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Kidneys > An introduction to kidneys & body fluid > Flashcards

An introduction to kidneys & body fluid Flashcards

1
Q

what % of body weight does Total body water take up?

A

60%

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2
Q

what % of body weight does Intracellular water take up?

A

40%

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3
Q

what % of body weight does extracellular water take up?

A

20%

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4
Q

What does osmosis of water determine?

A

The movement of water between ICF and ECF

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5
Q

What is the purpose of osmoregulation?

A

To prevent large fluid shifts between these compartment.

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6
Q

How is intracellular fluid treated?

A

Water outside all the cells of the body is not really one compartment, - but can be treated as one.

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7
Q

What two sub-compartments does the ECFV have?

A
  1. Plasma (3L)

2. Interstitial fluid (11L)

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8
Q

What do Starling forces determine?

A

Starling forces determine fluid and solute movement between plasma and interstitial fluid

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9
Q

What is the plasma compartment sometimes called?

A

Effective circulating volume:
It has to be defended to maintain adequate blood pressure for effective tissue perfusion. Normally it’s around 20% of the ECF.

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10
Q

What is osmolarity?

A

The total concentration of osmotically active solutes

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11
Q

Why must osmolarity of ECF and ICF be kept the same?

A

To avoid excessive shifts of water between ECF and ICF

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12
Q

What is the principal electrolyte of the ECF?

A

Sodium is the principal electrolyte of the ECF, therefore sodium (with associated anions) is the major determinant of ECF osmolarity

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13
Q

How to work out the osmolarity of extracellular Na?

A

e.g. 140 mmol/L + 140 mmol/L , so 280 mmol/L, - this is because you assume the same amount of anions to the sodium cations.

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14
Q

Why is the ECF the compartment that can be regulated?

A
  • The ECF is continuous

* the ICF in reality is 10^14 individual cellular compartments

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15
Q

ECF Na+ concentration

A

135-145 mmol/L

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16
Q

ICF Na+ concentration

A

5-10 mmol/L

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17
Q

ECF K+ concentration

A

3-5 mmol/L

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18
Q

ICF K+ concentration

A

130-150 mmol/L

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19
Q

Why is the control of body fluids important?

A
  1. Osmoregulation

2. Volume regulation

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20
Q

Why is the control of body fluids important in terms of osmoregulation?

A

Cell structure: Differences in osmotic pressure between IC and EC will lead to volume shifts, leading in turn to cell and tissue damage and function . – done by regulating the total solutes in the ECF

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21
Q

Why is the control of body fluids important in terms of volume regulation?

A

Depends on balance between circulating volume (plasma) and interstitial volume: this is done by regulating the total volume of the ECF

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22
Q

Salt and water balance depends on which two key processes

A
  1. Osmoregulation: maintain osmotic equilibrium between ICFV and ECFV
  2. Volume regulation: maintain adequate ECFV to support plasma volume
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23
Q

What is the principal electrolyte contributing to ECFV osmolarity?

A

Sodium (along with its associated anions)

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24
Q

How can plasma osmolarity be estimated?

A

2[Na] + 2[K] + [glucose] + [urea] (all in mmol L-1)

  • don’t double glucose and urea as they are not an electrolyte, so they don’t have charges
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25
Q

What are two ways to change the osmolarity of a solution?

A
  1. Add/remove solute

2. Add/remove water

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26
Q

How does the body accomplish osmoregulation?

A

By adding or removing water not sodium

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27
Q

How does the body respond to a rise in plasma osmolarity?

A

More water is needed so the kidneys response by producing small volumes of concentrated urine (water retention)

*also triggers thirst, a powerful behavioural response which will counteract the rise in osmolarity.

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28
Q

How does the body respond to a fall in plasma osmolarity?

A

There is too much water and so the kidneys respond by producing large volumes of dilute urine (water excretion)

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29
Q

What does volume regulation involve?

A

The control of the circulating plasma volume

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30
Q

How are changes in plasma volume detected?

A

Changes detected by stretch and pressure receptors in the cardiovascular system

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31
Q

How is a fall in blood volume opposed?

