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Renal > Physiology > Flashcards

Physiology Flashcards

1
Q

Define osmolarity

A

Concentration of osmotically active particles present in a solution

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2
Q

What is the osmolarity of most body fluids?

A

300mosmol/l

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3
Q

Define tonicity

A

Effect a solution has on cell volume

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4
Q

What is the effect of a hypotonic solution?

A

Causes a cell to swell and increases cell volume

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5
Q

What is the effect of a hypertonic solution?

A

Causes a cell to shrink and decreases cell volume

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6
Q

What percentage of the body weight is total body water?

A

50-60%

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7
Q

What are the two components of total body water?

A

Intracellular and extracellular

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8
Q

What makes up the extracellular fluid?

A

Plasma

Interstitial Fluid

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9
Q

What separates the intra/extracellular fluid?

A

Cell membrane

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10
Q

How can the distribution volume be calculated?

A

By use of a tracer - titrated water, inulin, labelled albumin

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11
Q

Describe the ionic differences between ICF and ECF

A

ICF - high potassium

ECF - high sodium, chloride, bicarbonate, magnesium, negative proteins

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12
Q

Define fluid shifts

A

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

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13
Q

What is the effect of water loss from ECF?

A

Increase in ECF osmotic concentration water will move out of the ICF and into the ECF so cells will shrink

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14
Q

What is the effect of water gain to the ECF?

A

Decrease in ECF osmotic concentration water will move out of the ECF into the ICF so cells will swell

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15
Q

Describe the effect of gain/loss of NaCl

A

Sodium excluded from ICF, if ECF gains salt osmolarity will increase so water will leave ICF to ECF
Loss of salt will increase ICF volume as ECF osmolarity will decrease

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16
Q

Other than salt/water changes what else can cause a fluid shift?

A

Change in volume - gain/loss of isotonic fluid, only change in ECF volume

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17
Q

Define an electrolyte

A

Any substance that dissociates into free ions when dissolved

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18
Q

Name two key ions that contribute to osmotic concentrations

A

Sodium - ECF

Potassium - ICF

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19
Q

What detrimental changes can occur due to changes in potassium?

A

Muscle weakness and paralysis

Cardiac irregularities and arrest

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20
Q

What is the recommended salt allowance?

A

6g/day

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21
Q

Name the function of the kidneys

A
  1. water balance
  2. salt balance
  3. maintain plasma volume
  4. maintain plasma osmolarity
  5. acid base balance
  6. excretion of metabolic waste
  7. excretion of exogenous compounds
  8. secretion of renin
  9. secretion of erythropoietin
  10. conversion of vit D to its active form
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22
Q

What percentage of blood is filtered by the glomerulus?

A

20%

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23
Q

Name the three components of the glomerular filter

A
  • glomerular capillary endothelium
  • basement membrane
  • slit processes of podocytes
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24
Q

Name the four forces that result in glomerular filtration

A

Glomerular capillary BP 55mmHg towards tubule
Capillary oncotic pressure 30mmHg towards capillary
Bowman’s capsule hydrostatic pressure 15mg towards capillary
Bowman’s capsule oncotic pressure towards tubule 0mmHg

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25
Q

What is the net filtration pressure?

A

10mmHg

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26
Q

Define GFR

A

Rate at which protein free plasma is filtered from the glomeruli in to Bowmans capsule per unit time

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27
Q

What is the normal GFR?

A

125ml/min

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28
Q

How is GFR regulated extrinsically?

A

Changes to vessel shape alter the GFR

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29
Q

Describe the effect of a fall in blood volume

A
  1. Decreased blood pressure
  2. Detected by baroreceptors
  3. Increase in sympathetic activity
  4. Vasoconstriction
  5. Decreased GFR
  6. Decreased urine volume (compensates for reduced blood volume)
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30
Q

What is the effect of auto regulation on GFR?

A

Prevents short term changes in systemic arterial pressure affecting GFR

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31
Q

Describe myogenic auto regulation

A

If vascular smooth muscle is stretched it contracts, constricting the arteriole

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32
Q

Describe tubuloglomerular auto regulation

A

Involves juxtaglomerular apparatus

If GFR rises more salt will through flow the tubule leading to constriction of afferent arterioles

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33
Q

What senses NaCl content in the tubular fluid?

A

Macula densa

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34
Q

Name three pathologies that can alter GFR

A

Kidney stones, increases bowmans fluid pressure, decreases GFR
Diarrhoea increases bowman oncotic pressure, decreases GFR
Severe burns decrease bowmans oncotic pressure and increases GFR

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35
Q

Define plasma clearance

A

Measure of how effectively the kidneys can clean the blood of a substance

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36
Q

Describe the clearance/GFR of inulin

A

Clearance = GFR as it is freely filtered and not reabsorbed or secreted

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37
Q

Describe the clearance/GFR of glucose

A

Filtered, completely reabsorbed and not secreted

Clearance = 0

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38
Q

Describe the clearance/GFR of urea

A

Filtered and partly reabsorbed but not secreted so clearance

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39
Q

Describe H+ clearance/GFR

A

Filtered and secreted but not absorbed
Clearance > GFR
All filtered plasma is cleared and some peritubular plasma too

