Physiology - Renal Flashcards
1
Q
Define “osmolarity”
A
The concentration of osmotically active particles in a solution
2
Q
What is the unit of osmolarity in the body?
A
mOsmol/L
3
Q
What 2 factors need to be known to calculate osmolarity?
A
Molar concn of the solution
Number of osmotically active particles present
4
Q
Calculate the osmolarity of a 150mM solution of NaCl
A
Osmotically active particles = NaCl = 2
Molar concn = 150
Osmolarity = 150 x 2 = 300 mOsmol/L
5
Q
What is the difference between osmolality and osmolarity?
A
Osmolality has units of osmol/kg water
Osmolarity has units of osmol/L
6
Q
What is the osmolarity of body fluids?
A
300 mOsmol/L
7
Q
Define “tonicity”
A
The effect a solution has on cell volume
8
Q
If a solution is isotonic, what does this mean?
A
Water ECF = Water ICF
Cell volume is unchanged - no net movement of water
9
Q
If a solution is hypotonic, what does this mean?
A
Water ECF greater than Water ICF
Cell volume increases - water moves into the cell
10
Q
If a solution if hypertonic, what does this mean?
A
Water ECF less than Water ICF
Cell volume decreases - water moves out of the cell
11
Q
The cell membrane is very permeable to urea and sucrose. True/False?
A
False
Permeable to urea, impermeable to sucrose
12
Q
If you placed a cell in a urea solution, what would happen?
A
Cell would increase in volume + burst, thus urea solution is hypotonic
13
Q
What are the 2 fluid compartments that make up total body water? State their proportions
A
Intracellular fluid (70%) Extracellular fluid (30%)
14
Q
List the components of extracellular fluid (ECF)
A
Plasma (20%)
Interstitial fluid (80%)
Lymph
Transcellular fluid
15
Q
How can body fluid compartments be measured?
A
Tracers - obtain distribution volume
16
Q
Give examples of tracers used to measure body fluid compartments
A
Total body water: tritated water
ECF: inulin
Plasma: labelled albumin
17
Q
TBW = ICF + ECF. Which tracers would enable you to calculate ICF?
A
Tritated water (TBW) Inulin (ECF)
18
Q
Give the equation to measure volume (V) of an unknown volume of water using a dosage (D) of tracer and sample concentration (C) of tracer
A
V = D/C
19
Q
List some methods of fluid input
A
Fluid intake
Food intake
Metabolism
20
Q
List some insensible (non-regulated) losses of fluid
A
Skin
Lungs
21
Q
List some sensible (regulated) losses of fluid
A
Sweat
Faeces
Urine
22
Q
Water imbalance manifests as change in body fluid osmolarity. True/False?
A
True
23
Q
How is water balance maintained?
A
By increasing/decreasing fluid intake
24
Q
Is the concn of Na higher in the ECF or ICF?
A
Na is higher in the ECF
25
Is the concn of Cl higher in the ECF or ICF?
Cl is higher in the ECF
26
Is the concn of K higher in the ECF or ICF?
K is higher in the ICF
27
Is the concn of HCO3 higher in the ECF or ICF?
HCO3 is higher in the ECF
28
The osmotic concn of the ECF = the osmotic concn of the ICF. True/False?
True
29
What is meant by fluid shift in body compartments?
Movement of water between ECF and ICF in response to an osmotic gradient
30
What would happen to the ICF if the osmotic gradient of the ECF increased?
Osmotic gradient increase = lose water
| Therefore, osmolarity increases, causing ECF to become hypertonic, so cell volume decreases i.e. ICF volume decreases
31
What would happen to the ICF if the osmotic gradient of the ECF decreased?
Osmotic gradient decrease = gain water
| Therefore, osmolarity decreases, causing ECF to become hypotonic, so cell volume increases i.e. ICF volume increases
32
If you add salt to the ECF, what happens to the ICF?
