The function of the cardiovascular/circulatory system is the
transport of materials to and from the cells. The organs of
multicellular animals are too far removed from the external environment to
enable them to exchange nutrients, oxygen and wastes directly by
diffusion. Instead, the materials needed by cells must be brought to the
cells by a circulatory system, and the cellular wastes must similarly be
The cardiovascular/circulatory system includes the circulating
medium of transport, the blood. The structures comprising the
cardiovascular/circulatory system include the heart, arteries, veins and
The heart and the large blood vessels at the anterior end of the heart
are enclosed by a fibrous, double-layered membranous sac, the
The heart is located in the center of the thorax within the mediastinum.
It is a muscular pump, conical in shape and slightly larger than a
human fist consisting of two atria and two ventricles.
The heart, responsible for the movement of blood, beats approximately
80,000 - 100,000 a day and pumps approximately 2,000 gallons of blood a
day through the body. To sustain this continuous beating, the heart
is made of specialized muscle tissue. The coronary arteries
and veins on the surface of the heart supply the heart itself with
blood. The parts of the heart are:
Atria- the two top chambers of the heart. The atria receive
the blood that has returned to the heart from the body and lungs.
The atria contract, transporting the blood into the ventricles.
There are two atria:
Right atrium -
receives blood returning from the body and releases it into the right
ventricle via the tricuspid valve.
Left atrium -
receives oxygenated blood from the pulmonary veins and releases it
into the left ventricle via the mitral valve.
Ventricles - the two bottom chambers of the heart. The
ventricles contract to pump the blood out of the heart to the body and
lungs. There are two ventricles:
- receives blood from the right atrium via the tricuspid valve and
releases the blood into the lungs to pick up oxygen via the pulmonary
- the largest and strongest chamber, receives blood from the left
atrium and pumps blood to the aorta via the aortic valve.
The septum is a thick wall of muscle that separates the left and right
side of the heart.
A heart valve is a set of flaps called leaflets or cusps. A
difference in pressure across the valves causes them to open, releasing
the blood in a forward direction then quickly closing to to keep the
blood from flowing backward. The four heart valves are:
Mitral - The mitral (bicuspid) valve has two flaps and releases the
blood from the left atrium to the left ventricle.
Tricuspid - The tricuspid valve has three flaps and released the blood
from the right atrium to the right ventricle.
Aortic - The aortic valve has three flaps and releases the blood from
the left ventricle to the aorta.
Pulmonary - The pulmonary valve has three flaps and releases the blood
from the the right ventricle to the pulmonary artery.
The fetal circulation has two adaptations for bypassing the inactive
lungs. The first is the ductus arteriosus. It is a short vessel
which connects the pulmonary artery to the aorta. The second is the
foramen ovale, a small opening in the septum between the right and
left atria which permits blood to enter the left atrium without first
going to the lungs.
Next, the venous system of the fetal pig is dissected. Veins generally lie
closer to the surface than arteries. In doubly injected specimens they are
colored blue. Arteries, injected with red latex, are studied last.
We begin our study of the major blood vessels with the veins which carry
blood to the heart from the head, forelimbs, shoulder, and thoracic
The anterior veins lie close to the surface of the body and are therefore
studied before the arteries which lie deep to the veins. In doubly
injected specimens veins will be blue, arteries will be red. This is due
to the latex dye with which they were injected. This permits you to see
these vessels more clearly and to differentiate between arteries and
You have already exposed the heart and some of the major veins in your
study of the thoracic cavity. Extend your incision into the neck area. If
you have not yet done so, expose the trachea, larynx, and thyroid gland as
in the photo. Remove the thymus gland carefully from the ventral surface
of the heart and lower trachea.
Your best dissection instrument at this point is the dissecting needle.
Use it instead of a scalpel or scissors to expose and follow the path of a
blood vessel. Scalpels and scissors, especially in the hands of the novice
tend to destroy rather than preserve or expose. It is used for clearing a
blood vessel of the connective tissue adhering to it, to tear into a thin
muscle layer to follow a vessel, to separate one blood vessel from
another, or from the nerves associated with it.
Proceed to expose the large veins surrounding the heart.
Push the heart gently to the left. Note a wide, blue blood vessel rising
anteriorly from the diaphragm mid-dorsally. This is the posterior vena
cava. In man, due to his upright position, this vessel is known as the
inferior vena cava. It returns blood from the lower portion of the
body and enters the heart at the right atrium. A similar, but shorter,
blood vessel is seen anterior to the heart. This is the anterior vena
cava, or superior vena cava, in man. It returns blood from the
upper positions of the body, from the head and forelimbs. It also enters
the heart at the right atrium.
