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What are Blood Vessels? Types, Structure, & Functions

Updated on February 10, 2017

Blood vessels are hollow tubes that circulate blood throughout the body. They carry oxygen, nutrients and hormones to the different parts of the body.

The blood that is pumped out by the heart is circulated throughout the body. The circulated blood is then returned back to the heart. The blood vessels help in the smooth and continuous circulation of the blood throughout the body.

The body has roughly around 62,000 miles of blood vessels. The length of the blood vessels when placed end to end will go around the earth two and half times.

Source

Types of Blood Vessels

There are three types of blood vessels -

  • arteries
  • veins
  • capillaries

They form an important part of the circulatory system.

Structure and Function of Arteries

Arteries carry oxygenated blood from the hearts to different parts of the body. The arteries divide into smaller branches called arterioles and the arterioles further break up into smaller branches called capillaries.

Each artery is a tube that is lined by three layers of tissues.

  • tunica adventia – the outermost layer, made up of connective tissues that attach the artery to the adjacent tissues
  • tunica media – is the middle layer that helps the arteries to withstand the high pressure of blood pumped out by the heart and is made up of muscles
  • tunica intima – the innermost layer called the endothelium that is lined by smooth endothelial cells

The largest artery is the aorta that originates from the left ventricle of the heart and carries oxygenated blood. The aorta further branches off into the artery, arterioles and capillaries that supply blood to the surrounding tissues.

Another artery called the pulmonary artery carries deoxygenated blood from the heart to the lungs to be replenished with oxygen.

All arteries carry oxygenated blood. The only exception is the pulmonary artery that carries deoxygenated blood.

The pulmonary artery branches off from the right ventricle and further divides into the left and right pulmonary arteries that enter the left and the right lungs respectively.

Structure of a Vein
Structure of a Vein | Source

Structure and Function of Veins

Veins are blood vessels that carry deoxygenated blood from the different parts of the body back to the heart.

The deoxygenated blood appears to be a darker shade of red due to the lack of oxygen in the blood that flows through the veins.

The largest vein in the body is called the vena cava. Vena cava in Latin means a hollow vein. Vena cava starts and ends with the right ventricle of the heart.

The vena cava branches off into two sections -

  • the superior vena cava
  • the inferior vena cava.

Superior vena cava - the superior vena cava runs above the heart and brings back deoxygenated blood from the head, neck, chest and hands back to the heart.

Inferior vena cava - the inferior vena cava runs below the heart and brings back blood from all the other parts of the body back to the heart.

The structure of a vein is similar to the structure of the artery. The vein has three layers just like the artery -

  • tunica adventia – the outermost layer, made up of loose fibrous connective tissues that attach the artery to the adjacent tissues
  • tunica media – the middle layer is made up of smooth muscles
  • tunica intima – the innermost layer lined by smooth endothelial cells

The difference is that the wall of the veins are not elastic in nature and are thinner when compared to the arteries. This is because the veins do not face the pressure of the blood pumped out by heart.

When the blood is returned to the heart through the veins, the blood has to flow against gravity. The valves present in the veins prevent the blood from flowing backwards,

The vein further divides into small branches called venules.

Capillaries
Capillaries | Source

What are capillaries?

Capillaries are the smallest of all the blood vessels running through the body. They form the network between the arteries and veins.

The capillaries have thin walls so that the surrounding tissues can easily absorb the oxygen and other substances from the blood.

The thin wall also helps the capillaries to absorb deoxygenated blood and other waste materials from the surrounding tissues.

Function of the capillaries -

  • to distribute oxygenated blood from the arterioles to the surrounding tissues
  • to collect deoxygenated blood from the venules and feed it to the veins to be carried back to the heart

Capillaries form the network between arteries and veins
Capillaries form the network between arteries and veins | Source
Types of Capillaries
Types of Capillaries | Source

Types of Capillaries

There are three types of capillaries in our body –

  • continuous
  • fenestrated
  • sinusoidal

Continuous capillaries have cells that have smooth lining without any perforations. These capillaries are tightly packed and allow only small molecules to enter and exit the cells. These capillaries are found in the central nervous system, muscles and skin.

Fenestrated capillaries have tiny pores called fenestra. These capillaries allow small molecules along with a few nutrients to enter and exit. Fenestrated capillaries are found in the kidneys, pancreas and intestines.

