Wednesday, April 8 Lecture

Wednesday’s lecture covered several topics of the cardiovascular system. We covered arteries (which carry blood away from the heart) and veins (which carry blood towards heart). Capillaries exchange carbon dioxide and oxygen and wastes and nutrients. Portal systems are two capillary networks, in which the first exchanges substances and the second exchanges wastes and gases. We also discussed the layers of blood vessels such as the tunica externa, tunica media, and tunica interna. The remainder of the class comprised of learning the locations of various important blood vessels. We covered such topics as the blood flow to and from the brain, the coronary circuit, the pulmonary circuit, the blood vessels of the thorax, the branches of the abdominal aorta, and the blood flow to the lower extremities.

The topic of anatomical redundancy explains how there are multiple blood routes to major organs. This allows for blood to remain flowing to the specific organ in case there is a blockage in one of the routes. For example blood to the brain is delivered via the vertebral arteries through the subclavian arteries as well as the internal carotid artery from the common carotid arteries. I wondered if, because of this dual-pathway of blood to the brain, if a slight blockage could occur in one of the pathways and a person could continue living as normal. Also, if a slight blockage would occur, could the other path have more blood pumped through it to make up the difference? With the help of Ms. Peterson and a few web sources I found that this in fact could happen. As we know there are two routes leading into the Circle of Willis. In fact, “as long as the Circle of Willis can maintain blood pressure at fifty percent of normal, no infarction or death of tissue will occur in an area where a blockage exists.” “Sometimes, an adjustment time is required before collateral circulation can reach a level that supports normal functioning; the communicating arteries will enlarge as blood flow through them increases. In such cases, a transient ischemic attack may occur, meaning that parts of the brain are temporarily deprived of oxygen.” I found it quite interesting that the body can make such adjustments, even in such a critical area such as the brain.