(Superior) Vena Cava Locate the trunk of this systemic vein
above the heart. In the pig the term anterior vena cava is more correct
and therefore preferred to superior vena cava. All anterior veins lead
into the anterior vena cava.
(Inferior) Vena Cava This is the major vein returning blood
from the lower extremities and from the abdominal area. Again, this
designation in the pig is preferred to inferior vena cava. It can
clearly be seen rising from the diaphragm, which it has penetrated, to
enter the heart at the right atrium together with the anterior vena
(Brachiocephalic) Follow the anterior vena cava cranially from the
heart. It divides into two equal branches, the V shaped innominate
veins also known as the brachiocephalic veins. Each of these is formed
by the union of the subclavian vein from the shoulder and the external
jugular vein from the neck.
Two jugular veins lie along each side of the neck. The external
jugular vein drains the head and neck, while the internal jugular vein
drains the brain and spinal cord. They join to form the innominate vein.
This vein is a continuation of the axillary vein in the shoulder joint
area. The axillary vein is a continuation of the brachial vein in the
(Sternal) Vein On the ventral surface of the anterior vena
cava about one inch above the heart the internal mammary or sternal vein
arises. It results from the union of the paired internal mammary veins
which drain the ventral thoracic body wall and the mammary glands of
This vein drains the shoulder region and arises from the underside of
the scapula. It enters the subclavian vein close to the base of the
external jugular vein.
This vein lies upon the lateral surface of the foreleg and was seen
when the pig was skinned. It is a long vein which continues up to the
shoulder area and enters the external jugular vein at its base. The
cephalic vein and the, deeper vein of the arm, the brachial vein, are
joined in the inner elbow by the median cubital vein.
Long Thoracic This vein arises along the inner surface of the
pectoralis minor muscle then passes to the latissimus dorsi. It joins
the axillary vein.
Thoracodorsal This vein arises from under the scapula and
similarly joins the axillary vein.
Hemiazygous Push the left lung and the heart medially. On the
dorsal body wall, to the left of the midline, and running parallel to
the aorta, observe a vein which enters the anterior vena cava near its
entrance into the right ventricle of the heart. This unpaired vessel is
the hemiazygous vein. It drains the dorsal body wall and the dorsal
musculature. Note that the intercostal veins between the ribs empty into
the hemiazygous vein. Dissect the pairs of intercostal veins to observe
this relationship. In man, the hemiazygous vein is replaced with the
which lies on the right side.
Veins - Posterior
The systemic veins below the heart empty into the posterior vena
cava. The upper portion of this enlarged blood vessel was observed when we
studied the thoracic veins. It passes through the diaphragm and lies along
the mid-dorsal body wall of the thorax. It then enters the right atrium of
the heart near the entrance of the anterior vena cava.
Cava This large blood vessel may be observed by displacing the
abdominal viscera toward the left. It lies along the mid-dorsal
abdominal body wall. Its major branches will be described in descending
order, in a caudal direction.
Phrenic Within the diaphragm the posterior vena cava receives
Below the diaphragm region the posterior vena cava passes through the
substance of the liver within which it receives the veins which drain
the liver, the hepatic veins.
Within the body of liver the inferior vena cava then receives the
ductus venosus. This vessel is a continuation of the umbilical vein.
The oxygen rich blood from the mother passes to the fetus through the
umbilical vein within the umbilical cord. The umbilical vein leads from
the cord to the liver where it forms the ductus venosus. In order to see
the relationship between these veins it is necessary to remove some of
the substance of the liver. Use your forceps or dissecting needles. You
will discover a rich network of blood vessels running through the liver.
The ductus venosus drains into the posterior vena cava posterior to the
Find the renal vein exiting from the medial surface of each kidney and
trace it to the posterior vena cava. In some specimens two renal veins
drain each kidney.
Adrenal The adrenal gland is an elongated oval structure lying medial
to the anterior portion of the kidney. It is drained by the adrenal vein
which empties the renal vein. In some specimens it enters the posterior
vena cava separately.
Genital (Utero-Ovarian and
The genital vein is known by different names in males and females.
