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2MB Renal > Physiology > Flashcards

Physiology Flashcards

1
Q

Define “osmolarity”

A

The concentration of osmotically active particles in a solution

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2
Q

What is the unit of osmolarity in the body?

A

mOsmol/L

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3
Q

What 2 factors need to be known to calculate osmolarity?

A

Molar concn of the solution

Number of osmotically active particles present

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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

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5
Q

What is the difference between osmolality and osmolarity?

A

Osmolality has units of osmol/kg water

Osmolarity has units of osmol/L

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6
Q

What is the osmolarity of body fluids?

A

300 mOsmol/L

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7
Q

Define “tonicity”

A

The effect a solution has on cell volume

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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

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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

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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

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11
Q

The cell membrane is very permeable to urea and sucrose. True/False?

A

False

Permeable to urea, impermeable to sucrose

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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

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13
Q

What are the 2 fluid compartments that make up total body water? State their proportions

A 
Intracellular fluid (70%)
Extracellular fluid (30%)
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14
Q

List the components of extracellular fluid (ECF)

A

Plasma (20%)
Interstitial fluid (80%)
Lymph
Transcellular fluid

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15
Q

How can body fluid compartments be measured?

A

Tracers - obtain distribution volume

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16
Q

Give examples of tracers used to measure body fluid compartments

A

Total body water: tritated water
ECF: inulin
Plasma: labelled albumin

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17
Q

TBW = ICF + ECF. Which tracers would enable you to calculate ICF?

A 
Tritated water (TBW)
Inulin (ECF)
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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

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19
Q

List some methods of fluid input

A

Fluid intake
Food intake
Metabolism

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20
Q

List some insensible (non-regulated) losses of fluid

A

Skin

Lungs

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21
Q

List some sensible (regulated) losses of fluid

A

Sweat
Faeces
Urine

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22
Q

Water imbalance manifests as change in body fluid osmolarity. True/False?

A

True

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23
Q

How is water balance maintained?

A

By increasing/decreasing fluid intake

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24
Q

Is the concn of Na higher in the ECF or ICF?

A

Na is higher in the ECF

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25
Q

Is the concn of Cl higher in the ECF or ICF?

A

Cl is higher in the ECF

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26
Q

Is the concn of K higher in the ECF or ICF?

A

K is higher in the ICF

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27
Q

Is the concn of HCO3 higher in the ECF or ICF?

A

HCO3 is higher in the ECF

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28
Q

The osmotic concn of the ECF = the osmotic concn of the ICF. True/False?

A

True

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29
Q

What is meant by fluid shift in body compartments?

A

Movement of water between ECF and ICF in response to an osmotic gradient

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30
Q

What would happen to the ICF if the osmotic gradient of the ECF increased?

A

Osmotic gradient increase = lose water

Therefore, osmolarity increases, causing ECF to become hypertonic, so cell volume decreases i.e. ICF volume decreases

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31
Q

What would happen to the ICF if the osmotic gradient of the ECF decreased?

A

Osmotic gradient decrease = gain water

Therefore, osmolarity decreases, causing ECF to become hypotonic, so cell volume increases i.e. ICF volume increases

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32
Q

If you add salt to the ECF, what happens to the ICF?

A

ECF becomes hypertonic so ICF decreases

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33
Q

If you remove salt from the ECF, what happens to the ICF?

A

ECF becomes hypotonic so ICF increases

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34
Q

If you administer 0.9% NaCl solution IV, what happens to fluid osmolarity?

A

No change in osmolarity; change in ECF volume only

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35
Q

Which ion is chiefly responsible for the osmolarity of the ECF?

A

Na

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36
Q

Which ion is chiefly responsible for the osmolarity of the ICF?

A

K

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37
Q

Salt imbalance manifests as change in ECV. True/False?

A

True

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38
Q

List the main functions of the kidney

A 
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
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39
Q

What % of the cardiac output goes to kidneys?

A

20-25%

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40
Q

What 3 processes occur in a nephron?

A

Filtration
Reabsorption
Secretion

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41
Q

Describe the flow of arterial blood into the kidney involving its transformation into tubular fluid

A

Renal artery - afferent arteriole - glomerulus - 20% to Bowman’s capsule, 80% to efferent arteriole - renal tubules - peritubular capillaries - renal vein

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42
Q

What are the 2 types of nephron?

A

Juxtaglomerular (20%)

Cortical (80%)

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43
Q

How do juxtaglomerular and cortical nephrons differ?

A

Juxtaglomerular: vasa recta instead of PT capillaries, long loop of Henle
Cortical: PT capillaries, short loop of Henle

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44
Q

Which nephrons produce concentrated urine?

