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Fluid & Electrolytes
Distribution of Body Fluids Water is the largest single component
of the body 60% of adult’s weight is water
Healthy people can regulate balance
Compartments
Intracellular Within the cells
Contains dissolved solutes essential to balance
Extracellular Outside of the cell
Interstitial Between and around the cells
Intravascular Also lymph and organ fluids
Within the blood vessels Plasma
Composition of Body Fluids
Water Electrolytes
Separates into ions when dissolved Carries an electrical charge
Positive charge – CATIONS Sodium, Potassium, Calcium
Negative charge – ANION Bicarbonate, Chloride
Movement of Body Fluids Cell membranes are
selectively permeable Water passes through easily Most ions and molecules move
through much slower
Osmosis Moving a liquid through the
membrane from lesser to greater solute concentration Rate depends on concentration Temperature Electrical charges Differences between osmotic
pressures Works at equalizing concentration
Osmotic Pressure (Osmolarity) Pulling power for water
Depends on number of molecules in solution
Higher the concentration, greater pulling power
(higher osmotic pressure) Rate is quicker
Continues until equilibrium is reached
Osmolarity Hypertonic
Higher osmotic pressure than RBC’s Pulls fluid from cells
Shrinks cell Isotonic
Same osmotic pressure as RBC’s No fluid shift
Hypotonic Lower osmotic pressure than RBC’s
Fluid moves into cells Enlarges cell
Osmotic Pressure (cont) Affected by plasma proteins
Albumin Keeps fluid in intravascular compartment
using osmotic pressure Hydrostatic pressure draws fluid back
into capillaries Force of fluid pressure outward against
surface
Diffusion Moving a solid across the
semipermeable membrane From higher concentration to lower
To reach equilibrium Difference between the two is
concentration gradient
Filtration Both water and solids move
together in response to fluid pressure Seen in capillary beds ACTIVE Transport
Requires energy Moves against gradient
Sodium and potassium pump Uses carrier molecule
Glucose entering cell
Regulation of Body Fluids To maintain homeostasis, fluids
are regulated by: Fluid intake Hormonal controls Fluid output
Fluid Intake Regulated primarily by thirst
mechanism In the hypothalamus
Osmoreceptors monitor serum osmotic pressure Hypothalamus stimulated when osmolarlity
increases Thirst mechanism stimulated
With decreased oral intake Intake of hypertonic fluids Loss of excess fluid Stimulation of renin-angiotensisn-aldosterone
mechanism Potassium depletion Psychological factors Oropharyngeal dryness
Fluid Intake (cont) Average adult intake
2200-2700 cc/day Oral – 1100-1400 Solid foods – 800-1000 Oxidative metabolism – 300
By-product of cellular metabolism of ingested foods
Fluid Intake (cont) Must be alert Able to perceive mechanism Able to respond to mechanism **At risk for dehydration:
Elderly Very young Neurological disorders Psychological disorders
Hormonal regulation ADH
Stored in posterior pituitary gland Released in response to changes in blood
osmolarity Makes tubules and collecting ducts more
permeable to water Water returns the systemic circulation
Dilutes the blood Decreases urinary output
Hormonal regulation (cont) Aldosterone
Released by adrenal cortex In response to increased plasma potassium Or as part of renin-angiotensin-aldosterone
mechanism Acts on distal tubules to increase reabsorption
of sodium and water Excretion of potassium and hydrogen
Hormonal regulation (cont) Renin
Secreted by kidneys Responds to decreased renal perfusion Acts to produce angiotensin I
Causes vasoconstriction Converts to Angiotensin II
Massive selective vasoconstriction Relocates and increases the blood flow to
kidney, improving renal perfusion Stimulates release of aldosterone with low
sodium
Fluid Output Regulation Kidneys
Major regulatory organ Receive about 180 liters of blood/day to filter Produce 1200-1500 cc of urine
Skin Regulated by sympathetic nervous system
Activates sweat glands Sensible or insensible-500-600 cc/day
Directly related to stimulation of sweat glands Respiration
Insensible Increases with rate and depth of respirations, oxygen
delivery About 400 cc/day
Gastrointestinal tract In stool
Average about 100-200 GI disorders may increase or decrease it.