A

By sodium retention; water flows osmotically, restoring volume

  • total amount of sodium will be increased but concentration (therefore osmolarity) isn’t really changed because the sodium brings water
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32
Q

Kidneys

A

Produces urine

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33
Q

Ureter

A

Transports urine towards the urinary bladder

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34
Q

Urinary bladder

A

Temporarily stores urine prior to elimination

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35
Q

Urethra

A

Conducts urine to exterior

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36
Q

Primary kidney function

A
  • Homeostasis: salt and water balance, this is done by regulating the amount of urine to conserve/excrete water, and its concentration (the amount of salt)
  • production of urine is a by-product
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37
Q

Urinary tract

A

Important for temporary storage and then to remove urine from the body

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38
Q

List functions of the kidney

A
  • Osmoregulation
  • Volume regulation
  • Acid-base balance
  • Regulation of electrolytes balance (eg potassium, calcium, phosphate)
  • Removal of metabolic waste products from blood
  • Removal of foreign chemicals in the blood (e.g. drugs)
  • Regulation of red blood cell production (erythropoietin)
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39
Q

What is the functional unit of the kidney?

A

The nephron

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40
Q

What does each nephron consist of?

A
  • special blood vessels and elaborate tubules
  • microscopic structures:
    • Blood vessels
    • The glomerulus
    • Bowman capsule
    • The renal tubule
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41
Q

How many nephrons per kidney?

A

1.25 million

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42
Q

What occurs at the nephron?

A

Urine production begins here

43
Q

Describe arrangement of blood vessels and blood flow through the kidneys

A

SEE DIAGRAMS

44
Q

What blood vessel is the whole kidney supplied by?

A

A major artery, the renal artery which subdivides many times into fine arterioles supplying each nephron, the afferent arteriole.

45
Q

What blood vessel is the kidney drained fro?

A

The renal vein, which is supplied by venules coming away from each nephron, joining together into larger veins which merge into the renal vein

46
Q

Structural organisation of the renal nephron?

A

SEE NOTES

47
Q

What are the four basic processes of urine formation?

A
  1. Glomerular Filtration
  2. Tubular reabsorption
  3. Tubular Secretion
  4. Excretion of water and solutes in the urine
48
Q

Describe glomerular filtration

A
  • The first step in the production of urine
  • Hydrostatic pressure forces fluids and solutes through (pressure difference in the afferent and efferent arteriole)
  • Small molecules pass readily: large ones (proteins) and cells cannot pass
  • This leads to a plasma ultra filtrate in the Bowman’s capsule
49
Q

What is GFR?

A

The amount of filtrate kidneys produce each minute

* averages 125 ml/min (approx 20% of real plasma flow)

50
Q

What can be used as an indication of GFR?

A

Plasma creatinine: breakdown product of creatinine phosphate in muscle

51
Q

Clinical significance of GFR

A

Reduced in renal failure

52
Q

Where does reabsorption occur?

A

Many substances are filtered and then reabsorbed from the tubular lumen into the peritubular capillaries

53
Q

Volume of H2O filtered a day?

A

180 L/day

54
Q

Volume of Na+ filtered a day?

A

25,000 mEq/day

55
Q

Volume of HCO3- filtered a day?

A

4,500 mEq/day

56
Q

Volume of Cl- filtered a day?

A

18,000 mEq/day

57
Q

Volume of Glucose filtered a day?

A

800 mM/day

58
Q

Volume of H2O excreted a day?

A

1.5 L/day

59
Q

Volume of Na+ excreted a day?

A

150 mEq/day

60
Q

Volume of HCO3- excreted a day?

A

2 mEq/day

61
Q

Volume of Cl- excreted a day?

A

150 mEq/day

62
Q

Volume of Glucose excreted a day?

A

~ 0.5 mM/day

63
Q

Volume of H2O reabsorbed a day?

A

178.5 L/day

64
Q

Volume of Na+ reabsorbed a day?

A

24,850 mEq/day

65
Q

Volume of HCO3- reabsorbed a day?

A

4,498 mEq/day

66
Q

Volume of Cl- reabsorbed a day?

A

17,850 mEq/day

67
Q

Volume of Glucose reabsorbed a day?

A

799.5 mM/day

68
Q

Percentage proportion of filtered H2O that is reabsorbed?

