Transcript Fluids & Electrolytes Part 1

ADVANCED PHYSIOLOGY
FLUID &
ELECTROLYTES
Part 1
Instructor Terry Wiseth
NORTHLAND COLLEGE
1
FLUID ELECTROLYTE
HOMEOSTASIS
In a healthy individual fluid volume and
electrolyte concentrations are
maintained within strict homeostatic
limits through the interaction of several
organ systems
2
FLUID ELECTROLYTE
HOMEOSTASIS
Total body water (TBW) can be divided
by cell membranes into two main
compartments:
1) Extracellular fluid (ECF)
fluid outside cells
1/3 of total body water
2) Intracellular fluid (ICF)
fluid inside cells
2/3 of total body water
3
FLUID ELECTROLYTE HOMEOSTASIS
The ECF is further divided into:
1) Blood plasma (80%)
2) Interstitial fluid (20%)
These two ECF compartments are
separated by a capillary membrane
Interstitial
fluid
4
FLUID COMPARTMENTS
Effectively there are three compartments
1) Intracellular
2) Interstitial
3) Plasma
5
FLUID COMPARTMENTS
Cell
CYTOPLASM
(Intracellular)
PLASMA
(Extracellular)
INTERSTITIAL
FLUID
Capillary
6
ELECTROLYTES
Dissolved ions in the:
Cell, interstitial fluid, blood
Potassium (K)
Sodium (Na)
Calcium (Ca)
Magnesium (Mg)
Chlorine (Cl)
Bicarbonate (H2CO3)
Proteins (Pr)
7
ELECTROLYTES
There are three key concepts in
consideration of fluid and
electrolyte management:
1) Cell Membrane Permeability
2) Osmolarity
3) Electroneutrality
8
CELL MEMBRANE PERMEABILITY
Refers to the ability of a cell membrane
to allow certain substances to pass
freely
Other substances like charged ions
(Na+) cannot cross the membrane and
are trapped on one side of it
H2O
Na+
H2O
H2O
H2O
Na+
H2O
Na+
H2O
Na+
Na+
H2O
Na+
H2O
Na+
Na+
9
CELL MEMBRANE PERMEABILITY
In other words
“No Trespassing”
Cell membranes allow some things to pass
and blocks passage of others
10
OSMOLARITY
Osmolarity is a property of particles
in solution
If a substance
can dissociate in
solution, it will
contribute to the
osmolarity of the
solution
11
OSMOLARITY
In other words
“Water, water every where but not
a drop to drink”
If you are thirsty, you cannot
drink salt water
12
ELECTRONEUTRALITY
The principle of Electroneutrality
means that the overall number of
positive and negative charges
balances
For instance, in conditions like renal
tubular acidosis where HCO3- is lost,
chloride is retained
Cl13
ELECTRONEUTRALITY
In other words
“Cells do not make good batteries”
Positive and negative charges
inside and outside the cell must be
equal
Click to show
a charged
+
battery
+
+
+
+
+
+
+
+
-
14
ELECTROLYTES
When the body is in “fluid balance” it
means that the various body
compartments (cells, tissues, organs)
contain the required amount of fluids
to carry out normal bodily functions
15
ELECTROLYTES
Fluid balance and electrolyte
balance are inseparable
In a healthy individual, the volume
of fluid in each compartment
remains stable
16
ELECTROLYTES
Loss of electrolytes can have
serious consequences for the body
In severe dehydration, the loss of
electrolytes can result in circulatory
problems such as tachycardia (rapid
heart beat) and problems with the
nervous system
such as loss of
consciousness
and shock
17
ELECTROLYTES
Electrolytes serve three general
functions to maintain:
1) Normal metabolism
2) Proper fluid movement
between compartments
3) The acid-base balance
18
ELECTROLYTE COMPOSITION OF
PLASMA AND INTERSTITIAL FLUID
(meq/liter) PLASMA INTERSTITIAL
FLUID
Na+
140.0
145.5
+
K
4.5
4.8
Ca++
5.0
2.8
++
Mg
1.5
1.0
Cl 104.0
116.6
HCO324.0
27.4
PROTEIN
14.0
8.0
19
ELECTROLYTES
Protein
HCO3ClMg++
INTERSTITIAL
FLUID
PLASMA
Ca++
K+
Na+
0
50
100
150
200
20
ELECTROLYTES
