2 A&P II Chapter 25 Countercurrent Multiplier

Question 1

What is the definition of osmolarity?

Answer 1

The number of solute particles dissolved in 1 kg (1 liter) of water

Question 2

Is osmolarity determined by the size of particles?

Answer 2

No by the number only

Question 3

What is osmolarity used to measure?

Answer 3

The amount of solutes in body fluids

Question 4

What does countercurrent mean?

Answer 4

That fluid flows in opposite directions through adjacent segments of the same tube connected by a hairpin turn

Question 5

What is the countercurrent multiplier?

Answer 5

The long loops of juxtamedullary nephrons

Question 6

What is the countercurrent exchanger?

Answer 6

THe flow of blood through the vasa recta

Question 7

When do the kidneys use the countercurrent multiplier mechansim?

Answer 7

When the kidneys produce a small volume of urine when the plasma concentration of ADH is high

Question 8

Is urine that is concetrated hyper or hypoosmotic?

Answer 8

Hyperosmotic

Question 9

What is the value for your obligatory water loss per day?

Answer 9

.444 L/day

Question 10

Why do we have obligatory water loss?

Answer 10

In order to excrete urea, sulfate, phosphate, and other wastes

Question 11

What happens if the body has inadequate water intake in the face of obligatory water loss?

Answer 11

Dehydration results

Question 12

Is the interstitial fluid the medulla hyper or hypoosmotic?

Answer 12

Hyperosmotic

Question 13

Where is the countercurrent flow?

Answer 13

THe opposing flow in the two limbs of the loop of Henle

Question 14

What does the loop of Henle function as a countercurrent multiplier system to create?

Answer 14

Hyperosmotic medullary interstitial fluid

Question 15

Is the fluid the enters the end of the PCT hyper or hypoosmotic?

Answer 15

Isoosmotic with plasma (300mOsmol/L)

Question 16

What processes make the fluid isoosmotic?

Answer 16

Both water and solutes are reabsorbed in the same proportions

Question 17

What are the values of the osmolarity of the descending loop of Henle?

Answer 17

300, 400, 600, 900, 1200 (in hairpin turn)

Question 18

What are the values of the osmolarity of the ascending loop of Henle?

Answer 18

1200 (hairpin turn), 700, 400, 200, 100

Question 19

How do the values of osmolarity of the ascending and descending loops compare?

Answer 19

The descending loop is 200 more than the corresponding part of the ascending loop

Question 20

What is the lowest osmolarity that occurs in the loop of Henle?

Answer 20

80-100 and the top of the ascending limb and by the end of the DCT

Question 21

What is the highest osmolarity that occurs in the loop of Henle?

Answer 21

1200-1400 at the hairpin turn

Question 22

Which limb is permeable to water?

Answer 22

Descending

Question 23

Which limb is permeable to NaCl?

Answer 23

Ascending

Question 24

Which limb is impermeable to water?

Answer 24

Ascending

Question 25

Which limb is impermeable to NaCl?

Answer 25

Descending

Question 26

What draws water out into the interstitium, therefore concentrating the fluid left in the tubules?

Answer 26

Hyperosmolarity in the interstitial fluid draws water out

Question 27

What does the term multiplier refer to?

Answer 27

The osmolarity difference that exists at each horizontal level is 200 mOsmols/L, therefore the difference is multiplied as the fluid goes deeper into the medulla

Question 28

Is the fluid entering the DCT hyper or hypoosmotic compared to plasma?

Answer 28

Hypoosomtic because it is 100 mOsmol/L

Question 29

What happens to water in the fluid if ADH is present?

Answer 29

It is reabsorbed in the collecting ducts

Question 30

What happens to the hypoosmotic urine if no ADH is present?

Answer 30

It is excreted

Question 31

What happens to water and sodium/chloride in the descending limb?

Answer 31

Sodium and chloride in the interstitium diffuse into the vasa recta, and water leaves the vasa recta

Question 32

What happens to water and sodium/chloride in the ascending limb?

Answer 32

Water enters the vasa recta and sodium and chloride diffuse out of the vasa recta

Question 33

How much urea is reabsorbed in the PCT?

Answer 33

50%

Question 34

What happens to the remaining 50% of urea?

Answer 34

Enters the loop of Henle

Question 35

Why is some urea trapped in the interstitium?

Answer 35

Contributes to the hyperosmotic nature of the interstitium