Chapter 29 - Urine Concentration

Question 1

Osmolarity definition

Answer 1

amount of solute (mainly sodium chloride) divided by the volume of the extracellular fluid

Question 2

Total body water is controlled by (#2)

Answer 2

(1) total fluid intake - determined by thirst
(2) renal water excretion - determined by kidney function

Question 3

Body osmolarity when there is an excess in water

Answer 3

osmolarity is reduced

Question 4

Body osmolarity when there is a deficit in water

Answer 4

osmolarity is high

Question 5

(True/False)

The kidney is able to excrete a large volume of dilute urine or a small volume of concentrated urine without major changes in rates of excretion of solutes such as sodium and potassium

• ability to regulate water excretion independently of solute excretion

Answer 5

True

Question 6

Increases water reabsorption and decreases urine volume but does not alter the rate of renal solute excretion

Answer 6

Antidiuretic Hormone (ADH) or vasopressin

Question 7

ADH is produced in (1) and secreted by (2)

Answer 7

(1) supraoptic nuclei of the hypothalamus
(2) posterior pituitary gland

Question 8

(1) ADH stimulus
(2) ADH action
(3) ADH target structure

Answer 8

(1) increase in the osmolality in the blood

(2) increase permeability to water by upregulating aquaporins

(3) distal convoluted tubules and collecting ducts

Question 9

(True/False)

Excess water in the body decreases osmolarity and increases secretion of ADH

Answer 9

False

reduced osmolarity will reduce the secretion of the ADH to reduce the permeability of the distal tubule and collecting ducts to water - less reabsorption, more excretion (diluted urine)

Question 10

(True/False)

THE RATE OF ADH SECRETION DETERMINES/CONTROLS URINE COCENTRATION

Answer 10

True

Question 11

Answer 11

• urine volume increased 6-times normal within 45 minutes of fluid intake
• solute excreted remained relatively constant
• urine osmolarity decreased from 600 to 100 mOsm/L

Question 12

Plasma osmolarity

Answer 12

300 mOsm/L

Question 13

Tonicity of the renal medulla (hypotonic, isotonic, hypertonic)

Answer 13

Hypertonic

Question 14

(True/False)

Tubular fluid becomes more concentrated as it flows into the inner medulla (descending loop of Henle)

Answer 14

True

as fluid descends to the loop of Henle, water is reabsorbed by OSMOSIS - filtrate becomes concentrated

Question 15

The proximal tubule reabsorbs water and solute in equal proportions.

There is no change in osmolarity where it remains () to the plasma

Answer 15

isotonic

Question 16

REGARDLESS OF WHETHER ADH IS PRESENT OR ABSENT, FLUID LEAVING THE EARLY DISTAL TUBULAR SEGMENT IS ()

Answer 16

Hypo-osmotic

osmolarity of only 1/3 of plasma osmolarity (100 mOsm/L)

Question 17

The thick ascending loop of Henle is permeable to (1) - avid reabsorption and impermeable to (2).

Filtrate the becomes (3)

Answer 17

(1) sodium, potassium, and chloride

(2) water

(3) diluted

Question 18

In the absence of ADH, the distal tubule and collecting duct will have additional absorption of solutes which will cause

Answer 18

tubular fluid to become more dilute (50 mOsm/L)

Question 19

MECHANISM TO FORMING DILUTE URINE

Answer 19

• continue reabsorbing solutes from the distal segments of the tubular system
• reducing water reabsorption

Question 20

KIDNEYS CONSERVE WATER BY

Answer 20

Excreting concentrated urine

Question 21

MECHANISM TO FORM CONCENTRATED URINE

Answer 21

• excrete solutes
• increasing water reabsorption - decreasing urine volume

Question 22

Maximal urine concentration ability

Answer 22

1200 mOsm/L

Question 23

Obligatory urine volume

Answer 23

0.5 L/day

Question 24

Specific gravity of a more concentrated urine

Answer 24

High specific gravity

Question 25

Normal specific gravity

Answer 25

1.002 to 1.028 g/mL

Question 26

High ADH and high osmolarity of the renal medullary interstitial fluid are the basic requirements that will lead to a

Answer 26

concentrated urine

Question 27

water that leaves the tubules via osmosis are carried away from the renal interstitium by

Answer 27

vasa recta

Question 28

Define Countercurrent multiplier mechanism

Answer 28

The process where renal medullary interstitial fluid remains hyperosmotic

Question 29

Components of the countercurrent multiplier mechanism

Answer 29

(1) loops of Henle

(2) vasa recta - of the juxtamedullary nephrons

(3) peritubular capillaries

(4) collecting ducts

Question 30

percentage of nephrons that are juxtamedullary nephrons in the kidney

Answer 30

25%

Question 31

(True/False)

The osmolarity of interstitial fluid in all parts of the body (except for the renal medulla) are about 300 mOsm/L - similar to the osmolarity of the blood

Answer 31

True

Question 32

Osmolarity of the renal medulla can increase progressively into

Answer 32

1200 to 1400 mOsm/L

Question 33

Major factors for increased osmolarity in the renal medulla

Answer 33

1. Active transport of sodium ions and co-transport of potassium, chloride, and other ions out of the thick portion of the ascending limb of the loop of Henle into the medullary interstitium
2. Active transport of ions from the collecting ducts into the medullary interstitium
3. Facilitated diffusion of urea from the inner medullary collecting ducts into the medullary interstitium
4. Diffusion of only small amounts of water from the medullary tubules into the medullary interstitium— far less than the reabsorption of solutes into the medullary interstitium

Question 34

TUBULE CHARCTERISTICS

Answer 34