ECF becomes hypertonic so ICF decreases
33
If you remove salt from the ECF, what happens to the ICF?
ECF becomes hypotonic so ICF increases
34
If you administer 0.9% NaCl solution IV, what happens to fluid osmolarity?
No change in osmolarity; change in ECF volume only
35
Which ion is chiefly responsible for the osmolarity of the ECF?
Na
36
Which ion is chiefly responsible for the osmolarity of the ICF?
K
37
Salt imbalance manifests as change in ECV. True/False?
True
38
List the main functions of the kidney
```
Water and salt balance
Maintaining fluid volume and osmolarity
Acid-base balance
Excretion of waste
Secretion of renin, erythropoietin
Convert inactive vitamin D to calcitriol
```
39
What % of the cardiac output goes to kidneys?
20-25%
40
What 3 processes occur in a nephron?
Filtration
Reabsorption
Secretion
41
Describe the flow of arterial blood into the kidney involving its transformation into tubular fluid
Renal artery - afferent arteriole - glomerulus - 20% to Bowman's capsule, 80% to efferent arteriole - renal tubules - peritubular capillaries - renal vein
42
What are the 2 types of nephron?
Juxtaglomerular (20%)
| Cortical (80%)
43
How do juxtaglomerular and cortical nephrons differ?
Juxtaglomerular: vasa recta instead of PT capillaries, long loop of Henle
Cortical: PT capillaries, short loop of Henle
44
Which nephrons produce concentrated urine?
Juxtaglomerular nephrons
45
The diameter of the afferent arteriole is greater/smaller than the efferent arteriole
The diameter of the afferent arteriole is greater than the efferent arteriole
46
Which cells secrete renin in the juxtaglomerular apparatus?
Granular cells
47
What do the cells in the macula densa do?
Sense salt composition of distal convoluted tube fluid
48
How do you calculate the rate of filtration of substance X in the kidney?
X = mass of X filtered per unit time = [X]plasma x GFR
49
How do you calculate the rate of excretion of substance X in the kidney?
```
X = mass of X excreted per unit time = [X]urine x Vu
(Vu = volume of urine)
```
50
How do you calculate the rate of reabsorption of substance X in the kidney?
Rate of reabsorption of X = rate of filtration of X - rate of excretion of X
51
How do you calculate the of secretion of substance X in the kidney?
Rate of secretion of X = rate of excretion of X - rate of filtration of X
52
If rate of filtration of X is greater than rate of excretion of X, has net reabsorption or secretion taken place?
Net reabsorption
53
If rate of filtration of X is less than rate of excretion of X, has net reabsorption or secretion taken place?
Net secretion
54
The endothelial pores in the glomerular capillary are 100x larger than the capillaries found elsewhere in the body. True/False?
True
55
What are the 3 main barriers to filtration in the glomerulus?
```
Glomerular capillary endothelium (barrier to RBC)
Basement membrane (barrier to plasma protein)
Slit processes of podocytes (barrier to plasma protein)
```
56
Name the 4 main forces that comprise net filtration pressure
BPgc - Blood pressure of capillary
HPbc - Hydrostatic pressure of Bowman's capsule
COPgc - Oncotic pressure of capillary
COPbc - Oncotic pressure of Bowman's capsule
57
Glomerular filtration is a passive process. True/False?
True
58
Describe the effect of BPgc (blood pressure of glomerular capillary)
High (55 mm Hg) pressure constant across the capillary that favours filtration
59
Describe the effect of HPbc (hydrostatic pressure of Bowman's capsule)
Fluid in the Bowman's capsule opposing filtration
60
Describe the effect of COPgc (oncotic pressure of glomerular capillary)
Opposes filtration of plasma proteins due to concn gradient
61
Describe the effect of COPbc (oncotic pressure of Bowman's capsule)
Negligible since there are no plasma proteins in Bowman's capsule
62
What is the rough normal value of net filtration pressure?
