This document provides an overview of body fluid compartments, water balance, and fluid volume regulation. It discusses the composition and distribution of total body water and extracellular fluid. Key points include: - Water balance is maintained through a balance of water intake and output, regulated by thirst and antidiuretic hormone (ADH). - ADH acts on the kidneys to increase water reabsorption and decrease urine output. It also causes vasoconstriction and decreased sweating. - Other hormones like aldosterone and atrial natriuretic peptide (ANP) also play roles in fluid volume regulation by modulating sodium and water balance. - The kidneys, hypothalam

1. Body fluid compartments, DailyBody fluid compartments, Daily
water intake and output, Bodywater intake and output, Body
fluid volume regulation, Volumefluid volume regulation, Volume
disorders & Diuresisdisorders & Diuresis
Dr. Ifat Ara Begum
Associate Professor
Dept of Biochemistry
Dhaka Medical College, Dhaka

2. Introduction to body fluidIntroduction to body fluid
Body fluid means body water along with
its dissolved constituents
It constitutes :
 55% of female total body weight
 60% of male total body weight

3. Composition of body fluidComposition of body fluid
1. Water
2. Solids:
 Organic : Glucose, AA, FA etc
 Inorganic : Different electrolytes like
sodium, potassium, chloride, phosphate,
calcium, magnesium etc

4. Body fluid compartmentsBody fluid compartments
Compartments Fluid content
Intracellular compartment
(Inside the cell)
Intracellular fluid (ICF)
Extracellular compartment
(outside the cell)
Extracellular fluid (ECF)
Intercellular compartment /
interstitial space (Between
the cells)
Interstitial fluid (ISF) or
Intercellular fluid
Intravascular compartment
(In blood)
Plasma

6. Total Body Water (TBW)Total Body Water (TBW)
It is about 72% of lean body mass (LBM)
 Highest water content: In brain
 Lowest water content: In adipose tissues
Female has 5-10% less TBW than that is
male because of their higher fat content

7. Distribution of TBW as % of body weightDistribution of TBW as % of body weight
 Early fetal life: 95% of body weight
 Infants & children: 75-80%
 Adult male: 60%
 Adult female: 55% (Fatty tissues contain
less water than muscle)
 Elderly male: 50% (due to loss of muscle
mass)
 Elderly female: 45%

8. Functions of body waterFunctions of body water
Acts as an universal medium without
which many biochemical reactions may be
impossible
Transport medium for many substances
Thermoregulation
Maintenance of
Metabolic integrity
Circulatory integrity
Body fluid osmolarity
Form & texture of tissues

9. Compartmental distribution of TBWCompartmental distribution of TBW
is 70 kg adult maleis 70 kg adult male
60% 0f body weight , i.e. 42 L
1.ICF: Two third of TBW or 40% of body
weight. i.e. 28 L
2.ECF: One third of TBW or 20% of body
weight. i.e. 14 L

11. ContdContd
Remember,
In early fetal life : ECF ˃ ICF
In newborn & infants: ECF = ICF
From puberty onwards: ECF ˂ ICF

12. Transcellular fluidTranscellular fluid
Part of ECF that is formed by the transport
activity or secretory activity of cells
It is separated from plasma by an
additional epithelial cell layer along with
the capillary endothelium
Rich in MPS &/or glycoprotein
Slippery

13. ContdContd
Present in potential body spaces
Acts as biological lubricant to avoid
mechanical injuries of tissues
Example: CSF, synovial fluid, pleural /
pericardial / peritoneal fluid,
gastrointestinal secretion etc

14. ECF vs. ICFECF vs. ICF
Points ECF ICF
Site Outside the cell Inside the cell
Protein content Less More
Major cation Na (mainly) , K,
Ca
K, Mg
Major anion Cl PO4

15. Cations in ECF & ICFCations in ECF & ICF
Points ECF (meq/L) ICF (meq/L)
Cation Na+
: 135-145 10-12
K+
: 3.5-5 140-150
Ca++
: 2-2.5 negligible
Mg++
: 3 40

