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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

filtration:

fluid moves out of capillary into interstitial spaces

reabsorption:

fluid moves back into capillary from interstitial spaces

CAPILLARY HYDROSTATIC PRESSURE:

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

CAPILLARY OSMOTIC PRESSURE:

osmotically attracts water from interstitial spaces back into the capillary

INTERSTITIAL HYDROSTATIC PRESSURE:

facilitates inward movement of water form interstitial spaces into capillary

INTERSTITIAL OSMOTIC PRESSURE:

osmotically attracts water from capillary into interstitial spaces

NET FILTRATION:

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

...

SODIUM

is responsible for ECF osmotic balance

POTASSIUM maintains

ICF osmotic balance

EDEMA:

excessive accumulation of fluid within interstitial spaces

CAUSES OF EDEMA:

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)

LOCALIZED EDEMA:

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)

GENERALIZED EDEMA:

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

EDEMA IS ASSOCIATED WITH:

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

ALDOSTERONE

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

NORMAL SERUM SODIUM CONCENTRATION: maintained by

kidneys; narrow range: 136-145 mEq/L

ALDOSTERONE:

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

VASOCONSTRICTION INCREASES

BLOOD FLOW

ALDOSTERONE PUTS OUT

SODIUM

Natriuretic hormones (peptides):

promote urinary excretion of sodium & water/decreased BP

Electrolytes carry electric charges when in water

...

TONICITY:

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

isotonic

(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)

HYPERNATREMIA:

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)

SODIUM GAINS cause

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

hyperchloremia:

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:

hyponatremia

potassium:

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:

KIDNEYS

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