The document describes the structure and function of blood vessels in the human body. It discusses the three main types of blood vessels - arteries, capillaries, and veins. It explains how arteries deliver oxygenated blood from the heart to tissues via smaller muscular and elastic arteries, arterioles, and capillaries. It then describes how deoxygenated blood is returned to the heart from the tissues through venules, veins, and the superior and inferior vena cavae. The document provides detailed information on the anatomy and branches of major arteries and veins throughout the body.

1. BLOOD VESSELS

2. • The average man has approximately 5 -6
liters of blood in his body. This blood is
carried by different types of blood vessels.

3. Types of Blood Vessels
• Arteries: deliver oxygenated blood to the
tissues. (with the exception of the
pulmonary artery)
• Capillaries - microscopic blood vessels that
allow exchanges between blood and tissues
also return deoxygenated blood to the veins.
• Veins: which bring it back to the heart (with
the exception of the pulmonary veins).

6. Structure of a blood vessels
• Tunica externa (adventitia) - outermost layer
made of loose connective tissue. Serves to anchor,
protect and prevent overstretching
• Tunica media - middle layer composed of
smooth muscle; functions in dilation and
constriction of blood vessels
• Tunica interna (intima) - innermost layer made
of endothelium

9. Blood flow through tissues
• From the heart blood flows into
– Aorta
– Arteries
– Arterioles
– Capillaries
– Venules
– Veins
– Superior/ Inferior Vena Cava
• Back to the heart

10. The Arterial System
• The arterial system takes oxygenated
blood from the heart, and delivers it to
the capillaries.
• There are four main types of artery in
the body, each with a distinct structure
and function

11. Major arterial supply
• The aorta and its major branches
• Arterial supply to neck and head
• Arterial supply to upper extremities
• Arterial supply to thorax
• Arterial supply to abdomen
• Arterial supply to pelvic region and lower
extremities

13. 1. Elastic arteries
Larger arteries and its function is to ‘conduct’ blood from
the heart to regions of the body
Structure:
• Tunica Intima: Endothelial cells with a thin
subendothelium of connective tissue and discontinuous
elastic laminae.
• Tunica Media: The tunica media is comprised of 40-70
fenestrated elastic membranes with smooth muscle cells
and collagen between these lamellae. It is the thickest
part of an elastic artery.
• Tunica Adventitia: Thin layer of connective tissue
containing lymphatics, nerves and vasa vasorum

14. 2. Muscular arteries
This are medium distributing arteries
Structure:
• Tunica Intima: Consists of an endothelium, a
subendothelial layer and a thick elastic lamina.
• Tunica Media: Consists of around 40 layers of
smooth muscle connected by gap junctions in
order to allow coordinated contraction.
• Tunica Adventitia: Thin layer of connective
tissue containing minor vasa vasorum,
lymphatics and nerve fibres.

15. 3. Arterioles
• Arterioles are part of the microcirculation. They
carry blood from the muscular arteries to the
metarterioles.
Structure:
• Arteries with a diameter of less than 0.1mm are
classed as arterioles. They generally have around 3
layers of smooth muscle cells and the internal
elastic lamina is absent. The external elastic
lamina is only present in larger arterioles.

16. 4. Metarteriole
• Arteries that supply capillary beds are
known as metarterioles.
• Instead of having a continuous layer
of smooth muscle cells, intermediate rings
of smooth muscle are located at certain
points. These rings are known as
as precapillary sphincters, which contract
to control blood flow to the capillary bed.

17. The Capillaries
• Capillaries consist of one layer of endothelium.
They are specially adapted to provide a short
diffusion distance for nutrient and gaseous
exchange with the tissues they supply.
Capillary Beds
• Capillaries do not function independently. Instead
they form interweaving networks called capillary
beds.

18. Open Capillary bed

19. Closed capillary bed

20. a. Continuous Capillaries
There are three types of
capillaries
– Continuous: Continuous
capillaries are endothelial
cells provide an
uninterrupted lining, and
allow smaller molecules,
such as water and ion.
Example: skeletal
muscles,
fingers, gonads, and
skin

21. b. Fenestrated Capillaries
– Fenestrated capillaries
have pores in the
endothelial cells.
Example: endocrine
glands, intestines,
pancreas, and
the glomeruli of
the kidney

22. c. Sinusoidal Capillaries
• Sinusoidal capillaries are
highly modified, leaky
capillaries and have large,
irregularly shaped lumens
Their endothelial lining has
fewer tight junctions and
larger intercellular clefts
than ordinary capillaries
• Example. bone marrow,
lymph nodes and adrenal
glands etc.

23. The Venous System
• The venous system takes deoxygenated
blood from the capillaries, and delivers it to
the heart (with the exception of the
pulmonary veins). From the heart, blood can
be pumped to the lungs and re-oxygenated.

