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5- Physiology II - Water and Electrolytes

rename
omarys's version from 2017-05-26 02:21

Section 1

Question Answer
% of body weight that is TBW?60 (e.g. in a 70-kg person there are 42 L of water)
% of body weight that is ECF water?20 (so 14 L in a 70-kg person; that's 1/3rd of the TBW)
TBW is ____ ECF and ___ ICF.1/3rd ; 2/3rds (20% and 40% of body weight)
ECF water makes up around 14 L in a 70-kg person. Where is the majority of these 14 L found, in the plasma or interstitial fluid (IF)?IF
What is necessary for adequate perfusion to the body's tissues?Plasma VOLUME
How is plasma volume (necessary for perfusion) maintained? By regulating ___________Na+ balance/amount (NOT EQUIVALENT TO [Na+])
While Na+ balance is used to regulate plasma VOLUME, water balance is used to regulate _______ ______.plasma OSMOLALITY
Plasma volume is important for perfusion (and regulated by Na+ balance). What is plasma OSMOLALITY important for/what does it affect?Cell size
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Section 2

Question Answer
Pressure is a type of force (force per area)
Osmotic pressure determines _____ ______ between ____ and ____.water distribution ; ECF (plasma+IF) and ICF
"the tendency of a solution to take in water by osmosis" definesosmotic pressure (i.e. where there's higher osmotic pressure, there's a larger tendency to take in water)
What creates the osmotic pressure in the ICF and ECF?K+ salts and Na+ salts respectively
What does NOT represent plasma VOLUME?[Na+] (what DOES affect/regulate plasma volume is Na+ BALANCE or AMOUNT)
If [Na+] does not represent plasma volume, what does it reflect?Osmolality (extracellular) / the ratio bwn water volume and amount of sodium
Plasma osmolality is roughly "synonymous" with[Na+]
Adding pure NaCl to the plasma (as if [Na+] = ∞) and adding pure water ([Na+] = 0), will have _____ ______ on plasma osmolality, but ______ ____ on plasma VOLUME.different effects (NaCl will raise osmolality) ; the same effect (this is why [Na+] doesn't regulate plasma volume)
Plasma volume can be increased by-administering pure water as well as adding pure NaCl
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Section 3

Question Answer
There's an _______ relation bwn plasma osmolality (= [Na+]) and cell size.inverse
What regulates [Na+] / plasma osmolality?Water balance (NOT Na+ balance/amount- this one regulates plasma VOLUME)
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Section 4

Question Answer Column 3 Column 4
Low BP means thatplasma VOLUME is lowThis is regulated/dealt with by sodium retention (=AMOUNT)We can check for this expected response by measuring urine [Na+], which will be low.
Hypernatremia means thatplasma OSMOLALITY is highThis is regulated/dealt with by WATER retention (=amount)We can check if water retention (as a response) has occurred by observing concentrated urine.
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Section 5

Question Answer
Hyper- and hyponatremia relate to sodiumconcentration in the plasma (i.e. plasma OSMOLALITY)
ECF =Extracellular fluid (includes plasma + IF)
ECV =Effective circulating volume (the part of ECF that is found within the arterial system)
In a 70-kg male, the ECV is around700 ml
Plasma volume in a 70-kg person is around3.5 L (plasma = 25% of ECF, which is = 33.333% of TBW, which is = 42 L)
What is in direct correlation with (or causes) the pressure felt by baroreceptors in the carotid arteries and afferent arterioles?the ECV
The ECV is a ____ value and cannot actually be ______.theoretical ; measured (it can be evaluated/estimated tho)
When one suddenly eats a lot of salt, the extra sodium will raise plasma VOLUME (thus pressure) by TWO MECHANISMS:1- it will raise plasma volume directly (since it is simply an AMOUNT of Na+ that's been introduced to the system)2- the Na+ will eventually be dissolved in the ECF (i.e. it "turns into" [Na+]), thus raising plasma OSMOLALITY, thus inducing the kidney to retain water --> plasma VOLUME rises (indirectly)
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Section 6

Question Answer
When plasma volume is suddenly elevated (due to e.g. ingestion of a lot of salt), so will the _____, which is sensed by ____, thus inducing the kidneys to ____ ____ into the ______, thus ____ the ____ back to normal.ECV ; baroreceptors (in Afferent A's) ; secrete Na+ ; urine ; lowering ; ECV
When [Na+] rises (i.e. blood OSMOLALITY rises), what effector(s) come into play to fix this?ADH
When plasma VOLUME/blood pressure rises, what effector(s) come into play to fix this?Aldosterone
ADH causes ____ _____, so it makes sense that it regulates _______ or plasma ______.water retention ; osmolality ; [Na+]
Aldosterone causes _____ _____, so it makes sense that it regulates ______ _____ / plasma _______.sodium retention ; blood pressure ; volume
As its name suggests, ANP causes ____ _____, which means it regulates plasma ______, same as _____ (which hormone?).sodium secretion (N = natriuretic) ; volume (blood pressure) ; aldosterone
memorize

