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My Renal > Physiology > Flashcards

Physiology Flashcards

1
Q

What is osmolarity?

A

the concentration of osmotically active particles present in a solution with units mosmol/l

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2
Q

How is osmolarity calculated?

A

using molar concentration of solution and number of osmotically active particles present

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3
Q

What is the difference between osmolarity and osmolality?

A
  • osmolality is osmol/kg
  • osmolarity is osmol/l
    they are used interchangeably for body fluids
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4
Q

What is tonicity?

A

the effect that a solution has on cell volume

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5
Q

What are the different tonicities of fluid?

A
  • isotonic= no change
  • hypotonic= increase in cell volume
  • hypertonic= decrease in cell volume
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6
Q

What does tonicity also take into account?

A

the ability of a solute to cross a cell membrane

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7
Q

How much is total body weight in a male or female?

A

male is 60% of body weight
female is 50% of body weight
(differences is due to the way fat is stored)

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8
Q

Where is body water stored?

A
  • ICF: 2/3rds

- ECF: 1/3rd

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9
Q

What is the breakdown of where water is in the ECF?

A
  • 80% interstitial fluid
  • 20% plasma
  • negligible% lymph and transcellular fluid
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10
Q

What does TBW equal?

A

ICF + ECF

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11
Q

What can be used to measure body fluid compartments?

A

tracers (ECF and TBW are calculable)

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12
Q

How can the volume of distribution be measured?

A

using a small amount of sample of a large container

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13
Q

What is the equation for distribution volume (l)?

A

(Qx(mol) of tracer) / X

the bottom is the equilibration volume of tracer in body

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14
Q

What are insensible losses of water from the body?

A

from skin and lungs

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15
Q

What are sensible losses of water from the body?

A

sweat, faeces and urine

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16
Q

How is water imbalance manifested in the body?

A

as changes in blood fluid osmolarity

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17
Q

Which ions are more concentrated in the ECF?

A

Na+
Cl-
HCO3-

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18
Q

What ion is more concentrated in the ICF?

A

K+

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19
Q

What are the osmotic concentrations of the ECF and ICF?

A

they are identical at around 300mosmol/l

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20
Q

How does fluid shift happen?

A

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

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21
Q

What is tightly intertwined with fluid balance?

A

electrolyte balance

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22
Q

What causes changes in fluid osmolarity?

A

gain or loss or water

gain or loss of NaCl

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23
Q

Where is Na+ excluded from?

A

the ICF

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24
Q

What happens if there is NaCl gain in the ECF?

A
  • increased ECF

- decreased ICF

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25
Q

What happens if there is NaCl loss in the ECF?

A
  • decreased ECF

- increases ICF

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26
Q

What changes the composition and volume of the ECF?

A

the kidneys

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27
Q

What does regulation of ECF volume cause?

A

long term BP regulation

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28
Q

Why is electrolyte balance important?

A
  • it determines water balance

- concentrations of Na+ and K+ can affect cell function

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29
Q

Which electrolyte determines ECF volume?

A

Na+ as water follows salt

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30
Q

What does K+ mainly do?

A

establishes membrane potential

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31
Q

What can changes to K+ cause?

A

paralysis and cardiac arrest so this must be monitored by the kidneys

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32
Q

What are the main kidney functions?

A
  • water balance
  • salt balance
  • maintenance of plasma volume
  • maintenance of plasma osmolarity
  • acid-base balance
  • excretion of metabolic waste products
  • excretion of exogenous foreign compounds eg drugs
  • secretions of renin (controls aBP)
  • secretion of erythropoietin
  • conversion fo vit D to active form (calcitriol which then does Ca2+ absorption from GI tract)
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33
Q

What is the nephron surrounded by?

A

peritubular capillaries

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34
Q

Is the nephron in the medulla or the cortex?

A
  • loop of Henle and the end of the collecting duct are in the medulla
  • the rest of the nephron is in the cortex
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35
Q

What are the two types of nephron?

A
  • juxtamedullary (20%)

- cortical (80%)

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36
Q

What are the features of juxtamedullary nephrons?

A
  • dip deep into the inner medulla
  • long loop of Henle into medulla
  • single capillary structure called the vasa recta
  • these concentrate urine
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37
Q

What are the features of cortical nephrons?

A
  • glomeruli in outer cortex

- short loops of Henle dipping into outer medulla

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38
Q

What is the inner layer of the Bowman’s capsule?

A

podocytes

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39
Q

What is the juxtamedullary apparatus?

A

the afferent and efferent arterioles run either side of the distal convoluted tubule which has a macula dense where it touches them

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40
Q

How much of the plasma is filtered in glomerular filtration?

A

20%

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41
Q

What does the rate of excretion equal?

A

rate of filtration (GF) + rate of secretion (TS) - rate of reabsorption (TR)

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42
Q

What are the two processes out of the four that are easy to measure?

A
  • rate of filtration of X= [X]plasma * GFR

- rate of excretion of X= [X]urine * Vu (urine production rate)

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43
Q

How is net reabsorption calculated?