16. Anions in ECF & ICFAnions in ECF & ICF
Points ECF (meq/L) ICF (meq/L)
Anions Cl-
: 95-105 3-8
HCO3
-
: 22-28 10-12
PO4
---
: 2 140
Protein: 16 40

17. ContdContd
Remember,
Ionic composition of plasma & ISF is
same except for the protein which is high
in plasma but negligible in ISF
ICF free (ionized) Ca conc. is very low/
negligible
ECF volume is the direct function of body
Na+ content

18. ContdContd
In the ECF, there are the ions & nutrients
needed by cells for maintaining the cellular
life. Therefore, all cells live in essentially
the same environment, the ECF, for which
reason, the ECF is called the internal
environment of the body or the “milieu
interior”

19. Measurement of body fluidMeasurement of body fluid
compartmentcompartment
By indicator (dye)/ isotope dilution
technique
Principle: C = m/v or V = m/c
Here,
V = Volume of the compartment
c = Conc. of the indicator in the
compartment
m = Total amount of indicator
injected in to the compartment

20. ContdContd
Criteria of the indicator used:
Nontoxic
Inert
Not metabolized
Easy to administer in to the desired
compartment & retains there for expected
period
Can be measured precisely before
introduction into the compartment
Urinary excretion: not too fast/slow

21. ContdContd
Indicator used:
For measurement of TBW: D2O, Tritium
oxide, antipyrine
For measurement of ECF: Sucrose,
mannitol, Isotope of Na / Cl etc
For measurement of plasma: Evan’s blue,
Radio-iodinated serum albumin (RISA)

22. ContdContd
Remember, ICF & ISF are calculated by
formula
i.e.
ICF vol. = TBW – ECF
ISF vol. = ECF – Plasma volume

23. Water homeostasisWater homeostasis
Two important things to consider here:
1.TBW & its compartmental distribution
inside the body
2.The water balance & its regulation

24. Water balanceWater balance
 Balance between water intake and output
 Water intake must be same as output to
maintain the water balance
 Two related term :
Obligatory intake or output
Facultative intake or output

25. Intak
e
Nature of
intake
Obligator
y (ml/day)
Facultati
ve
(ml/day)
Drinks (pure
water/
beverages)
650 1000
Food water 600 -
Metabolic
water
350 -
TOTAL 1600 – 2600 ml/day

26. Outpu
t
Nature
of output
Obligator
y (ml/day)
Facultati
ve
(ml/day)
As urine 500 1000
Perspiration
(via skin)
550 -
Transpiration
(via
expiration)
400 -
With stool 150 -
TOTAL 1600 – 2600 ml/day

27. ContdContd
Remember,
Perspiration =
insensible perspiration
+
sensible perspiration / sweating
 Sweating: 100 ml/day

28. Insensible water lossInsensible water loss
Evaporative water loss that occurs beyond
the consciousness of an individual.
It occurs via:
1.Skin: by perspiration
2.Expired air: by transpiration
Amount: 1000 ml/day and it depend on
temp of body & atmosphere, BSA & RR
Imp for thermoregulation of body

29. Obligatory urine volumeObligatory urine volume
The minimum volume of urine required to
excrete the excretable solute load at
maximum concentration in an individual
per day
Obligatory urine volume = Excretable
solute load / maximum concentrating
power of kidney
700 mOsm/day
1400 mOsm/L
= 0.5 L/day

30. ContdContd
Related terms:
Oligouria: Daily urine production < the
obligatory urine volume (i.e. 500 ml/day)
Polyuria: Daily urine production >3
liter/day

31. Metabolic waterMetabolic water
Endogenously synthesized water via
oxidation of carbohydrate, protein & fat at
cellular level .
Considered as insensible water gain to the
body
300 – 400 ml/day

