Pathophysiology of Sodium Handling

Question 1

What is average daily sodium intake a day in the US? How about for a no added salt diet? Low salt diet?

Answer 1

3-7 g/day

4 g/day

2 g/day

Question 2

How many grams is total body sodium?

Answer 2

50 g

Question 3

How much sodium is filtered at the glomerulus per day?

Answer 3

600g/day

Question 4

What is ICF and ECF sodium concentration in mEq/L?

Answer 4

ICF sodium concentration - 10 mEq/L

ECF sodium concentration - 140 mEq/L

Question 5

True or False: Sodium is the major and most important determinant of ECF volume

Answer 5

True

Question 6

Maintenance of ECF volume determines the _____ and _____ which are important for the existence of the organism

Answer 6

mean arterial pressure, left ventricular filling volume

Question 7

What are the sensors that respond to changes in blood volume? (5)

Answer 7

1. Low-pressure baroreceptors (located on venous side)
2. High-pressure baroreceptors (located on arterial side)
3. Intrarenal receptors (macula densa, juxtaglomerular cells)
4. Hepatic receptors
5. CNS receptors

Question 8

What is tubulo-glomerular feedback and glumerulo-tubular balance?

Answer 8

Tubulo-glomerular feedback is when increased distal delivery of sodium chloride to the macula densa increases afferent arteriolar tone and returns RBF and GFR towards normal values.

Glomerulo-tubular balance is where changes in GFR automatically induces proportional change in the rate of proximal tubular sodium reabsorption.

Question 9

True or False: There are physical forces, independent of GFR, that influence the renal reabsorption of sodium between the proximal tubule and the renal interstitium as well as the renal interstitium with the efferent arteriole.

Answer 9

True

Question 10

What are 4 humoral effector factors (hormones) that increase sodium reabsorption? (Antinatriuresis)

Answer 10

1. Angiotensin II
2. Aldosterone
3. Catecholamines
4. Vasopressin

Question 11

What are 4 humoral effector factors (hormones) that decrease sodium reabsorption (natriuresis)?

Answer 11

1. Natriuretic peptides
2. Prostaglandins
3. Bradykinin
4. Dopamine

Question 12

True or False: Activation of renal sympathetic nerves have an anti-natriuretic effect.

Answer 12

True.

Nerve stimulation enhances the release of renin from the JGA.

Question 13

At the proximal tubule, is movement of Na across the apical membrane passive or active? How about the basolateral membrane?

Answer 13

It is passive across the apical membrane and active (via Na/K-ATPase) across the basolateral membrane.

Question 14

What channel does Amiloride block?

Answer 14

Amiloride works by directly blocking the epithelial sodium channel (ENaC) thereby inhibiting sodium reabsorption in the late distal convoluted tubules, connecting tubules, and collecting ducts in the kidneys. This promotes the loss of sodium and water from the body, but without depleting potassium.

Question 15

Renal losses of sodium and water can happen due to failure of effector mechanisms or intrinsic renal diseases. Name 5 examples of each.

Answer 15

Failure of effectors

1. Solute diuresis, glucosuria
2. Diuretic agents
3. Adrenal insufficiency
4. Selective aldosterone deficiency
5. Mutations in sodium transporters (Bartter’s & Gitelman’s syndromes)

Intrinsic renal disease

1. Non-oliguric acute renal failure
2. Diuretic phase of acute renal failure
3. Post-obstructive diuresis
4. “Salt-wasting” nephropathy
5. Tubulo-interstitial disease

Question 16

What are 3 examples of extra-renal sodium and water losses?

Answer 16

GI tract fluid losses (vomiting, diarrhea)

Dermal fluid losses

Fluid losses into the “third space”

Question 17

Are extra-renal or intra-renal losses of sodium and water more common?

Answer 17

Extra-renal

Question 18

What 6 things happen in the cardiovascular system and sympathetic nervous system when there is ECF volume contraction?

Answer 18

1. Increased HR
2. Increased cardiac inotropic function
3. Systemic vascular resistance
4. Increased angiotensin II
5. Increased ADH (also called AVP apparently)
6. Increased endothelin (peptides that are potent vasoconstrictors)

Question 19

What 6 things happen in the kidneys when there is ECF volume contraction?