A

Juxtaglomerular nephrons

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45
Q

The diameter of the afferent arteriole is greater/smaller than the efferent arteriole

A

The diameter of the afferent arteriole is greater than the efferent arteriole

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46
Q

Which cells secrete renin in the juxtaglomerular apparatus?

A

Granular cells

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47
Q

What do the cells in the macula densa do?

A

Sense salt composition of distal convoluted tube fluid

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48
Q

How do you calculate the rate of filtration of substance X in the kidney?

A

X = mass of X filtered per unit time = [X]plasma x GFR

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49
Q

How do you calculate the rate of excretion of substance X in the kidney?

A 
X = mass of X excreted per unit time = [X]urine x Vu
(Vu = volume of urine)
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50
Q

How do you calculate the rate of reabsorption of substance X in the kidney?

A

Rate of reabsorption of X = rate of filtration of X - rate of excretion of X

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51
Q

How do you calculate the of secretion of substance X in the kidney?

A

Rate of secretion of X = rate of excretion of X - rate of filtration of X

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52
Q

If rate of filtration of X is greater than rate of excretion of X, has net reabsorption or secretion taken place?

A

Net reabsorption

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53
Q

If rate of filtration of X is less than rate of excretion of X, has net reabsorption or secretion taken place?

A

Net secretion

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54
Q

The endothelial pores in the glomerular capillary are 100x larger than the capillaries found elsewhere in the body. True/False?

A

True

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55
Q

What are the 3 main barriers to filtration in the glomerulus?

A 
Glomerular capillary endothelium (barrier to RBC)
Basement membrane (barrier to plasma protein)
Slit processes of podocytes (barrier to plasma protein)
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56
Q

Name the 4 main forces that comprise net filtration pressure

A

BPgc - Blood pressure of capillary
HPbc - Hydrostatic pressure of Bowman’s capsule
COPgc - Oncotic pressure of capillary
COPbc - Oncotic pressure of Bowman’s capsule

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57
Q

Glomerular filtration is a passive process. True/False?

A

True

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58
Q

Describe the effect of BPgc (blood pressure of glomerular capillary)

A

High (55 mm Hg) pressure constant across the capillary that favours filtration

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59
Q

Describe the effect of HPbc (hydrostatic pressure of Bowman’s capsule)

A

Fluid in the Bowman’s capsule opposing filtration

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60
Q

Describe the effect of COPgc (oncotic pressure of glomerular capillary)

A

Opposes filtration of plasma proteins due to concn gradient

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61
Q

Describe the effect of COPbc (oncotic pressure of Bowman’s capsule)

A

Negligible since there are no plasma proteins in Bowman’s capsule

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62
Q

What is the rough normal value of net filtration pressure?

A

10 mm Hg favouring filtration

63
Q

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

A 
GFR = Kf x net filtration pressure
Kf = filtration coefficient (how holey the glomerular membrane is)
64
Q

What is the normal GFR value?

A

125 ml/min

65
Q

Which pressure is the major determinant of GFR?

A

Glomerular capillary blood pressure (BPgc)

66
Q

A decreased GFR results in decreased urine volume. True/False?

67
Q

How is GFR controlled extrinsically?

A

Sympathetic control via baroreceptor reflex

68
Q

How is GFR controlled intrinsically?

A

Myogenic mechanism

Tubuloglomerular feedback

69
Q

If arterial blood pressure increases, what happens to GFR and net filtration pressure?

A

GFR and NFP increase with increasing arterial BP

70
Q

If vasoconstriction of the afferent arteriole occurs, what happens to GFR and net filtration pressure?

A

GFR and NCP decrease with vasoconstriction

71
Q

How does decreased urine volume arise from a fall in blood volume?

A

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
Q

Changes in arterial blood pressure always result in changes in GFR. True/False?

A

False
Autoregulation prevents short-term changes in arterial blood pressure affecting GFR
i.e. intrinsic control

73
Q

What is the equation for calculating mean arterial blood pressure?

A

(1/3 x [systolic - diastolic]) + diastolic

74
Q

How do the macula densa cells contribute to intrinsic control of GFR?

A

Sense salt in distal tubule and release vasoconstrictive mediators (in response to salt) in a -ve feedback loop, causing decreased GFR

75
Q

What effect does a kidney stone have on GFR?

A

Kidney stone causes increased HPbc, causing decreased GFR

76
Q

What effect does diarrhoea have on GFR?

A

Diarrhoea causes increased COPgc, causing decreased GFR

77
Q

What effect does severe burns have on GFR?

A

Severe burns causes decreased COPgc, causing increased GFR

78
Q

What is plasma clearance?

A

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
Q

Give the equation for plasma clearance of substance X

A

([X]urine x Vu) / [X]plasma

80
Q

Which substance has a plasma clearance equivalent to GFR?