A

net reabsorption (when filtration is greater than excretion) is calculated by rate of filtration - rate of excretion

44
Q

How is net secretion calculated?

A

net secretion (when filtration is smaller than excretion) is calculated by rate of excretion - rate of filtration

45
Q

What can be assumed if filtration > excretion?

A

net reabsorption

46
Q

What can be assumed if excretion > filtration?

A

net secretion

47
Q

What are the filtration barriers in the glomerulus?

A
  • glomerular capillary endothelium (barrier to RBC)
  • basement membrane/basal lamina (plasma protein barrier)
  • slit processes of podocytes (plasma protein barrier)
48
Q

What is the path of fluid during glomerular filtration?

A
  • from lumen of glomerular capillary
  • through large pore
  • into basement membrane
  • through filtration slit between podocytes
  • into lumen of Bowman’s capsule
49
Q

What are the filtration pressures of the glomerulus?

A
  • glomerular capillary blood pressure (favours)
  • glomerular capillary oncotic pressure (against)
  • Bowman’s capsule hydrostatic pressure (against)
  • Bowman’s capsule oncotic pressure (favours)
50
Q

What is GFR?

A

rate at which protein-free plasma is filtered from glomeruli into Bowman’s capsule per unit time

51
Q

What does GFR equal?

A

GFR = Kf (how ‘holey’ the membrane is) * net filtration pressure

52
Q

What is normal GFR and what is the main determinant of its value?

A

125ml/min

glomerular capillary blood pressure

53
Q

What is the intrinsic mechanism of GFR?

A

autoregulation

  • myogenic mechanism
  • tubuloglomerular feedback mechanism
54
Q

What is the extrinsic mechanism of GFR?

A

sympathetic control via baroreceptor reflex

55
Q

What happens when arterial BP increases to GFR?

A
  • there is more blood flow into glomerulus
  • increased glomerular capillary BP
  • increased net filtration pressure
  • increased GFR
56
Q

What do vasoconstriction and vasodilation do to GFR?

A

vasoconstriction of afferent decreases GFR

vasodilation of afferent increases GFR

57
Q

What does a fall in blood volume do to urine volume?

A
  • fall in blood volume and decrease in aBP
  • detected by aortic and carotid sinus baroreceptors
  • increased sympathetic activity
  • generalised arteriolar vasoconstriction
  • constriction of afferent arterioles
  • decreased BPgc
  • decreased GFR
  • decreased urine volume (compensates for decreased blood volume)
58
Q

What does auto regulation go to GFR?

A

stops short-term changes in systemic arterial pressure affecting GFR

59
Q

What is involved in myogenic auto regulation of GFR?

A

vascular smooth muscle stretched (increased arterial pressure) and it contracts so the arteriole is constricted

60
Q

What is involved in tubuloglomerular feedback?

A

involves the juxtaglomerular apparatus, if GFR rises, more NaCl flows through tube so constriction of afferent arterioles (macula densa in distal tubule senses the NaCl tubular fluid content)

61
Q

What do kidney stones do to GFR?

A

decrease GFR due to increased Bowman’s capsule fluid pressure

62
Q

What does diarrhoea do to GFR?

A

decreases GFR due to high capillary oncotic pressure

63
Q

What happens to GFR in severely burned patients with a low capillary oncotic pressure?

A

high GFR

64
Q

What happens if there is a decrease in surface area available for filtration?

A

low GFR

65
Q

What values contribute to the normal net filtration of 10?

A

——————————-> normal net filtration 10

——–>glomerular capillary fluid pressure 55
BC oncotic pressure 0

66
Q

What is plasma clearance?

A

the volume of plasma completely cleared of a particular substance per minute (each substance has its own specific plasma clearance)

67
Q

What is does clearance of X equal? (important)

A

([X]urine * Vurine) / [X]plasma

68
Q

What is special about inulin?

A

clearance = GFR as there is no secretion or absorption

69
Q

What does the amount of inulin filtered equal?

A

the amount of inulin excreted

70
Q

What does GFR of inulin equal?

A

([inulin]urine * Vurine) / [inulin]plasma = GFR= clearance

71
Q

What substances have a clearance of 0?

A

eg glucose which are filtered and then completely reabsorbed and not secreted

72
Q

What happens with substances which are filtered, partly reabsorbed and not secreted?

A

clearance < GFR eg urea

73
Q

What happens with substances that are filtered, secreted and not reabsorbed?

A

clearance > GFR eg H+

74
Q

What is the overall outcome in these situations?

a) clearance < GFR
b) clearance = GFR
c) clearance > GFR

A

a) net reabsorption
b) secretion and reabsorption cancel out or don’t exist
c) net secretion

75
Q

What is the special feature of PAH?

A

para-amino hippuric acid is completely cleared from the capillaries by filtration and secretion so is used to calculate RPF

76
Q

What should a clearance marker be?

A

non-toxic
inert
easy to measure

77
Q

What should a GFR marker be?

A

filtered freely and not secreted or reabsorbed

78
Q

What should a RPF marker be?

A

filtered and completely secreted

normal RPF is 650ml/min

79
Q

What is filtration fraction?

