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By the end of this section, you will be able to:
  • Compare and contrast the three tunics that make up the walls of most blood vessels
  • Distinguish between elastic arteries, muscular arteries, and arterioles on the basis of structure, location, and function
  • Describe the basic structure of a capillary bed, from the supplying metarteriole to the venule into which it drains
  • Explain the structure and function of venous valves in the large veins of the extremities

Blood is carried through the body via blood vessels. An artery is a blood vessel that carries blood away from the heart, where it branches into ever-smaller vessels. Eventually, the smallest arteries, vessels called arterioles, further branch into tiny capillaries, where nutrients and wastes are exchanged, and then combine with other vessels that exit capillaries to form venules, small blood vessels that carry blood to a vein, a larger blood vessel that returns blood to the heart.

Arteries and veins transport blood in two distinct circuits: the systemic circuit and the pulmonary circuit ( [link] ). Systemic arteries provide blood rich in oxygen to the body’s tissues. The blood returned to the heart through systemic veins has less oxygen, since much of the oxygen carried by the arteries has been delivered to the cells. In contrast, in the pulmonary circuit, arteries carry blood low in oxygen exclusively to the lungs for gas exchange. Pulmonary veins then return freshly oxygenated blood from the lungs to the heart to be pumped back out into systemic circulation. Although arteries and veins differ structurally and functionally, they share certain features.

Cardiovascular circulation

This diagram shows how oxygenated and deoxygenated blood flow through the major organs in the body.
The pulmonary circuit moves blood from the right side of the heart to the lungs and back to the heart. The systemic circuit moves blood from the left side of the heart to the head and body and returns it to the right side of the heart to repeat the cycle. The arrows indicate the direction of blood flow, and the colors show the relative levels of oxygen concentration.

Shared structures

Different types of blood vessels vary slightly in their structures, but they share the same general features. Arteries and arterioles have thicker walls than veins and venules because they are closer to the heart and receive blood that is surging at a far greater pressure ( [link] ). Each type of vessel has a lumen    —a hollow passageway through which blood flows. Arteries have smaller lumens than veins, a characteristic that helps to maintain the pressure of blood moving through the system. Together, their thicker walls and smaller diameters give arterial lumens a more rounded appearance in cross section than the lumens of veins.

Structure of blood vessels

The top left panel of this figure shows the ultrastructure of an artery, and the top right panel shows the ultrastructure of a vein. The bottom panel shows a micrograph with the cross sections of an artery and a vein.
(a) Arteries and (b) veins share the same general features, but the walls of arteries are much thicker because of the higher pressure of the blood that flows through them. (c) A micrograph shows the relative differences in thickness. LM × 160. (Micrograph provided by the Regents of the University of Michigan Medical School © 2012)

Questions & Answers

Process of bone healing
Thelma Reply
The fractured bones are brought closer (reduction of fracture). the fibroblast cells at broken ends divide rapidly and secrete collagen that forms collar of callus. The callus holds the bones together which slowly clacifies (remodelling) and later replaced by bone tissue.
Biplav
what is the name of the two subunits of L chain of a antibody structure
Arshi Reply
The pituitary gland lies in the
Aamir Reply
bony cavity,sella tursica
Arshi
how does endochrondral ossification start in short bones?
Steven Reply
the chondroblast cells forms a cartilaginous bone model which becomes calcified in mid region and is innervated by perosteal capillaries. These capillaris replaces cartilages with bone tissue.
Biplav
what is RH blood group
kuukyile Reply
It is a type of system for classifying blood groups according to the presence or absence of the Rh antigen.
Rakshith
What is the most important organ in the human body?
Gbemi Reply
the heart
Phodiso
or brain
Phodiso
Why?
Gbemi
heart
Kelly
the brain specifically is referred to as the control centre ..all nerve impulses are send to the brain which stimulates other specific parts of the body
Phodiso
please if l am Blood group B+ can l marry a lady with O- blood group?
kuukyile
structure of a serous membrane
Ziyanda Reply
are you asking?
Isa
yes
MOHD
In anatomy, serous membrane (or serosa) is a smooth tissue membrane consisting of two layers of mesothelium, which secrete serous fluid. The inner layer that covers organs (viscera) in body cavities is called the visceral membrane. A second layer of epithelial cells of the serous membrane, called th
Isa
The two layers of serous membranes are named parietal and visceral. Between the two layers is a thin fluid filled space.[2] The fluid is produced by the serous membranes and stays between the two layers to reduce friction between the walls of the cavities and the internal organs when they move with
Isa
a continuation from the 1st one:: A second layer of epithelial cells of the serous membrane, called the parietal layer, lines the body wall. Between the two layers is a potential space, mostly empty except for a few milliliters of lubricating serous fluid that is secreted by the two serous membranes
Isa
Lubricated secretion of skin is called sebum
Jazil
haematopoietic
oyewale
what is the greater tronchanter?
Phodiso
the greater trochanter is  femur is a large, irregular, quadrilateral eminence and a is a part of the system of the skeleton
Jessie
Thanks Jessie...
Phodiso
what is the easiest way to learn labels of Anatomical structures?
Phodiso
Name the two phases of metabolism
Grace Reply
reproduction and growth
Zozo
how about anabolism and catabolism?
Japhar
In Simply Anabolism means formation... Catabolism means breakdown
Jazil
two phases of reproductio?
Japhar
Anabolism indicates potential & catabolism potential converts to kinetic
Doctor
Name the most important life process in the human body in terms of anatomy and physiology
Grace
Nervous system
Nimco
Every system is important for body functions
Jazil
what is the difference between the functions of the adhesion belt and the desmosomes?
Mason Reply
what are the derivatives of the germ layer?
Miriam Reply
zygote
Zozo
Pls explain the atlas of the cervical vertebral column
Ifunanya Reply
why does the material not allow in mri
Simran Reply
what do you mean 'mri'
Nimco
short for magnetic resonance imaging. "the researchers used MRI to record the brain activity" a medical examination performed using magnetic resonance imaging. "he's having an MRI to determine the extent of the injury" an image obtained by magnetic resonance imaging. "after looking at the MRI, the d
Riyaz
what is the meaning of sutures
Ibrahim Reply
i do not know
Nimo
immovable joints btn two bones.eg the skull bones
Japhar
Really,it's true
Nimco
Sutures are immovable junction between two bones e.g those of the skull
Surphy
what should I do to get or to know what to do for me to be excellent in the course of anatomy and physiology
Sandra Reply
study harder
Japhar
Between the heart and the Brain which one is more important to human being... discuss
Faith Reply
well the brain is important for motor skills, the heart is important for involuntary muscle movement supporting body functions. the body can survive without brain involvement, but the body cannot last without the heart
john
granted the heart is important, but the brain gives the body purpose
john
the brain is more important
Kevin
why?
john
brain
tracey
Even though the brain helps the human being to behave normally and purposefully, I think the heart is much more important cos human being cannot live without the heart
Dzifa
why?
john
change the question
Bind
hello guys
Kevin
heart
Kevin
it is difficult to select which organ is more important, now you can replace the heart with a mechanical device and the body could still function, and with technology today brain activity can also be replicated. But life would not be the same
john
there's coordination btn the two..so without any of them no life
Japhar
the heart
The brain is important to humans.
Zozo

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Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
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