lecture 17- (T3) Urine Concentration and dilution

Question 1

what are the major functions of the kidneys

Answer 1

regulation of extracellular osmolality, including water loss and conservation

Question 2

what happens when there is a large excess of water in the body

Answer 2

kidneys can excrete as much as 20 liters per day with a concentration as low as 50 mOsm/L

Question 3

what is avidly reabsorbed in the ascending thick limb of henle

Answer 3

sodium. potassium and chloride

Question 4

is the ascending thick limb of henle permeable to water?

Answer 4

NOOOOO

Question 5

what is osmolarity at the early distal tubular segment of the ascending thick limb of henle

Answer 5

100 mOsm/L

Question 6

is the ascending thick limb of henle affected by ADH

Answer 6

NOOO

Question 7

what happens to urine output when ADH is present

Answer 7

it decreases

Question 8

what are attributes of the late distal convoluted tubule

Answer 8

addition reabsorption of sodium chloride
impermeable to water in absence of ADH
osmolarity reaches 50 mOsm/L

Question 9

what is the maximum urine concentration of the kidneys

Answer 9

1200 mOsm/L

Question 10

what are the requirements for forming concentrated urine

Answer 10

presence of ADH
high osmolarity of renal medullary interstitial tubule (establishes osmotic gradient necessary for water reabsorption to occur)

Question 11

what is the normal obligatory urine volume

Answer 11

0.5 L/Day

Question 12

what is the tubular osmolarity of the proximal tubule

Answer 12

300 mOsm/L

Question 13

where is about 65% of filtered electrolytes reabsorbed

Answer 13

proximal tubule

Question 14

is the descending loop of henle permeable to water?

Answer 14

YESSS

Question 15

what is the osmolarity of the descending loop of henle when ADH is high

Answer 15

1200

Question 16

what does the thin ascending loop of henle reabsorb

Answer 16

sodium chloride

urea also diffuses into ascending limb (comes from urea absorbed into interstitial from collecting ducts)

Question 17

what is the osmolarity in the thick ascending loop of henle

Answer 17

100 mOsm./L

Question 18

what does the osmolarity of fluid in the late distal tubule and cortical collecting duct dependent on

Answer 18

ADH

Question 19

what is the concentration gradient limited to in the countercurrent multiplier system

Answer 19

200 mOsm/L because of paracellular diffusion of ions back into tubule

Question 20

what parts of the kidney are impermeable to urea

Answer 20

ascending loop of henle and distal cortical collecting tubule

Question 21

what happens when ADH increases and cortical collection tubule

Answer 21

water is reabsorbed form cortical collecting tubule

urea is not very permeant here and becomes more concentrated in the tubule

Question 22

what happens when ADH increases and medullary collecting duct

Answer 22

more water is reabsorbed from medullary collecting duct, resulting in higher concentration of urea
higher concentration of urine results in diffusion of urea out of duct into interstitial fluid
facilitated by UT-A1 and UT-A3 (ADH activated) transporters

Question 23

how is the high concentration of urea in the tubular fluid and the urin maintained even though urea is being reabsorbed

Answer 23

simultaneous movement of water and urea out of the inner medullary collecting ducts

Question 24

what does vasa recta do

Answer 24

prevents medullary hyperosmolarity from being dissipated

Question 25

what is the role of osmoreceptor-ADH feedback mechanism

Answer 25

controls extracellular fluid sodium concentration and osmolarity

Question 26

where are int magnocelular neurons that form ADH found

Answer 26

supraoptic and paraventricular nuclei

Question 27

where are osmoreceptor cells found

Answer 27

vicinity of the AV3V region (anterior region of third ventricle)

Question 28

define isotonic volume depletion

Answer 28

osmolarity remains the same but volume decreases

Question 29

define isovolemic osmotic increase:

Answer 29

volume remains the same but osmolarity increases