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p99-113; 118-119; Module 3 on Evolve

Total Body Water:

sum of fluids within cells; 60% of body weight

Intracellular fluid:

all fluid WITHIN cells; 2/3 of TBW (40% of body weight)

Extracellular fluid:

all fluid OUTSIDE cells; 1/3 of TBW; divided into 2 main compartments (Interstitial & Intravascular)

Interstitial fluid:

fluid that is in spaces between cells and outside the blood vessels

Intravascular fluid:

blood plasma

Other compartments of ECF:

lymph and transcellular fluids (synovial, intestinal, cerebrospinal); sweat, urine, pleural, peritoneal, pericardial, intraocular)

Normal water losses:

sweat, urine (most), stool (least), skin, lungs

Normal water gains:

drinking water, food with water, water of oxidation (least)

Hydrostatic pressure:

PUSHES water

Osmotic pressure:

PULLS water


fluid moves out of capillary into interstitial spaces


fluid moves back into capillary from interstitial spaces


blood pressure: facilitates the outward movement of water from the capillary to the interstitial space


osmotically attracts water from interstitial spaces back into the capillary


facilitates inward movement of water form interstitial spaces into capillary


osmotically attracts water from capillary into interstitial spaces


movement of fluid back and forth across capillary wall (best described as Starling's forces)

ARTERIAL end of capillary:

hydrostatic pressure > capillary oncotic pressure - fluid moves into interstitial space

VENOUS end of capillary:

capillary oncotic pressure > capillary hydrostatic pressure - fluids are attracted back into capillary

Water moves between ICF & ECF primarily as a function of osmotic forces



is responsible for ECF osmotic balance

POTASSIUM maintains

ICF osmotic balance


excessive accumulation of fluid within interstitial spaces


INCREASED capillary hydrostatic pressure; LOWERED plasma oncotic pressure; INCREASED capillary membrane permeability; lymphatic channel obstruction

Pathophysiology of Edema #1: Venous obstruction (DVT) >

increased hydrostatic pressure behind obstruction > fluid pushed from capillaries into interstitial spaces

Common causes of DVT:

thrombophlebitis, hepatic obstruction, tight clothing around extremities, prolonged standing, CHF, renal failure

Interventions for DVT: Slow IV rate, girdle, "spanx"


pathophysiology of edema #2: lost or diminished plasma albumin production contributes to decreased plasma oncotic pressure >

decreased attraction of fluid within capillary causes filtered capillary fluid to remain in interstitial spaces > edema (low oncotic pressure=edema)

Causes of low plasma albumin production:

liver disease, protein malnutrition, serous drainage of open wounds, hemorrhage, burns, cirrhosis of liver

Pathophysiology of edema #3: capillaries become more permeable >

proteins escape from vascular space and produce edema through decreased capillary oncotic pressure & interstitial fluid protein accumulation (direct trauma to capillary membranes)

Causes of capillaries becoming more permeable:

inflammation, immune responses, trauma (burns, crushing injuries) neoplastic disease, allergic reactions

Pathophysiology of edema #4: lymphatic system normally absorbs interstitial fluid and a small amount of proteins;

lymphatic channels blocked or surgically removed > cause proteins and fluid to accumulate in interstitial spaces (lymphedema)


usually limited to a site of trauma or within a particular organ system; includes cerebral edema, pulmonary edema, pleural effusion, pericardial effusion (membrane around heart), ascites (in peritoneal space)


manifested by a more uniform distribution of fluid in interstitial spaces (dependent edema)


weight gain, swelling, puffiness, tight-fitting clothes/shoes, limited movement of affected joints, symptoms associated with underlying condition

Kidneys and hormones have central role in maintaining

sodium and water balance

Water balance is regulated primarily by

antidiuretic hormone: posterior pituitary gland secretes ADH or vasopressin

Sodium is regulated by renal effects of


ADH is secreted when

plasma osmolality increases or circulating blood volume decreases & blood pressure drops

WATER BALANCE: water deficit/sodium excess > increased plasma osmolality >

stimulated hypothalamic osmoreceptors > cause thirst, signal posterior pituitary gland to release ADH > stimulated water drinking, ADH increases permeability of renal tubular cells to water > water reabsorbed into blood from distal tubules and kidneys > urine concentration increases > reabsorbed water decreases plasma osmolality returning it to normal

SODIUM: accounts for 90%

of ECF cations; OUTSIDE!

