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153 Cards in this Set

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What do changes in electrolyte concentration affect?
the electrical activity of nerve and muscle cells and cause shifts of fluid from one compartment to another
What do alterations in acid-base balance disrupt?
cellular functions
What do fluid fluctuations affect?
blood volume and cellular function
What is total body wate (TBW)?
the sum of fluids within all body compartments
About what percentage of body weight does TBW make up?
about 60%
How much does 1 liter of water weigh?
2.2 lbs or 1 kg
After water, what is the rest of the body weight made up of?
fat and fat-free solids, particularly bone
What comprises intracellular fluid?
all the fluid in cells, about 2/3 of TBW
What comprises extracellular fluid?
all the fluid outside of cells (about 1/3 of TBW)
What are the 2 main ECF compartments?
(1) interstitial fluid (the space between cells and outside the blood vessels)
(2) intravascular fluid (blood plasma)
What is the TBW for a 70-kg person?
about 42 liters
Besides the interstitial and intravascular fluid compartments, what are the other ECF compartments?
lymph and transcellular fluids, such as synovial, intestinal, and cerebrospinal fluid; sweat; urine; and pleural, peritoneal, pericardial, and intraocular fluids
What are exchanged between compartments to maintain their unique compositions?
solutes (e.g., salts) and water
The percentage of TBW varies with the amount of ______ and _______.
(1) body fat
(2) age
Why is very little water contained in adipose cells?
because fat is water repelling
Why are individuals with higher body fat more susceptible to dehydration?
because they have proportionally less TBW
List the primary sources of body water.
(1) drinking
(2) ingestion of water in food
(3) water derived from oxidative metabolism
What are the largest amounts of water normally lost through? Lesser amounts?
renal excretion, with lesser amounts lost through the stool and vaporization from teh skin and lungs (insensible water loss)
What is the % of TBW in a normal adult male? Lean male? Obese male?
Normal: 60%
Lean: 70%
Obese: 50%
What is the % of TBW in a normal adult female? Lean female? Obese female?
Normal: 50%
Lean: 60%
Obese: 42%
What is the % of TBW in a normal infant? Lean infant? Obese infant?
Normal: 70%
Lean: 80%
Obese: 60%
What does the distribution of water adn the movement of of nutrients and waste products between the capillaries adn interstitial fluid occur as a result of?
changes in hydrostatic pressure (pushes water) and osmotic (oncotic) pressure (pulls water) at the arterial and venous ends of the capillary
How do plasma proteins (particularly albumin) maintain effective osmolality?
by generating plasma oncotic pressure
As plasma flows from the arterial to the venous end of the capillary, what 4 forces determine if fluid moves out of the capillary and into the interstitial space (filtration) or if fluid moves back into the capillary from teh interstitial space (reabsorption)?
(1) capillary hydrostatic pressure (blood pressure) facilitates the outward movement of water from teh capillary to the interstitial space

(2) capillary oncotic pressure osmotically attracts water from the interstitial space back into the capillary

(3) interstitial hydrostatic pressure facilitates the inward movement of water from the interstitial space into the capillary

(4) interstitial oncotic pressure osmotically attracts water from the capillary into the interstitial space
What is the movement of fluid back and forth across the capillary wall called? What is it best described as?
(1) net filtration
(2) Starling's forces
Describe Starling's forces.
Net filtration= (forces favoring filtration) - (forces opposing filtration)

Forces favoring filtration= capillary hydrostatic pressure and interstitial oncotic pressure

