Materials needed for a reusable class set:
1 standard garden hose
1 soaker hose
1 discharge hose (find in pool supply stores)
This is an easy way to have students carefully consider the characteristics of blood vessels. To set it up, you will need three hoses (or lengths of hose) of three different types: a simple garden hose with fairly thick walls (red?), a soaker hose with mesh walls, and a discharge hose (blue?) such as is used to drain the water from swimming pools. The latter can be ordered from a pool supply company. It will flatten when not full of liquid.
Directions: Simply cut the hoses in lengths of 12 to 18 inches. Each student or small group is then given one of each type of hose. They are asked to decide which best represents a capillary, vein, or artery. There is not one right answer, although some choices may seem more appropriate than others. Students must consider the properties of each type of blood vessel and make reasoned decisions regarding their choices, citing characteristics to back up their reasoning. It might be helpful to allow them to take the hoses to the sink and run water through them.
Arteries are thick-walled vessels that carry oxygenated blood away from the heart. (Exception: the pulmonary arteries carry deoxygenated blood on its way to the lungs.) The arterial walls contain more smooth muscle and elastic fibers than do the walls of the veins. This makes arterial walls thicker and more elastic, so they retain their circular shape in cross-section, even when emptied of blood on the commercially prepared slides your students may view. The walls are thicker than the walls of veins and more contractile. No valves are present.
Veins are vessels that carry deoxygenated blood on its return trip to the heart. (Exception: the pulmonary veins carry oxygenated blood returning to the heart.) In a tissue sample such as those on commercially prepared slides, the emptied veins may collapse and flatten. Valves are present inside the veins. Contraction of the surrounding skeletal muscles also helps to push the blood back to the heart.
Capillaries are very thin-walled vessels with a very small diameter. Some are only 4 microns across. (Compare this to the diameter of the red blood cell: 8 microns!) They are the site of gas exchange and chemical exchange between the blood and the body’s cells. The capillary walls are only one cell thick, being composed simply of epithelium, and oxygen and carbon dioxide can pass through them readily. They exist in capillary beds in all tissues of the body except epithelial tissue.
Blood vessel illustration by National Cancer Institute, National Institutes of Health – http://training.seer.cancer.gov/anatomy/cardiovascular/blood/classification.html, Public Domain, https://commons.wikimedia.org/w/index.php?curid=45154160