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Physiology > Exam 4: GFR and RBF > Flashcards

Exam 4: GFR and RBF Flashcards

1
Q

What are the renal functions?

A 
Excretion of metabolic waste products
Regulation of acid-base balance
Control of arterial pressure
Secretion, metabolism, and excretion of hormones
Excretion of foreign chemicals
Gluconeogenesis
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2
Q

What are the metabolic waste products from the kidney?

A

Urea

Creatinine

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3
Q

How does the regulation of acid-base balance occur?

A

Eliminate hydrogen ions, organic acids and bases

Conserve HCO3

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4
Q

How does control of arterial pressure occur?

A

Excrete or conserve Na and H2O and other electrolytes

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5
Q

What is renin?

A

Precursor for Angiotensin (I and II) for maintenance of arterial pressure

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6
Q

How much of the erythropoietin in the body is made in the kidney?

A

90%

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7
Q

What is phosphocreatine?

A

The main reservoir of rapidly available high energy phosphate bonds in muscle

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8
Q

What percentage of muscle creatine turns over on a daily basis to produce creatine?

A

1-2%

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9
Q

What is creatinine production proportional to?

A

Muscle mass

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10
Q

What may cause an increase in the amount of creatinine?

A

Acute muscle disease states

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11
Q

What may cause a decrease in the amount of creatinine?

A

Chronic muscle wasting

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12
Q

What is creatinine freely filtered by?

A

The glomerulus

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13
Q

Is creatinine secreted by renal tubules in the dog or horse?

A

No

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14
Q

Because creatinine is strictly filtered, what does it provide?

A

Glomerular filtration rate

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15
Q

What is age related to over a lifetime in terms of creatinine?

A

An increase in serum creatinine

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16
Q

What is one of the biggest causes of an increase in urea?

A

Our diet

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17
Q

What is the turnover of urea like?

A

Normal with wear and tear

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18
Q

What leads to greater urea production?

A

Excessive protein intake

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19
Q

Urea is a very potent osmotic particle. What does this mean?

A

Water will follow it

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20
Q

What will happen in excessive urea production?

A

GFR will increase and urine volume will increase

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21
Q

What will the kidney do with urea in dehydration?

A

It will actively reabsorb urea as a mechanism of retaining water or reducing water excretion

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22
Q

What is the most tightly controlled thing in the body?

A

H+

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23
Q

What are the 3 mechanisms of control of H+?

A

Buffers
Respiration
Kidney

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24
Q

What is the control of hydrogen with buffers like?

A

Instant acting- seconds

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25
Q

What is the control of hydrogen with respiration like?

A

Fast acting- minutes

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26
Q

What is the control of hydrogen like with the kidney?

A

Slow, but quantitatively the most important

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27
Q

When does urine formation begin?

A

When a large amount of fluid that is virtually free of protein is filtered from the glomerular capillaries into Bowman’s capsule

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28
Q

What happens to filtered fluid as it leaves Bowman’s capsule and passes through the tubules?

A

It is modified by reabsorption of water and specific solutes back into the blood or bu secretion of other substance from the peritubular capillaries into the tubules

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29
Q

What is an example of something that is freely filtered by the glomerular capillaries but it is neither reabsorbed or secreted?

A

Creatinine

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30
Q

What is the excretion rate like for substances that are freely filtered by the glomerular capillaries but are not reabsorbed or secreted?

A

It is equal to the rate at which it was filtered and provides a good estimate of GFR

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31
Q

What are examples of things that are freely filtered by the glomerular capillaries but they are partly reabsorbed from the tubules back into the blood?

A

Na
Cl
Ca
K

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32
Q

What is the excretion rate like for substances that are freely filtered by the glomerular capillaries but are partly reabsorbed from the tubules back into the blood?

A

It is less than t filtration rate at the glomerular capillaries

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33
Q

What are examples of things that are freely filtered at the glomerular capillaries but are not excreted into the urine because all the filtered substance is reabsorbed from the tubules back into the blood?

A

Glucose and amino acids

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34
Q

What are examples of things that are freely filtered at the glomerular capillaries and not reabsorbed, but additional quantities are secreted from the peritubular capillary blood into the renal tubules?

A

H

K

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35
Q

What is found in the cortex?