Forces opposing filtration= capillary oncotic pressure and interstitial hydrostatic pressure
What happens at the arterial end of the capillary?
hydrostatic pressure exceeds capillary oncotic pressure and fluid moves into the interstitial space (filtration)
What happens at the venous end of the capillary?
capillary oncotic pressure exceeds capillary hydrostatic pressure and fluids are attracted back into the circulation (reabsorption)
What does interstitial hydrostatic pressure promote?
the movement of about 10% of the interstitial fluid along with small amounts of protein into the lymphatics, which then returns to the circulation.
Why is interstitial oncotic pressure normally minimal?
because albumin does not normally cross the capillary membrane
Why does water move between the ICF and ECF?
as a function of osmotic forces
What is responsible for the ECF osmotic balance?
sodium
What is responsible for the ICF osmotic balance?
potassium
What is the osmotic force of ICF proteins and other nondiffusible substances balanced by?
the active transport of ions out of the cell
Why is the osmolality of TBW normally at equilibrium?
because water passes freely across cell membranes
What happens when ECF osmolality changes?
water moves from one compartment to another until osmotic equilibrium is reestablished
What is edema?
the excessive accumulation of fluid within the interstitial spaces
What increases the forces favoring fluid movement from the capillaries or lymphatic channels into the tissues?
(1) increased capillary hydrostatic pressure
(2) lowered plasma oncotic pressure
(3) increased capillary membrane permeability
(4) lymphatic channel obstruction
What does hydrostatic pressure increase as a result of?
venous obstruction or salt and water retention
What does venous obstruction cause?
hydrostatic pressure to increase behind the obstruction pushing fluid from the capillaries into the interstitial spaces
What are common causes of venous obstruction?
(1) thrombophlebitis (inflammation of veins)
(2) hepatic obstruction
(3) tight clothing around the extremeties
(4) prolonged standing
What are congestive heart failure and renal failure associated with? What does this cause?
(1) salt and water retention
(2) causes plasma volume overload, increased capillary hydrostatic pressure, and edema
What does lost or diminished plasma albumin production (liver disease or protein malnutrition) contribute to?
decreased plasma oncotic pressure
Where are plasma proteins lost?
(1) glomerular diseases of the kidney
(2) serous drainage from open wounds
(3) hemorrhage
(4) burns
(5) cirrhosis of the liver
What does the decreased oncotic attraction of fluid within the capillary cause?
filtered capillary fluid to remain in the interstitial space, resulting in edema
When do capillaries become more permeable?
with inflammation and immune responses, esp. with trauma such as burns or crushing injuries, neoplastic disease, and allergic reactions

proteins escape from the vascular space and produce edema through decreased capillary oncotic pressure and interstitial fluid protein accumulation
What does the lymphatic system normally absorb?
interstitial fluid and a small amount of proteins
What happens when lymphatic channels are blocked or surgically removed?
proteins and fluid accumulate in the interstitial space causing lymphedema

example, lymphedema of the arm or leg occurs after surgical removal of axillary or femoral lymph nodes for treatment of carcinoma.
What is localized edema?
edema that is usually limited to a site of trauma, such as a sprained finger.
Another type of localized edema occurs within particular organ systems. List them.
cerebral edema
pulmonary edema
pleural effusion (fluid accumulation in the pleural space)
pericardial effusion (fluid accumulation within the membrane around the heart)
ascites (accumulation of fluid in the peritoneal space)
What is generalized edema?
edema manifested by a more uniform distribution of fluid in interstitial spaces.
What is dependent edema?
edema in which fluid accumulates in gravity-dependent areas of the body, such as the feet and legs when standing and in the sacral area and buttocks when supine (face up)
How can dependent edema be identified?
by pressing on tissues overlying bony prominences. A pit left in the skin indicates edema (pitting edema).
What is edema usually associated with?
weight gain
swelling and puffiness
tight-fitting clothes and shoes
limited movement of the affected joints
symptoms associated with the underlying pathologic condition
What do fluid accumulations increase in regards to nutrients and waste products?
the distance required for nutrients and waste products to move between capillaries and tissues

blood flow may be impaired also, which causes wounds to heal more slowly, and with prolonged edema, the risk of infection and pressure sores over bony prominences increase
Edema of which organs can be life threatening?
brain, lungs, or larynx
As edematous fluid accumulates, it is trapped in a ___________ and is unavailable for ______________. __________ can develop as a result of this sequestering.
(1) "third space" (i.e., the interstitial space, pleural space, pericardial space)
(2) metabolic processes
(3) dehydration
What have a central role in maintaining sodium and water balance?
the kidneys and hormones
What is water balance regulated by? Sodium?
antidiuretic hormone (ADH; also known as vasopressin)

