Controlling Water Content

• What is the primary function of the kidneys in homeostasis?

  They help regulate water content.
• Why is balancing water content important for body cells?

  It ensures cells are surrounded by the right fluid environment for normal function.
• What happens when the water potential of a cell is higher than that of the tissue fluid?

  • Water moves into the cell from the tissue fluid.
  • The cell may swell as a result.
• What occurs if the water potential of the tissue fluid is higher than that of the cell?

  • Water moves into the cell.
  • The cell swells as a result.
• What happens when the water potential of the cell and tissue fluid are the same?

  • There is no net movement of water.
  • The cell remains in equilibrium.
• What is the consequence of a lower water potential in the cell compared to the tissue fluid?

  Water moves out of the cell, causing it to shrink.
• Why is it important to maintain the water content of the blood?

  To keep cells functioning normally.
• What role do the kidneys play in balancing water content?

  They control how much water is lost by varying urine volume and concentration.
• What structures inside the kidneys are responsible for filtering blood?

  Nephrons.
• What happens during urine formation in the tubules?

  1. Blood flows through the glomerulus at high pressure.
  2. Small molecules like water, sugar, salt, and urea are filtered into Bowman’s capsule.
  3. Useful substances are selectively reabsorbed:

  • All sugar is reabsorbed.
  • Sufficient salt is reabsorbed; excess is not.
  • Sufficient water is reabsorbed based on ADH levels.

  1. Unreabsorbed substances form urine, which is excreted.
• What is the role of ADH in the kidneys?

  It regulates the amount of water reabsorbed in the kidneys.
• Why might a person feel more thirsty than normal on a hot day?

  Increased sweating leads to a loss of water, triggering thirst.
• What are the components filtered out of blood into the Bowman’s capsule?

  • Water
  • Sugar
  • Salt (sodium chloride)
  • Urea
• What is the significance of selective reabsorption in the kidneys?

  • Ensures essential nutrients are retained.
  • Maintains electrolyte balance.
  • Regulates water levels based on body needs.
• What happens to urine concentration when the body is dehydrated?

  • Urine becomes more concentrated.
  • Less water is reabsorbed, leading to more concentrated waste.