32. Water turnoverWater turnover
Percentage of ECF volume that an
individual loses & gain again daily
Water turnover = (water intake or output /
ECF volume) x 100
= (2600/14000) x 100
= 18 % (in adult)

33. ContdContd
In children / infants : 40 – 45 %
So, they become quickly dehydrated
following any water losing episode like
diarrhoea, vomiting, excessive sweating
etc
Water turnover depends on:
 Atmospheric temp
 Physical activity
 Diet habit
 State of metabolism

34. Water requirement in infant is veryWater requirement in infant is very
high : why?high : why?
Because the water loss is very high due to:
I. Higher basal heat production leading to
increased evaporative water loss to
maintain temp balance
II.Increased BSA to body weight ratio
III.Poor renal concentrating power leading to
more urinary water loss

35. Regulation of body fluidRegulation of body fluid
Can be discussed under two
headings:
1. Regulation of water balance
2. Regulation of electrolyte balance
(esp. of sodium )

36. ContdContd
1. Regulation of water balance: Includes
a)Regulation of water intake : By thirst
mechanism
b)Regulation of water output: By primary
regulatory hormones like
ADH / Vasopressin
Aldosterone (RAAS)
ANP

37. ContdContd
2. Regulation of electrolyte balance:
a) For sodium:
Hormonal regulation by RAAS system,
ADH, ANP etc
b) For potassium:
i. Short term regulation by transmembrane
K-flux
ii. Long term regulation by aldosterone

38. Regulation of water balanceRegulation of water balance
Water balance is the result of interaction
of thirst & ADH to maintain a stable
plasma tonicity (OP)
The sensation of thirst promotes water
intake
and
ADH regulates urinary water excretion.

39. contdcontd
Positive / negative water balance and
the corresponding changes in tonicity
and cell volume are sensed by
osmoreceptor and thirst center cells in
the hypothalamus

40. contdcontd
The osmoreceptors are situated in the
supraoptic and paraventricular nuclei
of the hypothalamus;
The thirst center is situated in the
organum vasculosum of the anterior
hypothalamus.
Plasma hyperosmolarity &
hypovolemia are the stimulus for both.

41. contdcontd
Hypovolemia stimulates SNS (via
inhibition of baroreceptors) & activate
RAAS, both of which finally increase
angiotensin II production
Hyperosmolarity stimulates
osmoreceptors in hypothalamus

42. contdcontd
The activated osmoreceptors &
increased angiotensin II :
I. Stimulate thirst centre leasing to
increased water intake
II.Increase ADH secretion leasing to
increased renal water retention to
normalize plasma OP
Ultimately plasma OP normalizes.

43. contdcontd
Remember:
ECF Na+ concentration is the function
of water balance
Regulation of water balance is
equivalent to osmoregulation (ADH
mechanism & thirst)
ECF volume is the direct function of
body Na+ content

44. 1) Regulation of
water intake:
Thirst
mechanism

45. How acts?How acts?
Thirst centre is situated in the organum
vasculosum of the anterior hypothalamus.
Stimuli for thirst centre:
i. Plasma hyperosmolarity: 2-3% rise of
plasma osmolarity
ii. Hypovolemia: >10-15% reduction of
ECF (plasma) volume
iii.Baroreceptor input
iv.Angiotensin II etc

47. 2) Regulation of
water output:
Directly by ADH
& indirectly by
other hormones

48. 1. ADH/Vasopressin1. ADH/Vasopressin
A hormone made by the hypothalamus,
Stored and released in the posterior
pituitary gland
Primary function is to decrease the
amount of water lost at the kidneys
(conserve water), which reduces the
concentration of electrolytes
It also causes the constriction of
peripheral blood vessels, which helps to
increase blood pressure

49. ContdContd
Stimuli for ADH secretion:
i. Plasma hyperosmolarity: 1-2% rise of
plasma osmolarity that occurs due to rise
of electrolyte conc. in blood
ii. Hypovolemia: >10-15% reduction of ECF
(plasma / blood) volume
iii.Decreased blood pressure
These stimuli occur when a person
sweats excessively or is dehydrated.

