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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

why the heart is protected with that sac
Joshua Reply
To prevent collision with the lungs, lubricates the heart, protects the heart from infection in the event a peripheral organ is effected, and stabilizes the heart within the mediastinum.
Jeremiah
This app should be updated too much as there is very little information for some topics.I hope you will consider my information....
aman Reply
adenohypophysis is made up of what type of cells and what is the name of those cells?
Mannu Reply
whatpassesthroughmaleovale
armstrong Reply
motor root of the trigeminal nerve
Vandana
what is the nervous system about
Joshua
what passes through foramen ovale?
Farah Reply
what are the organelles of a cell
Amina Reply
muscular system
Vandana
nucleus ribosome Golgi body call membrane cytoplasm
Sabina
these are the cellular components that functions to provide energy,remove waste and cell division
Waziri
Organelles of the cell are: Mitochondria,Ribosome,golgi apparatus, nucleus, secretory granules, nuclear e t c
Khadijah
what are local hormones
Richard
Local hormones are hormones that effect the cell that released them or cells near the releasing cell and they do not circulate within the blood stream.
Jeremiah
the trachea bifurcated into how many branches on the right lung
barbie
three lobes
Richard
Explain the normal flow of blood.
Shikha
how can we maintain the internal living things
Choolwe Reply
how many seconds does a human will stop if you sneeze
Kharl Reply
idk
Erika
1 sec not specific
Jane
1_3seconds
Mannu
physiology of vision
Sudipta Reply
Can pure water become gel like?
ovie Reply
No
Abdulazeez
what is Homeostasis
Laura Reply
It is the ability of an organism to co ordinate it's internal environment so as to achieve balance in all areas
ovie
what is anatomy
Sandra Reply
what is physiology
Sandra
The study of how the body works
Joseph
the branch of biology dealing with the functions and activities of leaving organisms and their parts including all physical and chemical processes
Maria
the study of human body . phicically and chemically it's called anotomy physiology
Raj
the branch of biology dealing with the functions and activities of living organisms
Salman
which vein do we inject to give infusions
Belinda
it is the scientific study of the body structure
Choolwe
What Choolwe Muselitata said is the definition of anatomy
KWAKU
Physiology can also be described as the way in which a living organism or bodily part functions
KWAKU
Anotomy is the science which we humen body of structure and function know as the anotomy
Aman
study of the body funtion and structure
Kaoum
functional study of the body
Mosele
it is the study about the functions of body organs
Mannu
what are the vital sign procedure
jeniffer Reply
You start the TPR then BP after explaining the procedure to the patient and your requirements ready.
Dauda
which type of vein to you inject to give infusions?
Belinda
*do
Belinda
how long do u take radial pulse
Flavian Reply
1 minute
Mannu
You can take it for 15 seconds , the number you got you multiply wth 2
Likius
but in the aspect of the multiplying that isn't right
Sabina
radial pulse kya hai?
OM
?
OM
for more accurate values you must do the 1 minute
Jane
1 minute.
Andrew
60 seconds
Richard
1 minute
Kaoum
yes @sabina
Mannu
What is homeostasis
Winter Reply
Homeostasis is the state of relative stability of the body's environment
Laura
what are fluids
Laura
fluid is a substance that has no fixed shape and yield easily to external pressure
Laura
Difference between hemostasis and homeostasis
Abdulazeez
Hemostasis is blocking or stopping blood flow from a damaged blood vessel by coagulation of that vessel or obstructing it.
Jeremiah
Homeostasis is a balanced state. An equilibrium. The body does this by regulating itself by using hormones and neurotransmitters to keep chemicals balanced within the body.
Jeremiah
Examples of site of homeostasis
Abdulazeez
For example, to much calcium in the blood would stimulate the release of calcitonin from the thyroid gland. Calcitonin will decrease calcium levels by depositing it into the skeleton. This is known as bone deposition, a homeostatic mechanism. Parathyroid hormone is the opposite to calcitonin.
Jeremiah
There are a lot of homeostatic mechanisms in the body. Insulin and glucagon is another one. These two regulate glucose (sugar) levels in the blood. High glucose levels would cause insulin from the pancreas beta cells. Insulin lowers blood sugar. Glucagon increases blood sugar
Jeremiah

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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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