Regulation of body fluid Rao 4/11/13 Flashcards
Why is regulation of ECFV important?
ECFV determines plasma volume and plasma volume determines mean circulatory filling pressure and therefore cardiac output
ECFV is directly proportinal to what?
Total body Na content
What is the relationship between ECFV and plasma Na?
There isn’t one. ECFV is independent of PNa
What must you monitor with people on dialysis?
Body weight…a change in sodium retention can drive wt up or down in a matter of hours. Monitoring the wt tells you how much dialysis may be required
Where is most of the sodium reabsorbed?
65% is reabsorbed in the proximal tubule
Besides the proximal tubule, where is sodium reabsorbed?
Loop of henle, (25%), Collecting Duct (7%)
Signs of a decrease in ECFV?
Decreased ECFV means a decrease in plasma. This is seen as:
1) decrease in systemic blood pressure
2) blood pressure reduced but pulse high
3) orthostatic hypotension (drop in bp when standing up from laying down.)
Signs of increase in ECFV?
Edema in lower extremities with moderate to severe increase.
Severe increase can also cause pulmonary edema, this is worse.
Edema with normal ECFV?
Liver disease…no albumin
Nephrotic syndrome….losing albumin in the urine
How does a decrease in plasma albumin lead to swelling?
Decrease in plasma albumin means a decrease in plasma colloid pressure. This coloid pressure from the large albumin molecules usually keeps fluid in the plasma. Without the albumin, fluid rushes into the interstitial space and you get swelling.
Intake of water which drops plasma osmolarity leads to what?
Diuresis and an increase in fluid excretion
Why are high blood pressure pts advised to cut down sodium intake?
A high salt intake leads to a higher ECFV= higher PV= higher BP
What are the two receptors that sense ECFV?
Stretch receptors and baroreceptors. These are localized in large veins, atria, arteries
Where are neural stretch receptors found?
In large veins, respond to venous distension, signals pituitary glands to regulate AVP/ADH (either increase or suppres it.
Atrial stretch receptors secrete ANP, what is it?
atrial natriuretic peptide, regulates renal Na excretion.
Change in GFR does what to sodium excretion?
Raises it
Aldosterone has what effect of sodium
Aldosterone increases sodium reabsorption in the DT and CD. This makes sense, we know aldosterone inc blood pressure and it does this by inc sodium reabsorption and, in turn, water reabsorption which leads to hgher ECFV and higher BP!
What does Renin-Angiotensin system do to Sodium reabsorption>
Increases sodium reabsorption in response to low ECFV/BP
What is pressure natriuresis?
refers to the role of arterial pressure in regulating Na excretion. As arterial pressure goes up, renin-angiotensin aldosterone system is cut off and and you get less sodium reabsorption and more excretion in the urine
What stimulates aldosterone release?
Plasma potassium and angiotensin, inhibbited by plasma sodium.
What part of the nephron does aldosterone act on?
DCT and CD
ANP…how does it work and what does it do?
ANP is produced in cells in cardiac atria. Stimulated by rise in plasma Na. Inhibits Na reabsorption in the tubules. Raises GFR, tells teh adrenal cortex to stop making aldosterone. It has the opposite effect of aldosterone.
Point of teh renin angiotensin system?
To stimulate aldosterone production in adrenal cortex.
What do sympathetic nerves do?
Leads to decreae in GFR
Prostaglandins, Bradykinin, Dopamine?
Produced in kidneys, diuresis and natriuresis
Ouaban like factor does what?
diuresis and natriuresis
What are the 5 categories of Na regulation in the kidney?
- ) Changes in GFR…GFR goes up, NA reabsorption goes down.
2) Aldosterone: Na reabsorption up - ) Natriuretic Hormone Na reabsorption down
4) Renin-Angiotensin system: when the ECFV goes down, this drives up Na reabsorption
5) Sympathetic nerves, prostaglandins
