Who doesn’t love the Grinch? It’s a Christmas classic, but if you haven’t seen it, it’s about this entity living on top of a mountain who manages to steal an entire town’s Christmas decor in one night (impressive honestly). But then he learns the true meaning of Christmas (presents, obviously) (jk), causing his tiny little heart to grow three sizes in one day. As sweet as that is, the Grinch should probably go see a cardiologist, because an enlargedheartcan indicate a serious medical condition going on somewhere else in your body. We only bring him up because today we’re going to talk a little bit about the heart in this study guide. More specifically, we’re going to talk about the network of tubes it uses to deliver blood to your organs, muscles, and tissues to keep them alive and healthy–blood vessels!
What are Blood Vessels?
Blood vessels, along with the heart, are part of the Cardiovascular System, the organ system that carries oxygen, nutrients, and hormones to your cells while removing waste like carbon dioxide from your body.
The heart has four chambers: the left atrium, right atrium, left ventricle, and right ventricle. The right side of your heart collects deoxygenated blood from your body and sends it to the lungs, where it is reoxygenated and delivered to the left side of your heart which pumps it back into your body again.
Blood vessels are basically the network of pipes in your body that transport blood to and from your heart. There are three types: Arteries, Veins, and Capillaries. Arteries are the biggest, and capillaries are the smallest. These blood vessels differ not only in size, but also function. Let’s explore them below.
Arteries are the biggest kind of blood vessel in the circulatory system. Their main job is to deliver oxygen-rich blood from the heart to the rest of your body, which they do primarily through the largest blood vessel in the body, the aortic artery (or the Aorta). Because they connect directly to the heart, they have to withstand higher blood pressure than the other types of blood vessels, making them super thick comparatively.
Arteries connect directly to the capillaries, aka the smallest type of blood vessel. To make this transition, they branch into smaller and smaller tubes, the smallest of which are called Arterioles. In a process called Capillary Exchange, the arterioles transfer oxygen and nutrients from the blood to the capillaries which then deliver them to the rest of your body tissues.
Arteries are composed of three layers: the tunica externa, the tunica media, and the tunica intima. These layers surround the lumen, the inner space of the artery where blood flows through (like the hole in a straw).
See the 3D model below to visualize all three of these layers as we go through them (note that the graphic is red–this indicates that the blood is oxygenated and moving away from the heart to the rest of the body)
The Tunica Externa is the outermost layer. It’s made of elastic fibers and connective tissue and gives structural support to blood vessels.
The tunica externa surrounds the Tunica Media, which is made of smooth muscle fibers that help the vessels relax during vasodilation and contract during vasoconstriction (which basically just means that they widen and narrow the blood vessel to keep blood moving through you in between your heartbeats).
The innermost layer is the Tunica Intima. It’s surrounded by a thin layer of smooth tissue called the Endothelium, which allows blood to flow smoothly through the vessel.
Veins are the blood vessels that bring all of the oxygen-depleted blood your body’s already used back to your heart. Like arteries, they also have a tunica externa, media, and intima. But because they don’t have to withstand high blood pressure, their vessel walls are slightly thinner.
See the 3D model below to visualize all three of a vein (note that the graphic is blue–this indicates that the blood is deoxygenated and moving toward from the heart from the rest of the body)
Veins connect directly to the capillary bed. To do so, they start as Venules–super small veins that collect carbon dioxide and waste products from the capillaries via diffusion and eventually converge together to form veins.
Capillaries are the smallest type of blood vessel in the body. And when we say small, we mean SMALL, as in their walls are literally only one cell thick. If they were any bigger, they wouldn’t be able to exchange gases, nutrients, and waste between your tissue cells and your blood cells during capillary exchange via the venules and arterioles we were talking about earlier.
The cardiovascular system carries oxygen, nutrients, and hormones to your cells while removing waste like carbon dioxide from your body. It is composed of the blood vessels and the heart.
The heart has four chambers: the left atrium, right atrium, left ventricle, and right ventricle.
There are three types of blood vessels: arteries, veins, and capillaries.
Arteries deliver oxygen-rich blood from the heart to the rest of the body. They branch into arterioles, which transfer oxygen and nutrients from the blood to your capillaries which deliver them to your body tissues.
Veins bring oxygen-depleted blood from your body tissues back to your heart. They connect to the capillaries through small blood vessels called venules which converge to form veins.
Both arteries and veins are composed of a tunica externa, tunica media, and tunica intima.
Capillaries are the smallest blood vessel and the site of gas exchange. They connect to the arteries via arterioles, and to the veins via venules.
1. What are the 3 types of blood vessels?
Arteries , veins, and capillaries.
2. What are venules?
Small veins that exchange carbon dioxide and waste with the capillaries that converge together to form veins.
3. What type of blood vessel do arteries branch into?
4. What are the 3 functions of blood vessels in the circulatory system?
Transporting oxygen and carbon dioxideTransporting nutrientsCollecting waste from the body’s tissues
5. What is the largest blood vessel in the body?
6. What three layers make up arteries and veins?
The tunica externa, a connective tissue layer on the outsideThe tunica media, a middle band of smooth muscleThe tunica intima, a membranous layer of tissue on the inside
7. Which are the two largest veins in the body?
The superior vena cava, which carries the blood from the upper half of the body to the heart.The inferior vena cava which carries the blood from the lower half of the body to the heart.
We hope you enjoyed studying this lesson and learned something cool about Blood Vessels! Join our Discord community to get any questions you may have answered and to engage with other students just like you! Don’t forget to download our App to experience our fun, VR classrooms – we promise, it makes studying much more fun! 😎
Structure And Function of Blood Vessels. https://www.brainkart.com/article/Structure-And-Function-of-Blood-Vessels_21083/. Accessed 25 Nov, 2021.
Blood Vessels. https://flexbooks.ck12.org/cbook/ck-12-biology-flexbook-2.0/section/13.25/primary/lesson/blood-vessels-bio/. Accessed 25 Nov, 2021.
Your Viens. http://secondscount.org/heart-resources/heart-resources-detail-2/your-veins-2. Accessed 25 Nov, 2021.