water compartments Flashcards
what does water do in the body
lubricant
transport of nutrients
body temp regulation
waste disposal
how much of a newborn’s TBW is water
80%
how much of an adult woman’s TBW is water
50%
how much of an adult man’s TBW is water
60%
intracellular fluid contains what cations and anions
mostly K+
mostly PO4—
protein anions
ICF contains (very importantly) a large number of…
proteins
ECF contains what ions
Na+, Cl- and HCO3-
what should not be present in ECF
proteins
what is in plasma incl. cations and anions
Plasma consists of a water solvent containing product of digestion, hormones, electrolytes, waste products and plasma proteins.
Major cations: Na+
Major anions: Cl- & HCO3
describe how the fluid content of the body is divided up
60%ICF, 5% plasma (ECF), 30% interstitial fluid (ECF), 5% other fluid (GI secretions etc)
what is the average osmolality of the body
300mOsm/kg
when will a solute move through a membrane to correct eqm
when the membrane is permeable to that solute
what is osmotic pressure
the pull to bring water through a permeable membrane into a more concentrated solute in order to achieve eqm
what is hyperosmotic?
the solution has greater osmotic pressure than the other side of the membrane (eg the fluid in the cell)
what have the greatest osmotic power and why
electrolytes because they draw water across the membrane but can’t diffuse across themselves
give some examples of non-permeant solutes
NaCl, KCl, sucrose
give an example of a permeant solute
eg glucose, urea, glycerol
what is tonicity
volume of the cell at eqm
what is a hypotonic solution?
less concentrated solute than in the cell - water will diffuse into the cell
what is the physiological osmolality set point
280-300 mOsm/l
what is a hyperosmolar solution
one with higher osmotic pressure than on the other side of the membrane.
describe the thirst to drinking pathway
osmoreceptors in the hypothalamus respond to high plasma osmolality (increase os 1-2%), ADH vasopressin is released by the pituitary gland which causes water to be reabsorbed in the kidneys. Other signals are sent to encourage water-seeking behaviour
describe the blood loss ->normal hydration pathway
- decrease in plasma volume
- stimulation of specialised volume receptors
- increase of angiotensin II - vasoconstrictor
- in the ADRENAL CORTEX, aldosterone is released
- Reabsorption of Na+ in the kidney - wherever salt goes, water follows
what is the negative feedback loop when blood vol is too high
- Atria are stretched due to high BP
- ANP is released
- 3 targets: kidneys, hypothalamus &posterior pituitary, adrenal cortex
- Angiotensin goes down (vasodilation), ADH and aldosterone go up
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What is the Vd
The amount of water it would take to dilute the drug given to the concentration it currently is in the plasma