10 mm Hg favouring filtration
63
Glomerular filtration rate (GFR) is the rate of filtration of protein-free plasma is filtered from the glomeruli into the Bowman's capsule per unit time. Give the equation for calculating this
```
GFR = Kf x net filtration pressure
Kf = filtration coefficient (how holey the glomerular membrane is)
```
64
What is the normal GFR value?
125 ml/min
65
Which pressure is the major determinant of GFR?
Glomerular capillary blood pressure (BPgc)
66
A decreased GFR results in decreased urine volume. True/False?
True
67
How is GFR controlled extrinsically?
Sympathetic control via baroreceptor reflex
68
How is GFR controlled intrinsically?
Myogenic mechanism
| Tubuloglomerular feedback
69
If arterial blood pressure increases, what happens to GFR and net filtration pressure?
GFR and NFP increase with increasing arterial BP
70
If vasoconstriction of the afferent arteriole occurs, what happens to GFR and net filtration pressure?
GFR and NCP decrease with vasoconstriction
71
How does decreased urine volume arise from a fall in blood volume?
Fall in BP causes fall in arterial blood pressure which is detected by baroreceptors that fire to activate sympathetic nervous system; this causes arteriolar vasoconstriction to decrease BPgc and thus decrease GFR, causing decreased urine volume
72
Changes in arterial blood pressure always result in changes in GFR. True/False?
False
Autoregulation prevents short-term changes in arterial blood pressure affecting GFR
i.e. intrinsic control
73
What is the equation for calculating mean arterial blood pressure?
(1/3 x [systolic - diastolic]) + diastolic
74
How do the macula densa cells contribute to intrinsic control of GFR?
Sense salt in distal tubule and release vasoconstrictive mediators (in response to salt) in a -ve feedback loop, causing decreased GFR
75
What effect does a kidney stone have on GFR?
Kidney stone causes increased HPbc, causing decreased GFR
76
What effect does diarrhoea have on GFR?
Diarrhoea causes increased COPgc, causing decreased GFR
77
What effect does severe burns have on GFR?
Severe burns causes decreased COPgc, causing increased GFR
78
What is plasma clearance?
A measure of how effectively the kidneys can clear a substance from blood
= volume of plasma containing a substance cleared per minute (ml/min)
79
Give the equation for plasma clearance of substance X
([X]urine x Vu) / [X]plasma
80
Which substance has a plasma clearance equivalent to GFR?
Inulin - it is neither absorbed or secreted, so can be used as a measure of GFR
81
Why is creatinine not as good as inulin as a measure of GFR?
Creatinine undergoes small amount of secretion so not quite as accurate but easier to measure clinically
82
Glucose is normally completely reabsorbed and not secreted. True/False?
True
| Should have 0 clearance
83
Give an example of a substance that is partly reabsorbed and not secreted
Urea
| About 50% is reabsorbed
84
The clearance of urea will be less/greater than the GFR
The clearance of urea will be less than the GFR
85
Give an example of a substance that is secreted but not reabsorbed
H+
86
The clearance of H+ will be less/greater than the GFR
The clearance of H+ will be greater than the GFR
87
If clearance is less than the GFR, the substance is reabsorbed/secreted/neither reabsorbed or secreted
If clearance is less than the GFR, the substance is reabsorbed
88
If clearance is equal to the GFR, the substance is reabsorbed/secreted/neither reabsorbed or secreted
If clearance is equal to the GFR, the substance is neither reabsorbed or secreted
89
If clearance is greater than the GFR, the substance is reabsorbed/secreted/neither reabsorbed or secreted
If clearance is greater than the GFR, the substance is secreted
90
Which substance helps us calculate renal plasma flow?
Para-amino hippuric acid (PAH)
91
Why is PAH useful for measuring renal plasma flow?
