Unit 6: Blood Vessels
Dr. Moattar Raza Rizvi
NRSG231 Principles of Anatomy
Structure of blood vessels
• Tunica adventitia (externa)- outermost layer
– Fibrous connective tissue
– Holds vessels open; prevents tearing of vessels
walls during body movements
– Thickest layers of walls of veins
– Larger in veins than arteries
• Tunica media – middle layer
– Concentric layers of helically arranged smooth
muscle and elastic CT
– Helps vessels constrict and dilate
– Larger in arteries
Structure of blood vessels
• Tunica intima – innermost layer
– Composed of endothelium made of simple
squamous epithelium
– Semilunar valves present in veins
– One cell thick in capillaries
Structure of blood vessels
BLOOD VESSELS: Arteries
– Arteries
• Carry blood away from heart
• all arteries except pulmonary artery carry
oxygenated blood
• Elastic arteries are largest in body (e.g., aorta
and its major branches)
–Able to stretch without injury
–Accommodate surge of blood when heart
contracts and able to recoil when ventricles
relax
• Arteriole – small artery
• As blood travels from the aorta to the
capillaries: Resistance increases
BLOOD VESSELS: Arteries
Types of Arteries
• Muscular (distributing) arteries
–Smaller in diameter than elastic arteries
–Muscular layer is thick
–Examples: brachial, gastric, superior mesenteric
• Arterioles (resistance vessels)
–Smallest arteries
–Important in regulating blood flow to end organs
• Metarterioles
–Short connecting vessel between true arteriole
and 20 to 100 capillaries
–Encircled by precapillary sphincters
–Distal end called thoroughfare channel, which is
free of precapillary sphincters
BLOOD VESSELS - Capillaries
• Capillaries – arterial system switches to
venous system
• “primary exchange vessels”
• Transport materials to and from the cells
• Speed of blood flow decreases to increase
contact time
• Microcirculation: blood flow between
arterioles, capillaries and venules
• Not evenly distributed; highest numbers in
tissues with high metabolic rate; may be absent
in some “avascular” tissues, such as cartilage
BLOOD VESSELS
Types of Capillaries
– True capillaries: receive blood flowing from
metarteriole with input regulated by precapillary
sphincters
– Continuous capillaries
» Continuous lining of endothelial cells
» Openings called intercellular clefts exist between
adjacent endothelial cells
– Fenestrated capillaries
» Have both intercellular clefts and “holes,” or
fenestrations, through plasma membrane to facilitate
exchange functions
» Fenestrated capillaries are found in renal glomeruli
(kidney), intestinal villi, endocrine glands
TypesVESSELS
of Capillaries
BLOOD
(cont.)
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»
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Sinusoids
Absent or incomplete basement membrane
They have unusually wide lumens
They have abundant fenestrations (Very porous);
permit migration of cells into or out of vessel lumen
» They are not found in skeletal muscle
» They often have phagocytic cells inserted between the
endothelial cells of their lining
» Large diameter capillaries found primarily in the liver,
spleen, and bone marrow are called: Sinusoidal
capillaries
Types of Capillaries
Blood Vessels: veins
– Veins
• Carry blood toward
the heart
• Act as collectors
and reservoir
vessels; called
capacitance vessels
• One way valves
prevent backflow
“Building blocks” commonly present
• Lining endothelial cells
» Only lining found in capillary
» Line entire vascular tree
» Provide a smooth luminal surface; protect against
intravascular coagulation
» Intercellular clefts, cytoplasmic pores, and fenestrations
allow exchange to occur between blood and tissue fluid
» Capable of secreting a number of substances
» Capable of reproduction
• Collagen fibers
» Exhibit woven appearance
» Have only a limited ability to stretch (2% to 3%) under
physiological conditions
» Strengthen and keep lumen of vessel open
“Building blocks” commonly present
• Elastic fibers
»Composed of insoluble protein called elastin
»Form highly elastic networks
»Fibers can stretch more than 100% under
physiological conditions
»Play important role in creating passive tension to
help regulate blood pressure throughout the
cardiac cycle
• Smooth muscle fibers
»Present in all segments of vascular system except
capillaries
»Most numerous in elastic and muscular arteries
»Exert active tension in vessels when contracting
Circulatory routes
– Systemic circulation: blood flows from the left
ventricle of the heart through blood vessels to all
parts of the body (except gas exchange tissues of
lungs) and back to the right atrium
– Pulmonary circulation: venous blood moves from
right atrium to right ventricle to pulmonary artery
to lung arterioles and capillaries, where gases are
exchanged; oxygenated blood returns to left atrium
by pulmonary veins; from left atrium, blood enters
the left ventricle
Circulatory routes
Systemic Arteries
• Main arteries give off branches, which continue to
rebranch, forming arterioles and then capillaries
• End arteries: arteries that eventually diverge into
capillaries
• Arterial anastomoses: arteries that open into other
branches of the same or other arteries; incidence of
arterial anastomoses increases as distance from the
heart increases
• Arteriovenous anastomoses, or shunts, occur when
blood flows from an artery directly into a vein
Systemic Arteries
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Arch of aorta
Subclavian (L and R)
Brachiocephalic
common carotid (L and R)
Axillary (L and R)
Brachial (L and R)
Radial
Ulnar
Abdominal aorta
Common iliac
External iliac
Femoral
Popliteal
Posterior tibial
Anterior tibial
Dorsal pedis
Systemic Arteries
Left coronary
artery branches
off the aorta first
Systemic Arteries
Systemic Arteries
The internal carotids and the basilar artery are connected by an anastomosis
called the: Circle of Willis
Systemic Arteries
Systemic Arteries
Hepatic portal circulation
– Veins from the spleen, stomach, pancreas,
gallbladder, and intestines send blood to the liver by
the hepatic portal vein
– In the liver the venous blood mingles with arterial
blood in the capillaries and is eventually drained
from the liver by hepatic veins that join the inferior
vena cava
• Venous blood from the lower extremities and abdomen
drains into the inferior vena cava
Hepatic Portal Circulation
left gastric,
splenic, and
common hepatic
arteries come
from the ceoliac
artery
Superior mesenteric artery
supplies the small intestine and
the ascending colon.