by renal affects of aldosterone
What is water balance regulated by the secretion of?
ADH
When is ADH secreted?
when plasma osmolality increases or circulating blood volume decreases and blood pressure drops
When does increased plasma osmolality occur?
with water deficit or sodium excess in relation to water
What does the increased osmolality stimulate?
hypothalamic osmoreceptors
What do the hypothalamic osmoreceptors cause?
in addition to thirst, they signal the posterior pituitary gland to release ADH.
What does thirst stimulate? ADH?
thirst stimulates water drinking and ADH increases the permeability of renal tubular cells to water. Water is then reabsorbed into the plasma from the distal tubules and collecting ducts of the kidney. Urine concentration increases, and the reabsorbed water decreases plasma osmolality, returning it toward normal
What occurs as a result of fluid loss (dehydration) from vomiting, diarrhea, or excessive sweating?
a decrease in blood volume and blood pressure
Besides hypothalamic osmoreceptors, what else stimulates ADH release from the pituitary gland?
volume-sensitive receptors and baroreceptors (nerve endings that are sensitive to changes in volume and pressure)
Where are volume-sensitive receptors located?
in the right and left atria and thoracic vessels
Where are baroreceptors found?
in the aorta, pulmonary arteries, and carotid sinus
ADH secretion also occurs when ________ pressure drops, as occurs with decreased blood volume. The reabsorption of water mediated by ADH then promotes the restoration of ___________ and _________________.
(1) atrial pressure
(2) plasma volume
(3) blood pressure
What accounts of 90% of the cations in the ECF?
sodium
Along with its constituent anions chloride and bicarbonate, what does sodium regulate?
the extracellular osmotic forces and therefore regulates water balance
List other functions of sodium.
(1) works with potassium and calcium to maintain neuromuscular irritability for conduction of nerve impulses
(2) regulation of acid-base balance (through sodium bicarbonate and sodium phosphate)
(3) participation in cellular chemical reactions
(4) membrane transport
What is the major anion in the ECF?
Chloride
What does Chloride provide?
electroneutrality, particularly in relation to sodium
The transport of chloride is generally __________ and follows the active transport of _______________, so that increases or decreases in chloride are proportional to the changes in ___________.
(1) passive
(2) sodium
(3) sodium
The concentration of chloride tends to vary _________ with the changes in concentration of ____________, the other major anion in the ECF.
(1) inversely
(2) bicarbonate
The kidney maintains normal serum sodium concentrations with a narrow range. What is the range? How does the kidney maintain this range?
136 to 145 mEq/L

through renal tubular reabsorption
What is hormonal regulation of sodium balance mediated by?
aldosterone, a mineralocorticoid synthesized and secreted from the adrenal cortex
What is aldosterone secretion influenced by?
circulating blood volume and plasma concentrations of sodium and potassium (aldosterone is secreted when potassium levels are increased or sodium levels are depressed
What does aldosterone do when secreted?
increases the reabsorption of sodium and the secretion of potassium by the distal tubule of the kidney.

as a result, sodium concentration of the ECF is enhanced, and potassium is excrete with the urine
What is released when circulating blood volume and blood pressure is reduced?
renin, an enzyme secreted by the juxtaglomerular cells of the kidney
What does renin do when secreted?
stimulates the formation of angiotensin I, an inactive polypeptide
How is angiotensin I converted to angiotensin II?
by angiotensin-converting enzyme (ACE) in pulmonary vessels
What does the conversion of angiotensin I to angiotensin II by ACE, stimulate?
the secretion of aldosterone and also causes vasocontriction. the aldosterone then promotes sodium and water reabsorption, increasing blood volume.
What does vasocontriction do?
elevates the systemic blood pressure and restores renal perfusion. This restoration inhibits the further release of renin.
What is the complete mechanism of how the kidney maintains normal serum sodium levels called?
the renin-angiotensin-aldosterone system
What do natriuretic hormones (peptides) promote?
urinary excretion of sodium and water and decreases blood pressure.
What is atrial natriuretic hormone produced by? What is its function?
produced by the atrial muscle of th heart

functions in renal elimination of sodium to control sodium and water balance
What is atrial natriuretic hormone sometimes called?
the "third factor" in sodium regulation, after increased glomerular filtration rate and aldosterone
When do isotonic alterations occur?
when TBW changes are accompanied by proportional changes in electrolytes (osmolality remains within normal range [280 mOsm to 294 mOsm])

for ex., if an individual loses pure plasma or ECF, fluid volume is depleted but the concentration and type of electrolytes and the osmolality remain in the normal range.
What can excessive amounts of isotonic body fluids result from?
excessive administration of IV normal saline or oversecretion of aldosterone with renal retention of both sodium and water
How can isotonic body fluids be lost?
hemorrhage, severe wound drainage, and excessive diaphoresis (sweating)
What does isotonic fluid loss (isotonic dehydration) cause?
contraction of the ECF volume with weight loss, dryness of skin and mucous membranes, decreased urine output, and symptoms of hypovolemia
List the indicators of hypovolemia.
rapid heart rate, flattened neck veins, and normal or decreased blood pressure

