B2.044 Polyuria/Polydipsia

Question 1

what is normal daily urine output?

Answer 1

1-1.5 L/day

Question 2

what is polyuria?

Answer 2

increased urine output

>3L/day

Question 3

what is polydipsia?

Answer 3

excessive thirst and water ingestion

Question 4

what 2 mechanisms account for water intake?

Answer 4

ingestion- 2000 ml/day

metabolism- 400 ml/day

Question 5

what 4 mechanisms account for water loss?

Answer 5

skin- 400 ml/day
lungs- 400 ml/day
intestine- 100 ml/day
kidney- 1500 ml/day

Question 6

what percentage of your body is water content?

Answer 6

60-65%

Question 7

how is water content in the body distributed in tissues?

Answer 7

50% intracellular fluid
10% interstitial fluid
5% intravascular fluid

Question 8

what is the blood pressure at the arterial and venous ends of the blood vessels?

Answer 8

arterial - 30 mmHg out of capillary

venous- 10 mmHg into the capillary

Question 9

what is oncotic pressure?

Answer 9

pressure due to proteins in the body fluids

Question 10

what is the net oncotic pressure difference?

Answer 10

20 mmHg into the capillary, constant along vessel

Question 11

where is there a pressure difference favoring water efflux from vessel?

Answer 11

arterial end

Question 12

where is there a pressure difference favoring water entrance to vessel?

Answer 12

venous end

Question 13

what are the homeostatic functions of the kidney?

Answer 13

regulation of extracellular fluid volume
regulation of extracellular fluid electrolyte composition
regulation of extracellular fluid acid base balance

Question 14

what are the excretory functions of the kidney?

Answer 14

metabolic waste products

foreign substances and toxins

Question 15

describe the role of different nephron sections in water reabsorption/excretion

Answer 15

1. blood is filtered in the glomerulus
2. water is reabsorbed in the proximal tubule in a constitutive fashion
   - 60-70% of water
   - linked to Na+
3. loop of henle not directly involved in reabsorption, but is fundamental in ADH dependent water balance
4. distal tubule/collecting duct water reabsorption is regulated by ADH

Question 16

what two components are maintained in regulation of water balance?

Answer 16

ECF volume

ECF osmolarity

Question 17

when does the posterior pituitary release ADH?

Answer 17

increased ECF osmolarity

stimulation of thirst center and osmoreceptors

Question 18

what is the effect of ADH on urine and plasma H2O?

Answer 18

decreases urine volume and increases urine osmolarity to save water in the plasma
once there is enough plasma H2O, there is negative feedback which inhibits ADH

Question 19

a decrease in these metrics causes an increase in ADH

Answer 19

volume and pressure

Question 20

an increase in this metric causes and increase in ADH

Answer 20

plasma osmolarity

Question 21

what is the relative osmolarity and flow rate of urine during diuresis?

Answer 21

high flow

low osmolarity

Question 22

what is the relative osmolarity and flow rate of urine during antidiuresis?

Answer 22

low flow

high osmolarity

Question 23

what are the 2 factors required for water reabsorption in the kidney?

Answer 23

1. permeability across the renal tubule membrane

2. a gradient for water movement across the tubule

Question 24

how does ADH affect the distal tubule?

Answer 24

tubule impermeable

ADH increases permeability by creating channels for water to exit

Question 25

what is the difference between the dlh and the alh?

Answer 25

dlh is permeable, alh is not | this allows for the creation of a more dilute fluid in the alh

Question 26

describe the countercurrent mechanism

Answer 26

in the dlh, water exits and salt enters in the alh, salt exits and water is maintained due to impermeability, creating a dilute solution in the distal tubule and collecting tubule, there is now a gradient between the dilute filtrate and salty environment of the medullary interstitium so that water may flow out of the tubule if ADH is present and makes it permeable

Question 27

what is the response of the kidneys and the resulting effect on urine of an event resulting in loss of water > solutes?

Answer 27

water reabsorption in kidney decrease urine volume increase urine conc. (hypertonic)

Question 28

what is the response of the kidneys and the resulting effect on urine of an event resulting in excess water over solutes?

Answer 28

water excretion increase urine volume decrease urine conc. (hypotonic)

Question 29

what is the response of the kidneys and the resulting effect on urine of an event resulting in excess of isotonic fluid?

Answer 29

water and solute excretion | increase urine volume

Question 30

what are two mechanisms that lead to polyuria?

Answer 30

1. low solute reabsorption | 2. abnormal ADH levels

Question 31

what is the effect of low solute reabsorption?

Answer 31

``` solute diuresis due to: -salt wasting -diuretics -high glucose in renal tubule ```

Question 32

describe the mechanism for polyuria: solute diuresis

Answer 32

excess solutes in the filtrate (due to presence of osmolytes (DM), inhibition of salt reabsorption by drugs, or decreased ADH) decreased water reabsorption in the proximal tubule partial but insufficient compensation by distal tubule reabsorption urine osmolarity isotonic or close to plasma increased urine volume

Question 33

what are the 4 components of diabetic nephropathy?

Answer 33

1. thickening of the glomerular basal membrane due to accumulation of glycated proteins 2. efferent glomerular arteriole atherosclerosis 3. messangial and glomerular expansion 4. disruption of podocytes

Question 34

describe the mechanism of solute diuresis in DM

Answer 34

high plasma glucose increased glucose filtration glucose remains in tubule increases diuresis (polyuria)

Question 35

describe the mechanism for polyuria: water diuresis

Answer 35

``` excess water ingested decreased ECF osmolarity decreased ADH decreased nephron water permeability and reabsorption solute reabsorption continues increased urine dilution ```

Question 36

what are the two components of diagnosing polyuria?

Answer 36

history and testing

Question 37

what is the process for testing polyuria?

Answer 37

restrict water/raise plasma osmolarity monitor urine osmolarity/volume and ADH levels in plasma look at plasma and urine glucose levels

Question 38

what should happen to urine volume/osmolarity after the addition of ADH?

Answer 38

should level off

Question 39

what should happen to urine osmolarity as plasma osmolarity increases?

Answer 39

increase in a steep linear fashion

Question 40

what should happen to urine volume as plasma osmolarity increases?

Answer 40

decrease in a steep linear fashion

Question 41

how do presentations of nephrogenic diabetes insipidus and central diabetes insipidus differ on a polyuria test?

Answer 41

nephrogenic doesn't react to ADH addition while central does