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ADVANCED PHYSIOLOGY FLUID & ELECTROLYTES Part 1 Instructor Terry Wiseth. NORTHLAND COLLEGE. 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.

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fluid electrolyte homeostasis
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
fluid electrolyte homeostasis1
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
fluid electrolyte homeostasis2
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

fluid compartments
FLUID COMPARTMENTS
  • Effectively there are three compartments
    • 1) Intracellular
    • 2) Interstitial
    • 3) Plasma
fluid compartments1
FLUID COMPARTMENTS

Cell

CYTOPLASM

PLASMA

(Intracellular)

(Extracellular)

INTERSTITIAL

FLUID

Capillary

electrolytes
ELECTROLYTES
  • Dissolved ions in the:
    • Cell, interstitial fluid, blood
      • Potassium (K)
      • Sodium (Na)
      • Calcium (Ca)
      • Magnesium (Mg)
      • Chlorine (Cl)
      • Bicarbonate (H2CO3)
      • Proteins (Pr)
electrolytes1
ELECTROLYTES
  • There are three key concepts in consideration of fluid and electrolyte management:
    • 1) Cell Membrane Permeability
    • 2) Osmolarity
    • 3) Electroneutrality
cell membrane permeability
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+

Na+

H2O

Na+

cell membrane permeability1
CELL MEMBRANE PERMEABILITY
  • In other words
    • “No Trespassing”
    • Cell membranes allow some things to pass and blocks passage of others
osmolarity
OSMOLARITY
  • Osmolarity is a property of particles in solution
    • If a substancecan dissociate insolution, it willcontribute to theosmolarity of thesolution
osmolarity1
OSMOLARITY
  • In other words
    • “Water, water every where but not a drop to drink”
    • If you are thirsty, you cannot drink salt water
electroneutrality
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

Cl-

electroneutrality1
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

-

+

-

+

-

+

-

+

-

+

-

+

-

+

-

+

-

+

electrolytes2
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
electrolytes3
ELECTROLYTES
  • Fluid balance and electrolyte balance are inseparable
  • In a healthy individual, the volume of fluid in each compartment remains stable
electrolytes4
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 systemsuch as loss ofconsciousnessand shock
electrolytes5
ELECTROLYTES
  • Electrolytes serve three general functions to maintain:
    • 1) Normal metabolism
    • 2) Proper fluid movement between compartments
    • 3) The acid-base balance
electrolytes7
ELECTROLYTES

PLASMA

INTERSTITIAL

FLUID

ions and molecules

Na+

Cl-

IONS AND MOLECULES
  • Ions are charged atoms
    • ex: Na+, Cl-, Mg++
  • Molecules are formed when two or more atoms or ions are combined
    • ex: H2O, C6H12O6, NaCl
movement of body fluids
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
vesicular transport and diffusion
VESICULAR TRANSPORT AND DIFFUSION
  • Vesicular transport and diffusion are associated with the movement of solutes (electrolytes)
bulk flow
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
movement of ions and molecules
MOVEMENT OF IONS AND MOLECULES
  • Ions and molecules pass through membranes by:
    • Simple Diffusion
    • Passage through channels
    • Facilitated Diffusion
    • Active Transport (Na-K pump)
fluid compartments2
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
fluid compartments3
FLUID COMPARTMENTS

PLASMA

CAPILLARY WALL

CELL MEMBRANE

INTERSTITIAL

FLUID

CYTOPLASM

fluid shifts
FLUID SHIFTS
  • Fluid shifts may occur as the result of disease or injury
fluid shifts1
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
factors controlling exchanges of fluids
FACTORS CONTROLLING EXCHANGES OF FLUIDS
  • 1) Diffusion
  • 2) Filtration
    • a) Hydrostatic Pressure
    • b) Osmotic (Oncotic) Pressure
diffusion
DIFFUSION
  • Water, small molecules and ions
  • Movement of molecules from areas of higher concentration to areas of lower concentration

Click to View Animation

filtration
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

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

hydrostatic pressure hp
HYDROSTATIC PRESSURE (HP)
  • Fluid pressure
    • Ex: blood pressure in the capillaries

6

4

H2O

H2O

H2O

H2O

8

6

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

hydrostatic pressure hp1
HYDROSTATIC PRESSURE (HP)
  • Fluid pressure
    • Ex: blood pressure in the capillaries
    • Ex: pressure exerted by interstitial fluid

8

6

H2O

H2O

H2O

H2O

H2O

6

4

H2O

H2O

H2O

H2O

H2O

H2O

H2O

hydrostatic pressure in plasma
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
hydrostatic pressure in plasma1
HYDROSTATIC PRESSURE IN PLASMA