Hepatic Portal Circulation
Oxygenated blood is
brought to the liver by
the hepatic artery
Blood in the hepatic
portal vein tends to
be high in Nutrients
and low in Oxygen
Systemic Veins
• Veins are the ultimate extensions of capillaries; unite
into vessels of increasing size to form venules and then
veins
• Large veins of the cranial cavity are called dural sinuses
• Veins anastomose the same as arteries
Systemic Veins
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Superior vena cava
Inferior vena cava
External jugular
Internal jugular
Brachiocephalic (L and R)
Subclavian (L and R)
Cephalic
Axillary
Basilic
Median basilic
Median cubital
Common iliac
External iliac
Femoral
Popliteal
Great saphenous
Small saphenous
Systemic Veins
Subclavian vein
receives lymphatic
fluid
Systemic Veins
Systemic Veins
Systemic Veins
Systemic Veins
Longest vein in the body
draining blood from the
medial aspect of the leg and
thigh is great saphenous vein
Fetal Circulation
– The basic plan of fetal circulation: additional vessels
needed to allow fetal blood to secure oxygen and
nutrients from maternal blood at the placenta
• Two umbilical arteries: extensions of the internal
iliac arteries that carry fetal blood to the placenta
• Placenta: where exchange of oxygen and other
substances between the separate maternal and
fetal blood occurs; attached to uterine wall
• Umbilical vein: fetal structures carry most
oxygen-rich blood from the placenta to the fetus;
enters body through the umbilicus and goes to
the undersurface of the liver, where it gives off
two or three branches and then continues as the
ductus venosus
Fetal Circulation
In the fetus, partially oxygenated blood
is shunted from the right atrium to left
atrium through the foremen ovale.
Fetal Circulation
• Ductus venosus: continuation of the umbilical
vein; drains into inferior vena cava; allows blood
to bypass liver
• Foramen ovale: opening in septum between the
right and left atria; allows blood to bypass lungs
• Ductus arteriosus: small vessel connecting the
pulmonary artery with the descending thoracic
aorta; blood bypasses lungs
Placental Circulation
Changes in circulation at birth
• When umbilical cord is cut, the two umbilical
arteries, placenta, and umbilical vein no longer
function
• Umbilical vein within the baby’s body becomes the
round ligament of the liver
• Ductus venosus becomes the ligamentum venosum
of the liver
• Foramen ovale: functionally closed shortly after a
newborn’s first breath and pulmonary circulation is
established; structural closure takes approximately 9
months
• Ductus arteriosus: contracts with establishment of
respiration; becomes ligamentum arteriosum
Changes in circulation at birth
CYCLE OF LIFE: CARDIOVASCULAR ANATOMY
• Birth: change from placenta-dependent system
• Heart and blood vessels maintain basic structure and
function from childhood through adulthood
– Exercise thickens myocardium and increases the supply of
blood vessels in skeletal muscle tissue
• Adulthood through later adulthood: degenerative
changes
– Atherosclerosis: blockage or weakening of critical arteries
– Heart valves and myocardial tissue degenerate, reducing
pumping efficiency
6. Drains the lateral side of the arm …………basilic vein
7. Receives blood from the vertebral vein…………… subclavian vein
8. Receives lymphatic fluid…………………. subclavian vein
9. Deep vein in the brachium………..brachial vein
10. Drains the medial aspect of the leg and thigh ………..great saphenous vein
11. Received blood from the external jugular vein………subclavian vein
12. Drains the medial aspect of the arm………………… cephalic vein
13. Receives blood from the medial cubital vein……….. cephalic vein
14. Longest vein in the body…………. Great saphenous vein
15. Joins the internal jugular vein to form the brachiocephalic vein…….subclavian
16. Receives blood from the ulnar and radial veins ……………. brachial vein
17. Drains into the femoral vein…………. Great saphenous vein
18. Receives blood from the axillary vein……..subclavian vein
44. Empties into the brachial artery. Axillary artery
45. Supplies the small intestine and the ascending colon. Superior mesenteric artery
46. Traverses or runs through the armpit region. Axillary artery
47. First major, unpaired branch off the abdominal aorta. Celiac artery
48. Largest artery in the body.aorta
49. Second unpaired branch of the abdominal aorta. Superior mesenteric artery
50. Supplies the descending colon of the large intestine inferior mesenterid artery