Sinusoidal capillaries do not have the regular cylindrical shape like the other capillaries. They are irregular in shape and are found in organs such as the liver, spleen, bone marrow and some parts of the endocrine system. The sinusoidal capillaries can also have perforations on their wall.


To Summarize

Blood vessels transport blood, oxygen, hormones and other nutrients throughout the body. The blood vessels are of three different types - arteries, veins and capillaries.

The artery divides into small branches called arterioles, and the veins divide into small branches called venules.

The arteries carry oxygenated blood along with hormones and other nutrients to the different parts of the body.

The veins carry deoxygenated blood along with waste materials from the different parts of the body back to the heart.

The capillaries form the network between the arteries and veins. The capillaries distribute oxygenated blood from the arterioles to the surrounding tissues. They also transfer the deoxygenated blood from the surrounding tissues into the venules so that it can be sent back to the heart through the veins.

The blood vessels ensure the smooth and continuous distribution of blood throughout the body.

References

http://www.udel.edu/biology/Wags/histopage/vascularmodelingpage/circsystempage/capillaries/capillaries.html

http://www.uic.edu/classes/bios/bios100/lecturesf04am/lect20.htm

http://www.medicinenet.com/script/main/art.asp?articlekey=2622


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    • Jodah profile image

      John Hansen 20 months ago from Queensland Australia

      Top class hub Vellur! I knew about arteries, veins and capillaries but not all the specific details. Very thorough and interesting. Thank you for sharing.

    • whonunuwho profile image

      whonunuwho 20 months ago from United States

      Very well prepared and most interesting article for all to read. Thank you for sharing this.whonu

    • billybuc profile image

      Bill Holland 20 months ago from Olympia, WA

      Well the title didn't lie...those were very interesting facts about blood vessels. Thanks for sharing them...great informational hub.

    • FlourishAnyway profile image

      FlourishAnyway 20 months ago from USA

      Lots of excellent, useful detail here. I didn't know there were different types of capillaries.

    • BlossomSB profile image

      Bronwen Scott-Branagan 20 months ago from Victoria, Australia

      Thanks for an interesting and informative article, with great illustrations that help our understanding. I knew a lot of this, but some was new, and it's always good to refresh our knowledge of things like this. too.

    • always exploring profile image

      Ruby Jean Fuller 20 months ago from Southern Illinois

      This is a very good piece on the circulatory system. You explain in detail the way blood is circulated throughout the body. I felt like I was back in anatomy in my first year of nursing training. Well done!

    • Vellur profile image
      Author

      Nithya Venkat 20 months ago from Dubai

      Jodah thank you for stopping by and am glad you found this interesting.

      whounwho thank you for reading and leaving a comment.

      billybuc thank you for reading and leaving a comment.

      FlourishAnyway thank you for your visit and yes there are different types of capillaries.

      BlossomSB thank you for reading and leaving a comment. It is always great to recollect and refresh!

      always exploring thank you, am so happy my hub took your back to your nurse training days!

    • Ruchira profile image

      Ruchira 20 months ago from United States

      A thorough post, Nithya :)

      It could serve as a research material for kids trying to learn the subject.

      My son will be learning about it in the coming months...gotta book mark it!

    • Vellur profile image
      Author

      Nithya Venkat 20 months ago from Dubai

      Ruchira thank you and I sure hope this post helps your son to learn.

    • teaches12345 profile image

      Dianna Mendez 20 months ago

      62000 miles of blood vessels? That is amazing! I have to say this was not only informative but beautifully illustrated with meaningful application.

    • Vellur profile image
      Author

      Nithya Venkat 20 months ago from Dubai

      teaches12345 thank you for your visit and for your appreciation.

    • ChitrangadaSharan profile image

      Chitrangada Sharan 20 months ago from New Delhi, India

      Very interesting and informative hub about blood vessels that all of us must know!

      Reminds me of my school Biology lessons. Well researched and well presented.

      Thank you for sharing! Sharing on HP!

    • Vellur profile image
      Author

      Nithya Venkat 20 months ago from Dubai

      ChitrangadaSharan thank you for your visit and comments. Thanks for the share too, much appreciated.

    • annart profile image

      Ann Carr 20 months ago from SW England

      I was never very keen on biology and we had a very boring teacher, therefore I learnt very little in those lessons. It is an interesting subject and now I wish I knew more about it.

      If I'd had this hub back then, I'd be fine and would've learnt so much more! Shame the teachers couldn't make it as interesting nor as informative.

