Chapter 28: Urine Concentration And Dilution

Question 0

Excretion of excess water is done how?

Answer 0

Excretion of diluted urine

Question 1

Action of vasopressin

Answer 1

Increases water permeability of distal tubules and collecting ducts

Question 2

Osmolarity of glomerular filtrate in the proximal tubule

Answer 2

Isosmotic to plasma

Question 3

Tonicity of filtrate as it passes down the descending limb of the loop of Henle

Answer 3

Hypertonic

Question 4

Segment of tubular system which is impermeable to water even with the presence of ADH, which dilutes the tubular fluid

Answer 4

Ascending Loop of Henle

Question 5

Osmolarity of tubular fluid as it leaves the early distal tubule

Answer 5

Hyposmotic

Question 6

Minimal volume of urine that must be excreted

Answer 6

Obligatory urine volume

Question 7

Maximal urine concentration of the human kidney

Answer 7

1200 mOsm/L

Question 8

Weight of solutes in a given volume of urine

Answer 8

Urine specific gravity (1.002-1.028)

Question 9

Requirement s for excreting concentrated urine

Answer 9

1. High levels of ADH

2. Hyperosmotic renal medullary interstitial fluid

Question 10

Mechanism responsible for concentrating the renal medullary interstitial fluid

Answer 10

Countercurrent mechanism

Question 11

The most important cause of of the high medullary osmolarity is active transport of sodium and co-transport of K, Cl and other ions from what tubular segment?

Answer 11

Thick ascending limb of the loop of Henle

Question 12

Limit of the concentration gradient between tubular fluid and interstitial fluid

Answer 12

200 mOsm/L

Question 13

Refers to the repetitive reabsorption of NaCl by the thick ascending loop of Henle and continued inflow of new NaCl from the proximal tubule into the loop of Henle

Answer 13

Countercurrent multiplier

Question 14

Substance that contributes 40-50% of the osmolarity of the renal medullary interstitium when the kidney is forming a maximally concentrated urine

Answer 14

Urea

Question 15

Tubular segment which are impermeable to urea

Answer 15

Thick ascending limb of the loop of Henle up to cortical collecting duct

Question 16

Transport of urea from the inner medullary collecting ducts to the renal interstitial fluid occurs through which mechanism?

Answer 16

Facilitated diffusion utilizing urea transporters (UT-A1 and UT-A3)

Question 17

Secretion of urea in the thin loops of Henle is facilitated by which transporter

Answer 17

UT-A2

Question 18

Give two special features of the renal medullary blood flow that contribute to the preservation of the high solute concentrations

Answer 18

• low medullary blood flow (<5% of renal blood flow)

- vasa recta serve as countercurrent exchangers

Question 19

The vasa recta do not create the medullary hyperosmolarity, but they do prevent it from being dissipated. True / False

Answer 19

True

Question 20

Effect of increased medullary blood flow to urine concentrating ability

Answer 20

Reduced urine concentrating ability due to washing out of some of the solutes from renal medulla

Question 21

NaCl is one of the principal solutes that contribute to the hyperosmolarity of the medullary interstitium. However, the kidney can excrete a highly concentrated urine that contains little NaCl. True / False

Answer 21

True

Question 22

Condition wherein there is failure to produce ADH

Answer 22

Central DI

Question 23

Condition wherein the kidneys fail to respond to ADH

Answer 23

Nephrogenic DI

Question 24

Two primary systems involved in regulating the concentration of Na and osmolarity of extracellular fluid

Answer 24

• osmoreceptor-ADH system

- thirst mechanism

Question 25

Special nerve cells that shrink during an increase in ECF fluid osmolarity

Answer 25

Osmoreceptor cells

Question 26

stimuli for ADH secretion

Answer 26

• high osmolarity
• low arterial pressure
• low blood volume
• nausea
• hypoxia
• drugs (morphine, nicotine, cyclophosphamide)

Question 27

ADH is more sensitive to small changes in osmolarity than to similar changes in blood volume. True or False

Answer 27

True

Question 28

The desire to drink is completely satisfied only when?

Answer 28

Plasma osmolarity and/or blood volume returns to normal

Question 29

Threshold for drinking

Answer 29

Na concentration increases 2 mEq/L above normal

Question 30

Stimuli for thirst mechanism

Answer 30

Inc plasma osmolarity
Dec blood volume
Dec blood pressure
Inc angiotensin II
Dryness of mouth

Question 31

When either the ADH or the thirst mechanism fails, the other ordinarily can still control extracellular osmolarity and Na concentration with reasonable effectiveness. True or False

Answer 31

True

Question 32

Angiotensin II and aldosterone have great effect in Na concentration. True or False

Answer 32

False. Both have little effect except under extreme conditions

Question 33

Plasma sodium concentration

Answer 33

142 mEq/L (140-145 mEq/L)