Water, Electrolyte, and Acid-Base Balance Flashcards
approximately _____ to ______ of our total body weight is due to fluids
55% ; 60%
total body water
a function of age, sex, body mass, and body fat
about two-thirds of the water in our body is
intracellular fluid (ICF)
the remaining one-third of the water in the body is
extracellular fluid (ECF)
ECF
distributed among interstital fluid, blood plasma, lymph, and trans-cellular fluid
water movement
water moves between the ICF and the ECF by osmosis in order to maintain homeostasis
osmotic gradients bteween ICF and ECF
tend to be short-lived
water balance occurs when
fluid intake equals fluid output under normal conditions
fluid gain
primarily due to preformed water from ingested foods/liquids, but metabolic water from chemical reactions in cells contributes to fluid gain
fluid loss
comes from obligatory water loss (insensible or sensible)
insensible water loss
comes from expired breath, perspiration, cutaneous transpiration, and defecation
sensible water loss
comes from urine
volume of fluid lost
varies with physical activity and environmental conditions
water intake
controlled by hypothalamic “thirst center” that responds to dehydration
falling blood pressure
will trigger release of angiotensin II
rising blood osmolarity
will trigger release of ADH
increasing osmolarity of the ECF
will be detected by osmoreceptors
water output
controlled by variations in urine volume usually linked to sodium reabsorption
kidneys begin to eliminate water within
30 minutes of ingestion
ADH allows kidneys to
reabsorb more water and produce less urine
fluid deficiency
occurs when water output exceeds water input over a long period of time
hypovolemia
occurs when the body eliminates water and sodium without adequately replacing them
hypovolemia- total body water declines but
osmolarity remains stable
hypovolemia is caused by
hemorrhage, severe burns, chronic vomiting, or chronic diarrhea
cold weather affects fluid balance by
raising urine output
during cold weather, blood vessels
constrict in order to conserve heat but this raises blood pressure which inhibits ADH secretion and stimulates ANP secretion
cold, dry air affect on water loss
it increases water loss during respiration
dehydration
occurs when the body eliminates more water than sodium
dehydration can be caused by
diabetes mellitus, diabetes insipidus, profuse sweating, or overuse of diuretics
water intoxication
occurs if the body replaces water without replacing sodium
in water intoxication, the ECF becomes
hypotonic and water moves into tissue cells causing them to swell
fluid sequestration
occurs if excess fluid accumulates in interstitial spaces (edema)
electrolytes are physiologically important in order for the body to
maintain homeostasis
electrolytes are
- chemically reactive participants in metabolic pathways
- help to determine electrical potential across cell membranes
- control osmolarity of body fluids and water content and distribution
what is the usual reference point for measuring electrolyte concentration
blood plasma
sodium
the only electrolyte to exert significant osmotic pressure and it is essential for transmitting action potentials, for buffering the blood, and for creating the osmotic pressure that causes water to follow sodium from the blood plasma to the ICF to the interstitial fluid
adult’s daily needs of sodium
about 0.5 grams of sodium per day, but typically ingests between 3 and 7 grams per day, making sodium most abundant extracellular cation
what is the principal regulator of sodium levels
aldosterone
aldosterone- receptors are located in
ascending limb of nephron loop, DCT, cortical portion of collecting duct
estrogens
can mimic effects of aldosterone, causing female to retain sodium ions and water during her menstrual cycle and during pregnancy
hyponatremia
usually due to excessive water intake; decrease in sodium intake or increase in sodium loss can also contribute to hyponatremia
consequences of hyponatremia
include muscle weakness, dizziness, headache, hypotension, tachycardia
hypernatremia
due to dehydration or excessive sodium intake
consequences of hypernatremia
include intense thirst, hypertension, edema, and convulsions
potassium ions
the most abundant intracellular cations
potassium balance is maintained by the
kidneys
potassium ions help establish
resting membrane potentials and action potentials; they also determine intracellular osmolarity and cell volume
what is the principal regulator of potassium levels
aldosterone
action of aldosterone on potassium
when aldosterone stimulates reabsorption of sodium ions, it promotes secretion of potassium ions
hypokalemia
can be caused by heavy sweating, chronic vomiting, chronic diarrhea, or laxative abuse
consequences of hypokalemia
include muscle fatigue, loss of muscle tone, mental confusion, irregular heart activity
hyperkalemia
can be caused by injuries that crush tissues, renal failure, aldosterone deficiency
consequences of hyperkalemia
include irritability, nausea, vomiting, muscle weakness, death can occur if heart rate gets increased too much
calcium
the most abundant mineral in the body, but calcium ion concentration is kept low in cells
calcium storage
in bone tissue
calcium is involved in
