Fluid & Acid Balance

Question 1

Is most body fluid in the ICF or ECF?

Answer 1

ICF (67%)

Question 2

What are the main ions in the ECF?

Answer 2

Na+, Cl-, HCO3-, small amount of K+

Question 3

What are the main ions in the ICF?

Answer 3

K+, PO4 3-, small amount of Na+

Question 4

What two long-term control measures are used to maintain blood pressure in the face of
changes in ECF volume?

Answer 4

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

Question 5

Why does control of salt load go along with control of fluid volume?

Answer 5

either retain or excrete H2O

note… changing salt load does not change osmolarity of ECF — increased salt load always leads to water retention

Question 6

What are the two mechanisms by which the body regulates salt load?

Answer 6

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))

Question 7

What does hypertonicity and
hypotonicity do to cells?

Answer 7

hypertonicity: (dehydration) causes cells to shrivel

hypotonicity: (overhydration) causes cells to swell

Question 8

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?

Answer 8

1.) hypertonicity

2.) hypotonicity

Question 9

What is metabolic H2O?

Answer 9

cellular respiration produces CO2 and H2O

Question 10

What is insensible loss of H2O?

Answer 10

loss thru breathing out air humidified in lungs, or constant diffusion thru skin cells and evaporated

Question 11

What do hypothalamic osmoreceptors respond to? What triggers them? What does their
activity lead to?

Answer 11

cells that monitor ECF osmolarity can stimulate vasopressin secretion and thirst center
triggered by increased ECF osmolarity, increasing vasopressin secretion which increased H2O reabsorption

Question 12

Does an acid have a low or high pH? How about a base?

Answer 12

acid = pH below 7
base = high pH

Question 13

What is the pH of H2O? What
is the pH of body fluids? How much deviation of pH can we tolerate?

Answer 13

pH of water = 7
pH of body fluids = 7.4 (very small range)

Question 14

What does it mean that an acid is “strong” or “weak”? How does this relate to its
dissociation constant?

Answer 14

proportion of molecules that dissociate determine whether and acid is strong or weak… denoted by K (dissociation constant) larger K = stronger the acid

Question 15

What are the three main sources of H+ in the body? Which of these is the largest
source?

Answer 15

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

Question 16

What is acidosis and alkalosis?

Answer 16

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)

Question 17

What is the difference between respiratory acidosis and
metabolic acidosis?

Answer 17

respiratory acidosis: external respiration doesn’t keep up with CO2 production, increased H+

metabolic acidosis: increases in H+ due to non-respiratory reasons

Question 18

What are the three body defenses against changes in pH?

Answer 18

1.) chemical buffer systems
2.) respiratory mechanism
3.) renal mechanism

Question 19

What does a chemical buffer system do?

Answer 19

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

Question 20

How does bicarbonate act as a chemical buffer?

Answer 20

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)

Question 21

How fast do buffers act?

Answer 21

buffers act immediately (within a fraction of a second)

Question 22

What are other buffers in the body?

Answer 22

other buffers include protein, hemoglobin, and phosphate buffer systems

Question 23

Under a normal functioning respiratory system, does [H+] continually increase? Why or why not?

Answer 23

No, it is controlled by H2CO3:HCO3- buffer system and ventilation levels

Question 24

In metabolic alkalosis, how does regulation of ventilation bring the pH back to normal? How long does this take to kick in?

Answer 24

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

Question 25

In metabolic acidosis, how does regulation of ventilation bring the pH back to normal? How long does this take to kick in?

Answer 25

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

Question 26

Is all filtered HCO3- excreted or reabsorbed? How does H+ secretion play a role in this?

Answer 26

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

Question 27

Is more or less H+ secreted than HCO3- filtered into the filtrate?

Answer 27

active transport secretes more H+ out of tubular cells than there are HCO3- in the filtrate

Question 28

Secretion of H+ into the tubule is coupled with what?

Answer 28

secretion of extra H+ is coupled with absorption of newly produced HCO3-

Question 29

What are the two buffers in the urine that help bring up the pH of urine?

Answer 29

1.) phosphate buffer system (during acidosis, phosphate buffers become maxed out)
2.) tubular cells secrete ammonia (NH3) as additional buffer (NH3 +H+ <-> NH4+)

Question 30

During acidosis, what happens to H+ and HCO3- in the kidneys? How about during
alkalosis? How do these things change normalize pH?

Answer 30

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+

Question 31

How long does it take renal regulation of pH to kick in?

Answer 31

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)