      Thank you!

      Ann

    • Vellur profile image
      Author

      Nithya Venkat 20 months ago from Dubai

      annart thank you for your appreciation and lovely comments. You made my day!

    • AliciaC profile image

      Linda Crampton 20 months ago from British Columbia, Canada

      Thank you for sharing all the information about blood vessels, Vellur. This is a useful and interesting hub!

    • Vellur profile image
      Author

      Nithya Venkat 20 months ago from Dubai

      AliciaC thank you for your visit and comments. Blood vessels form an amazing network in the body system.

    • Frank Atanacio profile image

      Frank Atanacio 20 months ago from Shelton

      very concise and easy to follow .. awesome post

    • Vellur profile image
      Author

      Nithya Venkat 20 months ago from Dubai

      Frank Atanacio thank you.

    • Faith Reaper profile image

      Faith Reaper 20 months ago from southern USA

      Hi Vellur,

      Excellent hub here, full of a lot of useful information and well-presented too!

      The human body is simply amazing ...

      Thank you for this informative hub.

      Blessings

    • AudreyHowitt profile image

      Audrey Howitt 20 months ago from California

      What an informative Hub! Well done!!

    • Vellur profile image
      Author

      Nithya Venkat 20 months ago from Dubai

      Faith Reaper thank you, oh yes the human body is really amazing.

      AudreyHowitt thank you for your visit and comment.

    • DDE profile image

      Devika Primić 20 months ago from Dubrovnik, Croatia

      I Tweeted and a great read.

    • Vellur profile image
      Author

      Nithya Venkat 20 months ago from Dubai

      DDE thank you for your visit and tweet, much appreciated.

    • ocfireflies profile image

      ocfireflies 19 months ago from North Carolina

      With my dad just recently undergoing open-heart surgery-100% blockage in main right artery and 80% blockage in main left artery, I found this hub extremely fascinating and wished I could have read it prior to my dad's surgery for I know it would have been very helpful. Nice work my friend.

      Blessings,

      Kim

    • Vellur profile image
      Author

      Nithya Venkat 19 months ago from Dubai

      ocfireflies thank you. I hope your dad is okay now, take care.

    • suzettenaples profile image

      Suzette Walker 19 months ago from Taos, NM

      Very interesting and thorough hub. I didn't realize all this information about arteries, veins and capillaries. What a great overview of the human body and I enjoyed reading this.

    • Vellur profile image
      Author

      Nithya Venkat 19 months ago from Dubai

      suzettenaples thank you for your visit and am glad you enjoyed.

    • Jackie Lynnley profile image

      Jackie Lynnley 19 months ago from The Beautiful South

      Amazing facts. I think it is so great we are educating ourselves and learning so much about our own bodies. I think it puts many doctors on guard to have to shape up instead of trying to pass us on to other appointments time after time where it is all about money instead of doing something for us.

      There are some good doctors but there are many I know personally that will let you go years without even trying to help you. So hooray for learning all we can! Hooray to you for taking part in helping.

    • Vellur profile image
      Author

      Nithya Venkat 19 months ago from Dubai

      You are so right. Thank you for your appreciation and for sharing your views with us. Much appreciated.

    • MartieCoetser profile image

      Martie Coetser 18 months ago from South Africa

      I remember learning this decades ago, and here I still find the facts about blood vessels fascinating. "The body has roughly around 62,000 miles of blood vessels" - This is absolutely amazing.

      Thanks for refreshing my memory, Vellur :)

    • Vellur profile image
      Author

      Nithya Venkat 18 months ago from Dubai

      MartieCoetser thank you for stopping by. 62,000 miles is amazing!

    • AudreyHowitt profile image

      Audrey Howitt 18 months ago from California

      Just sending this great hub around again!

    • Vellur profile image
      Author

      Nithya Venkat 18 months ago from Dubai

      AudreyHowitt thank you for the visit and share, much appreciated.

    • vocalcoach profile image

      Audrey Hunt 14 months ago from Nashville Tn.

      What an amazing hub! I enjoy learning about my body. Knowing that my blood vessels reach 2 1/2 times around the earth just blows my mind. You've done a terrific job here. Thanks and sending good thoughts your way.

      Audrey

    • Vellur profile image
      Author

      Nithya Venkat 14 months ago from Dubai

      Audrey (v0calcoach) thank you and am glad you enjoyed reading, sending good thoughts to you all the way from Dubai.

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