A

99.2%

69
Q

Percentage proportion of filtered Na+ that is reabsorbed?

A

99.4%

70
Q

Percentage proportion of filtered HCO3- that is reabsorbed?

A

99.9%

71
Q

Percentage proportion of filtered Cl- that is reabsorbed?

A

99.2%

72
Q

Percentage proportion of filtered Glucose that is reabsorbed?

A

99.9%

73
Q

What is tubular secretion important for?

A
  • Disposing of substances not already in the filtrate
  • Eliminating undesirable substances such as urea and uric acid
  • Ridding the body of excess potassium ions
  • Controlling blood pH
74
Q

Describe excretion of fluid and solutes in the urine

A

SEE NOTES

75
Q

What is the control of water balance (osmoregulation) based on?

A

The osmolarity of the ECFV?

76
Q

Describe what occurs when there is changes in water intake/excretion

A 
Changes in body fluid osmolarity  
    I
SENSOR   
   I
EFFECTOR 
   I 
Changes in renal water excretion: intake ~ OUTPUT
   I 
back to beginning
77
Q

Where are neural sensors?

A

Neural sensors that are sensitive to the plasma osmalarity are in the hypothalamus.

78
Q

What kind of effector will it be?

A

The effector will be a hormonal response to rebalance intake and output

79
Q

How is total body water balance calculated?

A

Input - Output

80
Q

Types of water input

A
  • Drinks: 1000 ml
  • Food: 700 ml
  • Metabolism: 300 m l

2000 ml/day

81
Q

Types of water output

A
  • Gut: 100 ml
  • Insensible loss: 900 ml (lungs/skin)
  • Renal excretion: 1000 ml

2000 ml/day

82
Q

What leads to changes in water balance?

A
  • Changes in body fluid osmolality

- Shift of water between ICFV and ECFV

83
Q

Why should the total body water balance be zero?

A

Otherwise there will be a change in osmolality

84
Q

What are examples of insensible loss?

A

Breathing with the lungs and through the skin

85
Q

How can we control output?

A

Cannot control the output from the gut and insensible loss. – but can control renal excretion

86
Q

What are some physiological responses to water restriction?

A
  • Loss of water (sweat, breathing).
  • Thirsty, but no water is available to drink
  • Plasma osmolality rises
  • Response is increased secretion of hormone, ADH (antidiuretic hormone, also known as vasopressin)
87
Q

What does secretion of ADH result in?

A
  • Decreased urine volume
  • Increased urine osmolality
  • Will start to feel thirsty
88
Q

What are some physiological responses to increase in water intake?

A
  • Increase in water absorption through GIT
  • Plasma osmolality falls
    Response is reduced secretion of ADH
89
Q

What does reduced ADH secretion result in?

A
  • Urine volume increases
  • Urine osmolality decreases
  • Less water reabsorbed
90
Q

Renal output when water intake is excessive

A

20 L/day

91
Q

Renal output when water intake is restricted

A

0.5 L/day

92
Q

Osmolality when water intake is excessive

A

50 mM

93
Q

Osmolality when water intake is restricted

A

1200 mM

94
Q

What can happen when there is EXCESSIVE water intake?

A

Worst case scenario:

- water will move from ECF to ICF compartment

95
Q

What determines ECF volume?

A

Amount of sodium

96
Q

What must be balanced to maintain constant ECF volume?

A

Sodium intake and excretion

97
Q

Where are the main volume sensors located?

A

The cardiovascular system

98
Q

What is a fall in blood volume opposed by?

A

Hormonal signals promoting sodium retention; water follows osmotically, restoring volume

99
Q

How is total body Na+ concentration calculated?

A

Intake - Elimination

100
Q

Why is control of sodium balance important?

A

Sodium is the major electrolyte of the ECFV

101
Q

The maintenance of sodium balance is based mainly on?

A

The control off the ECFV

102
Q

What is the sodium retaining system?

A

Renin-angiotensin-aldoesterone system (RAAS)

103
Q

What is the sodium eliminating pathway?

A

Cardiac natriuretic peptides (ANP)

104
Q

Hormonal and renal responses to increases/reductions in sodium intake

A

SEE NOTES

Kidneys (6 decks)

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