in severe states, hypovolemic shock can occur
What are isotonic fluid excesses most commonly the result of?
excessive administration of IV fluids, hypersecretion of aldosterone, or the effects of drugs such as cortisone (which causes renal reabsorption of sodium and water)
What does isotonic fluid excess cause?
as plasma volume expands, hypervolemia develops with weight gain

neck veins may distend, and the blood pressure increases

increased capillary hydrostatic pressure leads to edema formation

ultimately, pulmonary edema and heart failure may develop
What does the diluting effect of excess plasma volume lead to?
decreased hematocrit and decreased plasma protein concentration
When do hypertonic fluid alterations develop?
when the osmolality of the ECF is elevated above normal (greater than 294 mOsm).
What are the most common causes of hypertonic fluid alterations? What happens in both situations?
(1) increased concentration of ECF sodium (hypernatremia) or
(2) deficit of ECF water

(1) ECF hypertonicity attracts water from the intracellular space, causing ICF dehydration.
What does a primary increase in ECF sodium cause?
an osmotic attraction of water and symptoms of hypervolemia.
What does a hypertonic state caused primarily by water loss lead to?
hypovolemia
When does hypernatremia occur?
when serum sodium levels exceed 147 mEq/L.
What may cause an increase in serum sodium levels?
an acute gain in sodium or a net loss of water
Because sodium is largely in the ECF, sodium gains cause _________________.
intracellular dehydration
What does the movement of water to the ECF cause?
hypervolemia
What is a common result of hypernatremia?
hyperosmolality
True or False. High amounts of sodium rarely cause hypernatremia.
True. More commonly high sodium levels occur with inappropriate administration of hypertonic saline solution or with oversecretion of aldosterone, as in primary hyperaldosteronism or Cushing syndrome caused by excess secretion of adrenocorticotropic hormone (ACTH), which also causes increased secretion of aldosterone. These conditions are associated with hypervolemia as some water is reabsorbed with sodium.
What is increased sodium in relation to water deprivation or water loss associated with?
fever or respiratory infections, which increase the resp. rate and enhance water loss from the lungs
What other diseases cause water loss in relation to sodium?
diabetes insipidus (decreased ADH), diabetes mellitus (hyperglycemia), polyuria (frequent urination), profuse sweating, and diarrhea
What can cause hypernatremia in individuals who are comatose, confused, or immobilized? What are these conditions associated with?
(1) insufficient water intake
(2) hypovolemia
What are the clinical manifestations of hypernatremia?
water is redistributed to the EC space, and IC dehydration ensues

thirst, fever, dry mucous membranes, and restlessness are assoc. with hypernatremia as a result of water loss

CNS symptoms include: muscle twitching and hyperreflexia (hyperactive reflexes)

Convulsions are the most serious symptoms
What is dehydration?
describes water deficit but also is commonly used to indicate both sodium loss and water loss (isotonic or isoosmolar dehydration)
Why are pure water deficits (hyperosmolar or hypertonic dehydration) rare?
because most people have access to water
What is the most common cause of water loss?
increased renal clearance of free water as a result of impaired tubular function or inability to concentrate the urine as with diabetes insipidus (decreased ADH)
How is water deficit manifested in the body?
by symptoms of dehydration: thirst, dry skin and mucous membranes, elevated temperature, weight loss, and concentrated urine (with the exception of diabetes insipidus)

Skin turgor may be normal or decreased.

Symptoms of hypovolemia include: tachycarida, weak pulses, and postural hypotension
When does hyperchloremia occur?
when there is too much sodium or too little bicarbonate.
What can more than normal amounts of chloride be expected with?
hypernatremia or metabolic acidosis
What are the symptoms associated with chloride excess?
no specific symptoms
When do hypotonic fluid imbalances occur?
when the osmolality of the ECF is less than normal (i.e., less than 280 mOsm)
What are the most common causes of hypotonic alterations?
(1) sodium deficit (hyponatremia)