PLASMA
Na+
K+
Ca++
Mg++
ClHCO3Protein
INTERSTITIAL
FLUID
21
IONS AND MOLECULES
Ions are charged atoms
ex:
Na+,
Cl-,
Mg++
Na+
Cl-
Molecules are formed when two or
more atoms or ions are combined
ex: H2O, C6H12O6, NaCl
22
MOVEMENT OF BODY FLUIDS
Fluid moves between the
compartments of the body through
various mechanisms
Substances leave and enter
capillaries via three mechanisms:
1) Vesicular transport
2) Diffusion
3) Bulk flow
23
VESICULAR TRANSPORT AND
DIFFUSION
Vesicular transport and diffusion
are associated with the movement
of solutes (electrolytes)
24
BULK FLOW
Bulk flow is the most important
process for the maintenance of
relative volumes (fluids) of blood
and interstitial fluid
Bulk flow involves the movement
of both solvent (fluids) and solute
into the interstitial space
25
MOVEMENT OF IONS AND
MOLECULES
Ions and molecules pass through
membranes by:
Simple Diffusion
Passage through channels
Facilitated Diffusion
Active Transport (Na-K pump)
26
CELL MEMBRANE
27
FLUID COMPARTMENTS
Describes the distribution of water in
the body
Fluid compartments are separated
by semipermeable membranes
Capillary wall separates the
plasma and the interstitial fluid
Cell membrane separates the
cytoplasm and interstitial fluid
28
SEMIPERMEABLE MEMBRANE
29
SEMIPERMEABLE MEMBRANE
30
FLUID COMPARTMENTS
PLASMA
CAPILLARY WALL
CELL MEMBRANE
INTERSTITIAL
FLUID
CYTOPLASM
31
FLUID SHIFTS
Fluid shifts may occur as the result
of disease or injury
32
FLUID SHIFTS
Accumulations of fluids in a
tissue or in a body cavity is
called third space compartment
Ex: liver disease may lead to
significant accumulations of
fluid in the peritoneal cavity
Represents a fluid loss as
it is trapped
33
FACTORS CONTROLLING
EXCHANGES OF FLUIDS
1) Diffusion
2) Filtration
a) Hydrostatic Pressure
b) Osmotic (Oncotic) Pressure
34
DIFFUSION
Water, small molecules and ions
Movement of molecules from areas
of higher concentration to areas of
lower concentration
Click to View
Animation
35
FILTRATION
Net flow of water is due to overall effect
of pressure on both sides of a membrane
Fluid is filtered out of capillaries in
response to changes in:
1) Hydrostatic Pressures
2) Oncotic (Osmotic) Pressures
36
HYDROSTATIC PRESSURE (HP)
Fluid pressure
Ex: blood pressure in the capillaries
H2O
H2 O
H2O
H2 O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
6
4
8
6
H2O
37
HYDROSTATIC PRESSURE (HP)
Fluid pressure
Ex: blood pressure in the capillaries
Ex: pressure exerted by interstitial
fluid
H2O
H2O
H2 O
H2 O
H2O
H2O
H2O
8
6
H2O
H2O
H2O
6
4
H2O
H2O
38
HYDROSTATIC PRESSURE IN PLASMA
Blood Pressure at Arterial end of
capillaries is 30 mm Hg
Blood Pressure at Venous end of
capillaries is 10 mm Hg
Difference in pressure forces
fluid out of plasma to the
interstitial fluid
39
Pressure IN PLASMA
HYDROSTATICOsmotic
PRESSURE
H2O
Net Pressure
on Fluids
H2O
H2O
H2O
Click to View
Hydrostatic
Hydrostatic
Pressure
Pressure
H2O
H2O
Osmotic Pressure
H2O
Netto
Click
Pressure
View Net
on Fluids
Pressure
on Fluids
Venule side
Arteriole side
Click to View
Osmotic
Pressure
H2O
40
HYDROSTATIC PRESSURE IN
INTERSTITIAL FLUID
The lymphatic system drains interstitial
fluid creating a negative interstitial
pressure
Hydrostatic pressure in interstitial space
is - 6 mm Hg
Supplies a pulling force (suction)
drawing fluid out of the capillaries
41
OSMOTIC (ONCOTIC) PRESSURE
Drawing force resulting from the
pressure created by presence of protein
dissolved in the:
Cytoplasm
Plasma
Interstitial fluid
Pressure which develops when there is
net movement of water across a
membrane (osmosis)
