Body fluids and Electrolytes Balance Part 1

Water

solvent in body fluids

solutes in body fluid

electrolytes, carbohydrates, proteins, lipids, vitamins, minerals

Intracellular

RBC, EBC, tissues

Extracellular

Intravascular and extravascular (intersitial and transcellular)

Increased blood volume

hypertension

decreased blood volume

hypotension

Functions of body fluids

dissolve and deliver substances (nutrients) to cells
account for blood volume  
protect and lubricate body tissues

cerebrospinal fluid

protects the brain and spinal cord

amniotic fluid

protects the fetus

synovial fluid

lubricates joints

pleural fluid

lubricates the lungs’ surface

Pericardial fluid

lubricates the sac in which the heart beats

Electrolytes

substances that will dissociate into ions in solution and so acquire the ability to conduct electricity
essential components of all living matter

Functions of electrolytes

regulate osmotice pressure and fluid distribution between compartments
transmit nerve signals
conduct neuromuscular impulses
acid-base balance
enzyme cofactors

Sodium

major extracellular cation

Potassium

major intracellular cation

Chloride

major extracellular anion

Bicarbonate

2nd major extracellular anion

Phosphate

major intracellular anion

Na/K - ATPase

active transport
an enzyme which actively pumps Na+ out of and K+ into the cell

Diffusion

Passive transport, requires no energy
Cl- and HCO3- move freely in/out of the cells

increased serum K+

Na/K ATPase loses its function
DM or hypoxia

adrenal cortex on topof the kidney

what organ secretes Aldosterone 

low blood volume/pressure

what is the stimulus of aldosterone

distal and collecting renal tubule

target organ of aldosterone

aldosterone action

stimulates Na+ (and water) reabsorption in exchange for K+ or H+
a Na+ saving hormone

antidiuretic hormone excetion hormone

produced by the hypothalamus and stored by the posterior pituitary

Antidiuretic hormone stimulus

secreted when plasma osmolality rises but also when BV/BP decreases, regardless of osmolality

renal collecting duct

Antidiuretic hormone site of action

H2O saving hormone

Antidiuretic hormone action

Antidiuretic hormone hypo-secretion

diabetes insipidus → urine volume increase, urine {Na+] and osmolal decreased while serum Na+ and Osmo increased

Antidiuretic hormone hypersecretion

syndrome of inappropriate diuretic hormone
urine [Na+] urine osmo and SG increased while serum [Na+] and serum osmo decrease

Crystalloid Osmotic pressure

the osmotic pressure that depends on dissociated ions and small molecules
regulates the distribution of water between intracellular and extracellular spaces → maintains cell shape
expressed as plasma osmolality

plasma osmolality

refelcts concentration of plasma in terms of the total number of electrolyres per kg plasma (mainly Na+)
Unit = milliosmoles of solutes/kg of solvent

280-310 mOs/kg

osmolality reference range

iso-osmolality

concentration of electrolytes is the same on either side of the cell membrane

hypo-osmolality

cerebral edema
caused by SAIDH (increased ADH)
concentration on the inside of the membrane is more than the plasma

hyper-osmolality

brain cells shrinkage
caused by dehydreation, DI, DM
concentration on the inside of the membrane is less than the plasma

urine osmolality

assesses
body’s state of hydration
the concentrating ability of the kidney tubules in renal failure
electrolyte balance

Diabetes insipidus

urine osmolality decreased while serum osmolality indreased

SAIDH

urine osmalality > 200 mOsmol/kg while serum osmolalitu is low

1

urine/serum osmo ratio should be 

2 Na + BUN/2.8 + Glu/18

serum osmolality equation

colligative properties

principle that measureing osmolality is based on

higher

the _____ the osmolality, the more its freezing point is depressed below 0°C

cryo-osmometer

measures serum and urine osmolality directly

osmolar gap

measures plasmal osmol - estimated plasma osmol

increased osmolar gap

indicates an excess of uncounted low MW particles

ketone bodies

endogenous osmolar gap ions

ethylene glycole

an exogenous osmolar gap ion

hydrostatic pressure

regulates the distribution of water between intravascular and extravacular spaces

intravascular hydrostatic pressure

the force of blood pressing outward against blood vessel wall ( fluid-pushing pressure inside a sapillary)
drives water out of the arteriole and venule blood vessels
propels blood with heartbeat

Colloidal Osmotic Pressure

depends on large, colloidal particals (proteins, lipids)
regulates the distribution of water between intravasculat and extravascular spaces
is essential to maintain intravascular fluid volume
albumin is the main regulator

edema

excessive accumulation of interstitial fluid

causes of edema

low serum protein (severe liver disease and renal disease)
heart failure
blockage of lymphatics

