Blood vessels | Types , Structure and regulations of blood flow

Diagram of Blood vessels


Blood vessels

The blood vessels are elastic, muscular tubes  and branching tube – like structure that carry blood in animals . The study of blood vessels  is called angiology .( G. angeion = vessels , logos = study ) . The blood vessels are part of  the cardiovascular system that transport blood throughout  the human body .

  • Who first discovered blood vessels ?

William Harvey was first discovered blood vessels . He was born  in April 1, 1578 in Folkestone ,Kent , England and died in  June 3 ,1657 in London . He was English physician who was the first to recognize the blood circulation in human body and also discovered of  arteries , vein . He is regarded the father of modern physiology .

  • Where are blood vessels located ?

Blood vessels are located in our body parts which are arteries (in redthat carry blood from the heart and  veins in blue ) that return blood in heart .

  •   What do blood vessels do in the body ?      

Flow of blood continuously through blood vessels  around the  human body  .These vessels are do  in the body to carry blood away from the heart and blood from the body back to the heart . 

           Types of blood vessels

  • What are the 5 major blood vessels ?
There are 5 major types of blood vessels i.e Arteries , Arterioles, Capillaries , Venules and Veins .
  1. Arteries carry blood away from the heart for distribution to the body . It contain aerated blood , except the pulmonary arteries . They have thick, elastic walls and narrow lumen . They have no valves in them. They are empty after the death of animal . In arteries their blood has considerable pressure .They are vary in size. The largest arteries have special elastic fibers in their walls .
  2. Arterioles are the smallest arteries in the human body. They deliver blood to capillaries. The arterioles play a key role in regulating blood flow into the tissue capillaries .
  3. Capillaries are smallest blood vessels and are  joined  arteries and veins together . They allow the exchange of nutrients and wastes between the blood and tissue .
  4. Venules is a very small blood vessel in the microcirculation that allows the blood to return from the blood vessels.
  5. Veins  bring blood from the body back to the heart . They contain nonaerated blood , except the pulmonary veins . They have thinner, scarcely elastic walls and wide lumen .They have valves to prevent back flow of blood and to counteract gravity . In vein their blood has low pressure . They contain blood even after the death of the animals .
Blood vessels
Types of Blood vessels

  • What is the biggest or largest blood vessels ? 

Aorta is the biggest blood vessels in human body heart and located in left ventricle of the heart and extending down to the abdomen . The heart pumps blood from the left ventricle into the aorta through the aortic valve . The aorta is most important for human body because it gives the body  access to the oxygen-rich blood it needs to survive.

  • Which blood vessel are the smallest ?

Capillaries are smallest blood vessels and are  joined  arteries and veins together . They allow the exchange of nutrients and wastes between the blood and tissue cells . The diameter of capillaries from 5 to 10 micrometer .

  • Which blood vessel carry blood to the heart ? 

Blood vessels connected to in human body heart are the aorta , the superior vena cava ( a large vein which carry deoxygenated blood from head,neck , upper extremity and thorax and deliver in right atrium and inferior vena cava (a large vein that carry deoxygenated blood from the lower body and deliver in right atrium to the heart  also pulmonary artery (which are carry deoxygenated blood from the heart to the lungs) , pulmonary veins (which  carry deoxygenated blood from the lungs to the heart) .

  • What is difference between Arteries and veins ? 

Arteries carry blood from the heart for distribution to the body whereas Veins bring blood from the body back to the heart.

Arteries blood has considerable pressure whereas Veins blood has low pressure .
Other difference showing in figure – 

Structure of blood vessels

Blood vessels are key components of the systemic and pulmonary circulatory systems that distribute blood throughout the body. There are two major types of blood vessels and it’s structure are explain below –

Artery – 

Wall of an artery is composed of three coats :-
  1. Tunica Interna – It is the inner coat . It further consists of  2 layers : inner endothelium of long ,thin cells resting on a basement membrane , and outer elastic membrane of yellow elastic tissue . Endothelium provides a smooth surface that minimize resistance to the blood flow .
  2. Tunica Media – It is the middle coat. It consists of smooth muscle fibers arranged in a circular manner and mixed with a network of elastic fibers also arranged in a circular manner .
  3. Tunica Externa – It is the outer coat . It consists of loose connective tissue with longitudinally arranged white and yellow fibers . This coat gives strength to and prevent undue expansion of the blood vessels . It is also called tunica adventitia .



 Wall is a vein consist of the same three coats that form the wall of an artery . However , in the wall of a vein , the elastic membrane of tunica Interna is relatively thin , and muscle fibers and elastic fibers in tunica Media are fewer . Therefore , a vein has a thinner and less elastic wall but a wider cavity than artery of the same diameter .
There are valves vin the heart between it’s chamber, at the outlets of major arteries ( aortic and pulmonary arches ) , and at the inlet of major vein ( inferior vena cava ) . The valves act like swing doors to ensure the flow of blood in a single direction . Veins also have to prevent the backflow of the blood .

Regulation of blood flow 

 There is a triple mechanism to regulate the flow of blood to the organs in a closed circulatory intense: arterial musculature , precapillary sphincters and arteriovenous anastomoses .
  1. Arterial Musculature –.                                                                                                                                                                      The small arteries, and especially the arterioles preceding the capillaries, have well muscular walls.  They expand and carry more blood if the organ becomes more active, and contract and send less blood if the organ becomes less active .
  2. Precapillary Sphincters –                                                                                                                                                     The capillary network of each organ has a few “thoroughfare” channels through which blood flows all the time. Other capillaries receive blood only at the time of intense activity of their organ.  These capillaries branch off the arterioles which have muscular precapillary sphincters at their origin. The sphincters open or close to meet the varying metabolic needs of the organ.
  3.   Arteriovenous Anastomoses-                                                                                                                                               In certain regions of the body occur direct arteriovenous connections, which act as short circuit routes between arterioles and venules . These circuits serve to regulate the quantity of blood which flows through the capillary bed according to the needs of the region .                                                                                                                                                                                                                   By varying the amount of blood supply to the organs, maximum use is made of the available blood.  The body does not contain enough blood to supply all the parts of the body fully at the same time.                                                                                 

      At any given time, only about 5-10% of the body’s  capillaries have blood flowing through them.  Capillaries in the brain, heart, kidneys and liver are usually full of blood, but in many other sites, blood supply varies from time to time.  After a meal, a larger quantity of blood is diverted to the alimentary canal . During exercise , blood is diverted from the alimentary canal to the skeleton muscle and skin . This is one reason why heavy exercise just after a big meal may cause indigestion .


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