42
OSMOTIC (ONCOTIC) PRESSURE
Pressure created is directly
proportional to solute concentration
Thus osmotic pressure is
dependent on the concentration of
urea, glucose, amino acids,
electrolytes and proteins
Oncotic pressure defines
pressures which are the result
of protein concentration differences
43
OSMOTIC (ONCOTIC) PRESSURE
Click to View
Change
Semi-permeable
membrane
Solute
Solvent
HIGH
OSMOTIC
PRESSURE
LOW
OSMOTIC
PRESSURE
44
ONCOTIC PRESSURE IN PLASMA
Oncontic pressure at the arterial end of
capillaries is 28 mm Hg
Oncotic pressure of interstitial fluid is
5 mm Hg
Due to a higher protein concentration
in plasma (albumin)
Pr
Pr
Capillary
Pr
Pr
- H2O
H
O
Pr
2
Pr
PrPr
Pr
PrPr
Pr-
Pr-
Pr-
Pr-
Pr-
Pr-
Pr-
Pr- PrPr-
45
ONCOTIC PRESSURE
Capillary
PROTEIN (OP)
H2 O
INTERSTITIAL
FLUID
PROTEIN (OP)
H2 O
Opposing oncotic pressure (OP) inside and outside
of a capillary. A higher protein concentration in
plasma as compared to interstitial fluid, thus it has a
46
greater oncotic pressure
CAPILLARY-INTERSTITIAL
FLUID EXCHANGES
Hydrostatic and osmotic (oncotic)
pressures create opposing inward and
outward forces on the capillary
Capillary
Hydrostatic
Pressures
Osmotic
Pressures
47
OUTWARD FORCES
Arterial end of capillary exerts
hydrostatic pressure (30 mm Hg)
Capillary
30
Hydrostatic
Pressures
48
OUTWARD FORCES
Interstitial fluid oncotic pressure
(5
mm Hg)
Negative interstitial fluid pressure
(-6 mm Hg)
Total outward pressure 41 mm Hg
Capillary
Osmotic
5
Pressures
Hydrostatic
30
Pressures
6 Interstitial
Fluid (Pull)
49
INWARD FORCES
Plasma oncotic pressure (28 mm Hg)
Capillary
28
Osmotic
Pressures
50
INWARD FORCES
Net outward filtration of 13 mm Hg
results in plasma fluid loss
41 mm Hg - 28 mm Hg = 13 mm Hg
Capillary
Osmotic
28 Pressures
Osmotic
5
Pressures
Hydrostatic
30
Pressures
6 Interstitial
Fluid (Pull)
51
Opposing forces that influence fluid shifts
across the capillary wall. The net effect is
outflow of fluid (41 - 28) with a net pressure
of 13
Arterial end
of capillary
30 mm Hg (HP)
Interstitial
fluid
- 6 mm Hg
(HP)
28 mm Hg (OP)
5 mm Hg
(OP)
Total pressure
drawing fluid out
Inward
drawing
force
52
ABNORMAL CAPILLARY
DYNAMICS
Loss of protein and fluid from plasma
to interstitial fluid is provided a return
to the circulatory system by way of the
lymphatic system
53
ABNORMAL CAPILLARY
DYNAMICS
Increased capillary fluid loss occurs
when there is:
1) Increased Capillary Hydrostatic
Pressure
2) Increased Interstitial Fluid
Oncotic Pressure
3) Decreased Plasma Oncotic
Pressure
Accumulations of fluid in interstitial
spaces is called edema
54
CONDITIONS FOR EDEMA
Increased
HP
Capillary
- HP
OP
OP
Interstitial fluid
Increased capillary
Hydrostatic Pressure (HP)
55
CONDITIONS FOR EDEMA
Capillary
HP
- HP
Decreased
OP
OP
Interstitial fluid
Decreased plasma Oncotic
Pressure (loss of protein)
56
CONDITIONS FOR EDEMA
Capillary
HP
- HP
OP
Increased
OP
Interstitial fluid
Increased Oncotic Pressure
in interstitial fluid
57
EDEMA
Various liver diseases that
result in decreased protein
synthesis lead to edema
Noxious gases, inflammation
(pneumonia), or respiratory
burns may cause increased
permeability of pulmonary
capillaries with loss of
proteins and fluid
Cause of pulmonary edema
in these cases may be a
combination of factors
58
CAUSES FOR EDEMA
I) Malnutrition
II) Capillary wall damage
III) Obstructed lymph flow
IV) Fluid accumulation in the lungs
V) Left ventricle heart failure
VI) Congestive heart failure
VII) Glomerulonephritis
VIII) Nephrotic syndrome
IX) Large doses of blood or salt sol.
