Exam 4: GFR and RBF Flashcards
(113 cards)
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
2
Q
What are the metabolic waste products from the kidney?
A
Urea
Creatinine
3
Q
How does the regulation of acid-base balance occur?
A
Eliminate hydrogen ions, organic acids and bases
Conserve HCO3
4
Q
How does control of arterial pressure occur?
A
Excrete or conserve Na and H2O and other electrolytes
5
Q
What is renin?
A
Precursor for Angiotensin (I and II) for maintenance of arterial pressure
6
Q
How much of the erythropoietin in the body is made in the kidney?
A
90%
7
Q
What is phosphocreatine?
A
The main reservoir of rapidly available high energy phosphate bonds in muscle
8
Q
What percentage of muscle creatine turns over on a daily basis to produce creatine?
A
1-2%
9
Q
What is creatinine production proportional to?
A
Muscle mass
10
Q
What may cause an increase in the amount of creatinine?
A
Acute muscle disease states
11
Q
What may cause a decrease in the amount of creatinine?
A
Chronic muscle wasting
12
Q
What is creatinine freely filtered by?
A
The glomerulus
13
Q
Is creatinine secreted by renal tubules in the dog or horse?
A
No
14
Q
Because creatinine is strictly filtered, what does it provide?
A
Glomerular filtration rate
15
Q
What is age related to over a lifetime in terms of creatinine?
A
An increase in serum creatinine
16
Q
What is one of the biggest causes of an increase in urea?
A
Our diet
17
Q
What is the turnover of urea like?
A
Normal with wear and tear
18
Q
What leads to greater urea production?
A
Excessive protein intake
19
Q
Urea is a very potent osmotic particle. What does this mean?
A
Water will follow it
20
Q
What will happen in excessive urea production?
A
GFR will increase and urine volume will increase
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
22
Q
What is the most tightly controlled thing in the body?
A
H+
23
Q
What are the 3 mechanisms of control of H+?
A
Buffers
Respiration
Kidney
24
Q
What is the control of hydrogen with buffers like?
A
Instant acting- seconds
25
What is the control of hydrogen with respiration like?
Fast acting- minutes
26
What is the control of hydrogen like with the kidney?
Slow, but quantitatively the most important
27
When does urine formation begin?
When a large amount of fluid that is virtually free of protein is filtered from the glomerular capillaries into Bowman's capsule
28
What happens to filtered fluid as it leaves Bowman's capsule and passes through the tubules?
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
29
What is an example of something that is freely filtered by the glomerular capillaries but it is neither reabsorbed or secreted?
Creatinine
30
What is the excretion rate like for substances that are freely filtered by the glomerular capillaries but are not reabsorbed or secreted?
It is equal to the rate at which it was filtered and provides a good estimate of GFR
31
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?
Na
Cl
Ca
K
32
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?
It is less than t filtration rate at the glomerular capillaries
33
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?
Glucose and amino acids
34
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?
H
| K
35
What is found in the cortex?
Glomeruli
| Proximal and distal convoluted tubules
36
What is found in the medulla?
```
Loop of Henle
Collecting ducts
Renal papillae
Pelvis
Ureter
```
37
What percentage of cardiac output goes to the kidneys at rest?
20-25%
38
What percentage of renal plasma flow is filtered?
20%
39
What percentage of GFR comes out as urine?
1%, the rest is reabsorbed
40
What percentage of the body's O2 consumption does the kidney use at rest?
10%
41
What percentage of the renal blood flow does the renal medulla receive?
1-2%
42
Describe the proximal convoluted tubule
High solute and water reabsorption
43
Describe the Loop of Henle
High water resorption
Electrolyte resorption
Distal end passe by original glomerulus
44
Describe the distal tubule
H2O and Na reabsorption
45
Describe the collecting duct
Final and variable H2O and Na reabsorption and K excretion
46
What is the physiological unit of the kidney?
Nephron
47
What are the glomerular capillaries like relative to normal capillaries?
They are under a high hydrostatic pressure
48
What does the high hydrostatic pressure with the increased permability of the glomerular capillary bed allow?
Allows 20% of the fluid and smaller solutes out of the capillary and into Bowman's capsule
49
What percentage of the filtrate is reabsorbed at the proximal convoluted tubule? Loop of Henle?
65%
| 25%
50
What are the 2 types of nephrons?
Cortical and juxtamedullary
51
Which of the 2 types of nephrons is the most abundant?
Cortical nephrons
52
Describe cortical nephrons
Loop of Henle is short
Tubule nor vasculature penetrate very far into medulla
Extensive peritubular capillary network
53
Describe juxtamedullary nephron
```
Long loop of henle
Tubule and vasculature penetrate deeply into medulla
Inner medulla hypertonic
Counter-current flow
Vasa recta
```
54
What makes the kidney unique?
It has 2 capillary beds in series being fed from the same arterial input
55
What does each capillary bed have?
Its own control valve that work independently controlling the path of least resistance
56
What does the path of least resistance determine?
Whether fluid is filtered to become urine or not
57
What does the low O2 tension and total RBF make the renal medulla very susceptible to?
