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intracellular fluid (ICF)

cytosol, the fluid within cells. 2/3rds

extracellular fluid (ECF)

outside cells and includes all other body fluids. about 80% is interstitial fluid which occupies the microscopic spaces between tissue cells and 20% is plasma.

how does water move between ICF and ISF

osmosis is the primary means of water movement between ICF and ISF, the concentration solutes in these fulids determines the direction of water movement.

body's sources of water

main source of body water are ingested liquids and moist foods absorbed from the GI tract which equals about 2300 mL/day. another source of water is metabolic water that is produced in the body mainly when electrons are accepted by oxygen during aerobic cellular respiration and to a smaller extend during dehydration synthesis reactions.

body's routes of water loss

kidneys excrete about 1500 mL in urine, the skin evaporates about 600 mL, the lungs exhale about 300mL as water vapor and the GI tract eliminates about 100mL in feces. women also lose additional water through their menstrual flow.


inorganic compounds that idssociate into ions, fluid balance is closely related to electrolyte balance. the ability of the kidneys to excrete excess water by producing dilute urine, or to excrete excess electrolytes by producing concentrated urine, is of utmost importance in the maintenance of homeostasis.

function of electrolytes

1. control the osmosis of water between body compartments
2. maintain acid base balance
3. create electrical current
4. cofactors for enzymes

function of electrolytes in sodium

is most abundant ion in extracellular fluid
performs action potentials
moves water in kidneys to maintain BP

function of electrolytes in potassium

most abundant ion in intracellular fluid
performs action potentials
maintains a balance in the heart

function of electrolytes in chloride

are most prevelant ions in extracellular fluid
moves easily between the extracellular and intracellular compartments b/c most plasma membranes contain many Cl leakage channels.
helps balance the level of anions in different fluid compartments.

function of electrolytes in phosphate

important intracellular anions
at the normal pH of body fluids phosphate is the most prevelant form.

function of electrolytes in calcium

most abundant mineral in the body because most of it is found in bone.
is mainly an extracellular cation.
plays important roles in blood clotting, neurotransmitter release, maintenance of muscle tone, and excitability of nervous and muscle tissue.


a decrease in volume and an increase in osmolarity of body fluids, when water loss is greater than water gain.
1. decrease flow of saliva leads to dry mouth and pharynx
.2. increased blood osmolarity leads to stimulation of osmorecetors in hypothalamus
3. decreased blood volume leads to decreased BP, which leads to increased renin release by juxtaglomerular cells of kidneys which leads to increased angiotensis II formation
all three of these lead to stimulation of thirst center in hypothalamus, increases thirst, increases water intake, and increases body water to normal level and relieves dehydration

three important hormones that regulate the extent of renal Na and Cl reabsorption...

1. angiotensin II
2. aldosterone
3. atrial natriuretic peptide (ANP)
when your dehydrated angiotensin II and aldosterone promote urinary reabsorpiton of Naand Cl conserving the volume of body fluids by reducing urinary loss.


an increase in blood volume, stretches the atria of the heart and promotes release of atrial natriuretic peptide. ANP promotes natriuresis, elevated urinary excretion of Na and Cl followed by water excretion, which decreases blood volume.
increases loss of water in urine

an increase in blood volume also slows release of renin from juxtaglomerular cells of the kidneys

when renin level declines, less angiotensin II is formed. decline in angio II from a moderate level to a low level increases glomerular filtration rate and reduces Na, Cl and water reabsorption in the kidney tubules. less angio II leads to lower levels of aldosterone, which causes reabsorption of filtered Na and Cl to slow in the renal collecting ducts.


major hormone that regulates water loss.
also known as vasopressin is produced by neurosecretory cells that extend from the hypothalamus to the posterior pituitary. stimulates the thirst mechanism. an increase in the osmolarity of body fluids stimulates release of ADH. promotes the insertion of water channel proteins into the apical membranes of principal cells in the collecting ducts of the kidneys. as a result the water permeability of these cells increases and more water is reabsorbed. reduces loss of water in urine

thirst center in hypothalamus

stimulates desire to drink fluids.
water gain is thirst i s quenched

angio II

stimulates secretion of aldosterone
reduces loss of water in urine.


by promoting urinary reabsorption of Na and Cl, increases water reabsorption via osmosis.
reduces loss of water in urine.

buffer systems

effects pH of our blood
work chemically and very fast
front line defense
when any kind of fluctuation occurs, buffer systems are there within seconds to correct pH
consist of weak acid and weak base in solution

3 principal buffer systems

1. carbonic acid- bicarbonate buffer system
2. protein buffer system (cytosol, plasma)
3. phosphate buffer system


depress CNS


stimulate CNS

respiratory acidosis

cause is elevation of PCO2 in fluids
reduced gas exchange in lungs

respiratory alkalosis

arterial blood PCO2 is too low

metabolic acidosis

blood bicarbonate ion concentration too low
H+ not secreted by kidneys

metabolic alkalosis

blood bicarbonate levels are too high
-nonrespiratory loss of acid

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