A

Inulin - it is neither absorbed or secreted, so can be used as a measure of GFR

81
Q

Why is creatinine not as good as inulin as a measure of GFR?

A

Creatinine undergoes small amount of secretion so not quite as accurate but easier to measure clinically

82
Q

Glucose is normally completely reabsorbed and not secreted. True/False?

A

True

Should have 0 clearance

83
Q

Give an example of a substance that is partly reabsorbed and not secreted

A

Urea

About 50% is reabsorbed

84
Q

The clearance of urea will be less/greater than the GFR

A

The clearance of urea will be less than the GFR

85
Q

Give an example of a substance that is secreted but not reabsorbed

86
Q

The clearance of H+ will be less/greater than the GFR

A

The clearance of H+ will be greater than the GFR

87
Q

If clearance is less than the GFR, the substance is reabsorbed/secreted/neither reabsorbed or secreted

A

If clearance is less than the GFR, the substance is reabsorbed

88
Q

If clearance is equal to the GFR, the substance is reabsorbed/secreted/neither reabsorbed or secreted

A

If clearance is equal to the GFR, the substance is neither reabsorbed or secreted

89
Q

If clearance is greater than the GFR, the substance is reabsorbed/secreted/neither reabsorbed or secreted

A

If clearance is greater than the GFR, the substance is secreted

90
Q

Which substance helps us calculate renal plasma flow?

A

Para-amino hippuric acid (PAH)

91
Q

Why is PAH useful for measuring renal plasma flow?

A

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
Q

A marker of renal blood flow should be filtered and completely secreted. True/False?

93
Q

What is filtration fraction?

A

Fraction of plasma that is filtered by the glomerulus (usually 20%)

94
Q

Give the equation for calculating filtration fraction

A

GFR/renal plasma flow

95
Q

Where does most reabsorption of substances occur in the nephron?

A

Occurs along whole length, but most occurs in proximal tubule

96
Q

List substances reabsorbed in the proximal tubule

A 
Sugar
Amino acid
Phosphate
Sulphate
Lactate
97
Q

List substances secreted in the proximal tubule

A 
H+
Hippurates (PAH)
Neurotransmitter
Bile
Uric acid
Drugs
Toxin
98
Q

Where is the Na-K pump always found?

A

Basolateral membrane

99
Q

Describe the movement of Na and K across the Na-K pump

A

2 K in, 3 Na out of cell against concn gradient

100
Q

Is the Na-glucose transporter an example of cotransport or antiport?

A

Co-transport

101
Q

Is the Na-H transporter an example of cotransport or antiport?

102
Q

How does water couple its reabsorption with ion transport?

A

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
Q

When does reabsorption of glucose stop?

A

When renal threshold is reached and cotransporters are fully saturated

104
Q

Tubular fluid is iso-osmotic when it leaves the proximal tubule. What does this mean?

A

Osmolarity = 300 mOsmol/L

105
Q

What is the function of the Loop of Henle?

A

Generate cortico-medullary concn gradient to enable production of hypertonic urine

106
Q

What is the term for opposing fluid flow in the two limbs of the Loop of Henle?

A

Countercurrent multiplication

107
Q

Which ions are reabsorbed in the ascending loop of Henle?

108
Q

Little or no water reabsorption occurs in the ascending loop of Henle. True/False?

109
Q

The descending loop of Henle reabsorbs a lot of salt. True/False?

A

False

Mainly water reabsorption

110
Q

The triple cotransporter enables reabsorption of which ions? Which drug class inhibits this cotransporter?

A

Na
Cl
K
Loop diuretics block the cotransporter

111
Q

How does salt pumped out of ascending limb affect the osmolarity of the interstitial fluid?

A

Osmolarity of interstitial fluid increases

112
Q

The distal tubule is not permeable to urea. True/False?

113
Q

Hormones (ADH, aldosterone) only influence permeability of distal tubule and collecting duct. True/False?

114
Q

ADH causes water excretion. True/False?

A

False

ADH causes water reabsorption

115
Q

What is the effect aldosterone upon K, H and Na?

A

Increases Na reabsorption

Increased K and H secretion

116
Q

What is the effect of ANP on Na?

A

Decrease Na reabsorption

117
Q

Is distal tubular fluid hypo, hyper or iso osmotic?

A

Hypo-osmotic

118
Q

What ion transport occurs in the early distal tubule?

A

Na-K-2Cl cotransport

119
Q

What ion transport occurs in the late distal tubule?

A

Reabsorption: Ca, Na, K
Secretion: H+

120
Q

Where are the aquaporin/vasopressin type 2 receptors (sensitive to ADH) located?

