Introduction to Blood Vessels

As You Travel…

You travel in a blood vessel away from the heart in the systemic circuitThe part of the circulatory system that carries oxygenated blood from the heart to the body and retu. In this route, you encounter a predictable series of vessels. These include elastic arteriesBlood vessels that carry oxygenated blood away from the heart (except pulmonary arteries, which carr, muscular arteries, and arteriolesSmall arteries that regulate blood flow into capillaries through vasoconstriction and vasodilation. I have capillariesThe smallest blood vessels where gas, nutrient, and waste exchange occurs between blood and tissues. here, but they are really their own category. As you travel from the heart to capillaries, the diameter of the vessel will decrease. However, there are also some structural changes to the artery wall. Most noticeably, there is less smooth muscle of the tunica mediaThe middle layer of a blood vessel, composed of smooth muscle and elastic tissue, responsible for va.  There are also fewer and fewer elastic fibers until there are ultimately none in a capillary. 

Elastic Arteries

Elastic arteries have an incredibly thick wall. As the heart pumps, it increases pressureThe force exerted by gases in the respiratory system, affecting airflow and gas exchange. to 120 mmHg. These elastic arteries don’t want to have a blowout or an aneurysm from all this pressure.  You can’t constrict these arteries, which is strange because there’s so much tunica media? Why is there so much muscle here if I can’t constrict them?  They won’t reduce the diameter of their lumenThe inside space of a hollow organ or structure., but they will construct to control or keep their shape.  These vessels recoil and fill again. As these vessels rebound, they push back against the heart. There is a valve in the heart called the aortic valve, which controlsVariables that remain constant to ensure a fair test. blood leaving the heart to the body. Elastic arteries like your aorta push back on this valve for a split second, and that is what’s called afterload. It’s the pushback.

Muscular Arteries

As you travel from the heart in the systemic circuit, elastic arteries transition to muscular arteries.  These can be referred to as distributing arteries since they distribute blood to specific organs. The renal arteryThe artery that supplies blood to the kidney. that comes off the aorta and brings blood to the kidney would be a distributing artery. During exercise, arterioles can redirect blood away from the stomach and digestive system, ensuring resources are directed to active muscles.  The term muscular arteryMedium-sized arteries with more smooth muscle, allowing them to regulate blood flow through vasocons refers to the very thick tunica media of these arteries.  They, too, have the internal and external elastic laminae, however, they are much less in thickness.

Arterioles

As we travel even farther away from the heart, the muscular arteries transition into arterioles.  These vessels have a relatively thin tunica media and not much smooth muscle compared to their diameter.  Their diameter is small, so small that you could see the red blood cellsThe basic structural and functional units of life. in the lumen and count them.  In muscular arterioes, you can see individual red blood cells, but there would be too many to realistically count. In elastic arteries, all you can see is a pink glob for the red blood cells.

On the picture on the left I have an arterial with its corresponding vein. The picture on the right also shows an arterial and you can see the darkly stained elastic fibers that are just superficialNear the surface of the body. to the simple squamous cells that are lining the lumen

Blood Pressure

Arterioles control blood pressure.  This picture explains how arterioles provide the most resistanceThe opposition to airflow in the respiratory tract, influenced by airway diameter. for blood flow. They are the greatest determinants of blood pressure. On the left side of this capillary bed is an arterial. It is wrapped with some smooth muscle. This muscle controls the flow of blood into this capillary bed. On the right side is the venule. It drains the capillary bed and offers very little resistance. Venules are always a bit larger than their corresponding arterioles.   So shown here are many capillaries that are all fed by 1 arterial.  This reminds me of skiing in the 1980s with my Mom.  I don’t know how things are done now. Back in the 80s, everybody would get in one line to get to a ski lift. As you approached the ski lift, you were sorted. Sorting was based on the number of people in your group. If you were one person, you went this way. If you were two people, you went in this line. If you were three people, you went in this line, and so forth and so on. But it was still a situation and where one big line of skiers was feeding into many smaller lines. This is the same situation with an arterial. One arteriole can feed many capillaries. Compared to the number of capillaries, the number of arterioles in your body is quite small.  This is why arterioles are like a bottleneck to flow.