Blood Vessels
Note: The structure and function of the heart and other aspects of the vascular system is part of training in therapies such as massage incl. Indian Head Massage, Swedish Massage, acupressure massage, aromatherapy, acupuncture, shiatsu, and others.
This page is intended to include information suitable for most basic (first level) courses in these therapies,
and some ITEC Diplomas.
The main types of blood vessels are:
These are described and compared on this page.
1. Diagrams
The following diagram summarises the sequence
of blood flow through the heart, arteries,
arterioles, capillaries, venules, veins,
then back to the heart:
The following diagram summarises
the structural differences between different
types of blood vessels.
More information about this also follows
in the next section.
2. Structure and Functions of Blood Vessels
|
Structure |
Functions |
Arteries
 |
The walls (outer
structure) of arteries contain
smooth muscle fibre that contract
and relax under the instructions
of the sympathetic nervous system. |
- Transport
blood away from the heart
- Transport
oxygenated blood only
(except in the case of
the pulmonary artery).
|
|
Arterioles |
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. |
- Transport
blood from arteries to
capillaries
- Arterioles
are the main regulators
of blood flow and pressure.
|
|
Capillaries |
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. |
- Function is to supply the tissues of the body with the components of blood, 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)
- Exchange
of oxygen, carbon dioxide,
water, salts, etc., between
the blood and the surrounding
body tissues.
|
|
Venules |
Venules are
minute vessels that drain blood
from capillaries and into veins.
Many venules unite to form a
vein. |
|
|
Veins
|
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. |
- Transport
blood towards the heart.
- Transport
deoxygenated blood only
(except in the case of
the pulmonary vein).
|
|
3. Comparison between Arteries and Veins
| |
Arteries |
Veins |
|
- Transport
blood away from the
heart
- Carry Oxygenated Blood
(except in the case of the
Pulmonary Artery)
- Have relatively narrow lumens (see
diag above)
- Have relatively more muscle/elastic
tissue
- Transports
blood under higher pressure (than veins)
- Do not
have valves (except for
the semi-lunar valves of the
pulmonary artery and the aorta).
|
- Transport
blood towards the heart
- Carry De-oxygenated Blood
(except in the case of the
Pulmonary Vein)
- Have relatively wide lumens (see diag
above)
- Have relatively less muscle/elastic
tissue
- Transports
blood under lower pressure
(than arteries)
- 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.
|
|
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.
|