50. ContdContd
How ADH acts?
Sweating/dehydration increases the blood
OP, which is detected by osmoreceptors
within the hypothalamus that constantly
monitor the osmolarity ("saltiness") of the
blood
Osmoreceptors stimulate groups of neurons
within the hypothalamus to release ADH from
the posterior pituitary gland.
ADH travels through the bloodstream to
its target organs (mainly DCT & CD of
kidney)

51. ContdContd
Main Target organ:
DCT & CD of Kidney (Main target site):
ADH makes the membrane more permeable
to water (that is it increases water
reabsorption) which leads to a decrease in
urine output.
[Remember, ADH promotes insertion of
aquaporins in to principal cells of CD to cause
more water reabsorption]

53. Remember, ADH promotes
insertion of aquaporins in
to principal cells of CD to
cause more water
reabsorption

55. ContdContd
Other Target organs:
a) Sweat glands : ADH stimulates them to
decrease perspiration to conserve water
b) Arterioles: ADH causes the smooth
muscle in the wall of the arterioles to
constrict. This narrows the diameter of the
arterioles which increases BP

56. 2. Aldosterone (RAAS)2. Aldosterone (RAAS)
Aldosterone is a hormone made by cells
in the adrenal cortex (zona glomerulosa)
It controls the levels of Na+
and K+
ions in
ECF ( blood)
Net result of its action is to reabsorb
Na+
ions into the blood and simultaneously
excrete K+
ions into the urine.
As because "water follows the ions," when
Na+
is reabsorbed, water is also
reabsorbed.

59. 3. ANP3. ANP
A hormone made by specific cells of
cardiac atria whenever blood volume
increases (atria are stretched)
In general, the effects of ANP are
opposite to those of angiotensin II (in
other words, ANP opposes RAAS)

61. ContdContd
It promotes
 The loss of Na+
and water at the kidneys in
the urine
 Inhibit renin release
 Inhibit the secretion of ADH and aldosterone
By inducing blood vessels to dilate and water
to be excreted in the urine, ANP reduce both
blood volume and blood pressure

62. Some related
topics
associated with
water
balance
regulation

63. 1. ADH escape1. ADH escape
Escape of renal water excretion
mechanism from the effects of
chronically elevated plasma ADH level
Function of ADH is to increase renal
water retention thus to decrease urine
volume
When plasma osmolarity is 280-290
mosm/L, ADH conc. is normal (3 pg/ml)

64. ContdContd
When plasma osmolarity is about
295 mosm/L, ADH conc. is 5 pg/ml
causing max renal water retention &
decreasing urine volume
When plasma osmolarity rises beyond
295 mosm/L, no further increase in
ADH concentration. So, renal water
retention decreases & urine volume
increases despite raised level of ADH.

65. 2. SIADH2. SIADH
A condition characterized by
excessive release of ADH from
pituitary gland or another
source, causing the body to
retain fluid and lower the blood
sodium level by dilution.
It is mainly caused by cancer,
esp. that of the lungs

66. ContdContd
The pituitary gland appropriately
produces and releases vasopressin
(ADH) when:
 The blood volume goes down or
 The blood pressure goes down or
 Levels of electrolytes (such as
sodium) become too high.

67. ContdContd
So, secretion of ADH is termed
inappropriate if it occurs when:
Blood volume is normal or high
Blood pressure is normal or high
Electrolyte concentrations are low
Other appropriate reasons
for vasopressin release are not present.

68. 3. Water intoxication3. Water intoxication
Also known as water poisoning or
hyperhydration
A potentially fatal disturbance
in brain functions that results when the
normal balance of electrolytes (precisely
of Na) in the body is pushed outside the
safe limits by overhydration
(excessive water intake).