A

Glomeruli

Proximal and distal convoluted tubules

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36
Q

What is found in the medulla?

A 
Loop of Henle
Collecting ducts
Renal papillae
Pelvis
Ureter
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37
Q

What percentage of cardiac output goes to the kidneys at rest?

A

20-25%

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38
Q

What percentage of renal plasma flow is filtered?

A

20%

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39
Q

What percentage of GFR comes out as urine?

A

1%, the rest is reabsorbed

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40
Q

What percentage of the body’s O2 consumption does the kidney use at rest?

A

10%

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41
Q

What percentage of the renal blood flow does the renal medulla receive?

A

1-2%

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42
Q

Describe the proximal convoluted tubule

A

High solute and water reabsorption

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43
Q

Describe the Loop of Henle

A

High water resorption
Electrolyte resorption
Distal end passe by original glomerulus

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44
Q

Describe the distal tubule

A

H2O and Na reabsorption

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45
Q

Describe the collecting duct

A

Final and variable H2O and Na reabsorption and K excretion

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46
Q

What is the physiological unit of the kidney?

A

Nephron

47
Q

What are the glomerular capillaries like relative to normal capillaries?

A

They are under a high hydrostatic pressure

48
Q

What does the high hydrostatic pressure with the increased permability of the glomerular capillary bed allow?

A

Allows 20% of the fluid and smaller solutes out of the capillary and into Bowman’s capsule

49
Q

What percentage of the filtrate is reabsorbed at the proximal convoluted tubule? Loop of Henle?

A

65%

25%

50
Q

What are the 2 types of nephrons?

A

Cortical and juxtamedullary

51
Q

Which of the 2 types of nephrons is the most abundant?

A

Cortical nephrons

52
Q

Describe cortical nephrons

A

Loop of Henle is short
Tubule nor vasculature penetrate very far into medulla
Extensive peritubular capillary network

53
Q

Describe juxtamedullary nephron

A 
Long loop of henle
Tubule and vasculature penetrate deeply into medulla
Inner medulla hypertonic
Counter-current flow
Vasa recta
54
Q

What makes the kidney unique?

A

It has 2 capillary beds in series being fed from the same arterial input

55
Q

What does each capillary bed have?

A

Its own control valve that work independently controlling the path of least resistance

56
Q

What does the path of least resistance determine?

A

Whether fluid is filtered to become urine or not

57
Q

What does the low O2 tension and total RBF make the renal medulla very susceptible to?

A

Hypoxia

58
Q

What is most of the oxygen consumed by the kidneys related to?

A

The high rate of active sodium reabsorption by the renal tubules

59
Q

What is a glomerulus?

A

A balled up network of brainching and anatomosing capillaries where the plasma is filtered in the first stage of urine formation

60
Q

What is the glomerulus surrounded by?

A

Bowman’s capsule

61
Q

What does the glomerulus receive its blood supply from?

A

An afferent arteriole of the renal circulation

62
Q

What does the glomerulus drain into?

A

An efferent arteriole rather than a venule

63
Q

What is the basic filtration unit of the kidney?

A

A glomerulus and its surrounding Bowman’s capsule

64
Q

What is the glomerular filtration rate?

A

The rate at which blood is filtered through all of the glomeruli and this the measure of the overall renal function

65
Q

What are the 3 major layers of the glomerular capillary membrane and make up the filtration barrier?

A

The endothelium
A basement membrane
A layer of epithelial cells (podocytes)

66
Q

What are the endothelial cells of the filtration barrier like?

A

Fenestrated

67
Q

What is the basement membrane of the filtration barrier like?

A

Collagen meshwork

68
Q

What are the podocytes of the filtration barrier like?

A

Finger-like extensions that surround capillaries with slits between fingers

69
Q

What does solute filtration depend on?

A

Molecular size

Ionic change

70
Q

What do small molecules do to filterability?

A

Increase it

71
Q

What do large molecules do to filterability?

A

Decrease it

72
Q

What do cations do to filterability?

A

Increase it

73
Q

What do anions do to filterability?

A

Decrease it

74
Q

What is an example of something that impact how charge and size change filterability?

A

Dextrans

75
Q

What are dextrans?

A

Polysaccharides that have been used to provide colloidal support in patients with low albumin levels

76
Q

What is the overall charge of the filtration barrier?