blood clotting, neurotransmitter release, excitability of nervous tissue and muscle tissue
what regulates the blood levels of calcium
parathyroid hormone and calcitriol
hypocalcemia
can be caused by increased calcium loss, vitamin D deficiency, thyroid and/or parathyroid gland problems
consequences of hypocalcemia
include numbness, and tingling, muscle cramps, convulsions, bone fractures
hypercalcemia
can be caused by thyroid gland problems, parathyroid gland problems, overuse of vitamin D
consequences of hypercalcemia
include lethargy, muscle weakness, cardiac arrhythmia, and mental disorientation
chloride ions
the major extracellular anions
functions of chloride ions
involved in regulating osmolarity between fluid compartments, forming stomach acid, loading and unloading carbon dioxide
aldosterone and chloride ions
aldosterone indrectly regulates chloride levels because chloride ions follow sodium ions
phosphate ions
highly concentrated in intracellular fluid
functions of phosphate ions
participate in metabolic pathways and act as buffers that help to maintain pH of body fluids
what regulates phosphate levels
parathyroid hormone
hydrogen ion concentration
must be controlled to maintain blood pH between 7.35 and 7.45, because all biochemical reactions are influenced by pH
buffers
salts of weak acids or salts of weak bases that resist changes in pH when strong acids or strong bases are added to the blood
physiological buffers
stabilize pH by controlling output of acids or bases or carbon dioxide
urinary system buffers
it buffers the greatest amount of acid or base, but it requires several hours to several days to exert maximum effects
respiratory system buffers
it can exert its effects within minutes, but cannot alter pH as much as urinary system can
chemical buffers
bidn hydrogen ions and remove them from solution when concentration rises; they release hydrogen ions into solution when their concentration falls
effectiveness of chemical buffers
they can restore pH within seconds, but amount of acid or base that can be buffered depends on concentration and pH of environment
bicarbonate buffer system
a solution of carbon acid and bicarbonate ions that serves as the principal buffer in the extracellular fluid
when carbonic acid dissociates
it releases hydrogen ions to lower pH
bicarbonate ions
bind hydrogen ions and remove them to raise pH
why are the lungs and kidneys constantly removing carbon dioxide
to prevent equilibrium from occurring
phosphate buffer system
a solution of dihydrogen phosphate ions and monohydrogen phosphate ions that can release hydrogen ions in order to lower pH, or bind hydrogen ions in order to raise pH in the urine and/or intracellular fluid
effectiveness of phosphate buffer system
stronger buffering system than bicarbonate buffer system, but less concentrated in ECF
phosphate buffers are very effective in
urine and ICF where phosphate ions are high
protein buffer system
has the most abundant buffers in the ECF and blood plasma, using hemoglobin to accomplish its goals
amino acid side groups
can release hydrogen ions to lower pH or bind hydrogen ions to raise pH
the equation for the bicarbonate buffer system indicates
the impact that CO2 has on pH
respiratory system and the control of pH
it can neutralize two to three times more acid than chemical buffers by increasing pulmonary ventilation to expel more carbon dioxide
pH restoration by the respiratory system
pH can be restored within minutes because changes in alveolar ventilation produce dramatic changes in pH
hypercapnia
stimulates deep and rapid breathing to eliminate more carbon dioxide and shift the reaction to the left
kidneys and the control of pH
kidneys neutralize more acid and base than the respiratory system or chemical buffers, because the renal tubules secrete hydrogen ions into tubular fluid rather than binding hydrogen ions to other chemicals
hydrogen ion gradient
happens as long as there is a gradient between tubule cells and tubular fluid and pH is higher than 4.5
for kidneys to reabsorb bicarbonate ions
they must secrete hydrogen ions
when kidneys excrete excess bicarbonate ions
they must retain hydrogen ions
hydrogen ion secretion
occurs in PCT and in intercalated cells of collecting ducts; these hydrogen ions bind to bicarbonate ions or ammonium ions or hydrogen phosphate ions
acidosis occurs when
blood pH falls below 7.35
consequences of acidosis
can depress CNS and cause confusion, disorientation, coma
an increase in hydrogen ions in nerve cells
requires removal of potassium ions, so RMP becomes hyperpolarized
respiratory acidosis
results from inability of respiratory system to eliminate carbon dioxide
metabolic acidosis
results from excessive production of hydrogen ions
1- lactic acid fermentation
2- ketone bodies produced by alcoholism or diabetes mellitus
3- overuse of aspirin or laxatives
alkalosis occurs when
blood pH rises above 7.45
consequences of alkalosis
can hyperexcite neuromuscular system and cause muscle spasms or tetany or convulsions; potassium ions replace hydrogen ions in neurons and shift resting membrane potential closer to threshold
respiratory alkalosis
results from hyperventilation
metabolic alkalosis
results from rapid elimination of hydrogen ions during severe, prolonged vomiting