69. ContdContd
When water intake is more than
maximum renal water excretion capacity
-------->Water retention ------>
Hyponatremia ----> hypoosmolarity of
ECF compared to that of ICF ---->Water
moves in to the cells by osmosis --->
cerebral edema -----> coma, death
Happens when water intake is ˃23 L/day.

70. ContdContd
A common phenomenon in CRF
May happen in normal individual if there is
rapid i/v infusion of hypotonic fluid/fluid
without Na

71. 4. Osmolarity/ osmolality4. Osmolarity/ osmolality
Osmolarity: The concentration of
osmotically active particles in solution,
which may be quantitatively expressed in
osmoles of solute per liter of solution
(osmole/L)
Osmolality: Here, concentration of
solution is expressed in terms of osmole
of solute per kg of solvent (osm/Kg )

72. ContdContd
Both are measures that are technically
different, but functionally the same for
normal use.
Plasma osmolarity: 280 – 300 mosm/L
Osmolarity = 2[Na+] + [Glucose] +[Urea]
All in mmol/L
If [glucose] and [urea] are in normal range,
only [Na+] will give the osmolar
concentration

73. 5. Effective osmolarity5. Effective osmolarity
This term is used for those extracellular
solutes that determine water movement
across the cell membrane
Plasma Na+ concentration is reliable
index of total/effective osmolarity
Changes in osmolarity often results from
changes in [Na+]

74. ContdContd
If ECF & ICF have same osmolarity:
Cells neither shrink nor swell
Increased osmolarity in ECF: Water
comes out of cell (cell shrinks)
Decreased osmolarity in ECF: Cell
swells up

75. Causes of hyperosmolarityCauses of hyperosmolarity
1. Hypernatremia
2. Uremia
3. Hyperglycemia etc

76. 6. Plasma osmolar gap6. Plasma osmolar gap
Difference between calculated plasma
osmolarity instrumentally measured
plasma osmolarity
Osmolar gap = (measured osmolarity) -
(calculated plasma osmolarity)
Normal: up to 12 mosm/L

77. ContdContd
Causes of increased plasma osmolar gap:
 Gross hyperproteinemia / hyperlipidaemia
 Keto/lactic acidosis
 CRF
 Alcohol poisoning

78. ContdContd
Remember:
ICF volume is the indirect function of ECF
osmolarity: If ECF osmolarity decreases,
ICF volume increases & vice versa
ECF osmolarity is the direct function of
ECF Na+ concentration

79. VOLUME
DISORDERS

80. Introduction to volume disordersIntroduction to volume disorders
Always indicates disorder of ECF (not
ICF)
Because sodium is the major osmotically
active ion in ECF, total body Na+ content
determines ECF volume.
Deficiency / excess of total body sodium
content causes ECF volume
depletion / volume overload accordingly
Serum Na+ concentration does not
necessarily reflect total body Na+.

81. ContdContd
There may be :
1.Hypovolemic disorders (Salt deficit state) :
State of dehydration
2.Hypervolemic disorders (Salt excess
state: State of overhydration
The disorders may have isotonic, ,
hypotonic or hypertonic variety

82. Three basic homeostatic challengesThree basic homeostatic challenges
1. Gain/loss of isotonic solution: It affects
only ECF volume
2. Gain/loss of pure water: Volume
changes proportionately in both the
ECF & ICF compartments. Osmotic
changes in each are equal
3. Gain/loss of pure salt: Na+
is confined to
ECF compartment, so loss results in vol.
shift from ECF to ICF & gain results in
vol. shift from ICF to ECF

84. 1. Isotonic hypovolemia1. Isotonic hypovolemia
It occurs when proportionally the same
amount of water and salt (sodium) is lost
from the body,
i.e. isotonic fluid loss

85. ContdContd
Changes:
 Osmolarity of lost fluid is 300 mosm/L
 Sodium conc. of lost fluid : equal to
plasma
 Body total sodium content : decreases
 ECF volume decreases
 ICF volume is normal
 Osmolarity (OP): normal in both ECF &
ICF

