BIOS 255
(EDAPT WEEK 3)
Anatomy & Physiology III course with a lab
,EDAPT WEEK 3
Arteries, Capillaries, and Veins
We previously discussed the different structures of the heart and learned
about the flow of blood to and from the lungs. This was our introduction to a
few of the major vessels including the pulmonary artery and veins. We will
now begin comparing and contrasting what it means to be an artery, a vein,
and a capillary.
Arteries are vessels that transport blood away from the heart towards the
capillaries. These vessels are typically oxygen rich.
Veins are vessels that drain blood from the capillaries and transport
it towards to the heart. These vessels are typically oxygen poor.
Capillaries are microscopic vessels that allow for the exchange of
substances between the blood and tissues.
The Three Tunics
Each of the major blood vessels consist of 3 layers of tissues known as
tunics.
The tunica intima (interna) consists of a layer of simple squamous
epithelium bound to a subendothelial layer of areolar connective tissue.
The tunica media consists primarily of smooth muscle with a framework of
elastic connective tissue.
,EDAPT WEEK 3
The tunica externa (adventitia) consists of areolar connective tissue with
elastic and collagen fibers.
The major structural differences between the vessels include:
The tunica media will be thicker in the arteries than veins as they will
need to supply more pressure to the blood.
Veins and venules are the only blood vessels that contain valves to
prevent back flow.
Capillaries are only composed of a layer of endothelium and a
basement membrane.
Structure and Function of the Specific Arteries
With this understanding of the layers of the vessels, we can take a closer
look at some of the different types of blood vessels. Of all of the blood
vessels of the body, the arteries are the strongest and, in some cases, the
most elastic. Arteries can be subdivided into two categories, the elastic
arteries and the muscular arteries.
The elastic arteries are the largest arteries (2.5-1.0 cm in diameter) that
conduct blood from the heart to the more distant muscular arteries. The
tunica media consists of large portion of elastic fibers and less smooth
muscle than other classes of arteries. These vessels stretch to
, EDAPT WEEK 3
accommodate blood being ejected from the left ventricle and the elastic
fibers help them ‘rebound’ to their original diameter, smoothing out pulsatile
blood flow (more on this later).
Vasoconstriction and Vasodilation
Another crucial function of the arteries is to
influence which regions of the body blood will
reach. The sympathetic nervous system
diverts blood flow to skeletal muscles, heart,
and lungs rather than the kidneys and GI
tract. To ensure blood makes it to where it
needs to be, the blood vessels can either dilate
or constrict.
Vasodilation results in an increase in the
diameter of the lumen of a blood vessel in
order to allow for greater blood flow to a
specific body region. Vasodilation is
accomplished by inhibiting, or relaxing, the
smooth muscle of the tunica media.
Vasoconstriction decreases the diameter of
the lumen of a blood vessel and is achieved by
contracting the smooth muscle of the tunica
media. This constriction of a blood vessel’s lumen lessens blood flow to a
specific body region downstream to that vessel.
The control of contraction and relaxation of the smooth muscle in these
vessels is conducted by the vasomotor center in the brainstem. The degree
of contraction can be modified leading to vasodilation and vasoconstriction
of vessels and is greatly influenced by the sympathetic nervous system
(sympathetic motor tone).
(EDAPT WEEK 3)
Anatomy & Physiology III course with a lab
,EDAPT WEEK 3
Arteries, Capillaries, and Veins
We previously discussed the different structures of the heart and learned
about the flow of blood to and from the lungs. This was our introduction to a
few of the major vessels including the pulmonary artery and veins. We will
now begin comparing and contrasting what it means to be an artery, a vein,
and a capillary.
Arteries are vessels that transport blood away from the heart towards the
capillaries. These vessels are typically oxygen rich.
Veins are vessels that drain blood from the capillaries and transport
it towards to the heart. These vessels are typically oxygen poor.
Capillaries are microscopic vessels that allow for the exchange of
substances between the blood and tissues.
The Three Tunics
Each of the major blood vessels consist of 3 layers of tissues known as
tunics.
The tunica intima (interna) consists of a layer of simple squamous
epithelium bound to a subendothelial layer of areolar connective tissue.
The tunica media consists primarily of smooth muscle with a framework of
elastic connective tissue.
,EDAPT WEEK 3
The tunica externa (adventitia) consists of areolar connective tissue with
elastic and collagen fibers.
The major structural differences between the vessels include:
The tunica media will be thicker in the arteries than veins as they will
need to supply more pressure to the blood.
Veins and venules are the only blood vessels that contain valves to
prevent back flow.
Capillaries are only composed of a layer of endothelium and a
basement membrane.
Structure and Function of the Specific Arteries
With this understanding of the layers of the vessels, we can take a closer
look at some of the different types of blood vessels. Of all of the blood
vessels of the body, the arteries are the strongest and, in some cases, the
most elastic. Arteries can be subdivided into two categories, the elastic
arteries and the muscular arteries.
The elastic arteries are the largest arteries (2.5-1.0 cm in diameter) that
conduct blood from the heart to the more distant muscular arteries. The
tunica media consists of large portion of elastic fibers and less smooth
muscle than other classes of arteries. These vessels stretch to
, EDAPT WEEK 3
accommodate blood being ejected from the left ventricle and the elastic
fibers help them ‘rebound’ to their original diameter, smoothing out pulsatile
blood flow (more on this later).
Vasoconstriction and Vasodilation
Another crucial function of the arteries is to
influence which regions of the body blood will
reach. The sympathetic nervous system
diverts blood flow to skeletal muscles, heart,
and lungs rather than the kidneys and GI
tract. To ensure blood makes it to where it
needs to be, the blood vessels can either dilate
or constrict.
Vasodilation results in an increase in the
diameter of the lumen of a blood vessel in
order to allow for greater blood flow to a
specific body region. Vasodilation is
accomplished by inhibiting, or relaxing, the
smooth muscle of the tunica media.
Vasoconstriction decreases the diameter of
the lumen of a blood vessel and is achieved by
contracting the smooth muscle of the tunica
media. This constriction of a blood vessel’s lumen lessens blood flow to a
specific body region downstream to that vessel.
The control of contraction and relaxation of the smooth muscle in these
vessels is conducted by the vasomotor center in the brainstem. The degree
of contraction can be modified leading to vasodilation and vasoconstriction
of vessels and is greatly influenced by the sympathetic nervous system
(sympathetic motor tone).