Hypoxia
58
What is most of the oxygen consumed by the kidneys related to?
The high rate of active sodium reabsorption by the renal tubules
59
What is a glomerulus?
A balled up network of brainching and anatomosing capillaries where the plasma is filtered in the first stage of urine formation
60
What is the glomerulus surrounded by?
Bowman's capsule
61
What does the glomerulus receive its blood supply from?
An afferent arteriole of the renal circulation
62
What does the glomerulus drain into?
An efferent arteriole rather than a venule
63
What is the basic filtration unit of the kidney?
A glomerulus and its surrounding Bowman's capsule
64
What is the glomerular filtration rate?
The rate at which blood is filtered through all of the glomeruli and this the measure of the overall renal function
65
What are the 3 major layers of the glomerular capillary membrane and make up the filtration barrier?
The endothelium
A basement membrane
A layer of epithelial cells (podocytes)
66
What are the endothelial cells of the filtration barrier like?
Fenestrated
67
What is the basement membrane of the filtration barrier like?
Collagen meshwork
68
What are the podocytes of the filtration barrier like?
Finger-like extensions that surround capillaries with slits between fingers
69
What does solute filtration depend on?
Molecular size
| Ionic change
70
What do small molecules do to filterability?
Increase it
71
What do large molecules do to filterability?
Decrease it
72
What do cations do to filterability?
Increase it
73
What do anions do to filterability?
Decrease it
74
What is an example of something that impact how charge and size change filterability?
Dextrans
75
What are dextrans?
Polysaccharides that have been used to provide colloidal support in patients with low albumin levels
76
What is the overall charge of the filtration barrier?
Negative
77
What is the charge of albumin? What happens to it because of it?
Negative
| It is mostly repelled. Some gets across, but is actively reabsorbed by the tubular epithelial cells
78
How do you get the capillary filtration coefficient?
Hydraulic conductivity x surface area
79
Is the capillary filtration coefficient under physiologic control?
No
80
When is the capillary filtration coefficient affected?
In some disease states
81
Is capillary hydrostatic pressure under physiologic control?
Yes
82
What is the capillary hydrostatic pressure the primary means of?
Physiologic regulation of GFR
83
Is capillary colloidal pressure under physiologic control?
No
84
Is Bowman's capsule under physiologic control?
No
85
Is Bowman's capsule colloidal pressure under physiologic control?
No
86
Why is the colloidal pressure negligible in Bowman's capsule?
Protein should not be filtered
87
What are factors that influence glomerular hydrostatic pressure?
Arterial pressure
Afferent arteriolar resistance
Efferent arteriolar resistance
88
What does increased resistance of afferent arterioles do?
Makes the path of least resistance to bypass the kidney, decreases renal blood flow, and decreases glomerular hydrostatic pressure decreasing GFR
89
What does increased resistance of the efferent arterioles do?
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
What does efferent constriction do?
Decreases RBF
| Increases GFR
91
What does efferent dilation do?
Increase RBF
| Decrease GFR
92
What does afferent constriction do?
Decrease RBF
| Decrease GFR
93
What does afferent dilation do?
Increase in RBF
| Increase in GFR even without efferent constriction
94
What is the goal of RBF control?
Maintain constant GFR over a wide range of flow and pressure ranges for waste excretion without excess loss of fluid
95
What could an increase in blood pressure by 25% do?
Increase urine output
96
What is a transient increase of blood pressure caused by?
Exercise
Fear
Excitement
97
What is a persistent increase of blood pressure caused by?
Hypertension in humans
Occasionally occurs in cats and dogs
Rare in horses
98
What would an increase in cardiac output do?
Increase urine output
99
What is necessary in hypovolemic states?
Minimize urine production yet maintain waste excretion
100
What may be necessary in severe hypovolemic states?
Conserve fluid at the expense of waste excretion
101
What does a strong sympathetic tone do?
Decreases RBF and GFR
102
What is endothelin?
Potent vasoconstrictor released by damaged vascular endothelial cells
103
What is the path of renal blood flow control?
```
Increased arterial pressure
Increased stretch of blood vessel
Increase smooth muscle Ca permeability
Increased intracellular Ca
Increased smooth muscle contraction and vascular resistance
```
104
What does angiotensin II formation occur during?
Hypovolemic "low flow" states and lowered arterial pressure
105
What does angiotensin II do?
Constricts efferent arteriole increasing glomerular hydrostatic pressure preserving GFR while reducing renal blood flow
106
What does the juxtaglomerular complex do?
Senses and regulates Na delivered to distal tubule
107
What does the macula densa sense?
Na
108
What is too much Na interpreted as?
Too high GFR, so it needs to decrease
109
What is too little Na interpreted as?
Too little GFR, so it needs to increase
110
What are the 2 effects that macula densa has with a decrease in Na?
Afferent arteriolar vasodilation decreasing resistance to blood flow into the glomerulus
Efferent arteriolar vasoconstriction increasing resistance to blood flow out of the glomerulus
111
What does the macula densa signal juxtaglomerular cells to do?
Release renin
112
Describe how protein impacts GFR
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
What is the most common form of acute renal failure in the horse?
Acute tubular nephrosis