Sodium

maintains fluid balance, nerve response to stimuli

potassium

myocardial rhythm and contactility, nerve response to stimuli

Chloride

fluid balance (fallows Na+) and acid-base balance

Carbon dioxide

acid-base balance

Na+ - (Cl-+ HCO3-)

anion gap equation

plasma sodium

determines > 90% of plasma osmolality

sodium fruntion

electrolyte balance and thus water distribution between intracellular and extracellular spaces a/w BP
required for nerve impulse transmission (CNS) and muscle contraction

Sodium regulation

Na-K0ATPase pump, thirst, kidney function (aldosterone, ADH)

Hyponatremia

most commone electrolyte D/O with diverse etiologies
hypotonicity of blood causing cerebral edema 

Isotonic hyponatremia

pseudohyponatremia
delusion

Hypertonic hyponatremia

dilution

renal salt loss

hypotonic hypovolemic hyponatremia 
urine Na >20
diuretics, ACEI, Addison’s disease 

Extrarenal salt loss

hypotonic hypovolemic hyponatremia 
urine Na <10
diarrhea/vomiting dehydration +

hypotonic euvolemic hyponatremia 

SAIDH
Post op
hypothroidism
water intoxication

hypotonic hypervolemic hyponatremia 

edemoatous states
CHF
Liver disease
renal failure

indirect method

what method of measuring sodium is affected when isotonic hyponatremia happens

Depletion hypovolemic hyponatremia

renal Na+ loss → increased urine Na+
extrarenal Na+ los → decreased urine Na+ (marathon deaths)

dilution hypovolemic hyponatremia

euvolemic (normal Na+, increased H2O): SAIDH, psychogenic polydipsia
hypervolemic (increased sodium): edema associated diseases

Hypertonic Hyponatremia

Dilutions: Normal Na+, increased water
high concentration of osmotically active moiety
extreme hyperglycemia uremia (endogenous)
mannitol (exogenous)

Hypernatremia

high serum [Na+]
increased plasma osmolality
increased Bv and BP
osmosis - water is drawn out of cells, causing then to shrink
CNS hyper-osmolar state

Fluid deficit hypernatremia

dehydration (common)
H2O loss (DI

Excess total body Na+ hypernatremia

primary cause - IV hypertonic saline use
increased renal conservation = hyperaldosteronism

potassium functions

regulation of neuromuscular excitability
contraction of heart muscle

why is potassium measured

ID cause or monitor treatment of hyperkalemia (kidney disease - most common, or metabolic acidosis - DKA)

potassium regulation

Kidney function (aldosterone and drugs)
Exchange between cells and plasma (Na+-K-ATPase pump
Blood pH: K and H ions echanges across cell membranes; acidosis DKA or lactic acidosis causes increased in plasma [K+])

Hypokalemia effects

muscle cramps
fatal cardias arrhythmias or arrest (K+ < 2.5 mmol/L)

True hypokalemia

renal losses → increased urine K+: hyperaldosteronism, K-wasting diuretics
extrarenal losses → decreased urine K+

redistribution hypokalemia

metabolic alkalosis or treatment of DKA

Hyperkalemia effects

cardiac failure

increase in total body K+ hyperkalemia

impaired renal excretion: renal failure, decreased aldosterone

redistribution hperkalemia

acidosis
hemolytic anemia

falsely increased potassium measurement

collection: traumatic collection (hemolysis), prolonged tourniquet application, vigorous mixing, wrong anticoagulant (EDTA)
handling: refridgeration, delayed separation from cells

chlorine function

maintains electrical neutrality, fluid an acid-base balance

chlorine regulation

renal
HCO3- (Cl- shift) → maintain the buffering capacity of blood

when is chlorine measured

in sweat to ID CF in children

hypochloremia

direct causes: low aldosterone
indirect causes: high plasma HCO3- → increased Cl- shift into cells

hyperchloremia

dehydration
Excess loss of HCO3-

Cystic fibrosis

CFTR gene mutations
increased secretion of NaCl → thick mucus
effects Lungs, Pancreas, intestine

Bicarbonate function

acid buffering system that maintains blood pH

Bicarbonate regulation

Kidneys filter and reabsorb HCO3- to regulate acid/base balance
if blood is alkalotic: HCO3- is excreted by kidney
if acidotic: H+ is excreted and HCO3- is reabsorbed 

why is bicarb measured

screens for acid-base disorders or monitors their treatment

Hypobicarbonate

metabolic acidosis

increased AG

Hypobicarbonate
increased endogenous acids (ketoacids, lactic acid, phosphoric acids)
toxic ingestion of exogenous acids (salicylate, ethylene glycol, MeOH)

AG normal

Hypobicarbonate
decreased renal excretion of acid: hypoaldosteronism (addison disease)
loss of BCO3- (chronic diarrhea)

hyperbicarbonate

metabolic acidosis
hyperaldosteronism (Conn’s) ir cushing syndrome