# Blood Vessels --- **Blood vessels** are a part of the [[cardiovascular system]] that [[circulatory system|carry blood]] around. Blood vessels that carry blood *away* from the heart are called [[arteries]] and blood vessels that carry blood *towards* the heart are called [[veins]]. The blood vessels certainly have a very large role in regulating [[blood pressure]] via vasodilation and vasoconstriction, pliability of the vessels (especially the arteries), and even the sheer total length of vessels plays a role. ## Anatomy Although there are many differences in different types of blood vessels, they all share some commonalities. - They are made up of three main layers, or "tunics", which are typically separated by a layer of connective or epithelia tissue - The **tunica externa** is the outer layer - The **tunica media** makes up the middle layer - The **tunica intima** is the innermost layer that blood actually runs past - This layer is also called the **endothelium** which is very smooth so as not to catch the blood and allow to to flow smoothly past. - The **vasa vasorum** are a small network of vessels that oxygenate the tissues of the larger blood vessels. (As far as I can find out they exist only really in the aorta and venae cavae, but I could be wrong there.) Like the heart's [[coronary circulation|coronary vessels]], the tissues of the large vessels can't just **slurp up the blood inside them, and need a specialized source. ## Types of Vessels There are three types of blood vessels; **arteries** that carry blood away from the heart, **veins** that carry blood towards the heart, and **capillaries** where systemic gas exchange occurs. Blood moves from the arteries through the capillaries and into the veins (although capillaries as sometimes bypassed where [[circulatory system|arteriovenous anastomoses]] are activated). >[!health] Do arteries only carry oxygenated blood? Do veins only carry deoxygenated blood? >No! Contrary to common understanding, whether a blood vessel is a vein or an artery does *not* correlate to if the blood *inside* the vessel is oxygenated or not. For example, most blood in the arteries *is* oxygenated, but the blood in the pulmonary *veins* is also oxygenated. > >The important distinction is what *direction* the blood is flowing in the vessels. Arteries move blood away from the heart and veins move blood back towards the heart. This makes more sense as anatomically this distinction is much more relevant than the state of the blood inside the veins. ![[blood vessels.png]] - [[Arteries]] must withstand the pulsing [[blood pressure|hydrostatic pressure]] of the blood being pressed against the vessel walls. Therefore arteries both thicker and stiffer, and more than veins. This allows the vessels to expand during systolic pressure and relax during diastolic pressure. - [[Veins]] do not have nearly as much blood pressure pushing the blood through them, and thus have many features that help the blood actually move through them. Most notably they have internal valves that prevent the back flow of blood. - [[Capillaries]] are small specialized blood vessels that connect arteries and veins, while allowing fluids and nutrients in and out of the surrounding tissue. ## The Great Vessels **Great vessels** are the large vessels that bring blood to and from the heart that are large pretty significant, and predictably located: - The great **veins**: - The **venae cavae** are two great vessels which empty into the [[heart|right atrium]]. - The **superior vena cava** carries blood from the head, neck, arms and chest. - The **inferior vena cava** carries blood from the legs, feet and organs in the abdomen and pelvis. - The **pulmonary veins** empty oxygenated blood into the [[heart|left atrium]]. - The great **arteries**: - The **pulmonary arteries** bring deoxygenated blood out of the [[heart|right ventricle]] and move it towards the lungs. - The **aorta** brings all of the oxygenated blood out of the [[heart|left ventricle]] to the body. ### Vasodilation & Vasoconstriction **Vasodilation** is when blood vessels get more dilated. **Vasoconstriction** is when blood vessels get more narrow. ![[vasodilation and vasoconstriction.png]] ### Length of Blood Vessels Blood vessel **length** is a large factor when determining [[peripheral resistance]]. The longer the blood vessel the greater the friction of the [[blood]] flowing along the [[epithelial tissue|endothelium]]. Blood vessel length increases as we grow to maturity, and also grows when an individual gains weight through [[healing|angiogenesis]]. Conversely the blood vessels can shrink down if an individual looses weight. ## Problems With the Blood Vessels **Vascular diseases** are [[disease|diseases]] that arise in the blood vessels. - [[peripheral arterial disease|PVD]] is an inefficiency of the vessels to carry blood - [[atherosclerosis]] is a type of PVD from buildup of plaque on the lumen of the blood vessels - [[venous thrombosis|deep vein thrombosis]] is a clot that forms in the deep veins, especially in the lower extremities - [[arteriovenous malformations]] are tangles of blood vessels that from instead of capillaries, returning oxygen rich blood to the heart and are prone to rupture due to increased pressure ___