Fluid and Electrolyte Balance

Ch 34: Control of Body Fluid Osmolality and Volume
Ch 2 : Homeostasis of Body Fluids
Fluid and Electrolyte Balance
Myoung Kyu Park MD. PhD.
Department of Physiology
Sungkyunkwan University School of Medicine
Fluid
uda
and
d Electrolyte
ect o yte Balance
a a ce
1.
2.
3.
4
4.
5.
Distribution and measurement of body
y fluid compartments
p
Compartmental fluid balance and compositions
Systemic fluid balance : water intake & output
Regulation mechanism of extracellular fluid volume
Electrolytes balance
Body Fluid
Young men
Young Women
60% of body weight
50% of body weight
cf. water content ; fat tissue (10%), other tissues (70-75%)
Body Fluid Compartments
70 kg man
Extracellular Fluid (ECF)
Intracellular fluid (ICF)
40% 28L
40%,
2/3
15%
10.5L
5%
3
3.5L
interstitial Fluid
(ISF)
Plasma
1/3
(ECF, 14L)
Total Body Water (42L)
60%
1-3%
transcellular
fluid
CSF
Aquaous humor
Synobial fluid
Measurement of body fluid compartments
C
amount
V=
amount
concentration
Substance
Methods
TBW
Tritiated water and D2O
ECF
sulfate, inulin, manitol
Plasma
radioiodinated serum
albumin, Evans blue
I t titi l
Interstitial
ECF voll – plasma
l
voll
ICF
TBW – ECF vol
Electrolyte Composition of the Body Fluids
1. Key ions determine fluid volumes
2 Osmolarity determines fluid volumes
2.Osmolarity
Electrolyte composition between ICF and ECF is different
different, but the osmolarity is the same
OsmECF = OsmICF
Osmotic Pressure determines Cell Volumes (ICF)
(
)
Solution
5% dextrose
10% dextrose
5% dextrose
in 0.9% saline
half strength
saline(0.45%)
normal saline
(0.9%)
Lactated Ringer's
solution
glucose(g/dL)
Hypotonic solution
Isotonic solution
Hypertonic solution
Na+
K+
Ca2+(mEq/L) Cl-
lactate
osmolarity(mOsm/L)
5.0
10.0
5.0


154












Isotonic (278)
hypertonic (556)
hypertonic (586)

77


77

hypotonic (154)

154


154

isotonic (308)

130
4
3
109
28
isotonic (274)
Importance of ECF volume
ICF
ISF
Plasma
ISF is a diffusion medium between plasma and ICF.
Maintenance of ECF volume
is essential for the adequacy of the circulation.
ECF volume is determined by mainly Na+ concentration
[Na+]
[N
ECF vol.
l
cf. cell memb. permeability
Evolutionary changes
sponges
j ll fi h
jellyfish
earthworm
Cariovascular system
separated from ECF
P
Pump
concentrated
and packed
T b
Tubes
Hemoglobin
RBC
Systemic circulation - High Pr, High Resis
Pulmonary circulation - Low Pr, Low Resis
Two Important Factors
70 Kg man
Fl id Volume
Fluid
V l
hypertension
edema
hyper-volemia
hyper-osmolarity
demyelination
42 L
hypo-volemia
hypotension
shock
Osmolarity
290
mOsm
hypo-osmolarity
swelling of brain cells
nausea, malaise, headache, confusion,
lethargy, seizures, and coma
Shifts of water between compartments
os
smolality
y
300 Add
pure water
Normal
mOsm
ICF
ECF
2/3 (28L)
1/3 (14L)
volume
Darrow-Yannet Diagram
SIADH (ADH)
Addition of Pure Water
hyposmotic vol expansion
Prot conc.
HCt
os
smolalitty
300
mOsm
ICF
0
ECF
volume
28
42 L
Shifts of water between compartments
(a) Normal
(b) Add pure water
SIADH (ADH)
hyposmotic vol expansion
Prot conc.
o
osmolarity
HCt
ECF
ICF
ICF
ECF
volume
(c) Add isotonic saline (0
(0.9%NaCl)
9%NaCl)
hyperosmotic vol expansion
Prot conc.
HCt
BP
(d) Add pure NaCl
0.9% saline IV
isosmotic vol expansion
Prot conc.
HCt
BP
Diarrhea
isosmotic vol contraction
Prot conc.
HCt
BP
ICF
ECF
Hemorrage
isosmotic vol contraction
Prot conc.
HCt
BP
ICF
ECF
Sweating (hypotonic)
hyperosmotic vol contraction
Prot conc.
HCt
ICF
ISF
Plasma
Fluid balance between ISF and Plasma : Starling's law
capillary
ill
arterial
end
hydrostatic
y
pressure
32 mmHg
osmotic p
pressure
22 mmHg
y
pressure
p
hydrostatic
12 mmHg
venous
end
Net Flow
(+10 mmHg)
(-10 mmHg)
Oncotic proteins – albumin, globulin, fibrinogen
Disorders of Fluid Balance
Etiology : liver, cardiovascular or renal disease, hormonal imbalance, or accidents
plasma-to-interstitial shift / plasma-to-transcellular space shift
Accumulation of fluid in interstices or connective tissues or transcellular spaces
due to increased hydrostatic pressure or decreased osmotic pressure (third space)
Edema, hydrothorax (pleural effusion), hydropericardium (pericardial effusion),
hydroperitoneum (ascites)