Regulation and Movement of Sodium
Most abundant cation in ECF Major contributor to maintaining
water balance By effect on serum osmolality, nerve
impulse transmission, regulation of acid-base balance and participation in chemical reactions
Regulated by dietary intake and aldosterone
Normal level : 135-145
normal osmolality290 mosm/ lWater deprivation,
solute ingestion,diarrhoea etc.
normal osmolality290 mosm/ lWater deprivation,
solute ingestion,diarrhoea etc.
increased ECFosmolality
normal osmolality290 mosm/ lWater deprivation,
solute ingestion,diarrhoea etc.
increased ECFosmolality
HYPOTHALAMIC OSMORECEPTORS
supraoptic ¶ventricular
Nuclei
lateral preoptic
area
normal osmolality290 mosm/ lWater deprivation,
solute ingestion,diarrhoea etc.
increased ECFosmolality
HYPOTHALAMIC OSMORECEPTORS
supraoptic ¶ventricular
Nuclei
lateral preoptic
area
ADH releasefrom posterior pituitary
normal osmolality290 mosm/ lWater deprivation,
solute ingestion,diarrhoea etc.
increased ECFosmolality
HYPOTHALAMIC OSMORECEPTORS
supraoptic ¶ventricular
Nuclei
lateral preoptic
area
ADH releasefrom posterior pituitary
CD made water permeable
normal osmolality290 mosm/ lWater deprivation,
solute ingestion,diarrhoea etc.
increased ECFosmolality
HYPOTHALAMIC OSMORECEPTORS
supraoptic ¶ventricular
Nuclei
lateral preoptic
area
ADH releasefrom posterior pituitary
CD made water permeable
WATER RETENTION by Kidney
normal osmolality290 mosm/ lWater deprivation,
solute ingestion,diarrhoea etc.
increased ECFosmolality
HYPOTHALAMIC OSMORECEPTORS
supraoptic ¶ventricular
Nuclei
lateral preoptic
area
ADH releasefrom posterior pituitary
thirst
drink water
CD made water permeable
WATER RETENTION by Kidney
Regulation works in both directions
normal osmolality290 mosm/ l excessive
fluid ingestion
normal osmolality290 mosm/ l excessive
fluid ingestion
decreased ECF osmolality
normal osmolality290 mosm/ l
HYPOTHALAMIC OSMORECEPTORS
supraoptic ¶ventricular
Nuclei
lateral preoptic
area
excessivefluid ingestion
decreased ECF osmolality
normal osmolality290 mosm/ l
HYPOTHALAMIC OSMORECEPTORS
supraoptic ¶ventricular
Nuclei
lateral preoptic
area
excessivefluid ingestion
decreased ECF osmolality
ADH releasesuppressed
normal osmolality290 mosm/ l
HYPOTHALAMIC OSMORECEPTORS
supraoptic ¶ventricular
Nuclei
lateral preoptic
area
excessivefluid ingestion
decreased ECF osmolality
ADH releasesuppressed
CD made waterimpermeable
normal osmolality290 mosm/ l
HYPOTHALAMIC OSMORECEPTORS
supraoptic ¶ventricular
Nuclei
lateral preoptic
area
excessivefluid ingestion
decreased ECF osmolality
ADH releasesuppressed
CD made waterimpermeable
WATER EXCRETION by Kidney
normal osmolality290 mosm/ l
HYPOTHALAMIC OSMORECEPTORS
supraoptic ¶ventricular
Nuclei
lateral preoptic
area
excessivefluid ingestion
decreased ECF osmolality
ADH releasesuppressed
thirstsuppressed
CD made waterimpermeable
WATER EXCRETION by Kidney
Regulation works in both directions
normal osmolality290 mosm/ lWater deprivation,
solute ingestion,diarrhoea etc.