59
I) MALNUTRITION
Decreased or cessation of food
intake leads to decreased synthesis
of protein by the liver
Resulting in marked
lowering of plasma protein
Decreased oncotic
pressure causes a lowered
tendency to draw water
into the capillaries
Thus fluids accumulate outside
the capillaries
60
MALNUTRITION
Normal
Protein
H2O
Malnutrition
Capillary
Decreased Protein
Decreased
Protein
H2O
In malnutrition, there is a decreased synthesis of
protein by the liver, resulting in a lowered protein
level in plasma. A decrease in oncotic pressure
causes a diminished tendency to draw water into
capillaries. The net result is edema
61
KWASHIORKOR AND
MARASMUS
Reduced osmolarity from lack of protein in the
diet results in a fluid shift, as more water
moves out of the capillaries into the interstitial
spaces like the peritoneal cavity
62
II) CAPILLARY WALL DAMAGE
Damage which increases capillary
permeability to proteins
Ex: exposure to certain chemicals
Venoms
Bacterial toxins
Inflammatory response
Protein loss leads to decrease in
capillary oncotic pressure
63
CAPILLARY WALL DAMAGE
Capillary
H2O
H2O
Normal
Venom or Toxins
(Increased Proteins)
64
III) OBSTRUCTED LYMPH FLOW
Excess fluids and proteins in interstitial
fluid are collected and returned to
plasma by lymphatic vessels
abdominal
surgery
mammogram
Tumor or surgical removal of lymph
nodes can obstruct flow which leads to
edema
65
IV) PULMONARY EDEMA
Fluid accumulates in alveoli of the
lungs
66
PULMONARY EDEMA
Pulmonary capillaries are more
permeable to proteins than
capillaries in other parts of the body
Thus lungs are more susceptible
to edema
67
PULMONARY EDEMA
Tendency toward increased oncotic
pressure (water drawing force)
Interstitial fluid space is limited in
lung tissue
Alveoli
RBC
Interstitium
Thus excessive fluid in the
interstitial fluid space leaks
readily into the alveoli interfering
with gas exchange
68
ALVEOLAR EDEMA
In this section of lung the alveolar
walls are congested (arrow A) and the
alveolar spaces are filled with pink
fluid (arrow B). A few alveolar
macrophages (arrow C) are present but
there is no significant inflammation
69
PULMONARY EDEMA
Factors which protect the lungs
from fluid accumulations:
1) A high rate of lymph flow away
from the lungs
2) Pulmonary capillary pressure
that is lower than systemic
capillary pressure
Great deal of congestion is present
as well as fluid in the alveoli
70
PULMONARY EDEMA
Principles of water balance in the
lungs are the same as in peripheral
tissues
Any condition that causes
increased capillary hydrostatic
pressure, decreased capillary
oncotic pressure, or increased
capillary permeability may lead to
pulmonary edema
71
V) LEFT VENTRICLE HEART
FAILURE
Pulmonary edema is characteristic of
various forms of heart failure
If the left ventricle of the heart fails as
a pump:
1) Pulmonary circulation is slowed
and there is a buildup of blood in the
pulmonary vessels
2) Blood pressure increases
72
HYDROSTATIC EDEMA
pulmonary
artery
pulmonary
artery
This radiograph demonstrates pulmonary arteries
that are much larger than their accompanying
bronchi (A). In addition the bronchial walls are
thickened. The patient was treated with diuretics
and the subsequent scan (right) shows normal
appearing bronchi (B) in which the bronchial
walls are thin and the pulmonary artery and
bronchus are the same size
73
VI) CONGESTIVE HEART
FAILURE
The heart
fails as a
pump
coronary
bypass
Increased pulmonary venous and
capillary pressure because of
increased blood volume (increased
hydrostatic pressure)
74
VII) GLOMERULONEPHRITIS
Inflammatory kidney disease
Edema is caused by fluid retention
Thus there is increased capillary
hydrostatic pressure
75
VIII) NEPHROTIC SYNDROME
