Tubular reabsorption (1.6)

Question 1

What is tubular reabsorption ?

Answer 1

As the filtrate moves along the renal tubule, the useful substances needed by the body are reabsorbed back into the blood in the capillaries surrounding the renal tubules. This takes place mainly in the proximal tubule.

Question 2

How is the proximal tubule adapted for reabsorption? (3)

Answer 2

• It is very long and coiled, which enables maximum reabsorption take place
• A dense capillary network closely surrounds the tubule, so the substances can easily move into the bloodstream to be transported away
• The walls of the tubule are made up specialised cuboidal epithelial cells.

Question 3

What adaptions do the specialized cuboidal epithelial cells? (3)

Answer 3

• A brush border of microvilli on their inner surface area for maximum reabsorption.
• The outer surface is folded to further increase the surface area.
• Many mitochondria to produce the ATP (energy) needed for active transport

Question 4

Some substances are ___ reabsorbed from the filtrate in the nephron into the bloodstream in the surrounding capillaries. Others are ____ reabsorbed.

Answer 4

Actively

Passively

Question 5

What is active reabsorption?

Answer 5

When molecules move actively, they combine with a carrier molecule and may move against the concentration gradient. This process needs energy in the form of adenosine triphosphate (ATP), to bring it about.

Question 6

Define concentration gradient.

Answer 6

The gradual difference in the concentration of solutes in a solution between two regions.

Question 7

Which substances are actively absorbed? (2)

Answer 7

• All the organic nutrients such as glucose, protein and most water soluble vitamins (eg. Vitamin C) are completely reabsorbed into the blood.
• Fat soluble vitamins and many ions, eg sodium ions are selectively reabsorbed according to the needs of the body

Question 8

True or false

There are glucose and protein molecules in normal urine

Answer 8

False. There are no glucose or protein molecules in normal urine. All these molecules are reabsorbed back into the blood.

Question 9

• About __% of the water is ___ (no energy is needed) reabsorbed from the filtrate into the blood, by osmosis.
• Chloride ions ___ follow the path of ___ ions, which are actively absorbed.

Answer 9

65%
Passively
Passively
Sodium

Question 10

___, ___ and ____ are not reabsorbed and remain in the filtrate. A little urea may be reabsorbed as it is a small molecule.

Answer 10

Urea
Uric acid
Creatinine

Question 11

What is the role of the loop of Henle?

Answer 11

It is to create a high concentration of salt in the medulla area which is necessary for the osmotic withdrawal of water from the distal tubules and the collecting ducts. Sodium ions are actively transported out of the filtrate in the ascending limb into the tissue fluid surrounding the limbs. This process uses energy and is called the ‘sodium pump’. As a result the tissue fluid in the medulla of the kidney becomes highly concentrated (hypertonic). Water does not follow as the cells of the ascending limbs are impermeable to water. As the filtrate loses salt but not water, it becomes increasingly hypotonic.

Question 12

What is the final outcome?

Answer 12

• The water is actively conserved and passes back into the blood and not lost in urine
• So less urine is formed. It is concentrated and dark yellow in colour.

Question 13

The longer the Loop of Henle, the greater the concentration of ___ in the medulla area. This will encourage more ___ to be reabsorbed result in the urine being ____ concentrated.

Answer 13

Salt
Water
Highly

Question 14

Why do desert animals have long loops of Henle?

Answer 14

Desert animals need to conserve as much water as possible so they have very long loops of Henle.