fluid and electrolytes Flashcards
how much does adult water account for in bodyweight?
60% for males and 50% for females
what percentage of water is an infant composed of?
75%
what are the two main fluid compartments?
intracellular fluid and extracellular fluid
what percentage of water does extracellular fluid account for?
40%
what percentage of water does intracellular fluid account for?
60%
what percentage of body water is in the plasma?
8%
what percentage of body water is in the interstitial fluid?
32%
what percentage of body water is in the cytosol?
60%
what is the major cation of the ECF?
Na+
what is the major cation of the ICF?
K+
what is the major anion of the ECF?
Cl-
what is the major anion of the ICF?
HPO42-
what two tasks are involved to maintain fluid homeostasis?
- maintaining water balance within cells
- maintaining water balance in plasma
what is maintained between narrow limits in the ECF composition?
- water balance
- water intake= output
- must maintain solute concentration
what are the percentages of water input sources?
- 60% fluids (approx 1500ml)
- 30% food (approx 750ml)
- plus 10% from cellular metabolism
what are changes in osmolarity detected by?
osmoreceptors in the hypothalamus
what organ primarily controls fluid and electrolyte homeostasis?
kidneys
where is the thirst centre located?
hypothalamus
what is the hypothalamic thirst centre stimulated by?
- 1-2% change in osmolarity
- 5-10% change in plasma volume
what are feedback mechanisms that inhibit thirst?
- moistening of mucosa
- stretch receptors of stomach and intestine
- decrease in osmolarity
what does ADH inhibit?
diuresis
what does ADH work to do?
maintains electrolyte balance of ECF by conservation of water at kidneys decreasing urine output
where is ADH made, stored, and released from?
posterior pituitary
where is aldosterone synthesised and secreted by?
adrenal cortex
what is aldosterone stimulated by?
angiotensin II plus elevated K+ in ECF
what is dehydration?
when water output exceeds water intake
what can losses in ECF be due to?
- severe burns
- severe vomiting and diarrhea
- profuse sweating
- low water intake
- haemorrhage
where is water lost from dehydration?
from ECF
what happens to cells during dehydration?
dehydrate and crenate
what does dehydration result in?
hypernatremia (high Na+ in ECF)
what are the early signs of dehydration?
- increased thirst
- dry mucous membrane
- dry flushed skin
what occurs if dehydration is prolonged?
- confusion, disorientation
- hypovolaemia
- hypovolaemic shock (esp. hemorrhaging)
what is hormonal systems are activated by decreased blood volume and pressure?
- RAAS
- aldosterone secretion
- ADH secretion
- sympathetic NS
what is hypotonic hydration?
when water intake exceeds water output
when does hypotonic hydration occur?
renal insufficiency and rapid excess water ingestion
what does hypotonic hydration result in?
hyponatremia (low Na+ in ECF)
what happens to cells during hypotonic hydration?
cells swell and lysis is possible
what is oedema?
an abnormal accumulation of fluid in the interstitial space
what is caused by?
- increases in capillary hydrostatic pressure
- increases in capillary permeability
- decreases in colloid osmotic pressure
what is lymphoedema?
accumulation of ISF due to surgically removed or blocked lymph glands
what is pH regulated by?
- chemical buffer system
- respiratory regulation
- renal mechanism
what is the slowest of the pH regulators?
renal takes hours or days but is the most potent
what is a chemical buffer?
a substance that minimises changes in pH by binding or releasing free H+ ions
what are the three main chemical buffer systems?
- carbonic acid-bicarbonate ion
- phosphate buffer
- protein buffer
if pH drops does the carbonic acid-bicarbonate buffer system bind or release H+?
bind
if pH rises does the carbonic acid-bicarbonate buffer system bind or release H+?
releases
does the respiratory regulator of pH have more or less capacity than the chemical buffering system?
more
what do the kidneys work to do during renal mechanism of pH?
- remove acids produced by metabolic reactions in the body
- conserve or renew acids when needed
what is the renal mechanism able to do?
- conserve HCO3- and generate new HCO3-
- excrete HCO3-
will HCO3- be reabsorbed or secreted if pH drops?
reabsorbed
will HCO3- be reabsorbed or secreted if pH increases?
secreted
will H+ be absorbed or secreted if pH drops?
secreted
will H+ be absorbed or secreted if pH increases?
absorbed
what is the absolute limit of blood pH?
6.8-7.8 (ideally 7.4)
when does respiratory acidosis occur?
when hypoventilation causes retention of CO2 leads to carbonic acid excess and a decrease in pH
when does metabolic acidosis occur?
with an excess of fixed acids in the body leads to a decrease in pH