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40
Q

State three things a clearance marker should be

A

Non-toxic
Inert
Easy to measure

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41
Q

Name some substances that are reabsorbed

A
  • sugars
  • amino acids
  • phosphate
  • sulphate
  • lactate
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42
Q

Name some substances that are secreted

A
  • hydrogen ions
  • hippurates
  • neurotransmitters
  • bile pigments
  • uric acid
  • drugs and toxins
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43
Q

Name two methods of reabsorption

A

Transcellular

Paracellular

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44
Q

State three methods of transport of a substance

A

Primary active
Secondary active
Facilitated diffusion

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45
Q

Describe primary active transport

A

Energy directly required to move the substance against the gradient

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46
Q

Describe secondary active transport

A

Molecule is transported, coupled to the concentration of an ion

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47
Q

Describe facilitated diffusion

A

Passive carrier mediated transport down the concentration gradient

48
Q

Describe three methods of sodium reabsorption

A
  • Sodium potassium pump on basolateral membrane
  • Co-transport with glucose/amino acids
  • Sodium/hydrogen exchanger using hydrogen ions produced by carbonic anhydrase
49
Q

How do water and chlorine leave the tubule?

A

Paracellular reabsorption
Standing osmotic gradient moves water by diffusion
As sodium leaves the lumen becomes more negative which causes chloride ions to leave

50
Q

How is glucose reabsorbed?

A

Co-transported with sodium into the epithelial cell, it then leaves via facilitated diffusion

51
Q

What is the renal threshold for glucose?

A

10-12mmol/l

52
Q

What is the function of the loop of henle?

A

Generates a cortico-medullary solute concentration gradient which enables formation of hypertonic urine

53
Q

Describe the movement of substances in the loop of henle

A
  1. Solute is removed from the ascending limb
  2. Tubular fluid is diluted and osmolality of interstitial fluid increases
  3. Water leaves the descending limb via osmosis
  4. Fluid in the descending limb is concentrated
54
Q

Describe the gradient created by countercurrent multiplication

A

The horizontal gradient has been multiplied into a large vertical gradient

55
Q

How is urea managed in the distal tubule?

A

Distal tubule is impermeable to urea so as water is removed it becomes more concentrated

56
Q

What happens to urea in the medullary collecting duct?

A

It is absorbed as transporters are activated by vasopressin as a result this drives water reabsorption from the descending limb

57
Q

What transporters are activated by vasopressin?

A

UTA3

A3

58
Q

Name the blood vessel that supplies the medulla

A

Vasa Recta

59
Q

How does the vasa recta prevent all the solute being washed away?

A
  • hairpin loops
  • capillaries are permeable to NaCl and water
  • low blood flow
60
Q

Name four hormones that control body fluid

A
  • antidiuretic
  • aldosterone
  • atrial natriuretic hormone
  • parathyroid hormone
61
Q

What ions are reabsorbed in the early distal tubule?

A

NaCl (NaK2Cl transport)

62
Q

What ions are reabsorbed in the late distal tubule?

A

Calcium
Hydrogen
Sodium
Potassium

63
Q

Describe the late collecting duct

A

Low ion permeability

Permeability to water and urea influenced by ADH

64
Q

Where is antidiuretic hormone synthesised?

A

Hypothalamus

65
Q

State the shape of antidiuretic

A

Octapeptide

66
Q

What signals to the hypothalamus to release ADH?

A

Osmoreceptors

Atrial volume receptors

67
Q

When is ADH released?

A

When action potentials down the nerves lead to calcium dependent exocytosis

68
Q

How does ADH increase the permeability to water?

A

Binds to receptor to turn ATP to cAMP

Increased the permeability by inserting new aquaporins to the luminal membrane

69
Q

What happens to water in the presence of ADH?

A

Moves from the collecting duct lumen along the osmotic gradient and into the medullary interstitial fluid

70
Q

Describe the effect of high/low ADH

A

High - small volume of concentrated urine

Low - large volume of dilute urine

71
Q

What extra-renal features can impact ADH level?

A

GI stretch receptors inhibit ADH
Nicotine stimulates ADH
Alcohol inhibits ADH

72
Q

Where is aldosterone secreted?

A

Adrenal cortex

73
Q

When is aldosterone secreted?

A

In response to increased potassium or decreased sodium in the blood

74
Q

What is the effect of aldosterone?

A

Increases sodium reabsorption and potassium secretion

75
Q

State the steps of the RAAS system in response to decreased salt, ECF or ABP

A
  1. Angiotensinogen converted into angiotensin I by renin
  2. Angiotensin I is converted into angiotensin II by ACE
  3. Angiotensin II causes vasoconstriction, thirst and ADH release
    Thirst increases fluid uptake
    ADH increases water reabsorption
76
Q

How does aldosterone act as part of RAAS?

A

Increases sodium reabsorption and chlorine follows this leads to osmotic hold of water and thus conservation of water

77
Q

Where is renin released from?

A

Granular cells in the juxtaglomerular apparatus

78
Q

What signals for renin to be released?