These are very narrow and difficult to locate and are most easily traced
from the ovaries or the testes. The right genital vein enters the
posterior vena cava next to the posterior end of the right kidney, while
the left genital vein generally enters the renal vein.
Posterior to the kidneys seven pairs of veins drain the deep dorsal and
lateral abdominal walls. The upper five to six pairs empty into the
posterior vena cava, while the last pairs empty into the common iliac
The venous blood from the pelvic region and from the legs moves
anteriorly toward the heart. The right and left common iliac veins serve
as receiving vessels for all of this blood. They converge to form the
posterior vena cava, forming the shape of an inverted Y. All veins
below this point are branches of the common iliac veins.
Internal Iliac The common iliac is a relatively short segment
of blood vessel. Near its origin it may be seen as formed by two
branches. The main, larger and thicker branch extends laterally. This is
the external iliac. It extends out toward the legs. A shorter and
narrower vessel, the internal iliac (hypogastric) vein extends
posteriorly on either side of the midline. It drains the rectum, urinary
bladder, and the genital organs.
This vein is a lateral branch of the external iliac vein.
It drains the pelvic muscles.
Femoral In the
thigh the external iliac vein is known as the femoral vein.
It receives several branches.
Deep Femoral This vein drains the deeper muscles of the thigh.
superficial vein may be seen lying on the medial surface of the thigh
and lower leg. Above the knee it joins the femoral vein.
Posterior to the knee the femoral vein is joined by a deeper vein from
the lower thigh and shank, the popliteal vein.
This, often paired vein, runs along the mid dorsal pelvic wall
draining the musculature. It empties into the common iliac veins.
Caudal This vein, extending into the tail, receives blood from
the most posterior structures and the musculature of the tail.
Anteriorly it joins the middle sacral vein.
System The veins from most of the abdominal viscera do not
join the posterior vena cava directly. Instead, blood from the stomach,
pancreas, spleen, small intestine, and large intestine drain into a
larger vein known as the hepatic portal vein which enters the
liver and there breaks up into capillaries called sinusoids. The
hepatic portal vein is rich in digested nutrients. Before these enter
the general circulation the liver transforms them according to the needs
of the body. Glucose may be stored as glycogen, amino acids deaminated,
or fatty acids may be converted to carbohydrates.
In order to expose the hepatic portal vessels move the stomach, spleen,
pancreas, small, and large intestines to the left. Frequently they are
not injected with blue latex even in injected specimens, therefore, only
the largest vessels can be readily identified.
Vein This is the main vein of the hepatic portal system. All
of the tributary vessels of the abdominal viscera merge with this single
large vein. It enters the liver where it breaks up into smaller vessels
then into capillaries. These are drained by the hepatic veins and
posterior vena cava. Some of the major veins joining the hepatic
Mesenteric This vein is a union of branches from the many
coils of the small intestines.
This vein drains the pyloric region of the stomach and the duodenum
before it joins the hepatic portal vein.
As its name indicates, this vein originates at the stomach and spleen.
Arteries are vessels which deliver oxygenated blood away from
the heart to the capillaries. The heart pumps blood out through the aorta,
which then divides and branches out into smaller arteries to each region
of the body. Consisting of three layers, an outer layer of tissue, a
middle layer of muscle that is elastic and strong, expanding when the
heart beats filling the artery with blood and contracting when the heart
relaxes to push the blood along, and and inner layer of smooth epithelial
cells allowing the blood to flow freely.
The large pulmonary
artery is seen leaving the heart from its ventral surface extending
toward the left side. More distally the aortic arch leaves the
heart and also extends toward the left side. In the fetal pig the
pulmonary artery is joined directly to the aortic arch by means of a short
vessel, known as the
It serves as a bypass to shunt the blood from the lungs into the
systemic circulation. This connecting link persists till birth. It then
shuts tightly, separating the two major blood vessels. It persists in the
adult as only a small tendinous band.
Arteries - Anterior
Remove the major veins surrounding the heart. This will enable you
to expose the arteries. Use your dissecting needle to clear arteries of
connective tissue, to separate them, and to follow them.
- On the ventral surface of the heart passing dorsally and to the left is
the large pulmonary artery. It originates in the right ventricle. Try
tracing its two branches to the lungs. The pulmonary is the only artery
injected with blue latex to indicate that it carries deoxygenated blood.
