fluid, electrolyte, and acid-base balance Flashcards
fluid sequestration
excess accumulation in a particular location
- total body water may be normal, but circulating blood volume may drop low enough to cause circulatory shock
edema
most common form of fluid sequestration
- accumulation of fluid in interstitial (ECF) spaces which causes swelling
pleural effusion
several liters of fluid can accumulate in the pleural cavity
- causes include some lung infections
hemorrhage
can cause fluid sequestration
- blood that pools in the tissue is lost to circulation
dehydration (negative fluid balance)
body eliminates WAY more water than sodium, ECF osmolarity rises
- affects all fluid compartments (ICF, blood, and tissue fluid)
causes of dehydration
lack of drinking water, diabetes, ADH hypo-secretion (diabetes insipidus), profuse sweating, overuse of diuretics
what age group is more vulnerable to dehydration?
infants, due to high metabolic rate which demands high urine excretion
- immature kidneys cannot concentrate urine effectively, greater ratio of body surfaces to volume
fluid replacement therapy
- drinking water (doesnt replace electrolytes tho)
- enema
- parenteral routes
enema
type of fluid replacement therapy
- fluid absorbed through the colon
parenteral routes
fluid administration other than digestive tract
- IV route
- subcutaneous
- intramuscular
different ways the body regulates fluid intake
- osmoreceptors in hypothalamus
- respond to angiotensin 2 produced when BP drops
- responds to a rise in osmolarity of ECF - Hypothalamus signals pituitary to produce antidiuretic hormone (ADH)
- promotes water conservation - Cerebral cortex produces conscious sense of thirst
why does the hypothalamus produce an antidiuretic hormone (ADH)?
ADH promotes water conservation which regulates fluid intake
what does the cerebral cortex produce (regulation of fluid intake)?
conscious sense of thirst
- intense thirst with increase in plasma osmolarity or blood volume goes down
- salivation is inhibited with thirst (sympathetic signals from thirst center to salivary glands)
short-term inhibition of thirst
last 30-45 min
- mouth cooling and moistening quenches thirst
- distension of stomach and SI
- prevents over drinking
- w/out water thirst returns
long-term inhibition of thirst
30+ minutes
- absorption of water from SI reduces osmolarity in blood
- stops osmoreceptor response, promotes capillary filtration, and makes saliva more abundant and watery
ONLY way to control water output significantly
variation in urine volume
- slow rate of water and electrolyte loss until water and electrolytes can be ingested (kidneys cannot replace water or electrolytes)
variation in urine volume/fluid output mechanisms
- limit water output
- adjust electrolyte reabsorption
- as Na+ is reabsorbed or excreted, water follows!!
water output is limited through what hormone:
ADH (antidiuretic)- secretion is triggered by hypothalamic osmoreceptors in response to dehydration
-causes kidneys to release less water, decreasing amount of urine produced. high ADH level causes body to produce less urine. low level results in greater urine production
ADH is an example of what type of feedback?
ADH system is NEGATIVE feedback
- if osmolarity rises or blood volume falls, more ADH is released
- if osmolarity falls or blood volume rises, ADH release is inhibited, so tubules reabsorb less water, urine output increases, and these trends are reversed
functions of electrolytes
- participate in metabolism
- determine electrical potential (charge difference) across cell membranes
- strongly affect osmolarity of body fluids
- affects bodys water content and distribution
major cations in electrolyte balance
Na+, K+, Ca2+, Mg2+, H+
major anions in electrolyte balance
Cl-, HCO3-(bicarbonate) and PO4-
sodium
cation in extracellular fluid, accounts for 90-95% of osmolarity in ECF (sensed by hypothalamus)
- MOST significant solute in total body water and distribution
sodium electrical signaling is important in
nerve and muscle cells
- resting membrane potential
- inflow of Na+ through channels is essential to depolarization in nerve and muscle action potentials
aldosterone
“salt-retaining hormone”
- adrenal cortex secretes aldosterone
- hyponatremia and hyperkalemia (low Na+, and too high K levels) directly stimulates the adrenal cortex to secrete aldosterone
- renin-angiotensin-aldosterone mechanism
- Renin is produced by the kidneys and controls the activation of the hormone angiotensin 1 and2, which stimulates the adrenal glands to produce aldosterone
hypotension (low BP) stimulates its secretion by
way of the renin-angiotensin-aldosterone mechanism
- bc aldosterone is released when BP is low so this mechanism is used
- raises salt levels which increases blood pressure
distal convoluted tubule has what type of receptors?
