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School

University of Ottawa *

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HSS 2101

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Health Science

Date

Oct 30, 2023

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BLOOD VESSELS The heart pumps blood, but that blood is carried by blood vessels. Let’s review blood vessel types. I’ll describe them, and you try to recall what they’re called. 1.Some blood vessels pump blood away from the heart. What are the largest of these vessels called? - The largest of the vessels that pump blood away from the heart are called arteries. 2.Other blood vessels pump blood toward the heart. What are the largest of these vessels called? - The largest of the vessels that pump blood toward the heart are called veins. 3.The last type of vessel does the work of exchanging gasses and nutrients. What are they called? - These vessels are called capillaries. The work of capillaries is accomplished in capillary beds, wherein nutrients are provided to cells, and gasses are exchanged. Oxygen and nutrients enter the capillaries from arterioles, and carbon dioxide is carried away from capillaries via venules. SYSTEMIC AND PULMONARY CIRCULATION So, you know that blood flow within the heart is simply moving blood from the atria into the ventricles. But, how did it get to the atria, and where does it go from the ventricles? Let’s start with the left side of the heart. Oxygenated blood, fresh from the lungs, enters the left atrium, which, through contraction of the left atrium, empties into the left ventricle. The left ventricle contracts, forcing blood out of and away from the heart, through the aorta. From there it proceeds through arteries, into arterioles, and finally into the capillaries. Within the capillary beds, blood provides oxygen and nutrients to cells and tissues, and takes away carbon dioxide and wastes. From the capillaries, the deoxygenated and waste-laden blood flows into venules, and then to progressively larger vessels that become veins. Blood enters the right atrium via the inferior vena cava and the superior vena cava – the largest veins in the human body. Note that the plural of “cava” is “cavae.” So, collectively, these are “vena cavae.” So far so good – this is called systemic circulation, as it provides blood flow to the entire “system” of the body. But we’re not done yet, because we still have to re-oxygenate that blood! For that, we need pulmonary circulation. In pulmonary circulation, blood is sent to the right ventricle from the right atrium. From the right ventricle, it passes through the pulmonary artery, through pulmonary arterioles, and into capillaries within the lungs (more about that in Lesson 9). Within the lungs, carbon dioxide is exchanged for oxygen. That newly re-oxygenated blood flows through lung venules and into four pulmonary veins that empty into the – you guessed it!! – left atrium, where we return to systemic circulation. Of course, the heart needs blood, too, which it gets from coronary circulation, via coronary arteries that branch off of the aorta. Deoxygenated blood from the heart finds its way back to pulmonary circulation the same way as systemic circulation: venules ⇒ veins ⇒ vena cava ⇒ right atrium.

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