86. ContdContd
Causes are:
 Severe hemorrhage
 Loss of small intestinal content by fistula,
ileostomy etc
 Intestinal obstruction
 Secretory diarrhoea
 Polyuric CRF etc

87. 2. Hypertonic hypovolemia2. Hypertonic hypovolemia
It usually occurs when proportionally
more water is lost than the salt (sodium)
from the body
i.e. hypotonic fluid loss

88. ContdContd
Changes:
 Osmolarity of lost fluid is <300 mosm/L
 Sodium conc. of lost fluid : Less than that
of plasma
 Body total sodium content : decreases
 ECF & ICF volume decrease (ECF due to
fluid loss & ICF due to osmotic water loss
from cells)
 Osmolarity (OP): increases in both ECF &
ICF

89. ContdContd
Causes are:
 Severe diarrhoea
 Persistent vomiting / NG suction
 Profuse sweating
 Severe burn
 Diuretic abuse & osmotic diuresis etc

90. 3. Hypotonic hypovolemia3. Hypotonic hypovolemia
It occurs following treatment of patient
with isotonic / hypertonic hypovolemia by
wrongly selected i/v fluid without NaCl (5
% DA)
Rare clinically
Proportionally more salt (sodium) is lost
than the water from the body

91. ContdContd
Changes:
 Body total sodium content : decreases
 ECF volume decrease but ICF volume
increases due to osmotic water gain in to
the cells
 Osmolarity (OP): Decreases in both ECF
& ICF

92. ContdContd
Causes are:
Occurs in condition with renal & extra-
renal salt & water loss leading to isotonic /
hypertonic hypovolemia
 Extra-renal causes: Diarrhoea, vomiting,
hemorrhage, burn etc
 Renal causes: Salt losing nephritis,
osmotic diuresis, diuretic abuse, adrenal
deficiency etc

93. Remember the hormones releasedRemember the hormones released
in hypovolemiain hypovolemia
I. ADH
II. Aldosterone
III. Renin
IV. Catecholamine

94. Courtesy: abc of medical biochemistry by Prof Mozammel HaqueCourtesy: abc of medical biochemistry by Prof Mozammel Haque

96. 1. Isotonic hypervolemia1. Isotonic hypervolemia
It occurs following isotonic fluid gain
Osmolarity of gained fluid : 300 mosm/L
Sodium concentration of gained fluid:
similar to plasma
Body total sodium content: Increases

97. ContdContd
ECF volume: increases
ICF volume: Normal
Osmolarity (OP): normal in both ECF &
ICF
No edema develops
Rarely found clinically
Iatrogenic

98. ContdContd
Causes :
 Excess infusion of normal saline

99. 2. Hypertonic hypervolemia2. Hypertonic hypervolemia
It occurs following hypertonic fluid gain
Osmolarity of gained fluid : more than
300 mosm/L
Sodium concentration of gained fluid: Is
more than that of plasma
Body total sodium content: Increases

100. ContdContd
ECF volume: increases
ICF volume: Decreases due to osmotic
water loss from cell
Osmolarity (OP): Increases in both ECF
& ICF
No edema develops
Rarely found clinically
Usually iatrogenic

101. ContdContd
Causes :
 Excess infusion of hypertonic saline
 Sea water intake
 Primary hyperaldosteronism (Conn’s
syndrome)
 Cushing syndrome

102. 3. Hypotonic hypervolemia3. Hypotonic hypervolemia
It occurs following hypotonic fluid gain
Osmolarity of gained fluid : Less than
300 mosm/L
Sodium concentration of gained fluid: Is
less than that of plasma
Body total sodium content: Increases

103. ContdContd
ECF volume: increases due to fluid gain
ICF volume: Increases due to osmotic
gain of water in to cells
Osmolarity (OP): Decreases in both ECF
& ICF
Usually associated with edema
Commonly found clinically

