Body Fluid Compartments and Water Balance Flashcards
for us to be healthy, what does water balance need to be like?
needs to be equal / at 0.
how is water distributed in the body?
60% of BW (of men) is fluid -> for a 70kg male = 42L
- intracellular fluid: 40% - 28L
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extracellular fluid: 20% - 14L
a) plasma: 3L
b) interstitial fluid: 10.5L (fluid around the cells - extension of plasma fluid)
c) other ECF - e.g. lymph, eye humor, synovial fluid etc
(how can you think of relationship between plasma and interstitial fluid?) / what are similar or differences between them?
difference between ECF and ICF?
(extension of plasma, just located around cells)
*important to remember*
-Plasma and interstitial fluid: same electrolyte components BUT plasma has proteins - e.g. albumin and anions c.f. interstitial fluid
Intracellular fluid c.f. extracellular fluid: ICF has very little Na+. Lots of K+ and PO43- - (buffers acid / base situation), protein anions (think - sea with Na+ is ECF, banana tree: ICF). ECF has high Na+ and Cl-
what are the main solutes need to think about in human physiology?
Na+, Cl-, glucose and urea
how can we classify solutes?
which one of these ^ has greater osmotic power?
what is osmotic pressure?
electrolytes:
- inorganic salts (Na+, K+, Cl-), all acids and bases, some proteins
non electrolytes:
- glucose, urea, lipids etc
electrolytes have greater osmotic power than non-electrolytes
osmotic pressure: process that controls movement of solvents across a membrane. movement occurs when there are differences in osmotic pressure across a membrane.
what is osmolarity and osmolality?
which is preffered?
osmolarity: the measure of solute conc expressed as no. of osmoles (Osm) of solute per litre of solution - mOsm / L
osmolality: the measure of osmoles (Osm) of soluter per kg of solvent - Osm / kg.
OSMOLALITY IS PREFFERED - (because is per unit mass, so not affected by changes in temp / pressure)
what is the osmolality of plasma?
normal plasma osmolality: 290-300 mOsm/kg
(dont need to memorise this - will probs be given)
what happens to cells in an hypertonic medium / hypotonic medium?
hypertonic medium: more solutes outside cell -> water moves out of cell. cell shrink
Hypotonic medium: more solutes in cell than outside -> water moves inside to the cell. swell
what are sources of intracellular osmolality?
why does this cause a problem? whats the solution?
sources of intracellular osmolality:
- charged molecules and their counter ions
- smaller metabolites and their counter ions
- small inorganic ions -> cause Donnan effect
Problem: all of the above attract counter ions, which could create a constant flow of water to counteract ion imbalance into the cell. cause cell repture?
solution: animal and bacteria cells actively pump out inorganic ions (esp K), so that cytoplasm contains a lower total conc of inorganic ions than the ECF.
what are different types of membrane transport can use?
- simple diffusion
- facilitated diffusion
( both 1&2 make use of gradient)
- primary active transport - needs energy
what facilitates the movement of water from one side of cell membrane to another?
Aquaporins
explain how sodium potassium exchanger works
Primary active transport:
- Na+ / K- pump must break ATP -> ADP to pump 3 Na ions outside cell
- 2 K ions are then transported into cell
Both transported agaisnt a gradient
where is Na+ mostly found?
why is Na+ important?
- in extracellular fluid / outside the cell (Na+ is the predominant extracellular cation)
- plays a key role in fluid and electrolyte balance: Na+ has strong osmotic power, where Na+ goes, water follows.
-
- how do you describe the relationship between plasma and ECF sodium? what does this mean?
- what happens if plasma volume and osmolality are regulated?
- Plasma and ECF sodium are in equilibrium
- If plasma volume is regulated - so will ECF volume
- If plasma volume and osmolality are regulated -> then both total water and total sodium will be regulated
explain how total body water is regulated?
- water input into body from diet and metabolic water = BODY WATER
- Body water + solutes = BODY FLUID OSMOLALITY
- Body fluid osmolality is monitored by osmoreceptors in CNS: informs body to drink
- Hormones (ADH) inform rest of body how to modulate body fluid osmolality
- Kidneys regulate water content through urination.
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which regions in the brain control thirst?
how are these structures characterised? - what does this allow?
- Subfornical organ: in the hypothalumus
- (Organum Vasculosum of the lamina terminalis (OVLT) - dont need to know
- characterised by: a) extensive vasculature b) lack of normal blood brain barrier
- allow for linkage between CNS and peripheral blood flow
explain thirst mechanism & CNS
1. increase in plasma osmolality: (less water in plasma. solutes are concetrated)
a) decrease in saliva = dry mouth -> feedback into hypothalamus thirst center
b) osmoreceptors in hypothalamus -> feedback into hypothalamus thirst center
@ the hypothalamus thirst centre:
a) sensation of thirst -> decide to drink -> water moistens mouth / throat -> water absorbed in GI tract = decrease in plasma osmolality
2. Plasma volume decreases (less efficient feedback)
a) causes blood pressure to decrease -> feedback into hypothalamus thirst center. also triggers the renin-angiotensin mechanism.
- where are the osmoreceptors found in brain?
- what is another stimuli that triggers sensation to drink?
- osmoreceptors: in hypothalamus
- baroreceptors: detect when there is decreased blood volume (in _great veins, right atrium of hear_t -> relied to vasomoto center) -> relayed to hypothalamus
what is the main stimulus for the thirst sensation?
increase in plasma osmolality
what secretes ADH? when is it released?
what does ADH do (basic)
released from: posterior pituitary
released when: increased plasma osmolality (osmoreceptors in hypo), decreased plasma volume (baroreceptors in great veins and right atrium)
function: ADH makes cells of collecting duct and distal tubule permeable to water - high ADH = concentrated water.
what are factors what can trigger ADH?
all processes that lose water: prolonged fever, excessive sweating, vom, diarrhea, blood loss
what is cellular mechanism of ADH making less concentrated?
- ADH binds to receptor on cell
- changes transcriptional activity of nucleus
- more aquaporin made & transported to membrane
- more water goes into cell via aquaporin from filtrate of urine
- water goes from cell into blood
