Essentials of Human Anatomy
Blood Vessels
Dr Fadel Naim
Ass. Prof. Faculty of Medicine
IUG
1
Blood Vessels
• An efficient mode of transport for oxygen, nutrients,
and waste products to and from body tissues.
• Heart is the mechanical pump that propels the blood
through the vessels.
• Heart and blood vessels form a closed-loop system.
• Blood is continuously pumped to and from the
tissues.
• Are not rigid and immobile.
• Can pulsate and change shape in accordance with
the body’s needs.
Blood Vessels
• Arteries
• Carry blood away from ventricles of heart
• Arterioles
• Receive blood from arteries
• Carry blood to capillaries
• Capillaries
• Sites of exchange of substances between
blood and body cells
• Venules
• Receive blood from capillaries
• Veins
• Carry blood toward atrium of heart
Three Main Classes of Blood Vessels
• Arteries become progressively smaller as
they divide and get further from the heart.
• Veins become progressively larger as they
merge and get closer to the heart.
• Anastomosis: Site where two or more
vessels merge to supply the same body
region.
– arterial anastomoses: alternate route
– Veins tend to form many more anastomoses
than do arteries.
Three Main Classes of Blood Vessels
• End arteries
– Arteries that do not form anastomoses
– Only one route
– E.g.: renal artery, splenic artery
• Functional end arteries
– Have small anastomoses
– E.g.: coronary arteries
Blood Vessel Tunics
• Tunica Intima, or Tunica
Interna
– innermost layer
– composed of:
• an endothelium (simple
squamous epithelium)
• subendothelial layer (areolar CT)
• Tunica Media
– middle layer of the vessel wall
– composed of:
• circularly arranged smooth
muscle cells
– Sympathetic innervation:
• Increase: vasoconstriction
(narrowing of the blood vessel
lumen)
• Decrease: vasodilation
(widening of the blood vessel
lumen)
Blood Vessel Tunics
Tunica Externa, or Tunica Adventitia
– outermost layer
– composed of:
• areolar connective tissue that contains elastic and collagen fibers
– helps anchor the vessel to other tissues
– Term adventitia is used to specify outer layer in blood vessels
that are buried in CT
• Vasa vasorum : blood vessels that supply large blood
vessels
– In the externa
• Arteries vs Veins:
– Media largest in arteries, externa largest in veins
– Lumen is smallest in arteries
– Artery wall have more elastic and collagen fibers
• Capillaries: only the Interna
Arteries
• In the systemic circulation, carry oxygenated
blood to the body tissues.
• Pulmonary arteries carry deoxygenated
blood to the lungs.
• Three basic types of arteries:
– elastic arteries, muscular arteries, and arterioles
– as an artery’s diameter decreases
• corresponding decrease in the amount of elastic fibers
• relative increase in the amount of smooth muscle
Capillaries
• Contain only the tunica intima, but this layer consists of
a basement membrane and endothelium only.
• Allow gas and nutrient exchange between the blood and
the body tissues to occur rapidly.
• Smallest blood vessels, connect arterioles to venules.
• Are called the functional units of the cardiovascular
system.
• A group of capillaries (10–100) functions together and
forms a capillary bed.
The Three Basic Kinds of Capillaries
• Continuous capillaries
– the most common type
• Fenestrated capillaries
• Sinusoids, or discontinuous
capillaries
Regulation of Capillary Blood Flow
Precapillary
sphincters
• may close a
capillary
• respond to
needs of the cells
• low oxygen and
nutrients cause
sphincter to
relax
Veins
• Drain capillaries and return the blood to the heart.
• Walls are relatively thin and the vein lumen is larger.
• Systemic veins carry deoxygenated blood to the
right atrium of the heart, while pulmonary veins carry
oxygenated blood to the left atrium of the heart.
• Blood pressure is substantially reduced by the time
blood reaches the veins.
• Hold about 60% of the body’s blood at rest.
• Veins function as blood reservoirs.
From Venules to Veins
• Venules merge to form veins.
• Venule becomes a “vein” when its diameter is greater
than 100 micrometers.
• Blood pressure in veins is too low to overcome the
forces of gravity.
• To prevent blood from pooling in the limbs, most veins
contain one-way numerous valves to prevent blood
backflow in the veins.
•
As blood flows superiorly in the limbs, the valves close
to prevent backflow.
• Numerous valves along its length to assist in moving
blood back to the heart.
From Venules to Veins
Many deep veins pass between skeletal
muscle groups.
• As the skeletal muscles contract, veins are
squeezed to help pump the blood toward
the heart.
