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AS · Practice questions · A closed double circulation and its blood vessels

Follow the blood, then explain the wall.

Six original Cambridge-style questions on the mammalian circulation, from naming the main vessels to relating the structure of elastic arteries, muscular arteries, veins and capillaries to their functions.

Original questions All questions on this page are original work, written in the Cambridge AS & A Level style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
Keep these straight

Circuit, then vessel, then wall.

01
Recall
[3 marks]

State what is meant by describing the mammalian circulatory system as a closed double circulation.

  • Closed: the blood remains inside blood vessels (and the heart) at all times. ✓
  • Double: the blood passes through the heart twice in one complete circuit of the body. ✓
  • There is a pulmonary circulation (heart to lungs and back) and a systemic circulation (heart to body and back). ✓
02
Recall
[4 marks]

Describe the functions of the pulmonary artery, pulmonary vein, aorta and vena cava.

  • Pulmonary artery: carries deoxygenated blood from the right ventricle to the lungs. ✓
  • Pulmonary vein: carries oxygenated blood from the lungs to the left atrium. ✓
  • Aorta: carries oxygenated blood at high pressure from the left ventricle to the body (systemic circulation). ✓
  • Vena cava: returns deoxygenated blood from the body to the right atrium. ✓
03
Explain
[4 marks]

Explain how the structure of a capillary is related to its function.

  • The wall is a single layer of thin, flattened endothelial cells, so the diffusion distance is short. ✓
  • Gaps between the endothelial cells let fluid and small solutes leave to form tissue fluid. ✓
  • The narrow lumen means red blood cells pass in single file, close to the wall, and flow slowly, giving time for exchange. ✓
  • Capillaries are very numerous and branched, giving a large surface area close to every cell. ✓
04
Explain
[4 marks]

Explain the differences between the walls of a muscular artery and a vein in terms of their functions.

  • The muscular artery has a thick tunica media of smooth muscle; the vein has a thin tunica media with little muscle. ✓
  • The artery's muscle contracts or relaxes to change the lumen diameter and control blood flow to organs, and the thick wall withstands high pressure. ✓
  • Blood in a vein is at low pressure, so a thick wall is not needed; the wide lumen reduces resistance to flow. ✓
  • Veins have valves to prevent backflow of low-pressure blood; arteries do not need them. ✓
05
Analysis
[3 marks]

The mean blood pressure in the aorta is about 13 kPa, while in the vena cava near the heart it is below 1 kPa. Suggest why the wall of the aorta contains a large amount of elastic tissue but the wall of the vena cava does not.

  • The aorta receives blood in surges at high pressure each time the left ventricle contracts. ✓
  • Elastic fibres stretch to absorb the surge, then recoil to push blood on and maintain pressure between beats, giving a smoother flow. ✓
  • In the vena cava the pressure is low and steady, so there are no surges to absorb and little elastic tissue is needed. ✓
06
Data
[3 marks]

On a photomicrograph at ×100, a vessel has a lumen 0.8 mm wide on the image and a wall 0.6 mm thick on the image. A second vessel has a lumen 4.0 mm wide and a wall 0.3 mm thick. Calculate the actual lumen width of the first vessel in μm and identify each vessel, giving a reason.

  • Actual lumen width = 0.8 mm ÷ 100 = 0.008 mm = 8 μm. ✓
  • First vessel: wall thick relative to its small lumen, so it is an artery (here a small artery or arteriole). ✓
  • Second vessel: thin wall relative to a wide lumen, so it is a vein. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.