Blood vessels can be divided into 3 principal categories:
ARTERIES are the efferent blood vessels of the CVS which carry blood away from the heart;
VEINS are the afferent blood vessels that carry deoxygenated blood back to the heart;
CAPILLARIES are microscopic thin-walled vessels that connect the smallest arteries to the smallest veins.
The artery and vein walls are composed by 3 layers called tunics. The tunica intima lines the inside of the vessel and acts as a selectively permeable barrier to materials entering or leaving the blood stream. The tunica media is the middle layer of the vessel (usually the thickest layer) which consists of smooth muscle, collagen and elastic tissue that help strengthen the vessels and prevent them from rupturing due to the blood pressure, and allows vasoconstriction or vasodilation of the vessels. The tunica adventitia, which is the outermost layer, consists of loose connective tissue that merges with neighbouring blood vessels, nerves or organs.
Arteries are resistance vessels of the cardiovascular system. Their muscular built allows them to retain their round shape even when they are empty. Due to the left ventricle pressure surge, arteries need to be able to resist the blood pressure surge, otherwise they would burst.
There are 3 types of capillaries:
- Continuous capillaries: present in most tissues;
- Fenestrated capillaries: found in kidneys, endocrine glands and small intestine;
- Sinusoids a.k.a. Discontinued capillary: found in the liver, bone marrow and spleen.
Veins are the capacitance vessels of the cardiovascular system. They are relatively thin and flaccid, and collapse when empty. However they are able to expand easily to accomodate blood volume increase. Different type of veins include:
- large veins (such as the vena cava)
- venous sinuses
- medium veins (containing venous valves, usually found in lower limbs)
- muscular venules
- post-vapillary venules
Below you can find a collection of videos that can help provide a more visual approach to Blood Vessels including Arteries, Veins and Capillaries.
blood vessel layers
3 types of capillaries
arteries vs veins
Post-capillary venules
Special thanks to the creators of the featured videos on this post, specifically Youtube Channels Khan Academy Medicine and Khan Academy.
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Claire is keen about public education on health-related subjects as well as holistic patient-centered care. She is also passionate about spreading awareness on the negative effects that domestic abuse leaves on its victims’ mental, emotional, social and physical wellbeing.
Claire aspires to continue studying following completion of her Nursing Degree, because she truly believes in lifelong education.
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