Kidney Structure 2

Question 1

Which substances are almost entirely reabsorbed by the nephron

Answer 1

Water
Sodium
Glucose

Question 2

What is osmotic pressure

Answer 2

The hydrostatic pressure produced by a difference in concentrations between solutions on the two sides of a surface such as a semi-permeable membrane

Question 3

What is osmolarity and osmolality

Answer 3

Osmolarity = moles of solute/litre of solution
Osmolality = moles of solute/kg of solvent

Question 4

What is the main substance reabsorbed in the proximal tubule and how is it reabsorbed

Answer 4

Na+/K+ pump using ATP pumps Na+ out of the cell into the capillaries to create an electrochemical gradient.
Then Na+ move into the cell via a Na+/Glucose co-transporter

Question 5

How is chloride reabsorbed in the PCT

Answer 5

Transport of Na+ into the interstitial fluid creates a potential difference.
And so Cl- passively moves from the lumen to the interstitial fluid

Question 6

How is water reabsorbed into the PCT

Answer 6

When Cl- moves into the interstitial fluid it forms NaCl, which accumulates in the interstitial fluid and osmolality and osmotic pressure increases.
Water moves by osmosis into permeable epithelial cells, then into interstitial and finally in to the peritubular capillaries.

Question 7

Name as many of the other substances that are reabsorbed in the PCT as you can

Answer 7

Urea (passive)
Chloride
Bicarbonate
Phosphate
Potassium
Glucose 
Amino Acids
Proteins

Question 8

What is glycosuria

Answer 8

A condition where the glucose carriers become saturated and excess glucose appears in the urine

Question 9

Name some things that are secreted into the tubule

Answer 9

Hydrogen ions, ammonia and organic acids

Question 10

Is urine hypo or hyper-osmotic to the plasma

Answer 10

Can be either u slag

Question 11

What is the role of the Loop of Hence

Answer 11

It removes water from the tubular fluid by creating an area of high osmotic pressure outside the nephron

Question 12

Describe the properties of the ascending limb and how the osmolarity of the tubular fluid changes as it goes through it

Answer 12

• virtually impermeable to water
• permeable to solute especially sodium and chloride ions that are actively pumped out
• the fluid firstly becomes isotonic and then becomes hypotonic

Question 13

What ion transporter transports, which ions in to the epithelium of the ascending limb

Answer 13

the 2Cl-/Na+/K+ ion symporter

Question 14

Describe the properties of the descending loop of henle and describe how the osmolarity of the tubular fluid changes as it goes through it

Answer 14

• relatively impermeable to solute
• permeable to water
• water moves out by osmosis and the fluid in the tubular becomes hypertonic

Question 15

How is the osmotic gradient that allows for the counter current multiplication formed in the loop of henle

Answer 15

The osmotic gradient is formed primarily by active transport of sodium and chloride by the ascending limb without the reabsorption of an osmotic equivalent of water.

Question 16

Besides NaCl what mainly contributes to the total osmolality of the interstitial fluid in the medulla

Answer 16

Urea

Question 17

Where is urea absorbed mostly

Answer 17

In the PCT and collecting duct (diffusion)

Question 18

What is the role of the vasa recta

Answer 18

To supply the medullary tissues with nutrients and oxygen

Question 19

What are the walls of the vasa recta freely permeable to

Answer 19

Water, NaCl and Urea

Question 20

How does the vasa recta affect osmolarity

Answer 20

As it passes into the inner medulla osmolarity increases, the opposite happens as blood returns to the cortex.

Question 21

Describe the route of the vasa recta in the medulla

Answer 21

Like the loop of henle it forms a parallel set of hairpin loops

Question 22

Where is most water reabsorbed in the nephron

Answer 22

PCT

Question 23

How can hormones affect water reabsorption in the LOH

Answer 23

they can’t

Question 24

How does the vasa recta act as a counter current exchanger

Answer 24

It carries away water and leaves solute in the medulla.
Blood flowing in descending vasa recta becomes more concentrated due to inwards diffusion of solutes and outwards diffusion of water. The reverse happens in the ascending limb and so these solutes are left in the medulla and water is removed from the medulla

Question 25

Ion diffusion/active transport from the ascending limb causes water to be drawn out of what structures

Answer 25

The descending limb and the collecting duct

Question 26

What structures does ADH have an effect on

Answer 26

DCT and CD