• This process is called the skeletal muscle
pump.
Venous flow occurs by:
1. muscle contraction
2. respiratory pump
3. valve assistance
4. Ventricular relaxation
Arteriole
• smallest arterioles only have a few smooth muscle fibers
• capillaries lack muscle fibers
Pulse
• alternate expanding and recoiling of the arterial wall
that can be felt
Varicose Veins
• Twisted, dilated superficial veins
– caused by leaky venous valves
• congenital or mechanically stressed from
prolonged standing or pregnancy
– allow backflow and pooling of blood
• extra pressure forces fluids into surrounding
tissues
• nearby tissue is inflamed and tender
• Deeper veins not susceptible because
of support of surrounding muscles
GREAT SAPHENOUS VEIN CUT DOWN
• Usually performed at the ankle
• Disadvantage that phlebitis is a potential
complication
• Also at the groin in the femoral triangle,
– Phlebitis is relatively rare
– Larger diameter of the vein
– Use of large-diameter catheters
– Rapid infusion of large volumes of fluids.
The Great Saphenous Vein In Coronary Bypass Surgery
• In occlusive coronary disease
caused by atherosclerosis, the
diseased arterial segment can be
bypassed by inserting a graft
consisting of a portion of the great
saphenous vein.
• The venous segment is reversed so
that its valves do not obstruct the
arterial flow.
• The great saphenous vein can also
be used to bypass obstructions of
the brachial or femoral arteries
Venipuncture of the Upper Limb
• Because of the prominence and accessibility of
the superficial veins of the upper limb, they are
commonly used for venipuncture
• These veins may be embedded with the
subcutaneous tissue (fat), making them difficult
to see
• By applying a tourniquet to the arm, the
venous return is occluded and the veins
distend and are usually visible and/or palpable.
Venipuncture of the Upper Limb
• The median cubital vein is commonly used for venipuncture
for:
– Drawing blood
– Inserting a catheter for right cardiac catheterization
• The dorsal venous network and the cephalic and basilic veins
arising from it are commonly used for intravenous feeding
FEMORAL ARTERY CATHETERIZATION
• A long, fine catheter can be inserted into
the femoral artery as it descends through
the femoral triangle.
• The catheter is guided under fluoroscopic
view along the external and common iliac
arteries into the aorta.
• The catheter can then be passed into the
inferior mesenteric, superior mesenteric,
celiac arteries, or renal arteries.
• Contrast medium can then be injected
into the artery under examination and a
permanent record obtained by taking a
radiograph.
• Pressure records can also be obtained by
guiding the catheter through the aortic
valve into the left ventricle.
Measuring Blood Pressure
• Arterial blood pressure measurement using
sphygmomanometer.
• A cuff is placed around the arm and inflated with air until it
compresses the brachial artery against the humerus and
occludes it.
• A stethoscope is placed over the artery in the cubital
fossa, the pressure in the cuff is gradually released
• The examiner detects the sound of blood beginning to spurt
through the artery.
• The first audible spurt indicates systolic blood pressure.
• As the pressure is completely released, the point at which the
pulse can no longer be heard is the diastolic blaod
pressure.
Major Vessels of Arterial System
Major Branches of the Aorta
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Coronary arteries
Brachiocephalic
Left common carotid
Left subclavian
Celiac
Superior mesenteric artery
Renals
Ovarian / testicular
Inferior mesenteric
Minor Branches of the Aorta
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•
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Pericardial
Bronchial
Esophageal
Mediastinal
Intercostal
Phrenic
Thoracic
Lumbar
Suprarenal
Major Blood Vessels of the Heart
Abdominal Aorta and Its Major Branches
Arteries to Neck, Head, and Brain
Cerebral Arterial Circle
• Circle of Willis
• formed by anterior and posterior cerebral arteries, which
join the internal carotid arteries
Arteries to Shoulder and Upper Limb
Arteries to Thoracic Wall
Arteries to Pelvic Region
Arteries to the Lower Limb
Major Vessels of the Venous System
Major Veins of the Brain, Head and Neck
Veins from the Upper Limb and Shoulder
Veins That Drain the Thoracic Wall
Veins That Drain the Abdominal Viscera
Veins of the Lower Limb and Pelvis
Hepatic Portal System
• A venous network that drains the GI tract
and shunts the blood to the liver for
processing and absorption of transported
materials.
• Blood exits the liver through hepatic veins
that merge with the inferior vena cava.
• Is needed because the GI tract absorbs
digested nutrients, and these nutrients must
be processed and/or stored in the liver.
THE END