Osmotic Pressure

H2O

H2O

H2O

H2O

Click to View Osmotic Pressure

NetPressureon Fluids

Click to View Hydrostatic Pressure

Click toView Net Pressureon Fluids

Venule side

Net Pressure on Fluids

Arteriole side

Hydrostatic Pressure

H2O

H2O

H2O

H2O

Osmotic Pressure

hydrostatic pressure in interstitial fluid
HYDROSTATIC PRESSURE ININTERSTITIAL 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
osmotic oncotic pressure
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)
osmotic oncotic pressure1
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 definespressures which are the resultof protein concentration differences
osmotic oncotic pressure2

Solute

Solvent

HIGHOSMOTIC PRESSURE

LOWOSMOTIC PRESSURE

OSMOTIC (ONCOTIC) PRESSURE

Click to View Change

Semi-permeable membrane

oncotic pressure in plasma

Capillary

ONCOTIC PRESSURE IN PLASMA
  • Oncontic pressure at the arterial end of capillaries is 28 mm Hg
  • Oncotic pressure of interstitial fluid is5 mm Hg
    • Due to a higher protein concentration in plasma (albumin)

Pr-

Pr-

Pr-

Pr-

Pr-

Pr-

H2O

H2O

Pr-

Pr-

Pr-

Pr-

Pr-

Pr-

Pr-

Pr-

Pr-

Pr-

Pr-

Pr-

Pr-

Pr-

Pr-

H2O

H2O

H2O

H2O

H2O

oncotic pressure

Capillary

ONCOTIC PRESSURE

PROTEIN (OP)

INTERSTITIAL

FLUID

PROTEIN (OP)

H2O

H2O

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 greater oncotic pressure

capillary interstitial fluid exchanges

Capillary

CAPILLARY-INTERSTITIAL FLUID EXCHANGES
  • Hydrostatic and osmotic (oncotic) pressures create opposing inward and outward forces on the capillary

Hydrostatic Pressures

Osmotic Pressures

outward forces

Capillary

OUTWARD FORCES
  • Arterial end of capillary exerts hydrostatic pressure (30 mm Hg)

30

Hydrostatic Pressures

outward forces1

Capillary

OUTWARD FORCES
  • Interstitial fluid oncotic pressure (5 mm Hg)
  • Negative interstitial fluid pressure (-6 mm Hg)
    • Total outward pressure 41 mm Hg

5

30

Osmotic Pressures

Hydrostatic Pressures

6

Interstitial Fluid (Pull)

inward forces

Capillary

INWARD FORCES
  • Plasma oncotic pressure (28 mm Hg)

28

Osmotic Pressures

inward forces1

Capillary

INWARD FORCES
  • Net outward filtration of 13 mm Hg results in plasma fluid loss
    • 41 mm Hg - 28 mm Hg = 13 mm Hg

5

30

Osmotic Pressures

Hydrostatic Pressures

6

28

Osmotic Pressures

Interstitial Fluid (Pull)

slide52

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)

28 mm Hg (OP)

- 6 mm Hg

(HP)

5 mm Hg

(OP)

Interstitial

fluid

Total pressure

drawing fluid out

Inward

drawing

force

abnormal capillary dynamics
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
abnormal capillary dynamics1
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
conditions for edema
CONDITIONS FOR EDEMA

Capillary

Increased

HP

OP

- HP

OP

Interstitial fluid

Increased capillary Hydrostatic Pressure (HP)

conditions for edema1
CONDITIONS FOR EDEMA

Capillary

Decreased

OP

HP

- HP

OP

Interstitial fluid

Decreased plasma Oncotic

Pressure (loss of protein)

conditions for edema2
CONDITIONS FOR EDEMA

Capillary

OP

HP

Increased

OP

- HP

Interstitial fluid

Increased Oncotic Pressure

in interstitial fluid

edema
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
causes for edema
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.
i malnutrition
I) MALNUTRITION
  • Decreased or cessation of food intake leads to decreased synthesis of protein by the liver
  • Resulting in markedlowering of plasma protein
    • Decreased oncoticpressure causes a lowered tendency to draw waterinto the capillaries
    • Thus fluids accumulate outside the capillaries
malnutrition
MALNUTRITION

Normal

Protein

Malnutrition

Capillary

Decreased

Protein

Decreased Protein

H2O

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

kwashiorkor and marasmus
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

ii capillary wall damage
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
capillary wall damage
CAPILLARY WALL DAMAGE

Capillary

H2O

H2O

Venom or Toxins(Increased Proteins)