A
  1. Reduced pressure in afferent arteriole
  2. Macula dense cells ones the amount of NaCl in distal tubule
  3. Increased sympathetic activity due to decreased ABP
79
Q

Where does atrial natriuretic peptide come from?

A

Produced in heart and stored in the atrium

80
Q

When is ANP released?

A

When atrial muscle cells are stretched due to increased plasma volume

81
Q

How does ANP decrease plasma volume?

A
  • decreases sodium reabsorption
  • decreases RAAS
  • vasodilation
  • reduces sympathetic activity
82
Q

What is micturition governed by?

A

Micturition reflex

Voluntary control

83
Q

What is the average pH of blood?

A

7.4

84
Q

Where can hydrogen ions come form?

A

Carbonic acid formation
Inorganic acids produced in breakdown of nutrients
Organic acids from metabolism

85
Q

What is the difference between a strong and weak acid?

A

Strong - completely dissociates in solution

Weak - partially dissociates in solution

86
Q

What is a buffer?

A

Pair of substances;
one can yield free hydrogen ions
one can bind free hydrogen ions

87
Q

What is the key physiological buffer?

A

CO2, HCO2 Buffer

88
Q

How is carbonic acid formed?

A

By the hydration of carbon dioxide by carbonic anhydrase

89
Q

How does the kidney control bicarbonate concentration?

A

Variable reabsorption of filtered bicarbonate

Addition of new bicarbonate to the blood

90
Q

What does control of bicarbonate depend on?

A

Hydrogen ion secretion

91
Q

Describe the reabsorption of filtered bicarbonate

A

Carbon dioxide moves into the epithelial cell and is hydrated to carbonic acid to produce
hydrogen ions - exchanged for sodium and move into tubule
bicarbonate - move into interstitial with sodium

92
Q

What happens to the bicarbonate in the filtrate?

A

It binds to hydrogen ions forming carbonic acid which can be broken down and moved into the epithelium

93
Q

What is the purpose of new bicarbonate formation?

A

Used to regenerate buffer stores depleted by an acid load

94
Q

If bicarbonate ion decreases how is new bicarbonate produced?

A

Hydrogen ions combine with phosphate to form HPO42- this combines with another hydrogen ion to form HPO4-which is excreted in urine. However the bicarbonate is still formed by hydration of carbon dioxide

95
Q

What is titratable acid?

A

Measure of strong bade (NaOH) added to titrate the urine back to 7.4

96
Q

How does ammonia contribute to acid base balance?

A

Glutamine form the liver leads to NH3 in the tubule which mops up the hydrogen ions forming NH4+ that can be secreted in the urine

97
Q

Define compensation

A

Restoration of pH irrespective of what happens to bicarbonate and carbon dioxide

98
Q

Define correction

A

Restoration of pH and bicarbonate and carbon dioxide to normal

99
Q

What is immediate buffering?

A

Dilution of acid/base in ECF, blood and ECF buffers respond very quickly but stores are quickly depleted

100
Q

What is respiratory acidosis?

A

Retention of carbon dioxide by the body

101
Q

What causes respiratory acidosis?

A

Lung diseases

102
Q

What happens to the equilibrium in respiratory acidosis?

A

Driven to the right to produce hydrogen ions and bicarbonate

103
Q

How does the body compensate for respiratory acidosis?

A

All bicarbonate is reabsorbed and hydrogen ions excreted with titratable acid

104
Q

What is needed to correct respiratory acidosis?

A

Ventilation

105
Q

What is respiratory alkalosis?

A

Excessive removal of carbon dioxide by the body

106
Q

State the causes of respiratory alkalosis

A

Panic attack
Hyperventilation
Altitude

107
Q

Describe the effect on the equilibrium of respiratory alkalosis

A

Moves to the left meaning both hydrogen ion and bicarbonate concentration fall

108
Q

How does the body compensate for respiratory alkalosis?

A

Reduces hydrogen ion secretion and bicarbonate is excreted in urine.
No titratable acid or new bicarbonate is generated

109
Q

What is metabolic acidosis?

A

Excessive hydrogen ions from any other source other than carbon dioxide

110
Q

What can cause metabolic acidosis?

A

Ketoacidosis
Diarrhoea
Ingestion

111
Q

How does the body compensate for metabolic acidosis?

A

Decreased pH stimulates chemoreceptors which increase ventilation to blow off CO2 and lower H+ and bicarbonate

112
Q

How is metabolic acid corrected?

A

Filtered bicarbonate is low and readily reabsorbed and new bicarbonate is generated
Hydrogen ion secretion continues and acid is excreted in the urine
Ventilation can then be normalised

113
Q

What is metabolic alkalosis?

A

Loss of hydrogen ions or addition of a base causes bicarbonate to rise

114
Q

How does the body compensate for metabolic alkalosis?

A

Increased pH is detected by chemoreceptors which slows ventilation to retain carbon dioxide and increase hydrogen and bicarbonate ions

115
Q

How is metabolic alkalosis corrected?

A

Filtered bicarbonate is so large that not all of it is reabsorbed, no titratable acid is generated so bicarbonate is secreted and falls back to normal

Renal (20 decks)

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