Fluids, Electrolytes, & Acid-Base Balance (5 Qs)

BMS 508

where is Na+ concentration the highest?

extracellular fluid (primarily interstitial fluid)

where is K+ concentration the highest?

intracellular fluid

What hormones are relevant to Na and K ion concentrations?

Aldosterone and ANP: promoting sodium reabsorption and potassium excretion in the kidneys

if there’s increased osmolality in ECF…

water flows into interstitial fluid

if there’s decreased osmolality in ECF…

water flows into cells (ICF)

what substances move unidirectionally among compartments?

• nitrogenous wastes: ICF—> interstitial fluid—> plasma—> kidneys

• O2: lungs—> plasma—> interstitial fluid—> ICF

• CO2: ICF—> interstitial fluid—> plasma—> GI tract

sensible water loss

water loss that can be measured (feces, sweat, urine)

insensible water loss

water loss that’s not easily measured (skin, lungs)

how does exercise disrupt water balance?

more water lost in sweat —> decreased urine production

how does ADH affect water regulation and output?

promotes water reabsorption in the kidneys —> low urine production

dehydration / hypohydration

1. excessive water loss from ECF

2. ECF osmotic pressure increases

3. cells lose water to ECF —> cells shrink

overhydration / hypotonic hydration

1. excessive water enters ECF

2. ECF osmotic pressure decreases

3. water moves into cells —> cells swell

hyponatremia

low sodium in ECF

• overhydration —> water enters cell (cells swell- edema)

role of aldosterone and angiotensin II in electrolyte balance

Na+ reabsorption, increased blood volume

role of ANP in electrolyte balance

Na+ secretion, decreased blood volume

• opposes aldosterone

role of estrogen in electrolyte balance

mimics aldosterone (Na/CL reabsorption)

role of progesterone in electrolyte balance

inhibits aldosterone release (no Na retention)

role of glucocorticoids in electrolyte balance

Na retention (increased water)

cardiovascular baroreceptors

detect blood pressure changes —> influence thirst and renal function

hypothalamic osmoreceptors

detect changes in plasma osmolality —> regulate thirst and ADH release.

where in the kidneys is K+ regulated

DCT and collecting duct

acidosis / acidemia

too acidic (pH < 7.35)

• results in increased breathing to expel CO2

respiratory acidosis/acidemia

caused by hypoventilation / CO2 retention

metabolic acidosis / acidemia

caused by conditions like kidney failure or excessive acid intake.

alkalosis / alkalemia

too basic (pH > 7.4)

• results in decreased breathing to keep CO2

respiratory alkalosis /alkalemia

caused by hyperventilation / decreased CO2

metabolic alkalosis / alkalemia

caused by excessive bicarb/loss of H+ (vomiting, diuretic use)

H+ is a byproduct of…

metabolism

how does CO2 behave like an acid?

causes free H+ to increase in blood

order from highest pH to lowest: arteries, veins, interstitial fluid

1. arteries (7.4-7.5)

2. veins (7.3-7.4)

3. interstitial fluid (7.0)

what are the 3 systems of H+ regulation?

• chemical buffer

• brain stem respiratory centers

• renal mechanism

bicarbonate buffer system

• main ECF buffer

• most powerful

• helps maintain pH by neutralizing excess acids or bases

phosphate buffer system

important buffer in urine and ICF

protein buffer system

• most important in ICF ; also in plasma

• amphoteric: can be acids or bases

CO2 unloading

blood reverse equilibrium reaction shifts left (H+ into H2O)

CO2 loading

blood reverse equilibrium reaction shifts right (H+ is buffered)

hypercapnia

elevated Pco2

• results in increased respiration to get rid of CO2 and raise blood pH

hypoventilation results in…

respiratory acidosis (CO2 and H+ buildup)

hyperventilation results in…

respiratory alkalosis (expelling more CO2, lowers pH)

renal regulation

adjusting bicarbonate by conserving / reabsorbing, creating, or excreting HCO3

• 1 trading bicarbonate for 1 H+ or 1 H+ for 1 bicarbonate

• powerful but slow

can bicarbonate pass through kidney tubules?

no; has to be converted to CO2

process of bicarbonate reabsorption

involves converting bicarbonate to CO2, diffusing into cells, and then regenerating bicarbonate for reabsorption in the kidney.

which buffer system is the most powerful?

renal

which buffer system is the fastest?

chemical

what happens when blood pH < 6.8?

global depression of nervous system

what happens when blood pH > 7.8?

extreme excitation of nervous system (random APs)

• muscle tetany

• convulsions

• death by respiratory arrest