Study the below diagram of a capillary network and answer the questions that follow.

Here are the answers to your questions about the capillary network:

3.1

• Vessel 1 is an arteriole.
• Vessel 2 is a venule.
  • Answer: $\boxed{\text{1: Arteriole, 2: Venule}}$

3.2
Here are three structural differences between blood vessels 1 (arteriole) and 2 (venule):

• Arterioles (1) have thicker, more muscular walls to withstand high blood pressure, while venules (2) have thinner, less muscular walls.
• Arterioles (1) have a smaller lumen (internal diameter) compared to venules (2) of similar size.
• Arterioles (1) carry blood away from the heart towards the capillaries, while venules (2) carry blood away from the capillaries towards the heart.

3.3
The lining of a capillary is called the endothelium.

• Answer: $\boxed{\text{Endothelium}}$

3.4

• Gas A is moving from the capillary to the body cells, indicating it is oxygen ($\text{O}_2$).
• Gas B is moving from the body cells to the capillary, indicating it is carbon dioxide ($\text{CO}_2$).
  • Answer: $\boxed{\text{A: Oxygen (O}_2\text{), B: Carbon dioxide (CO}_2\text{)}}$

3.5
The liquid which bathes the body cells is called tissue fluid (or interstitial fluid).

• Answer: $\boxed{\text{Tissue fluid}}$

3.6
Blood leaving a systemic capillary network is deoxygenated and returns to the heart via venules and veins, eventually entering the right atrium.

• Answer: $\boxed{\text{Right atrium}}$