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Knowledge of the structure and function of blood vessels and other
aspects of the heart and vascular system are essential parts of
training in many therapies, such as Massage (in its many forms,
"Indian Head Massage", "Swedish Massage", "Accupressure
Massage" etc.), Aromatherapy, Acupuncture, Shiatsu, and others.
This page is intended to include the detail required for most Basic
/ First Level Courses in these therapies, and some ITEC Diplomas.
The main types of blood vessels are: Arteries, Arterioles, Capillaries,
Venules, Veins.
These are described and compared on this page.
1. Diagrams
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The following diagram summarises the sequence of blood
flow through the heart, arteries, arterioles, capillaries,
venules, veins, then back to the heart:
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The following diagram summarises the structural differences
between different types of blood vessels. More information
about this also follows in the next section.
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2. Structure and Functions of Blood
Vessels
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Structure
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Functions
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Arteries
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The walls (outer structure) of arteries
contain smooth muscle fibre that contract
and relax under the instructions of the
sympathetic nervous system.
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Transport blood away from the heart;
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Transport oxygenated blood only (except
in the case of the pulmonary artery).
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Arterioles
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Arterioles are tiny branches of arteries
that lead to capillaries. These are also
under the control of the sympathetic nervous
system, and constrict and dialate, to regulate
blood flow.
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Transport blood from arteries to
capillaries;
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Arterioles are the main regulators
of blood flow and pressure.
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Capillaries
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Capillaries are tiny (extremely narrow)
blood vessels, of approximately 5-20 micro-metres
(one micro-metre = 0.000001metre) diameter.
There are networks of capillaries in most
of the organs and tissues of the body. These
capillaries are supplied with blood by arterioles
and drained by venules. Capillary walls
are only one cell thick (see diagram), which
permits exchanges of material between the
contents of the capillary and the surrounding
tissue.
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Function is to supply tissues with
components of, and carried by, the
blood, and also to remove waste from
the surrounding cells ... as opposed
to simply moving the blood around
the body (in the case of other blood
vessels);
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Exchange of oxygen, carbon dioxide,
water, salts, etc., between the blood
and the surrounding body tissues.
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Venules
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Venules are minute vessels that drain blood
from capillaries and into veins. Many venules
unite to form a vein.
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Drains blood from capillaries into
veins, for return to the heart
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Veins
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The walls (outer structure) of veins consist
of three layers of tissues that are thinner
and less elastic than the corresponding
layers of aerteries.
Veins include valves that aid the return
of blood to the heart by preventing blood
from flowing in the reverse direction.
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Transport blood towards the heart;
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Transport deoxygenated blood only
(except in the case of the pulmonary
vein).
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3. Comparison between Arteries
and Veins
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Arteries
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Veins
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Transport blood away from the
heart;
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Transport blood towards the heart;
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Carry Oxygenated Blood
(except in the case of the Pulmonary Artery);
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Carry De-oxygenated Blood
(except in the case of the Pulmonary Vein);
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Have relatively narrow lumens
(see diagram above);
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Have relatively wide lumens (see
diagram above);
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Have relatively more muscle/elastic
tissue;
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Have relatively less muscle/elastic
tissue;
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Transports blood under higher
pressure (than veins);
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Transports blood under lower pressure
(than arteries);
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Do not have valves (except for
the semi-lunar valves of the pulmonary
artery and the aorta).
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Have valves throughout the main
veins of the body. These are to prevent
blood flowing in the wrong direction,
as this could (in theory) return waste
materials to the tissues.
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Further information about the structure
and functions of the heart,
systemic circulation,
and the vascular system generally are included on other pages
of this website. (These are presented separately to minimise
the download-times of image-intensive pages.)
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