Renal 6

Question 1

Normal function requires ECF Osmolarity =

Answer 1

300

mOsm

Question 2

H2O and Na+ input via diet:

Answer 2

– Too much

– Not enough.

Question 3

H2O and Na+ loss: (4)

Answer 3

– Insensible
– Sweat
– Feces
– Urine - To a large extent, kidneys balance the
books by adjusting water reabsorption and
excretion.

Question 4

Mechanisms to eliminate excess water by excreting a

Answer 4

dilute urine;

Question 5

Mechanisms to conserve water by excreting a

Answer 5

concentrated urine;

Question 6

Renal feedback mechanisms that control the

Answer 6

extracellular fluid sodium concentration and osmolarity

Question 7

Thirst and salt appetite mechanisms that determine the
intakes of (2), which also help to control
extracellular fluid volume, osmolarity, and sodium
concentration

Answer 7

water and salt

Question 8

Concentration and Dilution of the Urine
Accomplished 
independently of major 
changes in solute 
excretion:
– Maximal urine concen-
tration:
– Minimal urine concen-
tration:

Answer 8

1200 mOsm (specific 
gravity ~ 1.030).

50 mOsm  (specific 
gravity ~ 1.003).

Question 9

Filtrate is — in proximal tubule.

Answer 9

isosmotic

Question 10

Filtrate is isosmotic in proximal tubule.
 Becomes hyperosmotic as passes 
through tDL (2)

Answer 10

– Water reabsorption

– No solute reabsorption.

Question 11

Becomes hyposmotic as passes

through TAL and early distal tubule (2)

Answer 11

– Solute reabsorption

– No water reabsorption.

Question 12

Osmolarity of fluid will vary as pass
through distal tubule and collecting
duct (2)

Answer 12

– Stays hyposmotic in absence of
ADH (dilute urine)
– Dilute Urine (as low as 50 mOsm/L)

Question 13

Urine Formed With ADH is Concentrated (4)

Answer 13

 ADH increases H2O permeability 
of distal tubule and collecting 
duct.
 Large volume of H2O diffuses 
into interstitium.
 Enters capillaries of Vasa Recta 
and removed.
 Creates concentrated urine (as 
high as 1200 mOsm/L)

Question 14

Obligatory Urine Volume

Answer 14

 The maximal concentration ability of the
kidney dictates how much urine volume
must be excreted each day to rid the body of
metabolic waste products and ions that are
ingested.

Question 15

Adult must excrete — mosmol daily
(solutes ingested and [mainly] produced by
metabolism).

Answer 15

600

(600 mosmol/day)/(1200 mosmol/L) = 0.5
L/day.

Question 16

(600 mosmol/day)/(1200 mosmol/L) = 0.5
L/day.
– Adds to

Answer 16

other sources of H2O loss (skin,

lungs, GI).

Question 17

Renal disease impairs — ability:

Answer 17

concentrating

Question 18

Requirements for Excreting a Concentrated

Urine (2)

Answer 18

1. High levels of ADH

2. Hyperosmotic medullary interstitial fluid

Question 19

Hyperosmotic medullary interstitial fluid (4)

Answer 19

Surrounds collecting duct
Sets gradient for water reabsorption
Requires Counter Current Multiplier Mechanism
Function of Juxtamedullary nephrons

Question 20

Function of Juxtamedullary nephrons (3)

Answer 20

• Long Loop of Henle
• Vasa Recta
• Slow flow rate

Question 21

High Interstitial fluid Osmolarity a result of: (4)

Answer 21

• Active transport of Na+ and other ions by ascending limb of LOH
• Active transport of ions from collecting duct into interstitium
• Facilitated diffusion of Urea by Inner medullary collecting ducts
• Movement of only small amounts of water into medullary
  interstitium

Question 22

Continuous delivery of NaCl from proximal convoluted tubule into

Answer 22

loop of Henle

Question 23

Concentration of filtrate by H2O reabsorption by

Answer 23

Descending Limb of Henle

Question 24

Continuous reabsorption of solute into interstitium by

Answer 24

thick ascending limb

Question 25

Na+-K+ pumps in CD pump Na+ into interstitium to

Answer 25

↑ osmolarity (to ≈1,200 mOsm/l) => formation of interstitial osmolar gradient

Question 26

In Absence of ADH (2)

Answer 26

 Reabsorb solute

 Little to no water reabsorption

Question 27

n Presence of ADH (3)

Answer 27

 Distal tubule and collecting 
ducts become highly 
permeable to water and 
reabsorb much water into 
cortical interstitium
 Medullary collecting duct cells 
reabsorb water but overall 
amounts much lower (keeps 
medullary interstitium from 
being diluted).
 Reabsorbed water carried 
away by Vasa Recta

Question 28

Role of Urea in Concentrating Urine

Answer 28

Waste product of protein metabolism; produced continuously by
liver.

Question 29

urea:

Normally excrete –% of filtered load

Answer 29

20-50

Question 30

urea:
Non—, but constitutes an osmotic load that must be —
(mw = 60 g/mol; plasma level 5 mM).

Answer 30

toxic

excreted

Question 31

urea:
Contributes —% of medullary interstitial osmolarity (500-600
mOsm/L)

Answer 31

40-50

Question 32

Reabsorbed passively by — collecting duct cells

Answer 32

medullary

Question 33

Secreted into descending limb and thin ascending limb of Loop of
Henle - Requires: ADH (2)

Answer 33

Concentrates urea in filtrate (water reabsorption in cortical and
medullary collecting ducts)
Activates carriers (UT-A1; UT-A3) for the facilitated diffusion of
urea by medullary collecting duct cells

Question 34

Countercurrent Multiplier Mechanism

 Depends on anatomical relationships of (3)

Answer 34

loop of Henle, vasa recta, & collecting ducts.

Question 35

~25% of nephrons are —, with long loops of Henle that extend into renal medulla parallel to vasa recta & collecting ducts.

Answer 35

juxtamedullary

Question 36

Filtrate in descending & ascending limbs of loop of Henle flows in opposite directions of blood flow in

Answer 36

Vasa Recta

Question 37

Clears Reabsorbed water so does not dilute

Answer 37

medullary interstitial fluid

Question 38

Blood flow only –%
of total but sufficient
for O2 supply and
CO2 removal

Answer 38

2

Question 39

Tubule Segment: Proximal Tubule
% H2O Reabsorbed
Filtrate Osmolarity

Answer 39

70

Isosmotic

Question 40

Tubule Segment: Descending LOH
% H2O Reabsorbed
Filtrate Osmolarity

Answer 40

20

Hyperosmotic

Question 41

Tubule Segment Ascending limb of LOH
% H2O Reabsorbed
Filtrate Osmolarity

Answer 41

0

hyposmotic

Question 42

Tubule Segment: Late DT and CCD
% H2O Reabsorbed
Filtrate Osmolarity

Answer 42

variable (adh)

variable

Question 43

Tubule Segment: MCD
% H2O Reabsorbed
Filtrate Osmolarity

Answer 43

variable (ADH)

variable