Regulation of fluid and electrolyte balance Flashcards
(52 cards)
What must overall salt and water balance equal?
What regulates ECF osmolality?
Input must equal output
Kidneys regulate ECF osmolality
What control systems regulate the volume and osmolality of the ECF? How do they regulate?
Effective Circulating Volume (~ ECF volume)
Regulated by monitoring arterial volume/pressure and regulating the total body content of Na
Extracellular osmolality
Regulated by monitoring and adjusting total body
water content
both have same actions on the kidneys, but use different mechanisms
How is the ECV determined?
by total body sodium content
How is the sodium concentration and osmolality of the ECF determined?
determined by water balance
What happens if the ECF osmolarity changes?
ECF osmolality and intracellular osmolality must be equal.
if ECF osmolality changes. then the ECF may become hypo or hyper tonic. causing cells to shrink or swell
What is the ECV? What is the ECV connected to?
When is it disconnected?
that part of the ECF volume that is in the arterial system and effectively perfusing tissues
connected to ECF, disconnected in disease states
What is ECV and ECF proportional to? How is long term regulation of fluid balance occurs?
proportional to total body Na+ content*
Na+ loading typically leads to volume expansion
and Na+ loss can lead to volume depletion (where salt goes water goes)
Long term regulation of fluid balance occurs
by regulating the rate of urinary Na+ excretion
Why are patients with HTN are told to watch there salt intake?
Where salt goes, water goes. its an increase in volume. which increases HTN
How does the kidneys respond to a change of ECF?
total body Na content (not concentration) is directly related to ECV
ECF volume increase
-> Kidneys Na excretion increases
ECF volume decreases-> kidneys retains Na
What are the sensors, efferent pathways (long term and short term) Effector(short term and long term and short term), and what is affected(short term and long term)?
ECV(Na content)->
sensed by (Baroreceptors in : carotid sinus, aortic arch, renal afferent arteriole, atria) ->
efferent pathway (RAAS, sympathetic nervous system, ANP, ADH) ->
Effector (Short term: heart, blood vessels Long term: kidney) -> affected: Short term: blood pressure Long term: Na+ excretion
What are the pathways activated that act on the kidney in response to low ECV ?
What are the sensors?
RAAS
Sensor = afferent arteriole -> renin
Sympathetic NS
Posterior pituitary (ADH) Sensors: carotid art., aortic arch
ANP secretion by the heart/atria
Sensor = atrial myocytes
How does the kidney respond in response of decreased ECV?
decrease sodium excretion by
increasing tubular reabsorption or by decreasing renal blood flow, GFR
What stimulates renin secretion?
Low pressure in afferent arteriole
Increased sympathetic tone(hypovolemia)
Low [NaCl] in tubule at macula dense (usually due to decreased GFR)
Where is renin found?
JG cells that line the afferent ateriole
What is going to decrease renin release?
Increase afferent arteriole pressure
Decreased sympathetic tone (hypervolemia)
Increased [NaCl] at macula densa (often due to increased GFR)
What is theRenin-Angiotensin-Aldosterone
System (RAAS)?
Angiotensinogen is a protein that is constitutively secreted from the liver and always circulating in the blood; inactive
Renin cleaves off a decapeptide from angiotensinogen to make angiotensin I (Ang I); little/no physiological activity
Ang I circulates through out the body, acted on by angiotensin converting enzyme, ACE. ACE is found on the lumenal membranes of capillary endothelial cells, particularly in the lung [note – ACE is not “in the lung”]
ACE cleaves off two a.a. to make the octapeptide angiotensin II. This is the primary physiologically active form.
While Ang II can act on multiple sites, one of its main targets is the adrenal cortex, where it stimulates aldosterone secretion.
Where does ANGII act?
Systemically
kidney
Aldosterone release
What are ANGII systemic effects?
Vasoconstriction (including afferent and efferent arterioles)
Potentiate release of NOR from postganglionic
sympathetic neurons
Induce thirst and ADH secretion (renal effects)
What are ANG II effects on the kidney?
Stimulates tubular Na+ reabsorption (PCT and eDT)
Impacts renal blood flow and GFR
How does ANG II act on PCT? (which receptors)
What is the effect?
AngII receptors* are found
on both the apical and
basolateral membranes
of the early PCT
Acts to stimulate Na+ reabsorption via the apical NHE3 and basolateral Na-HCO3 co-transporter and Na/K ATPase
Sodium reabsorption pulls water along with it, so water reabsorption increases proportionally
Which on on the receptors does ANGII act on on the eDCT?
NCC
ENAC
What is the effects on Aldosterone?
Regulates the reabsorption of the last 2-3% of the filtered Na+ load
Na reabsorption promotes
K+ secretion (vice versa) in principle cells of ICT, CCD, OMCD
H+ secretion from intercalated cells
What stimulates aldosterone release?
ANGII
Hyperkalemia
Which transporters does aldosterone stimulate the transcription of in the principal cells?
ENaC ROMK SGK1 (regulatory kinase) Na/K pump TCA cycle enzymes