Edema:
 Increased hydrostatic pressure
CHF, liver cirrhosis, constrictive pericarditis, venous obstruction, heat
 Reduced plasm osmotic pressure
nephrotic syndrome, Liver cirrhosis
 Lymphatic obstruction
inflamatory, neoplasmic, postsurgical
 Sodium Retention – pitting edema
Excessive salt intake
intake, Increased RAA system
 Inflammation
Fluid and Electrolyte Balance
Maximum 4L/h
W t Balance
Water
B l
habit
(at rest)
Water intake
Water output
constant
OsmICF

effective circ. bl vol.
renin
Thirst (emergency)
baroreceptors in CV sys.
Kidney
Cell vol. change
in ant HT osomoreceptor
p
cortex
ADH
hypothalamus
yp
cf. CHF – thirst feeling
Cirrhosis
Thirst : control mechanism for fluid intake
Thirst
 emergency mechanism
 controlled by hypothalamus
 conscious
i
sensation
ti
2
Peripheral
Volume
receptors
High threshold
1
Hypothalamus
Osmoreceptor
cells
Low threshold
supraoptic nucleus
paraventricular nucleus
ADH
Posterior
pituitary
Release
of ADH
into
capillaries
Regulation
g
of ECF Volume
effective circ. bl vol.
OsmICF
5-10 % change
g
High pressure baroreceptors
•carotid sinus & body
•aortic
i arch
h&b
body
d
•justaglomerular apparatus
(afferent arteriole)
Low pressure baroreceptors
•atrial receptors – ANP
•artium, ventricle, pulmonary vein
Circumventricular organs
•organum vasculosum
of the lamina terminalis
•subfornical organ
Hypothalamus
•supraoptic nucleus
•paraventricular nucleus
ADH(AVP)
Four Regulatory
g
y Pathways
y controlling
g
ECF volume
1.
2
2.
3.
4
4.
Renin-Angiotensin-Aldosterone Axis
Renal Sympathetic activation
Arginine Vasopressin (ADH)
Arterial Natriuretic Peptide (ANP)
1. Renin-Angiotensin-Aldosterone Axis
effective arterial
blood volume
(Lung)
1. Renin-Angiotensin-Aldosterone Axis
Aldosterone
principal cell
2. Renal Sympathetic activation
Enhanced activity of the renal sympathetic nerves
1.
1
2.
3.
Afferent
arteriole
increases renal vascular resistance
enhances renin release from granule cells
increases tubule reabsorption of Na+
Renal
nerves
Granular cells
Urinary space
Thick
ascending
limb
Bowman’s
capsule
Proximal
P
i l
tubule
Glomerular
capillaries
Macule
densa
Efferent
arteriole
Extraglomerular
mesangial cells
H2O and Na+ retension
3. Arginine Vasopressin (ADH)
Antidiuretic Hormone (ADH)
1
thirst
high
hi
h threshold
th
h ld
Osmoreceptors
Factors to release ADH
1. stretch receptors in heart LA
and Pul Vein
low threshold
2 Pr
2.
Pr. in carotid sinus and
aortic arch
3. kidney-granular cells – renin
- angiotensin II
2
Vasopressin – high conc of ADH
by more than 10% loss of blood volume
Raise plasma
osmolality  shrink hypothal.
osmoreceptors  ADH cells 
ADH release
Control of Secretion of Antidiuretic Hormone (ADH)
Osmolality
Volume
set point
set point
