Lecture 7 - Control of plasma volume

Question 1

Major osmotically effective solute in ECF

Answer 1

Na+

Water in ECF dependent on Na+

Question 2

Na+

Answer 2

Determines:

• ECF volume
• Plasma volume
• Blood pressure

Question 3

ECF contraction

Answer 3

Na+ excretion is more than Na+ ingested

ECF volume decreases as water is excreted decreasing BP

Negative balance

Question 4

ECF expansion

Answer 4

Na+ excretion is less than the Na+ ingested

The extra Na+ is retained in ECF therefore volume increases and water is drawn out of the nephron
Increases BP
Positive balance

Question 5

ECF volume detectors

Answer 5

Low pressure baroreceptors

Question 6

Transcellular reabsorption

Answer 6

From cell to cell

Question 7

Paracellular reabsorption

Answer 7

in between cells

Question 8

Basolateral membrane

Answer 8

Contains the 3Na+/ 2K+ ATPase - driving force for secondary active transport

Na+/HCO3- cotransporter

Question 9

Apical membrane

Answer 9

Lumen to epithelial cell

Question 10

Proximal convoluted tubule transporters

Answer 10

Na+ / H+ antiporter (exchanger)
Na+ / glucose symporter
Na+ / AA co transporter 
Na/ Pi
Aquaporins

Question 11

Loop of Henle transporters

Answer 11

NaKCC2 symporter

Question 12

Eary distal convoluted tubule transporters

Answer 12

Na+/ Cl- symporter

Question 13

Late DCT and collecting duct transporters

Answer 13

ENaC - epithelial Na Channels

Question 14

Reabsorption

Answer 14

Movement of water and solutes from the nephron tubule into the circulation

Question 15

Secretion

Answer 15

Movement of water and solutes from the circulation into the nephron tubule

Question 16

PCT

Answer 16

Reabsorption of: 
Na+
Cl- - paracellular 
K+
Ca2+
Urea
Glucose 
Amino acids
HCO3-  ( via carbonic anhydrase)
H2O

Secretion of:
Creatinine
Drugs
H+

Question 17

Descending limb

Answer 17

Water reabsorption

lots of aquaporin channels and gap junctions

Question 18

Ascending limb

Answer 18

NO water absorption as no aquaporins

Na+ , Cl- and K+ reabsorption takes place - NKCC2

Question 19

DCT

Answer 19

Reabsorption of:
Na+ 
Cl- 
Mg+ and Ca2+ - paracellular inbetween tight junctions
HCO3- 

Secretion of:
H+
K+
Contains Na+/K+ transporter - (aldosterone)

Question 20

Collecting duct

Answer 20

Reabsorption of:
Na+ 
Cl- 
Urea 
H2O - aquaporins

Question 21

Aldosterone

Answer 21

Produced and secreted by the adrenal cortex
In response to low BP
More Na+ reabsorbed thus more water
More K+ secreted - hypokalaemia

Question 22

ADH

Answer 22

Increase expression of aquaporins in collecting duct

Increase H2O reabsorption

Question 23

Amiloride

Answer 23

Diuretic
Inhibits NHE in PCT
Inhibits ENaC in DCT
Less Na+ reabsorbed so less water reabsorbed

Question 24

Loop diuretics - Furosemide

Answer 24

Furosemide - Inhibits NKCC2 in thick ascending limb

Less Na + reabsorption therefore less water reabsorption

Can cause hypokaleamia

Less vasoconstriction in afferent arteriole due to macula densa NKCC2 inhibition

Question 25

K+ sparing diuretic

Answer 25

Spironolactone - Inhibits ROMK Less K+ excreted so the concentration gradient inside the epithelium decreases. NKCC2 works less efficiently due to diminished gradient

Question 26

Thiazides

Answer 26

Inhibits Na+/Cl- (NCCT)

Question 27

Cell type of loop of Henle

Answer 27

squamous epithelium | few mitochondria

Question 28

Passive Na+ reuptake in thin ascending limb

Answer 28

water reabsorption in the descending limb creates a gradient for passive Na + reabsorption paracellularly

Question 29

Intercalated cell type A

Answer 29

Secrete H+

Question 30

Intercalated cell type B

Answer 30

Secrete HCO3-

Question 31

Ca2+ reabsorption

Answer 31

1. Apical channels in the DCT transport Ca2+ into the epithelium 2. It immediately binds to calbindin which shuttles it across to the basolateral membrane 3. Ca2+ is transported to the capillary via NCX 4. Tightly regulated by calcitriol and PTH

Question 32

Principal cells

Answer 32

Contains ROMK and ENaC on their apical surface

Question 33

Glucosuria

Answer 33

When the glucose transport maximum is reached, it exceeds the transporter capacity and therefore is excreted into the urine.

Question 34

How is HCO3- reabsorbed in the PCT?

Answer 34

1. The PCT contains NHE on its apical surface which secretes H+ ions into the lumen 2. HCO3- in the lumen reacts with H+ to produce H2CO3 (carbonic acid) 3. Carbonic acid is converted to CO2 and H2O by carbonic anhydrase. 4. CO2 is transferred into the tubular cells via transcellular transport. 5. Via carbonic anhydrase CO2 reacts with water to form HCO3- and H+ 6. The HCO3- is reabsorbed into the capillary via Cl- / HCO3- (anion exchanger) - non-sodium dependent