24. Major venous drainages
• Venous drainage of the head and neck
• Major tributaries of the inferior vena cava
• Venous drainage of the upper extremities
• Venous drainage of the lower extremities

25. Post-capillary Venules
• A post-capillary venule receives blood
from capillaries and empties into venules.
Structure:
• The wall is an endothelial lining with
associated pericytes and a diameter of 10-
30 micrometres.

26. Venules
• Venules are continuous with the post-capillary
venules. They move blood away from the capillary
beds.
Structure:
• The endothelium is associated with pericytes to
form a very thin wall. Venules can have a diameter
of up to 1mm. They also contain valves that press
together to restrict retrograde transport of blood.

28. Veins
• Veins are the major vessels of the venous
system. They are the final step in the return
of blood to the heart.
Structure:
• Veins generally have a larger diameter and a
thinner wall than the accompanying artery.
The vessel wall contains more connective
tissue, with less elastic and muscle fibres.

30. The structure may vary according to their size:
• Small and medium veins have a well developed
tunica adventitia and a thin tunica intima and media.
• Large veins have diameters greater than 10mm and
a thicker tunica intima. They have well developed
longitudinal smooth muscle in the tunica adventitia.
• Veins contain valves that primarily prevent the back-
flow of blood. They also act together with muscle
contraction, squeezing the veins to propel blood
towards the heart.

31. Great Arteries
• The aorta is the largest artery in the body. It
receives the cardiac output from the left
ventricle and supplies the body with
oxygenated blood via the systemic
circulation.

32. • The aorta can be divided into four sections:
1. The ascending aorta
2. The aortic arch
3. The thoracic (descending) aorta
4. The abdominal aorta.

34. 1. Ascending Aorta
• The ascending aorta arises from the aortic
orifice from the left ventricle and ascends to become
the aortic arch. It is 2 inches long in length and travels
with the pulmonary trunk in the pericardial sheath.
Branches
• The left and right aortic sinuses are dilations in the
ascending aorta, located at the level of the aortic
valve.
– Left coronary artery
– Right coronary artery

36. 2. Aortic Arch
• The aortic arch is a continuation of the ascending aorta and
begins at the level of the second sternocostal joint. It
arches superiorly, posteriorly and to the left before
moving inferiorly.
• The aortic arch ends at the level of the T4 vertebra. The
arch is still connected to the pulmonary trunk by
the ligamentum arteriosum. Aortic arch having three
branches
1. Brachiocephalic trunk
2. Left common carotid artery
3. Left subclavian artery

38. a. Brachiocephalic trunk
The first and largest branch that ascends laterally to
split into the right common carotid and right
subclavian arteries. These arteries supply the right
side of the head and neck, and the right upper limb.
• Right common carotid artery
• Right subclavian artery
• Thyroid ima artery

40. b. Left common carotid artery
Supplies the left side of the
head and neck.
– Internal carotid artery
– External carotid artery

43. c. Left subclavian artery
Supplies the left upper limb.

44. 3. Thoracic Aorta
• The thoracic (descending) aorta spans from
the level of T4 to T12. Continuing from the
aortic arch, it initially begins to the left of
the vertebral column but approaches the
midline as it descends. It leaves the thorax
via the aortic hiatus in the diaphragm, and
becomes the abdominal aorta.

45. Branches
In descending order:
1. Bronchial arteries: Paired visceral branches
arising laterally to supply bronchial and
peribronchial tissue and visceral pleura.
2. Mediastinal arteries: Small arteries that supply
the lymph glands and mediastinum.
3. Oesophageal arteries: Unpaired visceral
branches arising anteriorly to supply the
oesophagus.

46. 4. Pericardial arteries: Small unpaired arteries that
arise anteriorly to supply the dorsal portion of the
pericardium.
5. Superior phrenic arteries: Paired parietal branches
that supply the superior portion of the diaphragm.
6. Intercostal and subcostal arteries: Small paired
arteries that branch off throughout the length of the
posterior thoracic aorta. The 9 pairs of intercostal
arteries supply the intercostal spaces.
The subcostal arteries supply the flat abdominal wall
muscles.

48. 4. Abdominal Aorta
• The abdominal aorta is a continuation of the
thoracic aorta beginning at the level of the
T12 vertebrae. It is approximately 13cm
long and ends at the level of the L4 vertebra.
At this level, the aorta terminates by
bifurcating into the right and left common
iliac arteries that supply the lower body.

49. Branches
1. Inferior phrenic arteries: Paired parietal arteries
arising posteriorly at the level of T12. They supply
the diaphragm.