aldosterone receptors
- activates transcription of a gene for tubular Na+-K+ pumps (pumps are interested into plasma membrane)
- tubules reabsorb more sodium and secrete more hydrogen and potassium
- water and chloride passively follow sodium
sodium imbalances
ex. secondary hyponatremia
- elevated BP inhibits renin-angiotensin-aldosterone mechanism (sodium cant be absorbed as well bc aldosterone is not being secreted)
- kidneys reabsorb almost no sodium
potassium functions
- electrical signaling in nerve and muscle cells
- responsible for resting membrane
- repolarization and hyperpolarization of the action potential - abundant cation of INTRACELLULAR fluid
- greatest determinant in intracellular osmolarity and cell volume
* 90% in glomerular filtrate is reabsorbed by PCT
acids, bases, and buffers
very important aspects of homeostasis
- slight change in pH can shut down entire metabolic pathway
- metabolism depends on enzymes and enzymes are sensitive to pH
metabolism depends on
enzymes, and enzymes are sensitive to pH
challenges in acid-base balance:
- metabolism constantly produces acid which can throw off pH levels affecting enzymes
- lactic acids from anaerobic fermentation
- carbonic acid from carbon monoxide
what is the pH of a solution mainly determined by?
hydrogen ions
acids
any chemical that releases H+ into a solution
- strong acids ionizes freely (gives up most of its H+ and lowers pH)
- weak acids ionize only slightly (keeps most H+ and doesn’t affect pH much)
bases
any chemical that accepts H+
- strong bases usually bind to H+, which raises pH
- weak bases bind less to H+, and don’t affect pH much
buffer
any mechanism that resists changes in pH
- converts strong acids or bases to weak ones
physiological buffer
system that controls output of acids, bases, or CO2
- urinary system takes several hours or days to exert its acid or base affects
- respiratory system buffers within minutes and cannot alter pH as much and urinary system
bicarbonate buffer system
solution of carbonic acid and bicarbonate ions (participate in reversible reactions)
- the direction of the reaction determines whether it raises or lowers pH
- LOWERS pH by releasing H+
- RAISES pH by binding H+
bicarbonate buffer system coordinates with
the lungs and kidneys to help control pH and CO2
- to lower pH, kidneys excrete HCO3- (bicarbonate)
- to raise pH, kidneys excrete h+ and lungs excrete CO2 (kidneys get rid of acid)
respiratory control of pH
bicarbonate buffer system is the basis for the strong buffering capacity of the respiratory system
- addition of CO2 to body fluids raise the H+ conc. and lowers pH
- removal of CO2 has opposite affects
- neutralizes more acid as chemical buffers
respiratory control of pH with CO2
CO2 is constantly produced by aerobic metabolism
- CO2 from metabolism lowers pH by releasing H+
- CO2 expired from lungs raises pH by binding H+
CO2 affects on pulmonary ventilation
- increased CO2 and decreased pH stimulates pulmonary ventilation
- increased pH inhibits pulmonary ventilation
renal control of pH
kidneys can neutralize more acid or base than either the respiratory system or chemical buffers
- renal tubules secrete H+ into the tubular fliud
renal tubules secrete:
H+ into tubular fluid
- most bind to bicarbonate, ammonia, and buffers
- bound and free H+ are excreted in the urine which expells H+ from the body
kidneys regulate long-term acid-base balance via
blood bicarbonate concentration
- conservation (reabsorption) of HCO3-
- generate new HCO3- via H+ secretion
acidosis
pH below 7.35
- H+ diffuses into cells and drives out K+, elevating K+ conc. in ECF (causes hyperpolarization and nerve and muscle cells are hard to stimulate)
alkalosis
pH above 7.45
- H+ diffuses out of cells and K+ diffuses in (membrane depolarizes, nerves overstimulate causing spasms and more)
a person can not live w/ this pH for more than a few hours
if the blood pH is below 7.0 or above 7.7
respiratory acidosis
occurs when rate of alveolar respiration fails to keep pace with the bodys rate of CO2 production (hyperventilation)
- CO2 accumulates in ECF and lowers pH
respiratory alkalosis
results from hyperventilation
- CO2 eliminated faster than it is produced
metabolic acidosis
increased production of organic acids (lactic acid) in anaerobic fermentation
- ingestion of acidic drugs (asperin)
- loss of base due to chronic diarrhea
metabolic alkalosis
rare, but can result from overuse of bicarbonates (antacids)
- loss of stomach acid from chronic vomiting
compensated acidosis or alkalosis
- either kidneys compensate for pH imbalances of respiratory origin, or
- respiratory system compensates for pH imbalances of metabolic origin
uncompensated acidosis or alkalosis
pH imbalance that the body cannot correct without clinical intervention
respiratory compensation
changes in pulmonary ventilation to correct changes in pH of body fluids by expelling or retaining CO2
hypercapnia
excess CO2 from hypoventilation
- stimulates an increase in pulmonary ventilation, eliminating CO2 and pH increases
hypocapnia
lower CO2 from hyperventilation
renal compensation
pH adjusted by changing rate of H+ secretion of kidneys
- slows but better at restoring fully normal pH
- renal tubules increase rate of H+ secretion increasing pH
short term pH is not fixed by
the kidneys, they cannot act quickly enough to compensate for short-term pH imbalances
