BLOOD VESSEL STRUCTURE, BLOOD
PRESSURE AND SYSTEMIC VESSELS
Blood Vessels: The Vascular System
• Types of blood vessels:
– Arteries (in direct contact with the heart) and
Arterioles
• Carry blood away from the heart
– Capillaries
• Where substance exchange (gases, nutrients,
hormones, etc) between other tissues and the
blood occurs
– Venules and Veins (in direct contact with the
heart)
• Return blood toward the heart
Arteries and Arterioles
1. Arteries are strong, elastic vessels adapted for
carrying high-pressure blood.
2. The inside space of an artery through which blood
flows is the lumen.
3. The wall of an artery has 3 layers. From the inside to
the outside they are:
• Tunica interna (endothelium)- Elastic tissue
• Tunica media- Smooth muscle and elastic tissue
• Tunica externa (adventitia)- Elastic tissue
4. The structure of an artery helps it propel blood
onward while the ventricles are relaxing.
5. Arterioles are very small (almost microscopic)
arteries
Arteries and Arterioles continued..
6. When the sympathetic nervous system
(fight or flight) is active, the smooth muscle
of arteries contract, which narrows the
lumen (less blood flow). This is called
vasoconstriction. When the
parasympathetic nervous system is active,
the smooth muscle relaxes, which increases
the lumen diameter. This is called
vasodilation.
*When would vasoconstriction occur?
Vasodilation?
Tunica Interna
Tunica Media
Tunica Externa
Artery – Cross section
Capillaries
1. Capillaries are the smallest vessels, consisting
only of one cell layer through which substances
are exchanged with tissue cells. Consist only of
the tunica intima.
2. The number of capillaries throughout the body
varies, depending on metabolic activity. Tissues
with high metabolic requirements include the
muscles, liver, kidneys and nervous system.
3. Because they are so numerous, blood flows more
slowly through them which helps with substance
exchange.
4. Precapillary sphincters (rings of smooth muscle)
regulate the flow of blood into capillaries.
Capillary Beds
Exchanges in Capillaries
1. At the arteriole end of a capillary, the blood
pressure is high, which forces oxygen, water
and nutrients out of the capillary. This is called
filtration.
2.At the venule end of a capillary, the blood
pressure is lower, which causes most water and
solutes that were forced out before to diffuse
back into the capillary. This is called
reabsorption. About 85% of the fluid filtered is
reabsorbed. The carbon dioxide from the
surrounding cells gets absorbed as well.
Filtration
Reabsorption
Venules and Veins
1.Venules leading from capillaries merge to form
veins that return blood to the heart.
2. Veins have the same three layers as arteries,
but are much thinner. They do not carry the
same high pressure blood.
3. Veins have flap-like valves inside to prevent
backflow of blood.
4. Veins use the milking action of skeletal
muscles to move blood because they are not
lined with the same amount of smooth muscle
as arteries.
Movement of Blood Through Veins
Varicose Veins
• In people with weak vein
valves, gravity forces blood
backwards through the
valve. This increases
venous blood pressure,
which pushes the vein’s
wall outward. After this
repeatedly happens, the
walls lose their elasticity
and become stretched and
flabby. This is called
varicose veins.
Main Differences Between Blood
Vessels
• Walls of arteries are the thickest and their
smooth muscle helps move blood
• Lumens of veins are larger because walls are
thinner
• Larger veins have valves to prevent backflow
• Skeletal muscle “milks” blood in veins toward
the heart
• Walls of capillaries are only one cell layer thick
to allow for exchanges between blood and
tissue
Blood Pressure
• Blood pressure is the pressure exerted by blood on the
walls of a blood vessel. It is highest in the aorta and
large arteries branching off of the aorta.
• Blood pressure is affected by the distance from the left
ventricle , the total volume of blood,
vasoconstriction/vasodilation and blood viscosity.
– Pressure in an artery is approximately 93 mm Hg, in a
capillary is 35 mm Hg and in a venule is 16 mm Hg.
– Loss of blood would lower bp as water retention would raise
bp.
– Vasoconstriction raises bp as vasodilation lowers bp.
– Blood viscosity is “thickness” of blood. The greater the # of
blood cells and solutes, the greater the bp.
Comparison of Blood Pressures in Different Vessels
Systolic/Diastolic Pressure
A healthy blood pressure reading is 120 mm Hg/80 mm Hg.
