Fluid & Acid-Base Balance Flashcards
Ch 15
Is most body fluid in the ICF or ECF?
ICF
What are the main ions in the ECF? What are the main ions in the ICF?
ECF: mostly Na+, Cl-, HCO3-
ICF: mostly K+, PO43-, protein anions, small amount of Na+
What two things are regulated to maintain fluid balance in the body?
ECF volume and osmolarity
What does maintaining ECF volume do?
maintains arterial blood pressure
What does maintaining osmolarity do?
prevents swelling or shrinking of cells
What two long-term control measures are used to maintain blood pressure in the face of changes in ECF volume?
- Control of thirst; inc or dec input of fluids
- Control of salt in the body (Na+ load); retain or excrete H2O
Why does control of salt load go along with control of fluid volume?
increase salt always leads to water retention
How is salt load regulated in the body?
- Changing the amount of Na+ filtered at the kidneys (sympathetic control over glomerular filtration rate)
- Changing the amount of Na+ reabsorbed at the kidneys (hormonal control over reabsorption; renin-angiotensin-aldosterone system)
Hypertonicity
when water is lost but not solutes (dehydration)
Hypotonicity
when water is gained without solutes being gained (over hydration)
What does a hypotonic cell look like?
cell swells —> water enters cell; could burst if swells too much
What does a hypertonic cell look like?
cell shrinks –> water leaving the cell
What is metabolic H2O?
Cellular respiration produces CO2 and H2O
- created through metabolism, by oxidizing energy containing substances
Insensible loss of H2O?
loss due to breathing out air humidified in lungs or constant diffusion of H2O through skin cells and evaporated
How is control of ECF osmolarity mediated?
control of thirst (input) & kidney secretion (output)
Hypothalamic osmoreceptors
cells that monitor ECF osmolarity
- can stimulate vasopressin secretion and thirst center
Where is the thirst center?
Nucleus of cells in hypothalamus
How does vasopressin lead to INC water reabsorption? (review)
Vasopressin secreted –> binds to receptors on collecting ducts in kidney –> triggers insertion of aquaporins in cell membrane –> enhances permeability of collecting duct cells to water –> more water reabsorbed from urine
What happens during excess fluid intake?
Excess fluid intake –> decreased vasopressin secretion –> increased urinary output
Acid
pH lower than 7
- Acids dissociate in water and increase H+
Base
raise pH above 7
- dissociate in water and decrease H+
pH of water? pH of body fluids? how much deviation of pH can we tolerate?
pH water = neutral (7)
pH body fluids = 7.4, slightly basic
pH can deviate between 6.8-8.0 before death
What does it mean that an acid is “strong” or “weak”? How does this relate to its dissociation constant (K)?
- proportion of molecules that dissociate determine whether an acid is strong or weak
Dissociation constant (K) greater = stronger acid
3 main sources of H+ in the body? Largest?
1) carbonic acid formation (MAJOR)
2) Inorganic acid by-products produced during the breakdown of dietary proteins in meat, grain, dairy
3) Organic acids produced during intermediary metabolism
Respiratory Acidosis (example of carbonic acid formation)
external respiration doesn’t keep up with CO2 production = increased H+
Respiratory alkalosis (example of carbonic acid formation)
external respiration outpaces CO2 production = decreased H+
Respiratory acidosis vs. metabolic acidosis
Metabolic acidosis: H+ increases due to non-respiratory reasons
Respiratory acidosis: external respiration doesn’t keep up with CO2 production
Three body defenses against changes in pH of body fluids
1) Chemical buffer systems
2) Respiratory mechanism
3) Renal mechanism
Chemical [buffer] system
mixture of two chemical compounds in solution that [MINIMIZE] pH changed when either an acid/or base are added to solution
** Important example: H2CO3 <–> H+ (+) HCO3−
HCl (strong acid) added to unbuffered H2O
nearly all H+ dissociate = very low pH
HCl added to H2O with buffer
addition of dissociated H+ shifts the buffer equation to the left = much less H+ left dissociated = pH not as low
How fast do buffers act? what are other buffers in the body?
within a fraction of a second
- other buffers include: protein (ICF/ECF buffer), hemoglobin (buffer against carbonic acid changes), phosphate (urinary buffer, buffers ICF)
Regular cellular respiration, red blood cells, and pulmonary capillaries
Cell Resp: nutrients + O2 –> CO2 + H2O
Red blood cells: CO2 + H2O –> H+ + HCO3- (H+ added)
Pulmonary capillaries: H+ + HCO3- –> CO2 + H2O (H+ taken away; expiration removes H+ forming that results from cellular respiration)
metabolic acidosis
H+ increases due to non-respiratory reasons
metabolic alkalosis
H+ decreases due to non-respiratory reasons
how does body respond to metabolic acidosis? (H+ increases)
1) Buffering by H2CO3: HCO3- system: buffer reaction shifted to the left (H2CO3 <– H+ + HCO3-)
if buffering isnt sufficient in normalizing pH…
2) Ventilation increases:
more CO2 exhaled = H+ (+) HCO3- –> CO2 (+) H2O
(shifted more to the right; normalizes pH)
how does body respond to metabolic alkalosis? (decrease in pH)
1) buffering by H2CO3:HCO3- system: buffer reaction shifts to the right (H2CO3 –> H+ HCO3-)
if buffering isn’t sufficient…
2) Ventilation decreases –> less CO2 exhaled –> (H+ + HCO3- <– CO2 + H2O) shift to the left; normalizes pH
Under a normal functioning respiratory system, does [H+] continually increase? Why or why not?
[H+] does not continually increase; the respiratory system actively regulates the level of hydrogen ions (H+) in the blood by adjusting the rate and depth of breathing to maintain a stable pH level through the removal of carbon dioxide (CO2), which is a key factor in H+ production.
Inorganic and organic acids produced through digestion and metabolism giving us…
constant source of H+ (separate from CO2) –> kidneys must excrete extra H+
What is filtered into Bowman’s capsule at the glomerulus? Which is there more of?
H+ and HCO3- (much more HCO3-)
- Both are implement to tubular cells
- filtered HCO3- reabsorbed into tubular cells in (INDIRECT way
______ secretes more H+ out of tubular cells than there are HCO3- in the filtrate
Active transport
When extra H+ is secreted, coupled with ____ of newly produced HCO3-
absorption
H+ in urine buffered by _______ buffer system to reduce ____
phosphate; acidity
In BODY tissues: extra H+ produced, _____ removed from solution
HCO3-
At kidneys: ___ excreted, ____ put back into solution
H+ excreted; HCO3- put back into solution
Is all filtered HCO3- excreted or reabsorbed?
almost all HCO3- is reabsorbed
How does H+ secretion play a role in HCO3- reabsorption?
Active transport secretes lots of H+ –> couples with absorption of newly produced HCO3- –> extra HCO3- absorbed into capillaries
Is more of less H+ secreted than HCO3- filtered into the filtrate
MORE
Secretion of H+ into the tubule is coupled with what?
Secretion of extra H+ is coupled with absorption of newly produced HCO3− ; extra HCO3− gets absorbed into capillaries
What are the two buffers in the urine that help bring up the pH of urine?
1) Phosphate buffer system
~During acidosis (inc H+) phosphate buffers 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?
kidneys excrete additional H+; goes along with creation of additional HCO3-
During alkalosis, what happens to H+ and HCO3- in the kidneys?
kidneys excrete HCO3-, goes along with creation of H+
How long does it take renal regulation of pH to kick in?
takes hours to days to compensate
- completely restore pH to normal (unlike others)
- compensates for respiratory AND metabolic acidosis and alkalosis
