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Homeostasis and the Kidney

Water regulation and antidiuretic hormone

  • 3 things to know
  • Component 3

Overview

Role of the ascending limb of the loop of Henlé, role of the descending limb and countercurrent multiplier.

What you need to know

Answer each one before you reveal it.

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Key term

Describe the response to drinking a large volume of water.

Key term

Describe the response to dehydration.

Key term

Which part of the nephron creates the conditions for water reabsorption?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Which part of the nephron creates the conditions for water reabsorption?

    Model answer

    The loop of Henlé, which establishes a gradient of decreasing water potential down the medulla.

  2. 2

    Describe the role of the ascending limb of the loop of Henlé.

    Model answer

    It actively pumps sodium and chloride ions out into the medulla, and it is impermeable to water.

  3. 3

    Describe the role of the descending limb.

    Model answer

    It is permeable to water, which leaves by osmosis into the concentrated medulla, so the filtrate becomes more concentrated as it descends.

  4. 4

    What is the countercurrent multiplier?

    Model answer

    The arrangement by which the two limbs flow in opposite directions, so a modest difference at any level is multiplied into a large gradient down the medulla.

  5. 5

    Why does the gradient in the medulla matter to the collecting duct?

    Model answer

    The duct passes down through it, so water can leave the duct by osmosis all the way down if the duct is permeable.

  6. 6

    Which gland releases antidiuretic hormone?

    Model answer

    The posterior pituitary gland.

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