2?

A

Due to local production and release of vasodilators (nitric oxide, prostaglandins) which counteract vasoconstrictor effects of angiotensin 2

97
Q

Increased angiotensin 2 levels ____ glomerular hydrostatic pressure, and ____ renal blood flow

A

Increase; decrease

- occurs during decreased arterial pressure/volume depletion, which decreases GFR

98
Q

What cause vasodilation and increased renal blood flow/GFR?

A

Prostaglandins (PGE2, PGI2) and bradykinin

- oppose vasoconstriction of afferent arterioles, to prevent excessive reductions in GFR and renal blood flow

99
Q

Prostaglandins

A
  • COX2 dependent
  • critical for maintaining renal and medullary blood flow in hypotensive states
  • blocked by NSAIDs = reduction in RBF
100
Q

Endothelial-derived nitric oxide

A

Released by vascular endothelium, decreases renal vascular resistance

  • basal level of NO is required to excrete normal amounts of sodium and water
  • drugs that inhibit formation of NO increase renal vascular resistance and decrease GFR and urinary sodium excretion
101
Q

Juxtaglomerular complex

A

Consists of macula densa cells in initial portion of distal tubule and juxtaglomerular cells in the afferent and efferent arterioles

102
Q

Macula densa

A

Epithelial cells in the distal tubules that come in contact with afferent and efferent arterioles

  • contain Golgi bodies, suggesting secretions toward the arterioles
  • senses sodium
103
Q

Is reabsorption in the proximal portions of the tubules fixed?

A

Yes, is not regulated and occurs at a fixed rate

104
Q

A decrease in sodium presentation to the macula densa results in

A
  • afferent arteriolar vasodilation
  • efferent arteriolar vasoconstriction, increasing glomerular hydrostatic pressure
    = increased filtrate and urine production, increased GFR
105
Q

An increase in sodium presentation to the macula densa results in

A

An interpretation of a too high GFR, resulting in a flow that is too fast to allow time necessary to conserve essential nutrients that would then be lost into the urine
- GFR needs to be slowed

106
Q

Juxtaglomerular effect diagram

A

Drop in bp = drop in GFR –> decrease flow rate allows more time for loop of Henle to absorb more Na –> macula densa senses decreased Na –> MD signals juxtaglomerular cells to release renin –> angiotensin 2 increases GFR —> MD signals afferent arteriole to dilate = increase RBF and oppose drop in GFR

107
Q

How are amino acids absorbed by the proximal convoluted tubules?

A

Cotransport carrier that includes sodium

- so, when amino acids are reabosorbed from the filtrate, so is sodium

108
Q

How is urine volume increased in relation to decreased sodium presentation to the JG apparatus?

A

Remember: sodium follows amino acid reabsorption from protein degradation –> extra Na absorption leads to less Na presented to MD –> MD thinks GFR is too low, so it increases GFR
- liver is also producing more urea = increased amount of filtered urea in urine –> urea has osmotic effect!! = increase in water filtered due to increase in GFR is held further down in collecting tubules = increase in urine volume

109
Q

For every glucose reabsorbed, ___ is also reabsorbed

A

Sodium

110
Q

During states of dehydration that result in decreased renal blood flow, signals from MD induce _____ dilation

A

Afferent arteriolar, to preserve glomerular hydrostatic pressure and preserve GFR

111
Q

When does the autoregulatory mechanism fail?

A

In states of reduced cardiac output and reduced renal blood flow
- fails as afferent arteriolar vasoconstriction occurs = poor tubular perfusion and hypoxia

Physiology (33 decks)

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