Answer 19

1. decreased GFR resulting in a smaller filtered load of sodium
2. activation of the renal sympathetic nerves
3. decreased hydrostatic pressure and increased oncotic pressure in the peritubular capillaries
4. stimulation of renin-angiotensin-aldosterone system
5. increased secretion of ADH
6. inhibited secretion of atrial natriuretic peptide (ANP) from the atrial myocytes

Question 20

What are clinical manifestations of volume depletion? (12)

Answer 20

1. Thirst
2. Postural dizziness
3. Weakness
4. Heart palpitations (bc increased HR)
5. Decreased urinary output
6. Confusion
7. Weight loss
8. Orthostatic blood pressure
9. Tachycardia
10. Hypotension
11. Decreased elasticity or turgor of skin
12. Dry mucous membranes

Question 21

Upper GI loss of fluid causes metabolic _____ and lower GI loss causes metabolic _____

Answer 21

Upper GI loss of fluid causes metabolic alkalosis

Lower GI loss of fluid causes metabolic acidosis

(just think that upper GI loss causes pH to go up and lower GI loss causes pH to go down)

Question 22

True or False: Patients that are volume contracted get increased hematocrit and serum albumin

Answer 22

True. Because of hemoconcentration

Question 23

True or False: volume contracted patients have a decreased BUN/plasma creatinine ratio

Answer 23

False. Their BUN/plasma creatinine ratio is increased.

Question 24

What does urinary sodium tell you about a patient in a volume contracted state?

Answer 24

If the urinary sodium is greater than 20 mEq/L, the volume loss is renal.

If the urinary sodium is less than 20 mEq/L, the volume loss is extra-renal.

Question 25

In patients with volume depletion, what SG and osmolality would you expect in urine?

Answer 25

Urine SG should be greater that 1.010 and the urine osmolality is greater than 300 mOsm/kg

Question 26

What FENa value might you expect in a patient that is volume contracted?

Answer 26

FENa would be much less than 1% A normal value for FENa is about 1%. In states of volume depletion, the body is trying to hold on to as much Na as it can so that it can hold on to water too. This causes the FENa (fractional excretion of Na) to fall much below the normal value.

Question 27

If you give saline to correct for volume depletion, how much of the saline stays in the intravascular space?

Answer 27

About 25% of it. The other 75% goes to the interstitial fluid.

Question 28

Is D5W a good volume expander?

Answer 28

No. only about 9% of it will stay in the plasma/intravascular space.

Question 29

Is plasma a good volume expander?

Answer 29

Yes, 100% of it stays in the intravascular space. However, it's expensive.

Question 30

ECF volume expansion can happen because of 3 general mechanisms. What are they?

Answer 30

1. Disturbed starling forces 2. Primary hormone excess 3. Primary renal sodium retention

Question 31

Give 3 examples of disturbed starling forces that can cause ECF volume expansion

Answer 31

1. Congestive heart failure 2. Nephrotic syndrome 3. Liver cirrhosis

Question 32

Give 3 examples of primary hormone excess that can cause ECF volume expansion

Answer 32

1. Primary hyperaldosteronism 2. Cushing's syndrome (metabolic disorder caused by overproduction of corticosteroid hormones by the adrenal cortex and often involving obesity and high blood pressure) 3. Syndrome of inappropriate secretion of anti-diuretic hormoe (SIADH)

Question 33

What can cause primary renal sodium retention resulting in ECF volume expansion?

Answer 33

Acute glomerulonephritis

Question 34

What are clinical manifestations of volume expansion? (10)

Answer 34

1. Weakness 2. Exercise intolerance 3. Weight gain 4. Difficulty breathing during exertion 5. Orthopnea 6. Swelling in extremities 7. Increased urination at night 8. Basilar pulmonary rales 9. Distended neck veins 10. CXR with fluid overload and cardiomegaly

Question 35

How can liver cirrhosis cause sodium and water retention?

Answer 35

Cirrhosis causes severe vasodilation which causes activation of arterial baroreceptors. This causes activation of RAAS, SNS stimulation, and non-osmotic ADH stimulation resulting in water and sodium retention and increased peripheral arterial vascular and renal resistance.