increased ECFosmolality
HYPOTHALAMIC OSMORECEPTORS
supraoptic ¶ventricular
Nuclei
lateral preoptic
area
HYPOTHALAMIC OSMORECEPTORS
supraoptic ¶ventricular
Nuclei
lateral preoptic
area
ADH releasefrom posterior pituitary
thirst
drink water
CD made water permeable
WATER RETENTION by Kidney
excessivefluid ingestion
decreased ECF osmolality
ADH releasesuppressed
thirstsuppressed
CD made waterimpermeable
WATER EXCRETION by Kidney
Osmoreceptors are the main controllers of ADH levels, but other factors include.. Alcohol (inhibits ADH) Nicotine (stimulates ADH)
Increased circulating volume(Atrial stretch, ANP release,ADH release inhibited)... seelater
Volume Regulation
Since the osmolarity (i.e. concentration) of ECF is tightly controlled,
the volume of the ECF is determined by the total quantity of solute (mainly NaCl),
so regulation of ECF volume is all about Sodium Balance
Volume Regulation .. The total amount of Sodium in ECF dictates volume of ECF
add 0.2gNaCl
“Osmo-regulation”
1.2g NaCl1.2 litre H2O
1g / l1g / l
1.2g NaCl1 litre H2O
1.2g / l1.2g / l
1g NaCl1 litre H2O
1g / l1g / l
The Sensor
... well, one of them
The Juxtaglomerular Apparatus
The Juxtaglomerular Apparatus
reninrenin
Renin may be released by:
sympathetic activity (n.b. baroreceptor response to low BP)
wall tension in afferent arteriole (? drop in mean or pulse pressure)
??? a fall in Sodium delivery to Macula Densa
i.e. Low Blood Volume (Hypovolemia)
The Juxtaglomerular Apparatus
SympatheticNerves
renin
The Juxtaglomerular Apparatus
renin
Low Pressure
The Juxtaglomerular Apparatus
Na
renin
Renin may be released by:
sympathetic activity (n.b. baroreceptor response to low BP)
wall tension in afferent arteriole (? drop in mean or pulse pressure)
??? a fall in Sodium delivery to Macula Densa
i.e. Low Blood Volume (Hypovolemia)
Plasma angiotensinogen
Angiotensin I (10 - peptide)
RENIN
Hypovolemia
Plasma angiotensinogen
Angiotensin I (10 - peptide)
Angiotensin II (8 - peptide)
RENIN
plasma ‘converting enzyme’ (ACE)Hypovolemia
Plasma angiotensinogen
Angiotensin I (10 - peptide)
Angiotensin II (8 - peptide)
Aldosterone released from adrenal cortex
RENIN
plasma ‘converting enzyme’Hypovolemia
Plasma angiotensinogen
Angiotensin I (10 - peptide)
Angiotensin II (8 - peptide)
Aldosterone released from adrenal cortex
Increased Sodium Reabsorption in DCT
RENIN
plasma ‘converting enzyme’Hypovolemia
Plasma angiotensinogen
Angiotensin I (10 - peptide)
Angiotensin II (8 - peptide)
Aldosterone released from adrenal cortex
Increased Sodium Reabsorption in DCT
RENIN
plasma ‘converting enzyme’
osmoregulationVolume RegulationVolume Regulation
1g / l1g / l
add 0.2gNaCl
1.2g / l1.2g / l
1g NaCl1 litre H2O
1.2g NaCl1 litre H2O
“Osmo-regulation”
1g / l1g / l
1.2g NaCl1.2 litre H2O
Hypovolemia
Plasma angiotensinogen
Angiotensin I (10 - peptide)
Angiotensin II (8 - peptide)
Aldosterone released from adrenal cortex
Increased Sodium Reabsorption in DCT
RENIN
plasma ‘converting enzyme’Hypovolemia
osmoregulationVolume RegulationVolume Regulation
1g / l1g / l
add 0.2gNaCl
1.2g / l1.2g / l
1g NaCl1 litre H2O
1.2g NaCl1 litre H2O
“Osmo-regulation”
1g / l1g / l
1.2g NaCl1.2 litre H2O
Expansion of ECF
Plasma angiotensinogen
Angiotensin I (10 - peptide)
Angiotensin II (8 - peptide)
Aldosterone released from adrenal cortex
Increased Sodium Reabsorption in DCT
RENIN
plasma ‘converting enzyme’Restoration of Volume
osmoregulationVolume RegulationVolume Regulation
1g / l1g / l
add 0.2gNaCl
1.2g / l1.2g / l
1g NaCl1 litre H2O
1.2g NaCl1 litre H2O
“Osmo-regulation”
1g / l1g / l
