Group Case Discussions 1 - Renal Cases

Question 1

What is pyelonephritis? What does it lead to?

Answer 1

Inflammation of the kidney pelvis starting in the medulla and caused by UTIs => leads to destruction of all juxtomedullary nephrons and many outer-cortical nephrons (since their loops of Henle are in the medulla) => only functioning with a few outer cortical nephrons + no more gradient in the medulla so the collecting duct cannot reabsorb water => marked decrease in GFR and polyuria

Question 2

Normal plasma [urea]?

Answer 2

20-40 mg/100 mL

Question 3

What is specific gravity?

Answer 3

Density of substance/density of water

Question 4

What is the specific gravity of isosmotic urine? Max and min?

Answer 4

1.003 <=> 1.010 <=> 1.055

Question 5

How to calculate clearance if you are given excretion rate?

Answer 5

Simply divide by plasma concentration, since you already have Ux.V

Question 6

What is urine specific gravity a measure of? Exception?

Answer 6

Measure of urine concentration, except during proteinurea (SG would increase more than concentration)

Question 7

What is polyuria?

Answer 7

Frequent urination

Question 8

What does it mean if Cx «&laquo_space;Ccr

Answer 8

Net reabsorption in the kidney: E

Question 9

What is a paradigm caused by pyelonephritis?

Answer 9

Very low GFR but very high urine flow rate

Question 10

How do I know that a decreased GFR is not due to total obstruction of a kidney?

Answer 10

If the GFR decrease is by more than 50%, then it has to be something else

Question 11

Effect of low protein diet on kidney function?

Answer 11

Low protein diet => low albumin production => low peritubular oncotic pressure => high urine volume

Question 12

What effect would a low protein diet have on a patient with pyelonephritis?

Answer 12

It would simply decrease plasma and urine urea concentrations, but would have no effect on the clearance since the GFR is so low in these patients

Question 13

Are plasma urea concentration or excretion rate alone a valuable index of the severity of a patient’s kidney function? Why?

Answer 13

NOPE - because it can change with diet

Question 14

What is uremia? Symptoms?

Answer 14

High plasma urea

Symptoms: fatigue, loss of taste/metallic taste, anorexia, anemia

Question 15

Treatment for pyelonephritis?

Answer 15

1. Antibiotics to stop UTI
2. Decrease protein intake to avoid uremia and to decrease GFR (more urea in blood means vasodilation to increase filtration to get rid of it)

Question 16

What are the 5 types of diabetes insipidus (3 names for first one and 2 for second one)? Explain each.

Answer 16

1. Central = neurogenic = hypothalamic: inability to synthesize or secrete active vasopressin
2. Nephrogenic = renal: inability of kidney to detect vasopressin
3. Gestational: placenta secretes vasopressinase that degrades vasopressin
4. Dipsogenic: low thirst threshold
5. Psychogenic: excessive drinking

Question 17

What is diabetes insipidus characterized by?

Answer 17

Large dilute urine volume

Question 18

How can you diagnose DI?

Answer 18

Patient has to be shown to excrete a hypotonic urine despite the presence of a hyperosmolar serum (aka when the patient is dehydrated)
+ administer AVP to determine if the DI is central

Question 19

In what patients with polyuria do you see normal blood osmolarity and BP and why?

Answer 19

1. Osmotic diuresis
2. Central DI
3. Nephrogenic DI
4. Gestational DI
   Because their thirst is intact and regulates blood osmolarity and BP

Question 20

Treatments for DI? How do they work?

Answer 20

1. Water

2. Antidiuretic agents (for central DI only) - AVP analogs (e.g. DDAVP)

Question 21

What is diuresis?

Answer 21

Collecting duct is impermeable to water (normal state)

Question 22

How else can we differentiate central DI from nephrogenic DI? When is this usually done?

Answer 22

Measure plasma AVP when blood is hyperosmolar (dehydrated)

Usually done after a formal water deprivation test

Question 23

How come DDAVP can be administered orally or intranasally even though it’s a peptide?

Answer 23

It’s protected from degradation

Question 24

When does a patient require dialysis?

Answer 24

When GFR falls to 15mL/min or less

Question 25

How to calculate mOsm/L when given %NaCl in solution?

Answer 25

x% . 10 = x gram/L /58.44 (MW) . (# of particles = 2) . 1000 for mOsm = x mOsm/L

Question 26

If you are sailing in the Bermuda triangle, could you drink sea water? Could you drink your own urine?

Answer 26

Not sea water because metals in it will cause you to vomit

Not urine because urine is maximally concentrated if you are dehydrated

Question 27

How to calculate volume of urine based on osmolarity ingested and kidney gradient?

Answer 27

Urine volume = osmolarity ingested/urine concentration (TBD)

Question 28

What is the micturition reflex?

Answer 28

Stretch reflex initiated by sensory stretch receptors in the bladder wall, especially by the receptors in the posterior urethra when this area begins to fill with urine at the higher bladder pressures. Sensory signals from the bladder stretch receptors are conducted to the sacral segments of the cord through the pelvic nerves and then reflexively back again to the bladder through the parasympathetic nerve fibers by way of these same nerves.

When the bladder is only partially filled, these micturition contractions usually relax spontaneously after a fraction of a minute, the detrusor muscles stop contracting, and pressure falls back to the baseline. As the bladder continues to fill, the micturition reflexes become more frequent and cause greater contractions of the detrusor muscle.

Once the micturition reflex becomes powerful enough, it causes another reflex, which passes through the pudendal nerves to the external sphincter to inhibit it. If this inhibition is more potent in the brain than the voluntary constrictor signals to the external sphincter, urination will occur. If not, urination will not occur until the bladder fills still further and the micturition reflex becomes more powerful.