5- Physiology II - Water and Electrolytes

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

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

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)

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.

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)

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

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)
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).

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)

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)

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