Fluid & Acid Balance Flashcards
Is most body fluid in the ICF or ECF?
ICF (67%)
What are the main ions in the ECF?
Na+, Cl-, HCO3-, small amount of K+
What are the main ions in the ICF?
K+, PO4 3-, small amount of Na+
What two long-term control measures are used to maintain blood pressure in the face of
changes in ECF volume?
1.) control of thirst
2.) control of sal load in body (Na+ load)
note… changing salt load does not change osmolarity of ECF — increased salt load always leads to water retention
Why does control of salt load go along with control of fluid volume?
either retain or excrete H2O
note… changing salt load does not change osmolarity of ECF — increased salt load always leads to water retention
What are the two mechanisms by which the body regulates salt load?
1.) changing amount of Na+ filtered at the kidneys (SNS control over GFR)
2.) changing amount of Na+ reabsorbed at the kidneys (hormonal control over reabsorption (renin-angiotensin-aldosterone system))
What does hypertonicity and
hypotonicity do to cells?
hypertonicity: (dehydration) causes cells to shrivel
hypotonicity: (overhydration) causes cells to swell
1.) When water is lost but not solutes, does this lead to hypertonicity or hypotonicity?
2.) How about if water is gained without solutes being gained?
1.) hypertonicity
2.) hypotonicity
What is metabolic H2O?
cellular respiration produces CO2 and H2O
What is insensible loss of H2O?
loss thru breathing out air humidified in lungs, or constant diffusion thru skin cells and evaporated
What do hypothalamic osmoreceptors respond to? What triggers them? What does their
activity lead to?
cells that monitor ECF osmolarity can stimulate vasopressin secretion and thirst center
triggered by increased ECF osmolarity, increasing vasopressin secretion which increased H2O reabsorption
Does an acid have a low or high pH? How about a base?
acid = pH below 7
base = high pH
What is the pH of H2O? What
is the pH of body fluids? How much deviation of pH can we tolerate?
pH of water = 7
pH of body fluids = 7.4 (very small range)
What does it mean that an acid is “strong” or “weak”? How does this relate to its
dissociation constant?
proportion of molecules that dissociate determine whether and acid is strong or weak… denoted by K (dissociation constant) larger K = stronger the acid
What are the three main sources of H+ in the body? Which of these is the largest
source?
1.) carbonic acid formation ***
2.) inorganic acid by-products produced during the breakdown of dietary proteins in meat, grain, and dairy
3.) organic acids produced during intermediary metabolism
What is acidosis and alkalosis?
acidosis: condition where blood pH drops below normal range (becoming more acidic)
alkalosis: condition where blood pH rises above the normal range (becoming more basic)
What is the difference between respiratory acidosis and
metabolic acidosis?
respiratory acidosis: external respiration doesn’t keep up with CO2 production, increased H+
metabolic acidosis: increases in H+ due to non-respiratory reasons
What are the three body defenses against changes in pH?
1.) chemical buffer systems
2.) respiratory mechanism
3.) renal mechanism
What does a chemical buffer system do?
chemical buffer system: a mixture of 2 chemical compounds in solution that minimize pH changes when either an acid or base is added to the solution
How does bicarbonate act as a chemical buffer?
primary ECF buffer against noncarbbonic acid changes, addition of dissociated H+ shifts the buffer equation to the left, causing much less H+ to dissociate (keeping pH more constant)
How fast do buffers act?
buffers act immediately (within a fraction of a second)
What are other buffers in the body?
other buffers include protein, hemoglobin, and phosphate buffer systems
Under a normal functioning respiratory system, does [H+] continually increase? Why or why not?
No, it is controlled by H2CO3:HCO3- buffer system and ventilation levels
In metabolic alkalosis, how does regulation of ventilation bring the pH back to normal? How long does this take to kick in?
1.) buffering by H2CO3:HCO3- system: buffer reaction shifted to the left dueto law of mass action
2.) ventilation increases: more CO2 exhaled
buffering is almost instant, respiratory mechanism takes a couple of minutes
In metabolic acidosis, how does regulation of ventilation bring the pH back to normal? How long does this take to kick in?
1.) buffering by H2CO3:HCO3- system: buffer reaction shifted to the right due to law of mass action
2.) ventilation decreases: less CO2 exhaled
buffering is almost instant, respiratory mechanism takes a couple of minutes
Is all filtered HCO3- excreted or reabsorbed? How does H+ secretion play a role in this?
All HCO3 is reabsorbed into tubular cells in an indirect way (start with H+/K+ pump inside tubular cell)
extra H+ produced -> HCO3- removed from solution
H+ excreted -> HCO3- put back into solution
Is more or less H+ secreted than HCO3- filtered into the filtrate?
active transport secretes more H+ out of tubular cells than there are HCO3- in the filtrate
Secretion of H+ into the tubule is coupled with what?
secretion of extra H+ is coupled with absorption of newly produced HCO3-
What are the two buffers in the urine that help bring up the pH of urine?
1.) phosphate buffer system (during acidosis, phosphate buffers become maxed out)
2.) tubular cells secrete ammonia (NH3) as additional buffer (NH3 +H+ <-> NH4+)
During acidosis, what happens to H+ and HCO3- in the kidneys? How about during
alkalosis? How do these things change normalize pH?
during acidosis: kidneys excrete additional H+, which goes along with creation of additional HCO3-)
during alkalosis: kidneys actively excrete HCO3-, which goes along with the creation of H+
How long does it take renal regulation of pH to kick in?
takes hours to days to compensate
unlike other mechanisms, renal control can completely restore pH back to normal (compensates for resp. alkalosis and acidosis as well as metabolic acidosis and alkalosis)