Section 7

Question Answer
What do ANP and RAAS have in common?Both are controlled/induced by baroreceptors (which are in turn activated by changes in ECV/plasma VOLUME)
If baroreceptors control the RAAS, it follows that they regulateplasma volume / blood pressure (makes sense... baro=pressure)
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Which hormone has exactly the OPPOSITE effect of aldosterone?ANP (aldosterone = sodium retention; ANP = sodium secretion; both = regulate blood pressure/plasma volume)
3 effects of AII:vasoconstriction ; sodium absorption in PCT ; aldosterone release (leading to sodium absorption in collecting ducts)
Other than hormones, what plays an important role in ECV/blood pressure regulation?The SNS (NE)
What role does the SNS (namely norepinephrine) play in regulating ECV?1- increased renin release 2- vasoconstriction, positive inotropic and chronotropic effect
Low ECV will triggerAII and aldosterone release (=activation of RAAS system)
High ECV meansless activation of RAAS, thus less sodium retentionNote: This is the main mechanism by which high ECV is normalized- LESS sodium absorption (rather than increased secretion by e.g. ANP).
memorize

Section 8

Question Answer
AII causes sodium absorption in the PCT by activatingthe Na+/H+ exchanger (so AII increases urine acidity?)
Chloride ions are absorbed from the lumen to the blood ______paracellularly/passively (follows Na+)
In the principal cell of the tubuli, there is the _____ on the ____ side and the ___________ on the _______ side.ENaC ; luminal ; Na+/K+ ATPase ; basolateral (both proteins stimulated by aldosterone)
PRESSURE natriuresis (=/= ANP)mechanism by which high ECV prevents sodium absorption (high ECV >> a lot of water in the IF in the medulla >> more water enters the DL of LOH >> sodium is diluted >> sodium is not passively absorbed in AL of LOH) as well as significantly increases Na+ secretion
Pressure natriuresis is a _____ mechanism for neurohormonal regulation of ECV.backup (last resort kinda thing.. for extreme pressure overload)
When the ECV is high ("volume expansion"), the heartsecretes ANP (from atrial cells)
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Section 9: Osmoregulation (contrast w/ all the above, which is volume regulation)

Question Answer
Osmoregulation is regulation ofplasma osmolality (i.e. [Na+])
Osmoregulation is done by changing thewater balance
Plasma osmolality is not _____ ______ with ECV.directly associated (unlike plasma volume ofc)
An example of a situation where high osmolality =/= high ECV isrunner in hot day, sweats a lot, loses hypotonic fluids, so osmolality/[Na+] rises BUT plasma volume actually declines (ya3ni LOSS OF HYPOTONIC FLUIDS)
T or F- Osmoregulation involves changing sodium balance.False. It involves changing water balance (so as to change sodium CONCENTRATION).
Where are the receptors/sensing area of osmolality changes?Hypothalamus (affects thirst and ADH)
"Hypothalamic osmoreceptors ; osmoregulation" is analogous to"carotid/afferentA/atrial baroreceptors ; volume regulation"
"ADH ; osmoregulation" is analogous to"RAAS/SNS/ANP/ADH ; volume regulation" (ADH participates in both)
Where is most of the filtrate's water reabsorbed in the uriniferous tubule?PCT and DL of LOH (passively)- but this water is absorbed "parallel to" Na+ and salt absorption, so it's not "pure"/distilled water.
If the kidney is to regulate plasma osmolality, it must absorb or secretepure water/water without solutes (NOT the same absorption as in PCT and LOH)
memorize

Section 10

Question Answer
Effect of ADHabsorption of pure water in collecting ducts
What happens when one eats a lot of salt at once?Plasma osmolality rises (other than rise in volume...) >>> ADH secreted and feeling thirsty >>> very concentrated urine (>300mOsm)
What happens when one drinks a lot of water at once?Osmolality decreases >>> less ADH secretion and less thirst >>> very dilute urine (<100mOsm)
Other than its effect on water absorption, ADH is apotent vasoconstrictor (released in cases of extremely low BP)
The volemic trigger of ADH is _____ than the osmotic trigger.(much) stronger- a lot more ADH is released and much quicker
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