Normal

iii obstructed lymph flow
III) OBSTRUCTED LYMPH FLOW
  • Excess fluids and proteins in interstitial fluid are collected and returned to plasma by lymphatic vessels
  • Tumor or surgical removal of lymph nodes can obstruct flow which leads to edema

abdominal

surgery

mammogram

iv pulmonary edema
IV) PULMONARY EDEMA
  • Fluid accumulates in alveoli of the lungs
pulmonary edema
PULMONARY EDEMA
  • Pulmonary capillaries are more permeable to proteins than capillaries in other parts of the body
    • Thus lungs are more susceptible to edema
pulmonary edema1
PULMONARY EDEMA
  • Tendency toward increased oncotic pressure (water drawing force)
  • Interstitial fluid space is limited in lung tissue
    • Thus excessive fluid in the interstitial fluid space leaks readily into the alveoli interfering with gas exchange

Alveoli

RBC

Interstitium

alveolar edema
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

pulmonary edema2
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

pulmonary edema3
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
v left ventricle heart failure
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
hydrostatic edema
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

vi congestive heart failure
VI) CONGESTIVE HEART FAILURE
  • The heartfails as apump
  • Increased pulmonary venous and capillary pressure because of increased blood volume (increased hydrostatic pressure)

coronary

bypass

vii glomerulonephritis
VII) GLOMERULONEPHRITIS
  • Inflammatory kidney disease
  • Edema is caused by fluid retention
  • Thus there is increased capillary hydrostatic pressure
viii nephrotic syndrome
VIII) NEPHROTIC SYNDROME
  • Urinary protein loss and decreased plasma protein
  • Generalized edema as the result of lowered plasma oncotic pressure
ix administration of large amounts of blood or salt solutions
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
interstitial fluid cellular dynamics
INTERSTITIAL FLUID-CELLULAR DYNAMICS
  • Water movement between cells and the interstitial fluids
  • Electrolyte composition is a major factor in this exchange
    • Osmotic pressure is the drawing force
significant ions
SIGNIFICANT IONS

K+

Na+

PO4- - -

Cl-

fluid imbalance
FLUID IMBALANCE
  • Fluid imbalance may occur and result in either:
    • Cellular dehydration
    • Cellular hydration
cell dehydration in diabetes
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

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

glucose

cell hydration

Na+ loss

Hydration of

cells

Decreased solute

concentration

Decreased osmotic

pressure

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

Click to View Animation

cell hydration1
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

=

Cell hydration

+

Excess water

intake

effects of imbalance on compartments
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
sudden loss or gains of fluids
SUDDEN LOSS OR GAINS OF FLUIDS
  • Sudden loss or gain of fluids affect only intravascular compartments
    • ex: hemorrhage
  • Both compartments sharelosses or gains equally ifthey occur over a period of hours
  • Significant shifts of fluids between compartments require several hours
loss of hypotonic fluid
LOSS OF HYPOTONIC FLUID
  • Loss of hypotonic fluid(soluteconcentration less than that ofplasma) has a concentrating effect on extracellular fluid
    • This results in an increase of osmotic pressure
  • Water is drawn out of cellsin response to increasedextracellular osmoticpressure
fluid balance disorders
FLUID BALANCE DISORDERS
  • Total volume of water in the body is 60% of body weight
    • Intracellular fluid === 67%
    • Plasma =========== 8%
    • Interstitial fluid ===== 25%
regulation of fluid intake
REGULATION OF FLUID INTAKE
  • Thirst is a powerful regulator of fluid consumption
regulation of fluid intake1
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
thirst
THIRST
  • 1) Cellular dehydration
    • Inadequate intake of water
    • Increase in extracellular solute concentration
thirst1
THIRST
  • 2)Decreased salivary production
    • Dry sensation of the mucosa of the mouth and pharynx
thirst2
THIRST
  • 3)Increased blood osmotic pressure
    • Stimulates osmoreceptors in the hypothalamus which in turn stimulate the thirst centerof the hypothalamus
thirst3
THIRST
  • 4)Decreased blood volume

(decreased blood pressure)

    • Stimulates the release of renin by the kidney
    • Renin promotes synthesis of angiotensin II whichaffects the thirstcenter of thehypothalamus
stimulation of thirst by dehydration