All other arteries will appear red or pink because they have been injected
with red latex to indicate that the blood transported in them is
Locate the aorta, the largest systemic artery of the body. It
leaves the left ventricle, curves to the left, dorsal to the pulmonary
artery, and continues dorsally in a posterior direction along the left
side of the vertebral column. The proximal curved portion of aorta is
called the aortic arch, while the next segment of the aorta within
the thorax is known as the thoracic aorta.
Arteriosus In the fetal pig, as well as in all mammalian
fetuses, the pulmonary artery is joined directly to the aortic arch by
means of a short vessel, the ductus arteriosus. It serves as a
bypass to shunt the blood from the lungs toward the systemic circulation.
This connecting link is about 1/4 inch long in the older fetal
pigs. The ductus arteriosus persists as a connecting link till
birth. It then shuts tightly, separating the pulmonary artery from the
aorta and the two major circulatory pathways, the pulmonary from
the systemic. It persists in the adult as a narrow tendinous band.
Near its origin within the left ventricle of the heart, the aorta gives
off its first two branches, the right and left coronary
arteries. Branches of these vessels may be seen upon the surface of
the heart. These supply blood to the heart muscle (myocardium) directly.
The aortic arch
gives rise to arteries that supply the neck, head, shoulders and
forelimbs. Whereas in man three arterial trunks arise from the
aortic arch, in the pig there are only two. These are the:
(or Innominate) This major artery is the first of the two trunks
branching from the aortic arch. As its name indicates, it supplies blood
to the forelimb and the head. At the level of the second rib it divides
Subclavian This artery leaves the thorax, gives off major
branches to the musculature of the shoulder and thorax then continues
This artery is a continuation of the right subclavian in the
region of the armpit and shoulder.
This is the continuation of the axillary artery in the upper
These are branches of the brachial artery within the lower forelimb.
Trunk This artery is the second branch of the
brachiocephalic. It is only a short common pathway for blood to the
head. It soon divides to form the:
Left Common Carotids These two arteries arise from the
hi-carotid trunk, pass cranially, parallel to one another on either
side of the trachea. Near the head each divides into an
and external carotid artery.
The second branch of the aortic arch is the left subclavian artery. It
gives off branches to the musculature of the shoulder, then proceeds
into the left forelimb as the left axillary, the left
brachial, the left radial, and the left ulnar
arteries. The subclavian artery gives off major branches to the
musculature of the thorax and shoulder. Starting from its proximal end
these include the:
Trunk This is the first vessel to come off the subclavian
artery. It originates from the dorsal surface of the subclavian at the
level of the first rib. Some of its branches are the:
This is the most anterior branch of the costo-cervical trunk.
The artery passes through the transverse foramina (channels) of the
cervical vertebrae cranially toward the brain.
Deep Cervical This artery sends branches to the anterior
Dorsal This small artery is the third branch of the costo-cervical
trunk. It supplies blood to lower neck and anterior part of the back
(or Inferior Cervical) This comparatively large artery arises from
the dorsal surface of the subclavian near the first rib. It supplies
the thyroid gland, pectoral muscles, and parotid gland.
Thoracic (Lateral Thoracic) This arterial branch of the
subclavian supplies blood to both the superficial and deep thoracic
Mammary (Internal Thoracic) This artery also originates from
the subclavian opposite to the origin of the thyrocervical. It passes
posteriorly to supply the pectoral muscles, the skin, the thymus
gland, and the mammary gland. It is usually cut when exposing the
This artery originates just beyond the subclavian, in the
axillary artery. It passes anteriorly to the shoulder region where
it supplies the subscapular region with blood.
Thoraco-Dorsal This artery is a branch of axillary artery. It
originates opposite to the subscapular and passes posteriorly. In some
specimens it is a branch of the subscapular artery.
We have traced the common carotid artery to the head. Just
below the jaw it divides to form the internal carotid artery and
the external carotid artery.
This artery runs anteriorly into the skull to supply the brain. Near
its origin it gives off the occipital artery which passes
dorsally to supply the occipital region.
This artery supplies the remainder of the head with blood. Some of its
branches include the:
This artery supplies the tongue.
to the lower and upper jaws, the lips, and mouth
to the ear
found near the temple
Return to the aortic arch Trace its path to the left as it
descends mid-dorsally within the thorax. It will be necessary to
displace the left lung medially in order to observe this segment of the
aorta. It is here known as the thoracic dorsal aorta. Upon closer
examination, you will find paired arterial branches originating along
the length of the thoracic aorta. These pass into the musculature
between the ribs, and are known as the intercostal arteries.