Urinary protein loss and decreased
plasma protein
Generalized edema as the result of
lowered plasma oncotic pressure
76
IX) ADMINISTRATION OF LARGE
AMOUNTS OF BLOOD OR SALT
SOLUTIONS
Pulmonary edema is the result of
increased blood volume
Thus increased hydrostatic
pressure
Individuals with heart or kidney
disease are especially susceptible
77
INTERSTITIAL FLUIDCELLULAR DYNAMICS
Water movement between cells and
the interstitial fluids
Electrolyte composition is a major
factor in this exchange
Osmotic pressure is the drawing
force
78
ELECTROLYTE CONCENTRATIONS
Interstitial Muscle
Meq/liter
Fluid
Cells
+
Na
145.5
12
+
K
4.8
150
Ca++
2.8
0.0000001
Mg++
1.0
7
Cl
116.6
3
HCO3
27.4
10
--PO4
2.3
116
Protein 8.0
40
79
PRINCIPLE ELECTROLYTE IN
INTERSTITIAL FLUID
Meq/liter
+
Na
K+
Ca++
++
Mg
Cl HCO3
--PO4
Protein -
Interstitial
Fluid
145.5
4.8
2.8
1.0
116.6
27.4
2.3
8.0
Muscle
Cells
12
150
0.0000001
7
3
10
116
40
80
MAIN INTRACELLULAR IONS
Meq/liter
+
Na
K+
Ca++
++
Mg
Cl HCO3
--PO4
Protein -
Interstitial
Fluid
145.5
4.8
2.8
1.0
116.6
27.4
2.3
8.0
Muscle
Cells
12
150
0.0000001
7
3
10
116
40
81
ELECTROLYTE
COMPARISONS
82
SIGNIFICANT IONS
Na+
Cl-
K+
PO4- - -
83
FLUID IMBALANCE
Fluid imbalance may occur and
result in either:
 Cellular dehydration
 Cellular hydration
84
CELL DEHYDRATION IN
DIABETES
Ex: diabetes
 Glucose concentrations increase
in extracellular fluids
Increased conc. gradients outside
the cells draw water out of the cells
by creating an osmotic pull
H2 O
glucose
85
CELL HYDRATION
Na+ ions predominate in extracellular
fluid
Thus Na+ plays a major role in
determining osmotic pressure
Low Na+ in extracellular fluid creates
an intracellular osmotic pull on H20
Na+ loss
Click to View
Animation
Decreased solute
concentration
Hydration of
cells
Decreased osmotic
pressure
86
CELL HYDRATION
Low sodium levels can be caused
by diuretics, vomiting or low Na+
intake
If low sodium levels are combined
with excess water intake
Cell hydration is exaggerated
Low sodium
levels
+
Excess water
intake
=
Cell hydration
87
EFFECTS OF IMBALANCE ON
COMPARTMENTS
Intravascular (plasma)
compartment is the most likely to be
affected by volume changes first
Interstitial and intracellular
compartments are less likely to be
affected and thus represent fluid
reservoirs
88
SUDDEN LOSS OR GAINS OF
FLUIDS
Sudden loss or gain of fluids affect
only intravascular compartments
ex: hemorrhage
Both compartments share
losses or gains equally if
they occur over a period of hours
Significant shifts of fluids between
compartments require several hours
89
LOSS OF HYPOTONIC FLUID
Loss of hypotonic fluid (solute
concentration less than that of
plasma) has a concentrating effect
on extracellular fluid
This results in an increase of
osmotic pressure
Water is drawn out of cells
in response to increased
extracellular osmotic
pressure
90
FLUID BALANCE DISORDERS
Total volume of water in the body is
60% of body weight
Intracellular fluid === 67%
Plasma =========== 8%
Interstitial fluid ===== 25%
91
REGULATION OF FLUID INTAKE
Thirst is a powerful
regulator of fluid
consumption
92
REGULATION OF FLUID INTAKE
Thirst center in the hypothalamus is
stimulated by:
1) Cellular dehydration
2) Decreased salivary production
3) Increased blood osmotic pressure
4) Decreased blood volume
93
THIRST
1) Cellular dehydration
Inadequate intake of water
Increase in extracellular solute
concentration
94
THIRST
2) Decreased salivary production
Dry sensation of the mucosa of the
mouth and pharynx
95
THIRST
3) Increased blood osmotic pressure
Stimulates osmoreceptors in the
hypothalamus which in turn
stimulate the thirst center
of the hypothalamus
96
THIRST
4) Decreased blood volume
(decreased blood pressure)