1

dehydration

decreased

blood volume

decreased flow

of saliva

increased blood

osmotic pressure

2

dry mouth

and pharynx

stimulates osmoreceptors

in hypothalamus

decreased blood

pressure

3

increased renin release

by juxta-glomerular

cells of kidney

increased

angiotensin II

production

4

stimulates thirst center

in hypothalamus

5

increases thirst

6

increases fluid intake

7

increases body water to normal

level and relieves dehydration

STIMULATION OF THIRST BY DEHYDRATION
regulation of fluid loss
REGULATION OF FLUID LOSS
  • Fluid loss can be adjusted by:
    • 1) Antidiuretic hormone (ADH)
      • Vasopressin
    • 2) Atrial natriuretic peptide (ANP)
    • 3) Aldosterone
regulation of fluid output
REGULATION OF FLUID OUTPUT
  • ADH and aldosterone slow fluid losses
  • ANP causes diuresis(increased urine production)
dehydration
DEHYDRATION
  • If the body is dehydrated:
    • - Blood pressure falls
    • - Glomerular filtration decreases
  • Water is thus conserved
excessive fluid in blood
EXCESSIVE FLUID IN BLOOD
  • Excessive fluid in the blood causes:
    • - Increased blood pressure
    • - Increased glomerular filtration
  • Thus increased fluid output
other factors causing excessive fluid retention

HYPERTENSION

HYPERVENTILATION

EXCESSIVE

FLUID

RETENTION

HEAVY PERSPIRATION

VOMITING

EXTENSIVE SKIN

DESTRUCTION

DIARRHEA

FEVER

OTHER FACTORS CAUSING EXCESSIVE FLUID RETENTION

Click to View Animation

effects of fluid excess
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 inadequaterenal output rather than fluid intake
effects of fluid excess1
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 cellularvolume and changes in cellfunction occur
      • Most apparent in CNS tissue
intravenous infusion
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
intravenous infusion1
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
summary of overhydration or water intoxication
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
hypotonic
HYPOTONIC
  • 1) If the fluid is hypotonic
    • Increase in extracellular volume
    • A dilutional effect
    • Subsequent cellular dehydration
isotonic
ISOTONIC
  • 2) If the fluid retained is isotonic to plasma
    • Expansion of the extracellular compartment
    • No effect on cells
hypertonic
HYPERTONIC
  • 3) If the excess fluid is hypertonic
    • Increased extracellular volume
    • Cellular dehydration
causes for overhydration
CAUSES FOR OVERHYDRATION
  • 1) Psychiatric disorder of compulsive water drinking (psychogenic polydipsia)
    • 10 -15 liters/day
causes for overhydration1
CAUSES FOR OVERHYDRATION
  • 2) Forced water ingestion as a form of punishment (child abuse)
causes for overhydration2
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
causes for overhydration3
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
dehydration1
DEHYDRATION
  • Effects of a fluid deficit depend on:
    • Volume
    • Rate of loss
    • Amount of electrolytes lost with water
hypotonic loss
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 increasedosmolality andhypernatremia(increased Na+concentration)
hypotonic loss1
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 favorsNa+ and water retention
summary of hypotonic dehydration
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

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

causes for dehydration
CAUSES FOR DEHYDRATION
  • 1) Excessive sweating
  • 2) Insensible fluid loss
  • 3) Diuresis
  • 4) Diabetes insipidus
causes for dehydration1
CAUSES FOR DEHYDRATION
  • 1) Excessive sweating
    • Sweat is hypotonic
    • May result in hypernatremia with losses of electrolytes
causes for dehydration2
CAUSES FOR DEHYDRATION
  • 2) Insensible fluid loss
    • From the skin or lungs
causes for dehydration3
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 increasedurine output andwater loss
diuresis
DIURESIS
  • Mannitol (polysaccharide) is sometimes used in cerebral edema
    • Non-reabsorbable solute and creates an osmoticpull on waterpromoting water loss
causes for dehydration4
CAUSES FOR DEHYDRATION
  • 4) Diabetes insipidus
    • Deficiency of ADH
    • Excessive urination and thirst
elderly
ELDERLY
  • Older individuals havea decreased renalcapacity to save water
  • Significant if:
    • Fluid intake is limited (decreased diet)
    • Insensible fluid loss is increased (fever)
elderly1
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, liverdisease, drug induced hypotension
infants
INFANTS
  • Infants have a greater surface area compared to weight
    • Increased insensible fluid loss
  • Infants have less renal concentrating ability than an adult
movement of body fluids1
MOVEMENT OF BODY FLUIDS
  • Pressures acting to move substances out of the capillary include:
    • Blood Hydrostatic Pressure (BHP)
    • Interstitial Fluid Osmotic Pressure (IFOP)
movement of body fluids2
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)
movement of body fluids3
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
movement of body fluids4
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
movement of body fluids5
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