1.2g NaCl1.2 litre H2O
Expansion of ECF
Aldosterone
Increases Na+ reabsorption in DCT as well as from :
gut sweat glands salivary glands
Aldosterone
Increases Na+ reabsorption in DCT as well as from :
gut sweat glands salivary glands
N
Na+
K+
H+
Na+
DCT cell
Lumen
BloodBlood
+
+
Another volume sensor.... The Atria
Atrial Natriuretic Peptide (ANP) released when atria stretched ( blood volume)causing:
Aldosterone secretion Renin release ADH release (emergency
response)
Regulation and Movement of Potassium
Major cation in intracellular compartments Regulates metabolic activities, necessary for
glycogen deposits in liver and skeletal muscle, transmission and conduction of nerve impulses, normal cardiac conduction and skeletal and smooth muscle contraction
Regulated by dietary intake and renal excretion
Normal level – 3.5-5.0 Body conserves potassium poorly
Increased urine output decreased serum potassium
Movement and Regulation of Calcium
Stored in bone, plasma and body cells (Cation) 90% in bones 1% in ECF
In plasma, binds with albumin Necessary for bone and teeth formation,
blood clotting, hormone secretion, cell membrane integrity, cardiac conduction, transmission of nerve impulses, and muscle contraction
Normal level – 4.5-5.5 Regulated by bone resorption
Movement and Regulation of Magnesium
Cation Normal 1.5-2.5 Regulated by dietary, renal and PTH
Movement and Regulation of Chloride
Major anion in ECF Normal level – 95-108
Follows sodium Regulated by dietary intake
and the kidneys
Movement and Regulation of Bicarbonate
Major chemical base buffer in the body Carbonic acid-Bicarbonate buffering
system Needed for acid-base balance
Normal level 22-26 Regulated by kidneys
Movement and Regulation of Phosphate
Buffer anion found mainly in ICF Assists in acid-base balance
Inversely proportional to calcium Helps maintain healthy bones and teeth,
neuromuscular activity, and CHO metabolism Absorbed through GI tract Normal level 2.5-4.5 Regulated by dietary intake, renal excretion,
intestinal absorption and PTH
Common Disturbances Electrolyte Balance
Sodium Hypernatremia (Na > 145, sp gravity < 1.010)
Caused by excess water loss or overall sodium excess Excess salt intake, hypertonic solutions, excess
aldosterone, diabetes insipidus, increased s water loss, water deprivation
S&S: thirst, dry, flushed skin, dry, stick tongue and mucous membranes
Hyponatremia (Na < 135, sp gravity > 1.030) Occurs with net loss of sodium or net water excess
Kidney disease with salt wasting, adrenal insufficiency, GI losses, increased sweating, diuretics, SIADH
S&S: personality change, postural hypotension, postural dizziness, abd cramping, n&v, diarrhea, tachycardia, convulsions and coma
Common Disturbances Electrolyte Balance
Potassium Hyperkalemia (K > 5.3; EKG irregularities-
bradycardia, heart block, wide QRS pattern-cardiac arrest)
Primary cause: renal failure; major symptom: cardiac irregularity
Fluid volume deficit, massive cell damage, excess K+ given, adrenal insufficiency, acidosis, rapid infusion of stored blood, potassium-sparing diuretics
S&S: dysrhythmias, paresthesia Hypokalemia (K < 3.5; EKG irregularities-ventricular)
Most common electrolyte imbalance; affects cardiac conduction and function. Most common cause: potassium wasting diuretics
Diarrhea, vomiting, alkalosis, excess aldosterone secretion, polyruia, extreme sweating, insulin to treat diabetic ketoacidosis
S&S: weakness, ventricular dysrhythmias, irregular pulse
Common Disturbances Electrolyte Balance
Calcium Hypercalcemia (Ca > 5; x-rays show calcium
