Regulation of body fluid Rao 4/11/13

Question 1

Why is regulation of ECFV important?

Answer 1

ECFV determines plasma volume and plasma volume determines mean circulatory filling pressure and therefore cardiac output

Question 2

ECFV is directly proportinal to what?

Answer 2

Total body Na content

Question 3

What is the relationship between ECFV and plasma Na?

Answer 3

There isn’t one. ECFV is independent of PNa

Question 4

What must you monitor with people on dialysis?

Answer 4

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

Question 5

Where is most of the sodium reabsorbed?

Answer 5

65% is reabsorbed in the proximal tubule

Question 6

Besides the proximal tubule, where is sodium reabsorbed?

Answer 6

Loop of henle, (25%), Collecting Duct (7%)

Question 7

Signs of a decrease in ECFV?

Answer 7

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.)

Question 8

Signs of increase in ECFV?

Answer 8

Edema in lower extremities with moderate to severe increase.

Severe increase can also cause pulmonary edema, this is worse.

Question 9

Edema with normal ECFV?

Answer 9

Liver disease…no albumin

Nephrotic syndrome….losing albumin in the urine

Question 10

How does a decrease in plasma albumin lead to swelling?

Answer 10

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.

Question 11

Intake of water which drops plasma osmolarity leads to what?

Answer 11

Diuresis and an increase in fluid excretion

Question 12

Why are high blood pressure pts advised to cut down sodium intake?

Answer 12

A high salt intake leads to a higher ECFV= higher PV= higher BP

Question 13

What are the two receptors that sense ECFV?

Answer 13

Stretch receptors and baroreceptors. These are localized in large veins, atria, arteries

Question 14

Where are neural stretch receptors found?

Answer 14

In large veins, respond to venous distension, signals pituitary glands to regulate AVP/ADH (either increase or suppres it.

Question 15

Atrial stretch receptors secrete ANP, what is it?

Answer 15

atrial natriuretic peptide, regulates renal Na excretion.

Question 16

Change in GFR does what to sodium excretion?

Answer 16

Raises it

Question 17

Aldosterone has what effect of sodium

Answer 17

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!

Question 18

What does Renin-Angiotensin system do to Sodium reabsorption>

Answer 18

Increases sodium reabsorption in response to low ECFV/BP

Question 19

What is pressure natriuresis?

Answer 19

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

Question 20

What stimulates aldosterone release?

Answer 20

Plasma potassium and angiotensin, inhibbited by plasma sodium.

Question 21

What part of the nephron does aldosterone act on?

Answer 21

DCT and CD

Question 22

ANP…how does it work and what does it do?

Answer 22

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.

Question 23

Point of teh renin angiotensin system?

Answer 23

To stimulate aldosterone production in adrenal cortex.

Question 24

What do sympathetic nerves do?

Answer 24

Leads to decreae in GFR

Question 25

Prostaglandins, Bradykinin, Dopamine?

Answer 25

Produced in kidneys, diuresis and natriuresis

Question 26

Ouaban like factor does what?

Answer 26

diuresis and natriuresis

Question 27

What are the 5 categories of Na regulation in the kidney?

Answer 27

1. ) Changes in GFR…GFR goes up, NA reabsorption goes down.
   2) Aldosterone: Na reabsorption up
2. ) Natriuretic Hormone Na reabsorption down
   4) Renin-Angiotensin system: when the ECFV goes down, this drives up Na reabsorption
   5) Sympathetic nerves, prostaglandins