While most of them originate in this way directly from the aorta, the
upper few originate from the costo-cervical trunk.
Arteries - Posterior
Follow the aortic arch dorsally and caudally through the thorax.
Push the left lung toward the right and observe the thoracic aorta
along the dorsal body wall to the left of the vertebral column.
Arteries Between each two ribs note the intercostal arteries.
They are given off by the thoracic aorta in pairs, to the right
and left sides, to supply the intercostal muscles.
Other branches of the thoracic aorta above the diaphragm include
Bronchial These arteries supply the lung tissues with oxygenated
Esophageal This artery supplies the esophagus.
This artery supplies blood to the diaphragm.
Trace the dorsal aorta as it continues caudally and passes through the
diaphragm into the abdominal cavity. It is here known as the abdominal
aorta. It gives rise to a number of arteries supplying the organs of
the abdominal region. These include the:
Immediately posterior to the diaphragm the abdominal aorta gives off
ventrally a short unpaired blood vessel, the celiac artery, which
branches extensively to supply blood to the organs of the upper abdomen.
It divides into two main branches:
Gastro-Splenic This artery supplies blood to the stomach and to
Gastric - This portion of the gastro-splenic artery passes to the
underside of the stomach.
Splenic The second portion of the gastro-splenic passes medially along
the length of the spleen to supply blood to that organ.
Gastro-Hepatic - This branch supplies blood to other portions of
the stomach and to the liver. It passes through the pancreas to
supply blood to that organ. Then it divides to form the:
Hepatic - This artery supplies the liver.
Gastro-Duodenal - This artery supplies the duodenum and stomach.
This is the next arterial branch of the abdominal aorta below the celiac
artery. It supplies the small intestine and the anterior portion of the
This artery comes off the aorta near the anterior end of the kidney.
It supplies the diaphragm and the lateral abdominal body wall with blood.
Each kidney is supplied with blood by the renal artery.
Adrenal The adrenal gland is
supplied by the adrenal arteries which may originate directly from the
abdominal aorta or from the renal artery.
Genital These arteries supply the
male and female glands with blood. They are called:
These arteries pass posteriorly to become part of the spermatic cord
to the testes within the scrotal sac in males.
Utero-Ovarian The corresponding
artery in females leads to the uterus and ovaries.
This unpaired vessel originates from the aorta below the genital artery.
It divides to supply blood to the anterior as well as the posterior
portions of the large intestines.
Follow the abdominal aorta in the mid-dorsal region of the abdomen. Note
six pairs of arteries passing laterally to the dorsal muscle wall. Those
are the lumbar arteries.
At the level of the hip the aorta divides into two major vessels, one to
each hind leg.
This artery gives off many branches to the organs of the pelvis, the
genital and structures and to the hind legs.
Note: Unlike the venous system, there is no common iliac artery. The
external and internal iliac arteries arise as separate branches of the
This lateral branch of the external iliac artery supplies blood to the
Internal Iliac As already indicated, this artery arises from the
aorta at the same level as the external iliac. It is, however, more
medially located, thus serving the organs of the pelvis.
The narrow internal iliac arteries soon enlarge as the umbilical
arteries. These major prominent features of the fetal circulation
carry deoxygenated blood from the developing fetus to its mother. The
arteries lie on either side of the elongated urinary bladder before
exiting the body. They were already observed when the ventral abdominal
wall was removed. After birth these arteries atrophy. Beyond the umbilical
arteries, the internal iliacs continue posteriorly within the pelvis.
(continued) Return to the external iliac artery.
The segment of the external iliac within the thigh is known as the
femoral artery. It supplies the hind leg with blood.
This artery is a branch of the femoral artery. It supplies the medial
upper region of the hind leg.
Saphenous Just above the knee joint the femoral artery gives off
the saphenous artery which passes medially down the leg.
This segment of the femoral artery originates at the back of the knee cap
and passes to the lower portion of the hind leg.
Capillaries, the narrowest blood vessels, are a web-like
network connecting oxygen-rich arteries to veins so the blood can be
transported back to the lungs and heart. Capillaries are fragile and very
thin enabling them to exchange oxygen and carbon dioxide through the thin
capillary wall. Red blood cells inside the capillary release their oxygen
which passes through the wall and into the surrounding tissue, the tissue
then releases waste products such as carbon dioxide, which passes through
the wall and into the red blood cells to be transported back to the heart.
Capillaries also aid in the release of the body's heat.