Stimulates the release of renin by
the kidney
Renin promotes synthesis of
angiotensin II which
affects the thirst
center of the
hypothalamus
97
STIMULATION OF THIRST BY DEHYDRATION
1
2
3
decreased flow
of saliva
dehydration
increased blood
osmotic pressure
dry mouth
and pharynx
stimulates osmoreceptors
in hypothalamus
decreased
blood volume
decreased blood
pressure
increased renin release
by juxta-glomerular
cells of kidney
4
stimulates thirst center
in hypothalamus
5
6
7
increased
angiotensin II
production
increases thirst
increases fluid intake
increases body water to normal
level and relieves dehydration
98
REGULATION OF FLUID LOSS
Fluid loss can be adjusted by:
1) Antidiuretic hormone (ADH)
Vasopressin
2) Atrial natriuretic peptide (ANP)
3) Aldosterone
99
REGULATION OF FLUID OUTPUT
ADH and aldosterone slow fluid losses
ANP causes diuresis
(increased urine production)
100
DEHYDRATION
If the body is dehydrated:
- Blood pressure falls
- Glomerular filtration decreases
Water is thus conserved
101
EXCESSIVE FLUID IN BLOOD
Excessive fluid in the blood causes:
- Increased blood pressure
- Increased glomerular filtration
Thus increased fluid output
102
OTHER FACTORS CAUSING EXCESSIVE
FLUID RETENTION
HYPERTENSION
HYPERVENTILATION
HEAVY
PERSPIRATION
Click
to View
Animation
VOMITING
EXCESSIVE
FLUID
RETENTION
EXTENSIVE SKIN
DESTRUCTION
DIARRHEA
FEVER
103
EFFECTS OF FLUID EXCESS
Fluid excess initially affects the
extracellular compartments
Increased fluid volume can result
in cerebral, pulmonary or
generalized edema
Usually the result of inadequate
renal output rather than fluid intake
104
EFFECTS OF FLUID EXCESS
If the retained water is hypotonic as
compared to plasma the effect is to
dilute the extracellular fluid
This causes a decrease in osmolality
When interstitial fluid is dilute as
compared to intracellular fluid, water
is drawn into the cells by osmotic pull
Results in increased cellular
volume and changes in cell
function occur
Most apparent in CNS tissue
105
INTRAVENOUS INFUSION
If the total body water is increased
by IV infusion of an isotonic solution
the result will be:
Increased extracellular volume
With little or no effect on cellular
volume
Net result is no change in solute
concentrations in plasma, interstitial
fluids and intracellular fluid and no
effect on cells
106
INTRAVENOUS INFUSION
Infusion of a hypertonic solution
results in:
Diffusion of both solute and water
into the interstitial fluid occurs
This concentration of solutes in
interstitial fluid is higher than
normal
Creates an osmotic drawing
force
Pulls water out of the cell
107
SUMMARY OF OVERHYDRATION
OR WATER INTOXICATION
1) If the fluid is hypotonic
2) If the fluid retained is isotonic
to plasma
3) If the excess fluid is hypertonic
108
HYPOTONIC
1) If the fluid is hypotonic
Increase in extracellular volume
A dilutional effect
Subsequent cellular dehydration
109
ISOTONIC
2) If the fluid retained is isotonic
to plasma
Expansion of the extracellular
compartment
No effect on cells
110
HYPERTONIC
3) If the excess fluid is hypertonic
Increased extracellular volume
Cellular dehydration
111
CAUSES FOR
OVERHYDRATION
1) Psychiatric
disorder of
compulsive water
drinking
(psychogenic
polydipsia)
10 -15 liters/day
112
CAUSES FOR
OVERHYDRATION
2) Forced water
ingestion as a form of
punishment (child
abuse)
113
CAUSES FOR
OVERHYDRATION
3) Inappropriate ADH secretion
ADH also called Vasopressin
Promotes water retention
(reabsorption) by increasing
permeability of the collecting
ducts in the kidney
114
CAUSES FOR
OVERHYDRATION
ADH is also a powerful
vasoconstrictor of arterioles
Head trauma, lung cancers,
pneumonia, CNS diseases,
encephalitis
Some types of tumors secrete
substances with ADH-like
