Blood Vessels

• What is the role of arterioles?

  They connect arteries to capillaries.
• What is the role of capillaries?

  They connect arterioles to veins.
• Order the blood vessels from thickest to thinnest muscular layer.

  1. Artery- enables constriction and dilation to control blood flow.
  2. Arterioles- restricts blood flow to capillaries.
  3. Veins- no control over blood flow.
  4. Capillaries- no muscular layer.
• Order the blood vessels from thickest to thinnest elastic layer.

  1. Artery- maintains blood pressure. Walls can stretch and recoil in response to heartbeat.
  2. Arteriole- thinner as pressure is lower
  3. Vein- thinner as pressure is lower.
  4. Capillary- no elastic layer.
• Order the blood vessels from thickest to thinnest wall.

  1. Artery- prevents vessel bursting due to high pressure.
  2. Arteriole- thinner as lower pressure.
  3. Vein- thinner as lower pressure. Easily flattened to help blood flow to the heart.
  4. Capillary- one-cell thick for a short diffusion pathway.
• Which is the only blood vessel to contain valves?

  Veins
• Explain the benefit of capillaries having a narrow diameter.

  • Slows blood flow for exchange time.
  • Red blood cells are squashed against the walls, which maximises diffusion.
• What is tissue fluid?

  A fluid containing water, glucose, amino acids, fatty acids, ions and oxygen which bathes the tissues.
• How is tissue fluid formed?

  1. Capillaries have small gaps in the walls so that liquid and small molecules can be forced out.
  2. As blood enters the capillaries from arterioles, the smaller diameter results in a high hydrostatic pressure so small molecules are forced out. This is called ultrafiltration.
• What is forced out through capillary walls?

  1. Water molecules
  2. Dissolved minerals and ions
  3. Glucose
  4. Fatty acids
  5. Small proteins and amino acids
  6. Oxygen
• What remains in the capillaries?

  • Red blood cells
  • Platelets
  • Large proteins
• How is tissue fluid reabsorbed?

  • Large molecules remain in the capillaries, creating a lowered water potential.
  • Towards the venule end of the capillaries, hydrostatic pressure is lowered due to the loss of liquid.
  • Water re-enters the capillaries via osmosis.
  • This water contains dissolved waste molecules such as carbon dioxide and urea.
• Why is not all liquid reabsorbed this way?

  An equilibrium is reached.
• What happens to the rest of the fluid?

  • It is absorbed into the lymphatic system.
  • Eventually, it drains back into the bloodstream near the heart.
• What blood vessel are lymph vessels similar to?

  Veins- they both contain valves.