Cardiovascular System
c. Tightly joined epithelial cells of alveoli walls
prevent most substances from entering the alveoli.
d. Osmotic pressure rapidly draws water out of
alveoli into the interstitial fl
uid, so alveoli do not
ll with fl
2. Systemic circuit
a. The systemic circuit is composed of vessels that
lead from the left ventricle to all body parts
(including vessels supplying the heart itself) and
back to the heart.
b. It includes the aorta and its branches as well as the
system of veins that return blood to the right atrium.
1. Principal branches of the aorta
a. The branches of the ascending aorta include the
right and left coronary arteries.
b. The branches of the aortic arch include the
brachiocephalic, left common carotid, and left
subclavian arteries.
c. The branches of the descending aorta include the
thoracic and abdominal groups.
d. The abdominal aorta terminates by dividing into
right and left common iliac arteries.
2. Arteries to the brain, head, and neck include branches
of the subclavian and common carotid arteries.
3. Arteries to the shoulder and upper limb
a. The subclavian artery passes into the arm, and
in various regions, it is called the axillary and
brachial artery.
b. Branches of the brachial artery include the ulnar
and radial arteries.
4. Arteries to the thoracic and abdominal walls
a. Branches of the subclavian artery and thoracic
aorta supply the thoracic wall.
b. Branches of the abdominal aorta and other arteries
supply the abdominal wall.
5. Arteries to the pelvis and lower limb
The common iliac artery supplies the pelvic organs,
gluteal region, and lower limb.
1. Characteristics of venous pathways
a. The veins return blood to the heart.
b. Larger veins usually parallel the paths of major
2. Veins from the brain, head, and neck
a. The jugular veins drain these regions.
b. Jugular veins unite with subclavian veins to form
the brachiocephalic veins.
3. Veins from the upper limb and shoulder
a. Sets of superF
cial and deep veins drain the upper
b. Digital veins drain into pairs of radial veins and ulnar
veins, which merge to form a pair of brachial veins.
c. The major superF
cial veins are the basilic and
cephalic veins.
d. Basilic and brachial veins merge to form the
axillary vein.
e. The median cubital vein in the bend of the elbow
is often used as a site for venipuncture.
3. Venules and veins
a. Venules continue from capillaries and merge to
form veins.
b. Veins carry blood to the heart.
c. Venous walls are similar to arterial walls but are
thinner and contain less muscle and elastic tissue.
Blood pressure is the force blood exerts against the insides
of blood vessels.
1. Arterial blood pressure
a. The arterial blood pressure is produced primarily
by heart action; it rises and falls with phases of the
cardiac cycle.
b. Systolic pressure occurs when the ventricle
contracts; diastolic pressure occurs when the
ventricle relaxes.
2. ±actors that infl
uence arterial blood pressure
a. Heart action, blood volume, resistance to fl
ow, and
blood viscosity infl
uence arterial blood pressure.
b. Arterial pressure increases as cardiac output, blood
volume, peripheral resistance, or blood viscosity
3. Control of blood pressure
a. Blood pressure is controlled in part by the
mechanisms that regulate cardiac output and
peripheral resistance.
b. Cardiac output depends on the volume of blood
discharged from the ventricle with each beat
(stroke volume) and on the heart rate.
(1) The more blood that enters the heart, the
stronger the ventricular contraction, the
greater the stroke volume, and the greater the
cardiac output.
(2) The cardiac center of the medulla oblongata
regulates heart rate.
c. Changes in the diameter of arterioles, controlled
by the vasomotor center of the medulla oblongata,
regulate peripheral resistance.
4. Venous blood fl ow
a. Venous blood fl
ow is not a direct result of heart
action; it depends on skeletal muscle contraction,
breathing movements, and venoconstriction.
b. Many veins contain fl
aplike valves that prevent
blood from backing up.
c. Venous constriction can increase venous pressure
and blood fl ow.
5. Central venous pressure
a. Central venous pressure is the pressure in the right
b. ±actors that infl
uence it alter the fl
ow of blood into
the right atrium.
c. It affects pressure in the peripheral veins.
1. Pulmonary circuit
a. The pulmonary circuit consists of vessels that
carry blood from the right ventricle to the alveolar
capillaries in the lungs, and vessels that lead back
to the left atrium.
b. Alveolar capillaries exert less pressure than those
of the systemic circuit.
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