activity
115
DEHYDRATION
Effects of a fluid deficit depend on:
Volume
Rate of loss
Amount of electrolytes lost with
water
116
HYPOTONIC LOSS
Simple dehydration is sometimes
called hypotonic loss
Effects of hypotonic fluid loss
(water loss exceeds solute loss) has
a concentrating effect
Results in increased
osmolality and
hypernatremia
(increased Na+
concentration)
117
HYPOTONIC LOSS
Water is drawn out of cells into the
extracellular compartment
Cell volume depletion stimulates the
release of ADH (antidiuretic
hormone) and aldosterone
ADH mediates renal water
retention
Aldosterone favors
Na+ and water retention
118
SUMMARY OF HYPOTONIC
DEHYDRATION
Immediate effect of water loss is
hypernatremia
Physiological responses to correct the
imbalance:
Movement of cellular water to
extracellular compartments
Hormonal responses that increase
extracellular volume
H2 O
119
CAUSES FOR DEHYDRATION
1) Excessive sweating
2) Insensible fluid loss
3) Diuresis
4) Diabetes insipidus
120
CAUSES FOR DEHYDRATION
1) Excessive sweating
Sweat is hypotonic
May result in hypernatremia with
losses of electrolytes
121
CAUSES FOR DEHYDRATION
2) Insensible fluid loss
From the skin or lungs
122
CAUSES FOR DEHYDRATION
3) Diuresis
Solute cleared from the blood by
the kidney and not reabsorbed
remains in the glomerular filtrate
This high solute concentration
creates an osmotic pull that draws
water in that direction
Results in increased
urine output and
water loss
123
DIURESIS
Mannitol (polysaccharide) is
sometimes used in cerebral
edema
Non-reabsorbable solute and
creates an osmotic
pull on water
promoting water loss
124
CAUSES FOR DEHYDRATION
4) Diabetes insipidus
Deficiency of ADH
Excessive urination and thirst
125
ELDERLY
Older individuals have
a decreased renal
capacity to save water
Significant if:
 Fluid intake is limited (decreased
diet)
Insensible fluid loss is increased
(fever)
126
ELDERLY
Elderly are also susceptible to water
intoxication
Increased ADH secretion (stress of
surgery, pneumonia, meningitis)
Reduction in renal blood flow
Decreased urine volume and
water retention
Heart failure, liver
disease, drug induced
hypotension
127
INFANTS
Infants have a greater
surface area compared
to weight
Increased insensible fluid loss
Infants have less renal
concentrating ability than an adult
128
END
FLUID AND
ELECTROLYTES
PART 1
129
MOVEMENT OF BODY FLUIDS
Pressures acting to move
substances out of the capillary
include:
Blood Hydrostatic Pressure
(BHP)
Interstitial Fluid Osmotic
Pressure (IFOP)
130
MOVEMENT OF BODY FLUIDS
Blood colloid osmotic pressure
(BCOP) and interstitial fluid
hydrostatic pressure act to push
substances into the capillary
At the arterial end of the capillary
the sum of the outward moving
pressures is dominant and
substances move into the interstitial
fluid (filtration)
At the venous end the inward
pressure is dominant and the
substances move into the capillary
(reabsorption)
131
MOVEMENT OF BODY FLUIDS
The exchange of interstitial and
intracellular fluid is controlled
mainly by the presence of the
electrolytes sodium and potassium
Potassium is the chief intracellular
cation and sodium the chief
extracellular cation
132
MOVEMENT OF BODY FLUIDS
Because the osmotic pressure of
the interstitial space and the ICF are
generally equal water typically does
not enter or leave the cell
A change in the concentration of
either electrolyte will cause water to
move into or out of the cell via
osmosis
133
MOVEMENT OF BODY FLUIDS
A drop in potassium will cause fluid
to leave the cell whilst a drop in
sodium will cause fluid to enter the
cell
Aldosterone, ANP and ADH regulate
sodium levels within the body, whilst
aldosterone can be said to regulate
potassium
134