CHLORIDE: major anion in

ECF; proportional to changes in sodium; provides electroneutrality in relation to sodium


kidneys; narrow range: 136-145 mEq/L


maintains hormonal regulation of sodium balance; secreted when sodium levels DECREASE or potassium levels INCREASE

RENIN-ANGIOTENSIN-ALDOSTERONE system: circulating blood volume/pressure reduced > renin is released > angiotensin-converting enzyme (ACE) in pulmonary vessels converts angiotensin I to angiotensin II > stimulates secretion of aldosterone (puts out sodium) >

causes vasoconstriction > sodium & water reabsorption > increased blood volume > elevated systemic blood pressure > restores renal perfusion > restoration inhibits further release of renin





Natriuretic hormones (peptides):

promote urinary excretion of sodium & water/decreased BP

Electrolytes carry electric charges when in water



The ability of a solution to cause a cell to gain or lose water


(used of solutions) having the same or equal osmotic pressure; normal range 280-294 mOsm

Losses of isotonic fluids:

hemorrhage, severe wound drainage, excessive diaphoresis, decreased urine output, symptoms of hypovolemia (tachycardia, flattened neck veins, normal/decreased BP)

isotonic fluid volume deficit:

SAME concentration, just less total amount (hypovolemic)

isotonic fluid excess

aka hypervolemia; fluid overload; still SAME concentration

causes of hypervolemia:

excessive administration of IV fluids, hypersecretion of aldosterone, effects of drugs, excessive intake, ineffective regulation (heart/renal failure)

pathophysiology of hypervolemia:

causes diluting effect which leads to decreased hematocrit and plasma protein concentration, weight gain, edema, hypervolemia, JVD, bounding pulse, pulmonary congestion, HTN

hypertonic alterations:

alterations in Na concentration

hypertonicity develops

when osmolality of ECF is elevated above normal (>294 mOsm)


occurs when serum sodium levels exceed 145 mEq/L (HIGHER AMOUNTS OF SODIUM THAN WATER IN ECF)

Hypernatremia: water leaves cells

and moves into ECF causing cells to shrink

hypernatremia: water leaves cells in order to

dilute the blood (cells shrink due to too much Na/too little water)


intracellular dehydration

manifestations of hypernatremia:

fever, thirst, dry mucous membranes, restlessness, muscle twitching, hyperreflexia, convulsions

most common cause of dehydration:

increase renal clearance of free water as reults of impaired tubular function or inability to concentrate urine

manifestations of dehydration:

thirst, dry skin, elevated temperature, weight loss, concentrated urine, tachycardia, weak pulse, postural hypotension


occurs when too little sodium or too little bicarbonate

hypotonic alterations:

too much water, too little salt

hypertonicity = hypernatremia


hypotonic causes:

sodium deficit/water excess, vomiting, diarrhea, NG suction, excessive perspiration, diuretics, excessive administration of D5W (water intoxication), increased ADH secretion, heart failure

pathophysiology of hypotonicity:

osmotic pressure of ECF decreases > water moves into cells where osmotic pressure is greater > plasma volume decreases > symptoms of hypovolemia

hypoosmolar hyponatremia:

renal excretion of water is impaired during acute oliguric renal failure, severe CHF, or cirrhosis > TBW and sodium levels increase > TBW exceeds increase in sodium

manifestations of hyponatremia:

legthargy, confusion, apprehension, depressed reflexes, seizures, coma, cerebral edema, muscle cramps, nausea

water excess is usually accompanied by:



major intracellular electrolyte (98% in ICF); normal range 3.5-5.0 mEq/L; active transport

functions of potassium:

required for glycogen and glucose deposition in liver & skeletal muscle cells; maintains resting membrane potential; maintains normal cardiac rhythms; skeletal/smooth muscle contractions

most efficient regulator of potassium:


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