• Systolic Blood Pressure is the top number of a blood
pressure reading (120). This is the pressure that the
blood is putting on the arteries as the ventricles
contract, forcing blood out of the heart.
• Diastolic Blood Pressure is the bottom number of a
blood pressure reading (80). This is the pressure that
the blood is putting on the arteries as the ventricles
relax.
• The surge of blood that occurs with ventricular
contraction can be felt at certain points in the body as a
pulse. The pulse rate normally is about 70-80 bpm.
Measuring Arterial Blood Pressure
Pulse
• Pulse - Pressure
wave of blood
• Monitored at
“pressure points” in
arteries where pulse
is easily felt
• Pulse averages 70–
76 beats per minute
at rest
Variations in Blood Pressure
• Normal human range is variable:
– Normal
• 140–110 mm Hg systolic
• 80–70 mm Hg diastolic
– Hypotension
• Low systolic (below 110 mm HG)
• Often associated with illness
– Hypertension
• High systolic (above 140 mm HG)
• Can be dangerous if it is chronic
What helps maintain normal blood
pressure?
• Baroreceptors- Pressure receptor nerve cells
which are located in the aorta and other large
arteries and send messages to the brain.
• Chemoreceptors- Measure the chemical
composition (O2 and CO2) of blood. These
cells send messages to alter respiration rate.
• Hormones- Regulate blood flow and pressure
– Renin, Adrenaline, ADH
Systemic Circulation
The systemic circuit
includes the aorta and
its branches leading to
all body tissues as well
as the system of veins
returning blood to the
right atrium.
Major Arteries of Systemic Circulation
Areas that they feed
1. External carotid-external to skull
2. Internal carotid- internal to skull
3. Common carotid- branches into
external and internal
4. Vertebral- posterior brain
5. Brachiocephalic trunk-branches
into right subclavian and right
common carotid
6. Brachial-arm
7. Renal-kidney
8. Radial-radial side of forearm
9. Common iliac-branches into
internal and external iliac
10. Internal iliac- pelvis
11. Subclavian- parts of brain, spinal
cord, neck, chest, shoulder
12. Axillary- shoulder
13. Ulnar- ulna side of forearm
14. External iliac- lower limbs
15. Femoral- groin and thigh
16. Posterior tibial- posterior
muscles and bones of leg and
foot
17. Popliteal- knee and posterior leg
muscles
18. Anterior tibial-anterior muscles
and bones of leg and foot
Major Arteries of Systemic Circulation
Parts of the Aorta
• The aorta has 4 parts:
– Ascending aorta- Emerges from the left ventricle;
where the coronary arteries branch to feed the heart.
– Arch of the aorta- As the name implies, where the
aorta “arches” to the left. The brachiocephalic trunk,
left common carotid artery and left subclavian arteries
branch off of this.
– Thoracic aorta- The descending portion that is begins
at the 4th/5th thoracic vertebrae and continues until
the diaphragm opening.
– Abdominal aorta- The descending portion between
the diaphragm opening and the 4th lumbar vertebra.
Label the 4 parts of the aorta
Major Veins of Systemic Circulation
Areas that they drain
1. Internal jugular- head
2. Vertebral- neck, cervical
vertebrae
3. Brachiocephalic-dumps into the
SVC
4. Brachial-forearm, elbow, and
humerus
5. Renal- kidney
6. Radial- radius side of forearm
7. Common iliac- Pelvis and upper
leg
8. Internal iliac- pelvis
9. Greater saphenous-longest in
the body- femur region
10. Posterior tibial- back side of
lower leg
11. Subclavian- arms, neck, thoracic
wall
12. Axillary- arms and upper chest
13. Cephalic- lateral upper limbs
14. Hepatic-liver
15. Median cubital-elbow
16. Ulnar- ulna side of forearm
17. Femoral- thigh
18. Popliteal- knee
19. Small saphenous-Foot and
posterior leg
20. Anterior tibial-anterior portion of
leg, ankle and knee
Major Veins of Systemic Circulation
Common Blood Vessel Disorders
• Hypertension- High blood pressure
– Systolic greater than 140 mm Hg and Diastolic
greater than 90 mm Hg
– Effective treatments include: lose weight, limit
alcohol intake, exercise, reduce sodium intake,
don’t smoke and manage stress.
• Aneurysm- A thin, weakened section of the
wall of an artery or a vein. If it bursts, massive
hemorrhaging could result.
• Aneurysm video
• Endovascular aneurysm repair
Abdominal Aortic AneurysmEEEKKK!!!