A

fraction of plasma flowing through the glomeruli that is filtered into the tubules

80
Q

What does the filtration fraction equal?

A

GFR / renal plasma flow which is 20% normally

81
Q

What is the wall of the nephron made of?

A

single-layer of cuboidal epithelial cells

82
Q

Where is renin made in the kidneys?

A

granular cells make renin at afferent arteriole where it meets the macula densa

83
Q

What is the normal pH, HCO3- and arterial PCO2 of the blood?

A

pH= 7.4
[HCO3-]= 25
arterial PCO2= 35-45

84
Q

What does acidosis and alkalosis lead to?

A

acidosis = CNS depression
alkalosis = overactive CNS and PNS
changes in [H+] also affects enzymes and K+ levels

85
Q

Where is H+ added from?

A
  • carbonic acid from CO2 and H2O (resp system)
  • inorganic acids made during nutrient breakdown
  • organic acids made from metabolism
86
Q

What is the main equation for acid base balance?

A

CO2 + H2O H2CO3 H+ + HCO3-

lungs (carbonic anhydrase) kidneys

87
Q

What is the simplified equation for pH of the body?

A

pH= kidneys/lungs

88
Q

What can the kidneys do to the amount of HCO3-?

A
  • variable reabsorption of filtered HCO3-

- kidneys can add new HCO3- into the blood

89
Q

How does HCO3- enter the blood?

A
  • HCO3- joins with H+ and then dissociates into H20 and CO2
  • this enters cell
  • CO2 passes through and together they join to make H2CO3 which dissociates inside cell
  • H+ moves back into tubule against Na+
  • HCO3- moves out into interstitium with Na+ and KNa makes the Na gradient
90
Q

What is needed for HCO3- to be reabsorbed?

A

H+ is needed for reabsorption to prevent acidosis

91
Q

What does an increase in CO2 do to H+ exchange at PCT?

A
  • increase in H2CO3 so increase in secretion of H+ from tubular cell
  • more CO2 breathed in = more H+ in tubular fluid
92
Q

Normally, what is the situation with H+ and HCO3- in the PCT?

A

more H+ is secreted than HCO3- is filtered so all HCO3- is reabsorbed

93
Q

What happens when HCO3- is low?

A
  • H+ combines with phosphate to make H2PO4- which is expected and HCO3- is reabsorbed into the blood to add to buffer stores
  • NH4+ is made from H+ which is excreted and new HCO3- is reabsorbed into the blood which uses glutamate from the liver
94
Q

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

A
  • compensation is restoration of the pH irrespective of the PCO2 and [HCO3-]
  • correction is restoration of pH, PCO2 and [HCO3-] to normal
95
Q

What are the causes of respiratory acidosis?

A

retention of CO2 by the body eg COPD, chest injury, airway restriction or respiratory depression

96
Q

What does uncompensated respiratory acidosis look like?

A

high PCO2 and a low pH

97
Q

What is the compensation and correction of respiratory acidosis?

A
  • compensation= the kidneys secrete H+ in response to the CO2 retention (HCO3- rises as a result)
  • correction= decreasing PCO2 by restoration of normal ventilation
98
Q

What is the cause of respiratory alkalosis?

A

excessive removal of CO2 from the body eg altitude, hyperventilation or hysterical over breathing

99
Q

What does uncompensated respiratory alkalosis look like?

A

low PCO2 and high pH

100
Q

What is the compensation and correction of respiratory alkalosis?

A 
compensation= kidneys lower the [HCO3-] so H+ is conserved 
correction= restoration of normal ventilation
101
Q

What is the cause of metabolic acidosis?

A

COMMON

excess of H+ from other sources than CO2 eg ingestion fo acid, excessive metabolic production of H+ ie DM or diarrhoea

102
Q

What does metabolic acidosis look like?

A
  • decrease in [HCO3-] as a result of buffering for H+

- low pH

103
Q

What is the compensation and correction for metabolic acidosis?

A
  • compensation= CO2 is blown off by increase in ventilation due to low H+ which happens first
  • correction= increase in acid load excretion and new HCO3- into. blood as H+ secreted and then the respiration can go back to normal
104
Q

What is metabolic alkalosis caused by?

A

excessive H+ loss from the body eg vomiting, ingestion of alkali or aldosterone hyper secretion

105
Q

What does metabolic alkalosis look like?

A

decrease in H+ and increase in [HCO3-] so increased pH

106
Q

What is the compensation and correction for metabolic alkalosis?

A 
compensation= CO2 is retained which shifts buffer to increase [H+] which also increases HCO3-
correction= HCO3- excretion in the urine and after, the respiratory function can return to normal
107
Q

What does the graph of all acid-base disturbances look like?

A

HCO3- against pH
top left= resp acidosis which goes diagonally up to comp and straight down to correct
top right= met alkalosis diagonally up to comp and straight down to correct

bottom left= met acidosis which goes diagonally down to comp and straight up to correct
bottom right= respiratory alkalosis which goes diagonally down tpo comp and straight up to correct

My Renal (8 decks)

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