145 - Kidney function, fluid and electrolyte balance 3

Question 1

Osmolarity trough the kidney

Answer 1

~300 miliosmols/L at cortex to 1200 miliosmols/L near papilla (most-central part)

Question 2

Significance of 300 miliosmols/L osmolarity at cortex of kidney

Answer 2

Same as osmolarity of the rest of the body

Question 3

Role of the proximal convoluted tubule

Answer 3

iso-osmotically reabsorbs ~65% of filtrate (without changing osmolarity of fluid)

Question 4

Osmolarity of fluid entering thick descending limb

Answer 4

Iso-osmotic (300miliosmolar/L)

Question 5

Where is most glucose reuptaken?

Answer 5

Proximal tubule

Question 6

Where is the concentration of renal filtrate the highest?

Answer 6

Loop of Henle

Question 7

Type of epithelium in descending loop of Helne

Answer 7

Few mitochondria, thin membranes.
Very permeable to water.
Impermeable to almost everything else (lacks channels, transporters). Very lipid-soluble substances can still pass through wall.

Question 8

Why is the descending limb water-permeable?

Answer 8

Aquaporins

Question 9

Effect of impermeability of descending limb wall to everything but water.

Answer 9

Increase in concentration of renal filtrate (only water can leave).
Gradual increase in concentration of solutes of renal filtrate by a factor of four.

Question 10

Solute responsible for a lot of the high osmotic pressure in the renal papilla

Answer 10

Urea

Question 11

Permeabilities in the epithelium of the thin ascending limb

Answer 11

High permeability to sodium.

Low water permeability

Question 12

Effect of permeabilities of thin ascending limb

Answer 12

Movement of sodium out of thin ascending limb

Question 13

Proportion of sodium reabsorbed in thick ascending limb

Answer 13

~25%

Question 14

Proportion of water reabsorbed in descending limb

Answer 14

~10-12%

Question 15

Distal tubule sodium reabsorption

Answer 15

Regulated, according to body needs

Question 16

Difference in sodium reabsorption between proximal tubule, descending limb and distal tubule

Answer 16

Proximal tubule and descending limb maintain the same amount of sodium reabsorption all the time.
Distal tubule is regulated according to body needs

Question 17

Fluid entering the collecting duct

Answer 17

Dilute

Question 18

Possible effects of collecting duct on filtrate

Answer 18

Travels through gradient of 300- 1200mOsM.
Can alter permeability to water.
This means that filtrate can be diluted or concentrated, depending on body needs.

Question 19

What regulates aquaporins in collecting duct

Answer 19

Vasopressin or antidiuretic hormone (the same hormone, just different names)

Question 20

Effect of antidiuretic hormone

Answer 20

Insertion of aquaporins into collecting duct.

This means that water is removed from filtrate, concentrating urine in collecting duct.

Question 21

Effect of acute renal failure on urine concentration

Answer 21

Will be roughly equal to plasma.

Won’t be filtered, reabsorbed, etc very much.

Question 22

When is kidney filtrate less concentrated that extracellular fluid?

Answer 22

At the end of the loop of Henle (just before the distal tubule)

Question 23

Osmolarity of fluid in Bowman’s capsule

Answer 23

300mOsM

Question 24

Osmolarity of fluid at the end of loop of Henle

Answer 24

100mOsM

Question 25

Mechanism of tubular reabsorption

Answer 25

1) Na+/K+ ATPase pumps Na+ into extracellular fluid
2) This leads to diffusion of anions from filtrate following electrochemical gradient
3) Water moves by osmosis into extracellular fluid
4)

Question 26

Examples of renal cotransporters

Answer 26

Na+/glucose

Na+/phosphate in proximal tubule

Question 27

Why isn’t all filtered phosphate reabsorbed?

Answer 27

Na+/phosphate cotransporter in proximal tubule doesn’t have a very high capacity

Question 28

How can chlorides and water be reuptaken in the kidneys?

Answer 28

From reuptake of Na+, there is a small negative charge in the lumen,
Cl- doesn’t have an epithelial channel, but can travel between epithelial cells of the tubule (through tight junctions). Paracellular route

Question 29

Things that can be reabsorbed via paracellular route

Answer 29

Cl- and water

Question 30

Broad routes of reabsorption

Answer 30

Paracellular and transcellular

Question 31

Proportion of O2 absorbed by the kidney that is for active transport

Answer 31

80%

Question 32

What is required for renal active transport?

Answer 32

Reabsorption of water, chloride, glucose, amino acids, urea

Secretion of potassium, hydrogen

Question 33

NHE

Answer 33

Sodium-hydrogen exchanger.

Located on apical membrane of epithelial cells of renal tubule.

Question 34

What makes Na+ reabsorption less efficient?

Answer 34

Reabsorbed Na+ can leak back into lumen through paracellular pathway

Question 35

What increases concentration of K+ in renal epithelial cells?

Answer 35

K+/Na+ antiporter (3Na+ out of cell, 2K+ into cell)

Question 36

What do sodium pumps drive reabsorption of?

Answer 36

K+, water, Cl-, HCO3-