Freely filtered at glomerulus
Secreted into tubule (not reabsorbed)
Completely cleared from plasma
i.e. all PAH in plasma that escapes filtration is secreted from peritubular capillaries anyway
92
A marker of renal blood flow should be filtered and completely secreted. True/False?
True
93
What is filtration fraction?
Fraction of plasma that is filtered by the glomerulus (usually 20%)
94
Give the equation for calculating filtration fraction
GFR/renal plasma flow
95
Where does most reabsorption of substances occur in the nephron?
Occurs along whole length, but most occurs in proximal tubule
96
List substances reabsorbed in the proximal tubule
```
Sugar
Amino acid
Phosphate
Sulphate
Lactate
```
97
List substances secreted in the proximal tubule
```
H+
Hippurates (PAH)
Neurotransmitter
Bile
Uric acid
Drugs
Toxin
```
98
Where is the Na-K pump always found?
Basolateral membrane
99
Describe the movement of Na and K across the Na-K pump
2 K in, 3 Na out of cell against concn gradient
100
Is the Na-glucose transporter an example of cotransport or antiport?
Co-transport
101
Is the Na-H transporter an example of cotransport or antiport?
Antiport
102
How does water couple its reabsorption with ion transport?
Movement of Na towards blood creates electrochemical gradient for Cl movement which follows Na; this creates an osmotic gradient for movement of water
(Water follows sodium)
103
When does reabsorption of glucose stop?
When renal threshold is reached and cotransporters are fully saturated
104
Tubular fluid is iso-osmotic when it leaves the proximal tubule. What does this mean?
Osmolarity = 300 mOsmol/L
105
What is the function of the Loop of Henle?
Generate cortico-medullary concn gradient to enable production of hypertonic urine
106
What is the term for opposing fluid flow in the two limbs of the Loop of Henle?
Countercurrent multiplication
107
Which ions are reabsorbed in the ascending loop of Henle?
Na
| Cl
108
Little or no water reabsorption occurs in the ascending loop of Henle. True/False?
True
109
The descending loop of Henle reabsorbs a lot of salt. True/False?
False
| Mainly water reabsorption
110
The triple cotransporter enables reabsorption of which ions? Which drug class inhibits this cotransporter?
Na
Cl
K
Loop diuretics block the cotransporter
111
How does salt pumped out of ascending limb affect the osmolarity of the interstitial fluid?
Osmolarity of interstitial fluid increases
112
The distal tubule is not permeable to urea. True/False?
True
113
Hormones (ADH, aldosterone) only influence permeability of distal tubule and collecting duct. True/False?
True
114
ADH causes water excretion. True/False?
False
| ADH causes water reabsorption
115
What is the effect aldosterone upon K, H and Na?
Increases Na reabsorption
| Increased K and H secretion
116
What is the effect of ANP on Na?
Decrease Na reabsorption
117
Is distal tubular fluid hypo, hyper or iso osmotic?
Hypo-osmotic
118
What ion transport occurs in the early distal tubule?
Na-K-2Cl cotransport
119
What ion transport occurs in the late distal tubule?
Reabsorption: Ca, Na, K
Secretion: H+
120
Where are the aquaporin/vasopressin type 2 receptors (sensitive to ADH) located?
Apical membrane
121
High ADH causes hypotonic urine. True/False?
False
| High ADH causes water reabsorption, so urine will be hypertonic
122
Decreased atrial pressure causes increased/decreased ADH release
Decreased atrial pressure causes increased ADH release
123
What is the effect of nicotine and alcohol on ADH?
Nicotine stimulates ADH release
| Alcohol inhibits ADH release
124
What is the effect of aldosterone on Na and K?
Aldosterone promotes Na reabsorption and K release
125
What 3 mechanisms increase renin release in the juxtaglomerular apparatus?
Reduced BP in afferent arteriole
Macula densa cells sense decreased salt
Increased sympathetic stimulation
126
What is the equation for calculating pH?
pH = 1/log[H]
127
The pH of arterial blood is more alkali than the pH of venous blood. True/False?