loss, cardiac irregularities) Frequently symptom of underlying disease with
excess bond resorption and release of calcium Hyperparathyroidism, malignant neoplastic disease,
Paget’s disease, Osteoporosis, prolonged immobization, acidosis
S&S: anorexia, nausea and vomiting, weakness, kidney stones
Hypocalcemia (Ca < 4.0, EKG abnormalities) Seen in severe illness
Rapid blood transfusion with citrate, hypoalbuminemia, hypoparathyroidism, Vitamin D deficiency, Pancreatitis, Alkalosis
S&S: numbness and tingling, hyperactive reflexes, positive Trousseau’s sign (wrist), positive Chvostek’s sign (cheek), tetany, muscle cramps, pathological fracture
Common Disturbances Electrolyte Balance
Chloride Usually seen with acid-base imbalance
Hyperchloremia (Na >145, Bicarb <22) Serum bicarbonate values fall or sodium rises
Hypochloremia (pH > 7.45) Excess vomiting or N/G drainage; loop of
thiazide diuretics because of sodium excretion Leads to metabolic alkalosis due to reabsorption of
bicarbonate to maintain electrical neutrality
Common Disturbances Fluid Balance
Isotonic imbalances When water and electrolytes are
gained or lost in equal proportions Osmolar imbalances
Loss or gain of only water Osmolality is affected
Isotonic imbalances Fluid volume deficit (Sp Gravity > 1.025, Hct >50%, BUN > 25)
GI losses, loss of plasma or whole blood, excess perspiration, fever, decreased intake, diuretics
S&S: postural hypotension, tachycardia, dry mucous membranes, poor skin turgor, thirst, confusion, rapid weight loss, slow vein filling, lethargy, oliguria, weak pulse, sunken, dry conjunctiva
Fluid volume excess (Hct < 38%, BUN < 10 Congestive heart failure, renal failure, cirrhosis, increased
aldosterone and steroid levels, excess sodium intake S&S: rapid weight gain, edema, hypertension, polyuria,
neck vein distention, increased venous pressure, crackles in lungs
Osmolar Imbalances Dehydration (Hyperosmolar imbalance)
(Na > 145) Diabetes insipidus, neurological damage to
block thirst drive, diabetic ketoacidosis, osmotic diuresis, hypertonic IV fluids of tube feedings
S&S: dry, sticky mucous membranes, flushed and dry skin, thirst, elevated temp
Water Excess (Hypoosmolar imbalance) (Na < 135)
SIADH, excess water intake S&S: decreased level of consciousness,
convulsions, coma
Variables Affecting Normal Fluid, Electrolyte and Acid-Base Imbalances
Age Orientation status Mobility level Prolonged illness
Cancer, CHF, endocrine disease, COPD Medications
Diuretics, steroids, IV therapy, TPN Gastrointestinal losses
Clinical Assessment for Fluid, Electrolyte and Acid-Base Imbalances
Pre-existing disease processes Cancer, cardiovascular, renal, GI
Age Infants have higher % water- loss felt faster Elderly –kidneys decreased filtration rate, less functioning
nephrons, don’t excrete mediations as fast, lung changes may lead to respiratory acidosis
Acute illness Surgery, burns, respiratory disorders, head injury
Environmental Vigorous exercise, temperature extremes
Diet Fluids and electrolytes gained through diet
Lifestyle Smoking or alcohol
Medications Side-effects may cause fluid and/or electrolyte imbalances
Medications Likely to Cause
F&E Imbalances Diuretics
Metabolic alkalosis, hyperkalemia, hypokalemia Steroids
Metabolic alkalosis Potassium supplements
GI disturbances Respiratory center depressants (narcotic analgesics)
Respiratory acidosis Antibiotics
Nephrotoxicity, hyperkalemia, hypernatremia Calcium carbonate (TUMS)
Metabolic alkalosis Magnesium hydroxide (Milk of Mag)
hypokalemia
References To be added