• Continuous control of ADH level over the set point (278mOsm) and under the -10%
10%
change in circulating blood volume
• Osmolarity and effective circulating blood volume work together and reinforce each other
Cellular mechanisms of ADH action
AQP2
1.
2.
Insertion
Expression
Water Absorption
ADH
Diabetes insipidus – ADH deficiency (nephrogenic or neurogenic)
20 L/day urine
Systemic responses to changes in blood osmolarity and volume
4. Atrial Natriuretic Peptide (ANP)
•ANP
ANP - atrium
ti
•BNP - ventricle
•Urodilantin - kidney
BNP / urodilantin
vasodilation
Feedback Control of Effective Circulating Volume
Na+
Na+ ion
• determines ECF volume
• generates electrical activities
• supplies energy for cellular transport
GFR = 180 L/day, PNa+ = 142 mM
Filtered Load = 25,500 mmole/day (1.5kg)
Diet 120 mmole/day
Na+ Transport
ADH
Transcellular pathway
Paracellular pathway
Regulation of Na+ Transport
Na-Cl transporter
5%
100
5
Na channels
3
67%
Na cotransporter
Na/H exchanger
Solvent drag
1
2
1. Glomerulotubular balance
2. Aldosterone
3. Sympathetic nerves
8
cortex
1. Decrease RBF & GFR
3
medulla
2. Release renin
33
4
25%
H2O channels
3. Stimulate tubular Na+
reabsorption (activates NHE3 &
Na pump)
Na/K/2Cl transporter
4. Arginine vasopression –ADH
4
5. Atrial Natriuertic Hormone
3%
Na channels
5
1. increase RBF & GFR
2. inhibit Na reabsorption in
the medulla
6. PG, bradykinin, & dopamine
inhibit Na+ reabsorption
inhibition
stimulation
0.4
Sodium Balance
major factor determining ECF Vol.
Sodium in diet
100 - 300 mEq/day
INPUT
Extracellular fluid
small
OUTPUT
Skin (sweat,
burns,
hemorrhage)
positive Na+ balance
95%
Gastrointestinal
losses (diarrhea
vomiting)
ECF vol.
Kidneys
generalized edema
High intake  hypertension
Renal Responses to Na+ intake
water intake
ECF
Wt gain
(
(Walser,
198
1985, Kidney Int))
Higher Na+ intake  pos. sodium balance  increase excretion  restore equal balance
• hypernatremia > 148 mEq/L
hyperaldosteronism, sweating
hyperaldosteronism
burns, diabetes indipidus, diarrhea
• hyponatremia < 135 mEq/L
diuretics, hypoaldosteronism
SIADH, CHF, RF
Kidney Failure
Uremia ((urine in blood))

Lack of erythropoietin  anemia

Plasma urea creatinine and uric acid  azotemia

Lack of vitamin D activation  bone disease

Increased ECF  hypertension
yp

Decreased H+ secretion  metabolic acidosis

decreased GFR  hyperkalemia
ERDS: End State Renal Disease, GFR <10% of Normal
Superficial
vein
From dialyzer
y
T dialyzer
To
di l
Hemodialysis: pump
blood through dialyzer;
more efficient than
peritoneal dialysis
p
y
Arteriovenous
fistula
Radial
artery
Bubble
trap
Dialyzer
membrane
Fresh
F
h dialyzing
di l i
solution
(c) 2003 Brooks/Cole - Thomson Learning
Constant
temperat re bath
temperature
Used dialyzing
sol tion
solution