True
pH of arterial blood = 7.45
pH of venous blood = 7.35
128
What is the average pH of blood?
7.4
129
Small changes in pH reflect small changes in [H+]. True/False?
False
| Large changes in [H+] cause small changes in pH
130
What is the effect of increasing [H+] on pH?
pH decreases with increasing [H+]
131
How do fluctuations in [H+} alter nerve/CNS activity?
Acidosis causes CNS depression
| Alkalosis causes overexcitability of PNS and CNS
132
List the 3 sources of [H+] addition into the body
```
Carbonic acid formation
Inorganic acids (from breakdown of nutrients)
Organic acids (from metabolism)
```
133
What is the relationship between strong + weak acids and dissociation in solution?
Strong acids dissociate completely in solution
| Weak acids dissociate partially in solution
134
HA --- H+ + A-
| If acid [H+] is added, what happens to equilibrium?
Equilibrium shifts to left to produce more HA
| A- ions mop up H+ ions to buffer any decrease in pH
135
HA --- H+ + A-
| If base [A-] is added, what happens to equilibrium?
Equilibrium shifts to right to dissociate more HA
| Rise in pH (caused by excess A-/fall in H+) is buffered by dissociation of HA
136
What is the equation for calculating equilibrium constant (K)?
K = [H][A]/[HA]
137
State the Henderson-Hasselbach equation
pH = pK + log[A]/[HA]
138
State the equation for calculating pK
pK = -logK = -log[H][A]/[HA]
139
The most important physiological buffer is the CO2-HCO3 buffer. What is the equilibrium equation?
CO2 + H20 --- H2CO3 --- H+ + HCO3-
140
Which enzyme catalyses the formation of carbonic acid?
Carbonic anhydrase
141
What does control of [HCO3-] depend on?
H+ secretion into the tubule
142
How can the kidneys generate new HCO3- when buffer stores are low (i.e. when [HCO3-]tubular-fluid is low)?
H+ combines with phosphate buffer to cause net gain of HCO3-
143
What is meant by titratable acid?
The amount of H+ excreted via phosphate buffer in the kidney (when tubular HCO3 is low)
Measure the amount of strong base added to the titrate to buffer the pH back to 7.4
i.e. to reverse addition of H+
144
What 3 things happen as a result of H+ tubular secretion?
Reabsorption of HCO3 (prevent acidosis)
Formation of acid phosphate
Formation of ammonium ion
145
What is the difference between compensation and correction of acid-base balance?
Compensation: restore pH regardless of HCO3 and CO2 levels
Correction: restore pH, HCO3 and CO2 to normal
146
Respiratory acidosis is caused by CO2 retention. List some disease causes
COPD
Chest injuries
Respiratory depression
147
What is the compensatory mechanism for respiratory acidosis?
Increase H+ secretion and generate titratable acid which forms new HCO3
i.e. ultimately increase HCO3
148
Respiratoy alkalosis is caused by excess CO2 removal. List some disease causes
Low inspired PO2 at altitude
| Hyperventilation
149
What is the compensatory mechanism for respiratory alkalosis?
HCO3 excretion - no titratable acid is formed so no generation of new HCO3
i.e. ultimately decrease HCO3
150
Metabolic acidosis is caused by excess H+ from any source other than CO2. List some disease causes
Ingestion of acid foodstuff
Metabolic production (lactic acid)
Loss of base from body (diarrhoea)
151
What is the compensatory mechanism for metabolic acidosis?
Hyperventilation - blow off CO2
| i.e. ultimately lower H+
152
Metabolic alkalosis is caused by excess loss of H+ from body. List some disease causes
Vomiting (loss of HCl)
Ingestion of alkali (antacid)
Aldosterone hypersecretion
153
What is the compensatory mechanism for metabolic alkalosis?
Slow ventilation - retain CO2
| i.e. ultimately increase H+