50. 2. Superior mesenteric artery: Unpaired visceral arteries
arises at the lower level of L1. It supplies the distal
duodenum, jejuno-ileum, ascending colon and part of the
transverse colon.
• Superior Mesenteric A.
• Jejunal and Ileal Arteries
• Inferior Pancreaticoduodenal A.
• Middle Colic A.
• Right Colic A.
• Ileocolic A
– Anterior Cecal A.
– Posterior Cecal A.
– Appendicular A.
– Ileal A.
– Colic A

52. 3. Coeliac artery: A large, unpaired visceral artery arising
anteriorly at the level of T12. It is also known as the celiac
trunk and supplies the liver, stomach, abdominal oesophagus,
spleen, the superior duodenum and the superior pancreas.
• Left Gastric A.
• Splenic A.
– Short Gastric Arteries (6)
– Splenic Arteries (6)
– Left Gastroepiploic A.
• Common Hepatic A.
– Cystic A.
– Right Gastric A.
– Gastroduodenal A.
• Right Gastroepiploic A.
• Superior
Pancreaticoduodenal A.
– Right Hepatic A.
– Left Hepatic A.

53. 4. Middle suprarenal arteries: Small paired
visceral arteries that arise either side posteriorly
at the level of L1 to supply the adrenal glands.
5. Renal arteries: Paired visceral arteries that arise
posteriorly at the level between L1 and L2. They
supply the kidneys.
6. Gonadal arteries: Paired visceral arteries that
arise anteriorly at the level of L2. Male gonadal
artery is referred to as the testicular artery and in
females, the ovarian artery.

55. 7. Inferior mesenteric artery: A large, unpaired
visceral artery that arises anteriorly at the level
of L3. It supplies the large intestine from the splenic
flexure to the upper part of the rectum.
• Left Colic A.
• Sigmoid Arteries (2 or 3)
• Superior Rectal A.
8. Median sacral artery: An unpaired parietal artery
that arises posteriorly at the level of L4to supply the
coccyx, lumbar vertebrae and the sacrum.

56. 9. Lumbar arteries: There are four pairs of parietal
lumbar arteries that arise posterolaterally
between the levels of L1 and L4 to supply the
abdominal wall and spinal cord.

59. 10.Common iliac arteries:
It is the terminal branch of abdominal artery. It arises posteriorly
at the level of L4 and supply blood to pelvis and lower limb.
• External Iliac A.
– Inferior epigastric artery
– Deep circumflex iliac artery
– Femoral artery
» Superficial epigastric artery
» Superficial iliac circumflex
» Superficial external pudendal
» Deep external pudendal
» Deep femoral artery
» Continues as popliteal artery
• Internal Iliac A.

62. 1. Superior vena cava
2. Inferior vena cava
Venous System

64. 1. Superior vena cava
• This great vein receives systemic blood
draining from all areas superior to the
diaphragm, except the heart wall. The major
branches are
 Right brachiocephalic vein
 Left brachiocephalic vein
• Brachiocephalic veins are formed by the
joining of the internal jugular and
subclavian veins on its side.

65. 2. Inferior vena cava
• The widest blood vessel in the body, this vein
returns blood to the heart from all body regions
below the diaphragm. The abdominal aorta lies
directly to its left.
• The paired common iliac veins join at L5 to
form the distal end of the inferior vena cava.
From this point, it receiving venous blood from the
abdominal walls, gonads, and kidneys.
Immediately above the diaphragm, the inferior
vena cava ends as it enters the inferior aspect of
the right atrium.

66. Veins of the Head and Neck
• Three pairs of veins collect most of the
blood draining from the head and neck
– The external jugular veins, which empty into
the subclavians
– The internal jugular veins
– The vertebral veins, which drain into the
brachiocephalic vein

67. Dural venous sinuses
• Veins of the brain
drain into the dural
venous sinuses, an
interconnected series
of enlarged chambers
located between the
duramater layers.

68. • The inferior sagittal sinus drains into the
straight sinus posteriorly. The superior sagittal
and straight sinuses then empty into the
transverse sinuses. These drain into the S-
shaped sigmoid sinuses, which become the
internal jugular veins.
• The cavernous sinuses receive venous blood
from the ophthalmic veins of the orbits and the
facial veins, which drain the nose and upper lip
area

70. • External jugular veins. The right and left external
jugular veins drain superficial scalp and face
structures and then empty into the subclavian
veins.
• Vertebral veins. drain the cervical vertebrae, the
spinal cord, and some small neck muscles. They
run inferiorly through the transverse foramina of
the cervical vertebrae and join the brachiocephalic
veins at the root of the neck.

71. • Internal jugular veins (paired): It receive blood draining
from the brain.
• They arise from the dural venous sinuses, exit the skull via
the jugular foramina, and then descends, as they move
inferiorly, they receive blood from some of the deep veins
of the face and neck branches of the facial and superficial
temporal veins.
• At the base of the neck, each internal jugular vein joins the
subclavian vein on its own side to form a brachiocephalic
vein.