(2) water excess
What does hypotonic fluid imbalances lead to?
(1) intracellular overhydration (cellular edema) and
(2) cell swelling
What happens when there is a sodium deficit?
the osmotic pressure of the ECF decreases and water moves into the cell, wehre the osmotic pressure is greater. The plasma volume then decreases, leading to symptoms of hypovolemia.
What happens when there is an excess of water?
increases in both the ECF and ICF volume occur, causing symptoms of hypervolemia and water intoxication with cerebral and pulmonary edema
When does hyponatremia develop?
when the serum sodium concentration falls below 135 mEq/L.
What do sodium deficits usually cause?
hypoosmolality with movement of water into cells
List the clinical syndromes causing hyponatremia.
(1) sodium loss
(2) inadequate sodium intake
(3) dilution of the body's sodium level by water excess
What are pure sodium deficits usually caused by?
extrarenal losses, such as vomiting, diarrhea, GI suctioning, and burns, or renal losses from use of diuretics
When do dilutional hyponatremias occur?
when the proportion of TBW to total body sodium is excessive
How does the replacement of fluid loss with IV 5% dextrose in water cause dilutional hyponatremia?
once the glucose is metabolized to CO2 and water, leaving a hypotonic solution with a diluting effect
Excessive __________ may also stimulate thirst and intake of large amounts of water, which dilute sodium.
sweating
Hyponatremia may also be ___________ or ____________.
hypoosmolar

hypertonic
What is impaire during acute oliguric renal failure, severe congestive heart failure, or cirrhosis?
renal excretion of water. TBW and sodium levels are increased, BUT TBW exceeds the increase in sodium, producing a hypoosmolar hyponatremia
When does hypertonic hyponatremia develop?
with hyperlipidemia, hyperproteinemia, and hyperglycemia.
What do increases in plasma lipids and proteins do?
displace water volume and decrease sodium concentration
What does hyperglycemia do?
increases ECF osmolality and attracts water from the ICF compartment. The osmotic fluid shift to the ECF in turn dilutes the concentration of sodium and other electrolytes
Describe the clinical manifestations of hyponatremia?
deficits of sodium alter the cell's ability to depolarize and repolarize normally.

Behavioral and neurologic changes characteristic of hyponatremia include: lethargy, confusion, apprehension, depressed reflexes, seizures, and coma.

Pure sodium losses may be accompanied by loss of ECF, causing an isotonic hypovolemia with symptoms of hypotenison, tachycardia, and decreased urine output.

Weight gain, edema, ascites, and jugular vein distention are characteristic of dilutional hyponatremias. Water restriction is a common treatment.
What disorders/diseases can precipitate water excess during IV infusion of 5% dextrose in water?
renal failure, severe congestive heart failure, and cirrhosis
Decreased urine formation from which diseases can contribute to water excess? What is the overall effect?
renal disease or decreased renal blood flow

the overall effect is dilution of the ECF, with water moving to the IC space by osmosis. Water excess produces a hypotonic or hypoosmolar water imbalance and is usually accompanied by hyponatremia
What is water excess usually accompanied by?
hyponatremia
When does the syndrome of inappropriate secretion of ADH (SIADH) occur?
when factors other than hyperosmolality or hypovolemia stimulate the secretion of ADH.
What are several clinical conditions that result in SIADH?
fear, pain, acute infection, brain trauma, surgery, and drugs such as analgesics and anesthetics
What is the most common cause of SIADH?
bronchogenic cancer because the cancer cells produce ADH. SIADH is not caused by excess water intake but by decreased renal excretion of water. Therefore, SIADH increases the risk of water excess if intravenous fluids are being administered. Serum sodium and osmolality are reduced. The kidney continues to excrete sodium and urine-specific gravity elevates, but urine volume decreases.
What is the treatment for SIADH?
water restriction medications and treatment of the underlying cause of the disorder
What are the symptoms of water excess related to?
the rate at which water loading has occurred.
What are the symptoms of acue water excesses?
confusion and convulsions
What are the symptoms of long-term water accumulation?
weakness, nausea, muscle twitching, headache, and weight gain
What is hypochloremia usually the result of?
hyponatremia or elevated bicarbonate concentration, as in metabolic alkalosis
What causes hypochloremia?
vomiting and loss of hydrochloric acid (metabolic alkalosis)

sodium deficit related to restricted intake or use of diuretics

cystic fibrosis
What is the major intracellular electrolyte essential for normal cellular functions?
potassium
What is total body potassium content? Where is most of it located?
about 4000 mEq

98% located in the cells
What is the ICF concentration of potassium? The ECF?
150 to 160 mEq/L

3.5 to 5.0 mEq/L
How is the difference between potassium concentrations in the ECF and ICF maintained?
by a sodium-potassium adenosine triphosphatase active transport system