<< Chapter < Page Chapter >> Page >

The smooth muscle layers of the tunica media are supported by a framework of collagenous fibers that also binds the tunica media to the inner and outer tunics. Along with the collagenous fibers are large numbers of elastic fibers that appear as wavy lines in prepared slides. Separating the tunica media from the outer tunica externa in larger arteries is the external elastic membrane    (also called the external elastic lamina), which also appears wavy in slides. This structure is not usually seen in smaller arteries, nor is it seen in veins.

Tunica externa

The outer tunic, the tunica externa    (also called the tunica adventitia), is a substantial sheath of connective tissue composed primarily of collagenous fibers. Some bands of elastic fibers are found here as well. The tunica externa in veins also contains groups of smooth muscle fibers. This is normally the thickest tunic in veins and may be thicker than the tunica media in some larger arteries. The outer layers of the tunica externa are not distinct but rather blend with the surrounding connective tissue outside the vessel, helping to hold the vessel in relative position. If you are able to palpate some of the superficial veins on your upper limbs and try to move them, you will find that the tunica externa prevents this. If the tunica externa did not hold the vessel in place, any movement would likely result in disruption of blood flow.

Arteries

An artery    is a blood vessel that conducts blood away from the heart. All arteries have relatively thick walls that can withstand the high pressure of blood ejected from the heart. However, those close to the heart have the thickest walls, containing a high percentage of elastic fibers in all three of their tunics. This type of artery is known as an elastic artery    ( [link] ). Vessels larger than 10 mm in diameter are typically elastic. Their abundant elastic fibers allow them to expand, as blood pumped from the ventricles passes through them, and then to recoil after the surge has passed. If artery walls were rigid and unable to expand and recoil, their resistance to blood flow would greatly increase and blood pressure would rise to even higher levels, which would in turn require the heart to pump harder to increase the volume of blood expelled by each pump (the stroke volume) and maintain adequate pressure and flow. Artery walls would have to become even thicker in response to this increased pressure. The elastic recoil of the vascular wall helps to maintain the pressure gradient that drives the blood through the arterial system. An elastic artery is also known as a conducting artery, because the large diameter of the lumen enables it to accept a large volume of blood from the heart and conduct it to smaller branches.

Types of arteries and arterioles

The left panel shows the cross-section of an elastic artery, the middle panel shows the cross section of a muscular artery, and the right panel shows the cross-section of an arteriole.
Comparison of the walls of an elastic artery, a muscular artery, and an arteriole is shown. In terms of scale, the diameter of an arteriole is measured in micrometers compared to millimeters for elastic and muscular arteries.

Farther from the heart, where the surge of blood has dampened, the percentage of elastic fibers in an artery’s tunica intima decreases and the amount of smooth muscle in its tunica media increases. The artery at this point is described as a muscular artery    . The diameter of muscular arteries typically ranges from 0.1 mm to 10 mm. Their thick tunica media allows muscular arteries to play a leading role in vasoconstriction. In contrast, their decreased quantity of elastic fibers limits their ability to expand. Fortunately, because the blood pressure has eased by the time it reaches these more distant vessels, elasticity has become less important.

Questions & Answers

jaundice causes by when bilirubin blockage of bilary system
mahamed Reply
hi pls what causes jaundice
Umar Reply
where the love feelings emotions and hate lies in the body?
Loving Reply
what is Regional anatomy
Sharon Reply
Please information on dialysis
Agbo Reply
what is the relationship between Clinical officer general, unqualified professionals and traditional healers?
Purity Reply
is that how the microscopic anatomy is
Elizabeth Reply
to understand the structures of the body. to understand how the structures of the body work . To understand how the structures of the body work and support the functions of life.
Dora Reply
procedures that removes waste from body when kidneys dont function properly..
maribel Reply
Want to join
Ordeal
dialysis
kimunya
dialysis is a process to remove extra fluid , impurities and waste product from the blood and to correct electrolytes imbalance such as sodium, potassium and calcium with the help of dialysis machine. when the kidneys can't do their job.
Kishan
what will lead a person to dialysis
Agbo
what's metabolic acidosis
Nana
A condition in which too much acid accumulates in the body. Causes of metabolic acidosis can include buildup of body toxins, kidney failure, and ingestion of certain drugs or toxins, such as methanol or large doses of aspirin. It can be a rare complication of diabetes.
Loving
What is dialisis
Friday Reply
When kidney is not functioning properly than with the help of dialysis blood filtration is occur Or we can say that it is a process through which filtration of blood is done
sonugora
dialysis is a process of removing wastes, excess fluid ,impurities from the blood and to correct electrolytes imbalance such as sodium, potassium and calcium etc with the help of dialysis machine.when the kidney can't do their job.
Kishan
describe anatomical position
Getrude Reply
The erect position of the body with the face directed forward, the arms at the side, and the palms of the hands facing forward, used as a reference in describing the relation of body parts to one another
Jean
Somebody to explain for me the duties of specialist obstetrician
Irene
Definition of an anatomy
Oppong Reply
hy oppong wat course do u offer
Desmond
b pharmacy all subject complete notes
Sayed
the study of the body's structures scientifically
Dora
what is regional anatomy ?
Jharana Reply
regional anatomy - the study of anatomy based on regions or divisions of the body and emphasizing the relations between various structures (muscles and nerves and arteries etc.) in that region.
Noor
it's the scientific study of the body's structures in a particular region of the body, to study and understand how the body's structures in that region work together and the relations between them.
Dora
Regional anatomy is the study of the interrelationships of all of the structures in a specific body region, such as the abdomen. Studying regional anatomy helps us appreciate the interrelationships of body structures, such as how muscles, nerves, blood vessels, and other structures work together to
Loving
together to serve a particular body region
Loving
what is joint
ISHQ Reply
I want to learn English
Hussein
who are you?
carina
joining the academy
Noor
what is gross anatomy ?
Jharana Reply
what is pharynx
Kishan
membrane behind the nose
Oloruntoba
Gross anatomy is the study of anatomy at the visible or (macroscopic) level
Noor
how does blood gets into the heart
Kity
through the inferior and superior vena cava
Oloruntoba
it's the anatomy of complex body structures that can be seen without the aid of a microspe.
Dora
it is the study of large body structures that can be observed without the aid of a microscope
Purity
state factors that affect sterilization (10marks)
Bright
Gross anatomy is the study of anatomy at the visible or (macroscopic) level. The counterpart to gross anatomy is the field of histology, which studies microscopic anatomy.
Loving

Get the best Anatomy & Physiology course in your pocket!





Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Anatomy & Physiology' conversation and receive update notifications?

Ask