A

Apical membrane

121
Q

High ADH causes hypotonic urine. True/False?

A

False

High ADH causes water reabsorption, so urine will be hypertonic

122
Q

Decreased atrial pressure causes increased/decreased ADH release

A

Decreased atrial pressure causes increased ADH release

123
Q

What is the effect of nicotine and alcohol on ADH?

A

Nicotine stimulates ADH release

Alcohol inhibits ADH release

124
Q

What is the effect of aldosterone on Na and K?

A

Aldosterone promotes Na reabsorption and K release

125
Q

What 3 mechanisms increase renin release in the juxtaglomerular apparatus?

A

Reduced BP in afferent arteriole
Macula densa cells sense decreased salt
Increased sympathetic stimulation

126
Q

What is the equation for calculating pH?

A

pH = 1/log[H]

127
Q

The pH of arterial blood is more alkali than the pH of venous blood. True/False?

A

True
pH of arterial blood = 7.45
pH of venous blood = 7.35

128
Q

What is the average pH of blood?

129
Q

Small changes in pH reflect small changes in [H+]. True/False?

A

False

Large changes in [H+] cause small changes in pH

130
Q

What is the effect of increasing [H+] on pH?

A

pH decreases with increasing [H+]

131
Q

How do fluctuations in [H+} alter nerve/CNS activity?

A

Acidosis causes CNS depression

Alkalosis causes overexcitability of PNS and CNS

132
Q

List the 3 sources of [H+] addition into the body

A 
Carbonic acid formation
Inorganic acids (from breakdown of nutrients)
Organic acids (from metabolism)
133
Q

What is the relationship between strong + weak acids and dissociation in solution?

A

Strong acids dissociate completely in solution

Weak acids dissociate partially in solution

134
Q

HA — H+ + A-

If acid [H+] is added, what happens to equilibrium?

A

Equilibrium shifts to left to produce more HA

A- ions mop up H+ ions to buffer any decrease in pH

135
Q

HA — H+ + A-

If base [A-] is added, what happens to equilibrium?

A

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
Q

What is the equation for calculating equilibrium constant (K)?

A

K = [H][A]/[HA]

137
Q

State the Henderson-Hasselbach equation

A

pH = pK + log[A]/[HA]

138
Q

State the equation for calculating pK

A

pK = -logK = -log[H][A]/[HA]

139
Q

The most important physiological buffer is the CO2-HCO3 buffer. What is the equilibrium equation?

A

CO2 + H20 — H2CO3 — H+ + HCO3-

140
Q

Which enzyme catalyses the formation of carbonic acid?

A

Carbonic anhydrase

141
Q

What does control of [HCO3-] depend on?

A

H+ secretion into the tubule

142
Q

How can the kidneys generate new HCO3- when buffer stores are low (i.e. when [HCO3-]tubular-fluid is low)?

A

H+ combines with phosphate buffer to cause net gain of HCO3-

143
Q

What is meant by titratable acid?

A

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
Q

What 3 things happen as a result of H+ tubular secretion?

A

Reabsorption of HCO3 (prevent acidosis)
Formation of acid phosphate
Formation of ammonium ion

145
Q

What is the difference between compensation and correction of acid-base balance?

A

Compensation: restore pH regardless of HCO3 and CO2 levels
Correction: restore pH, HCO3 and CO2 to normal

146
Q

Respiratory acidosis is caused by CO2 retention. List some disease causes

A

COPD
Chest injuries
Respiratory depression

147
Q

What is the compensatory mechanism for respiratory acidosis?

A

Increase H+ secretion and generate titratable acid which forms new HCO3
i.e. ultimately increase HCO3

148
Q

Respiratoy alkalosis is caused by excess CO2 removal. List some disease causes

A

Low inspired PO2 at altitude

Hyperventilation

149
Q

What is the compensatory mechanism for respiratory alkalosis?

A

HCO3 excretion - no titratable acid is formed so no generation of new HCO3
i.e. ultimately decrease HCO3

150
Q

Metabolic acidosis is caused by excess H+ from any source other than CO2. List some disease causes

A

Ingestion of acid foodstuff
Metabolic production (lactic acid)
Loss of base from body (diarrhoea)

151
Q

What is the compensatory mechanism for metabolic acidosis?

A

Hyperventilation - blow off CO2

i.e. ultimately lower H+

152
Q

Metabolic alkalosis is caused by excess loss of H+ from body. List some disease causes

A

Vomiting (loss of HCl)
Ingestion of alkali (antacid)
Aldosterone hypersecretion

153
Q

What is the compensatory mechanism for metabolic alkalosis?

A

Slow ventilation - retain CO2

i.e. ultimately increase H+

2MB Renal (16 decks)

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