104. ContdContd
Causes :
 CCF
 NS
 Cirrhosis of liver
 Hepatic failure
 Protein losing enteropathies
 Kwashiorkor

105. Remember, the hormone releasedRemember, the hormone released
in hypervolemiain hypervolemia
ANP

106. Courtesy: abc of medical biochemistry by Prof Mozammel HaqueCourtesy: abc of medical biochemistry by Prof Mozammel Haque

107. Clinically found volume disordersClinically found volume disorders
Isotonic hypovolemia
Hypertonic hypovolemia
Hypotonic hypervolemia

108. Diuresis

109. DefinitionDefinition
Diuresis is increased urination and
the physiologic process that produces
such an increase
It involves extra urine production in the
kidneys as part of the body's
homeostatic maintenance of fluid
balance

110. TypesTypes
Three types:
I. Water diuresis
II.Osmotic diuresis
III.Pressure diuresis

111. 1. Water diuresis1. Water diuresis
The excretion of large volume of
hypotonic urine due to excessive intake
of water/hypotonic fluid
It results from reduced secretion of ADH
in response to lowered plasma
osmolarity (OP) &/or increased blood
volume following increased water intake

112. ContdContd
Reduced secretion of ADH causes
decreased water reabsorption from CD:
either directly
or by decreased urea reabsorption from
CD causing poor development of
medullary interstitial hyperosmolarity
Finally diuresis occurs

113. ContdContd
At zero ADH conc. there occurs max.
diuresis (23 L/Day)
Conditions (clinical type as well) leading
to water diuresis:
 Excess water intake
 Excess infusion of hypotonic fluid (5 %
D/A)
 DI

114. Features of water diuresisFeatures of water diuresis
Water reabsorption from PCT :Normal
Water reabsorption from DCT & CD :
Decreased
ADH conc. : Decreased
Urinary osmolarity: Hypotonic
Electrolyte loss: Minimum
Urine vol. : Max 23 L/day
ECF vol. : Usually normal
Medullary interstitial hyperosmolarity:
Poorly developed due to reduced urea
reabsorption from CD

115. 2. Osmotic diuresis2. Osmotic diuresis
The excretion of large volume of isotonic
/ hypertonic urine due to presence of
excess unabsorbed osmotically active
particles (like NaCl, glucose etc) in the
glomerular filtrate
The osmotically active particles prevent
water reabsorption by holding water with
them , ultimately causing an increase in
urine volume
Huge loss of electrolytes happen

116. ContdContd
Clinical conditions presenting with
osmotic diuresis:
 DM
 Diuretic use in HTN/RF etc
 Mannitol infusion etc

117. Features of osmotic diuresisFeatures of osmotic diuresis
Water reabsorp. from PCT :Decreased
Water reabsorp. from DCT & CD :
Decreased
ADH conc. : Normal
Urinary osmolarity: Iso/hypertonic
Electrolyte loss: Huge
Urine vol. : May be >23 L/day
ECF vol. : May develop hypovolemia
Medullary interstitial hyperosmolarity:
Poorly developed due to reduced NaCl &
H2O reabsorption in renal tubule

118. 3. Pressure diuresis3. Pressure diuresis
The excretion of large volume of urine
as a result of high mean systematic BP
>200 mm Hg
Here urine volume can be 7-8 times
normal

119. ContdContd
At high systemic BP (>200 mm Hg),
renal auto-regulation fails & GFR
becomes the direct function of systemic
BP leading to high GFR & rapid flow of
filtrate
Because of rapid flow of filtrate, tubular
system can’t reabsorb water, electrolytes
& nutrients efficiently
So, diuresis develops with loss of
electrolytes & nutrients

120. Diuresis versus polyuriaDiuresis versus polyuria
Diuresis is excessive urination
Polyuria is the production of an
abnormally large amount of urine