74. Veins of the Upper Limbs and Thorax
• The superficial veins of the upper limbs are
larger than the deep veins and are easily
seen just beneath the skin. The median
cubital vein, crossing the anterior aspects of
the elbow
• Blood draining from the mammary glands
and the first two to three intercostal spaces
enters the brachiocephalic veins.

75. Deep Veins of the Upper Limbs
• The distal deep veins of the upper limb are the radial and
ulnar veins. The deep and superficial venous palmar arches
of the hand drains into the radial and ulnar veins of the
forearm, which then unite to form the brachial vein of the
arm. As the brachial vein enters the axilla, it becomes the
axillary vein, which becomes the subclavian vein at the
level of the first rib.
Superficial Veins of the Upper Limbs
• The superficial venous system begins with a plexus of
superficial veins in the dorsum of the hand distal forearm,
this plexus drains into two major superficial veins the
cephalic and basilic veins. Both veins are drained in to
auxiliary vein.

77. The Azygos System
• Thoracic tissues and the thorax wall are drained
by a complex network of veins called the azygos
system. It consists of the following vessels.
• Azygos vein. Located against the right side of the
vertebral column. It originates in the abdomen,
from the right ascending lumbar vein that drains
right abdominal cavity wall and from the right
posterior intercostal veins that drain the chest
muscles.
• At the T4 level, it arches over the great vessels that
run to the right lung and empties into the superior
vena cava.

78. 1. Hemiazygos vein: This vessel ascends on the
left side of the vertebral column. Its origin,
from the left ascending lumbar vein and the
lower (9th - 11th) posterior intercostal veins
2. Accessory hemiazygos vein. The accessory
hemiazygos completes the venous drainage of
the left (middle) thorax. It receives blood from
the 4th–8th posterior intercostal veins
Both veins are empty into the azygos vein.

80. Veins of abdomen
• Lumbar veins:- drain the posterior abdominal wall. They
empty both directly into the inferior vena cava and into the
ascending lumbar veins of the azygos system of the thorax.
• Gonadal (testicular or ovarian) veins:- The rt gonadal
vein drains the ovary or testis on the right side of the body
and empties into the inferior vena cava. The left gonadal
vein drains into the left renal vein superiorly.
• Renal veins:- The right and left renal veins drain the
kidneys.
• Suprarenal veins:- drains the adrenal gland on the right
and empties into the inferior vena cava. The left suprarenal
vein drains into the left renal vein.

82. Portal Circulation
• Hepatic portal vein begins at the L2 level. Numerous
tributaries from the stomach and pancreas contribute to
the hepatic portal system. The major vessels are as follows:
1. Superior mesenteric vein: Drains the entire small
intestine, part of the large intestine and stomach.
2. Splenic vein: Collects blood from the spleen, parts
of the stomach and pancreas, and then joins the
superior mesenteric vein to form the hepatic portal
vein.
3. Inferior mesenteric vein: Drains the distal portions
of the large intestine and rectum and joins the splenic
vein just before that vessel unites with the superior
mesenteric vein to form the hepatic portal vein.

83. • Hepatic veins. The right, left, and middle
hepatic veins carry venous blood from the
liver to the inferior vena cava.
• Cystic veins. The cystic veins drain the
gallbladder and join the portal veins in the
liver.
• Inferior phrenic veins. The inferior phrenic
veins drain the inferior surface of the
diaphragm.

86. Deep veins of Lower
extrimities
• After being formed by the union of the medial and lateral
plantar veins, the posterior tibial vein ascends deep in the
calf muscle and receives the fibular vein.
• The anterior tibial vein, which is the superior continuation
of the dorsalis pedis vein of the foot, unites at the knee
with the posterior tibial vein to form the popliteal vein,
which crosses the back of the knee.
• The popliteal vein emerges from the knee, it becomes the
femoral vein, which drains the deep structures of the thigh.
The femoral vein becomes the external iliac vein as it
enters the pelvis. In the pelvis, the external iliac vein unites
with the internal iliac vein to form the common iliac vein.

87. • Superficial veins - The great and small
saphenous veins issue from the dorsal
venous arch of the foot.

89. Fetal Circulation
• Placenta - site where exchange of materials
between fetus and mother occur
• Umbilical arteries (2) - carry fetal blood high
in CO2 / low in O2 to the placenta
• Umbilical vein - returns oxygenated blood
from the placenta to the fetus

90. Fetal Circulation
• Ductus venosus - allows blood to bypass the
liver
• Foramen ovale - opening in interatrial
septum allowing blood to bypass the lungs
Blood flows from right atrium to the left
atrium
• Ductus arteriosus - vessel connecting
pulmonary artery to the aorta

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