A

Negative

77
Q

What is the charge of albumin? What happens to it because of it?

A

Negative

It is mostly repelled. Some gets across, but is actively reabsorbed by the tubular epithelial cells

78
Q

How do you get the capillary filtration coefficient?

A

Hydraulic conductivity x surface area

79
Q

Is the capillary filtration coefficient under physiologic control?

A

No

80
Q

When is the capillary filtration coefficient affected?

A

In some disease states

81
Q

Is capillary hydrostatic pressure under physiologic control?

A

Yes

82
Q

What is the capillary hydrostatic pressure the primary means of?

A

Physiologic regulation of GFR

83
Q

Is capillary colloidal pressure under physiologic control?

A

No

84
Q

Is Bowman’s capsule under physiologic control?

A

No

85
Q

Is Bowman’s capsule colloidal pressure under physiologic control?

A

No

86
Q

Why is the colloidal pressure negligible in Bowman’s capsule?

A

Protein should not be filtered

87
Q

What are factors that influence glomerular hydrostatic pressure?

A

Arterial pressure
Afferent arteriolar resistance
Efferent arteriolar resistance

88
Q

What does increased resistance of afferent arterioles do?

A

Makes the path of least resistance to bypass the kidney, decreases renal blood flow, and decreases glomerular hydrostatic pressure decreasing GFR

89
Q

What does increased resistance of the efferent arterioles do?

A

Still can reduce overall renal blood flow, but increases glomerular hydrostatic pressure making the path of least resistance across the glomerulus into bowman’s capsule thereby increasing GFR

90
Q

What does efferent constriction do?

A

Decreases RBF

Increases GFR

91
Q

What does efferent dilation do?

A

Increase RBF

Decrease GFR

92
Q

What does afferent constriction do?

A

Decrease RBF

Decrease GFR

93
Q

What does afferent dilation do?

A

Increase in RBF

Increase in GFR even without efferent constriction

94
Q

What is the goal of RBF control?

A

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

95
Q

What could an increase in blood pressure by 25% do?

A

Increase urine output

96
Q

What is a transient increase of blood pressure caused by?

A

Exercise
Fear
Excitement

97
Q

What is a persistent increase of blood pressure caused by?

A

Hypertension in humans
Occasionally occurs in cats and dogs
Rare in horses

98
Q

What would an increase in cardiac output do?

A

Increase urine output

99
Q

What is necessary in hypovolemic states?

A

Minimize urine production yet maintain waste excretion

100
Q

What may be necessary in severe hypovolemic states?

A

Conserve fluid at the expense of waste excretion

101
Q

What does a strong sympathetic tone do?

A

Decreases RBF and GFR

102
Q

What is endothelin?

A

Potent vasoconstrictor released by damaged vascular endothelial cells

103
Q

What is the path of renal blood flow control?

A 
Increased arterial pressure
Increased stretch of blood vessel
Increase smooth muscle Ca permeability
Increased intracellular Ca
Increased smooth muscle contraction and vascular resistance
104
Q

What does angiotensin II formation occur during?

A

Hypovolemic “low flow” states and lowered arterial pressure

105
Q

What does angiotensin II do?

A

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

106
Q

What does the juxtaglomerular complex do?

A

Senses and regulates Na delivered to distal tubule

107
Q

What does the macula densa sense?

A

Na

108
Q

What is too much Na interpreted as?

A

Too high GFR, so it needs to decrease

109
Q

What is too little Na interpreted as?

A

Too little GFR, so it needs to increase

110
Q

What are the 2 effects that macula densa has with a decrease in Na?

A

Afferent arteriolar vasodilation decreasing resistance to blood flow into the glomerulus
Efferent arteriolar vasoconstriction increasing resistance to blood flow out of the glomerulus

111
Q

What does the macula densa signal juxtaglomerular cells to do?

A

Release renin

112
Q

Describe how protein impacts GFR

A

Increase in amino acids
Increase in proximal tubular amino acid reabsorption
Increase in proximal tubular NaCl reabsortion
Decrease in macula densa NaCl
Decrease in afferent arteriolar resistance
Increase in GFR

113
Q

What is the most common form of acute renal failure in the horse?

A

Acute tubular nephrosis

Physiology (70 decks)

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