|Laboratory Exercise 15: Anatomy of the Blood Vessels
Blood vessels, the tubes, transport blood to and from the tissues. Arteries carry blood away from the heart to the tissues. In the tissues, the arterioles divide into smaller vessels, the capillaries, where nutrients and wastes are exchanged.
From the tissues, the capillaries merge to form venules and veins, which return blood to the heart. Lymphatic vessels act as auxiliary veins helps return tissue fluid to the circulation. The lymphatic vessels originate as blind-ended vessels in the tissues. Blood capillaries are open-ended vessels.
where exchange occurs
A. Gross Anatomical Features of Blood Vessels
Arteries – are thick-walled structures to withstand high blood (hydrostatic) pressure. The elastic membranes in their walls allows for expansion and control of the blood pressure. The lumen is round and small in diameter.
Veins – are thin-walled structures, with less elastic membranes, and large diameter lumen. Many veins and lymphatic vessels have valves in their walls. A valve consists of two semilunar flaps that open to allow return of blood or lymph to the heart and close to prevent backflow that results from the effect of gravity.
B. Microscopic Anatomy of Artery and Vein
The wall of a muscular artery is composed of three layers:
1. Tunica intima – inner layer of simple squamous epithelium (endothelium), a small amount of loose connective tissue, and the internal elastic membrane circling the lumen as the outer most part of the tunica intima.
2. Tunica media – thick middle layer composed of circular smooth muscle and broken elastic membranes (fenestrated membranes). The external elastic membrane is the outer most part of the tunica media.
3. Tunica externa (adventitia) – outer layer composed of loose connective tissue, containing small nutrient vessels, vasa vasorum and small nerves of the autonomic nervous system, nervi vasorum.
The smooth muscle of the tunica media regulates the lumen diameter of the muscular arteries via the autonomic nervous system. Relaxation of the muscle increases lumen diameter – vasodilation – and blood volume to a particular area. Contraction of the muscle decreases lumen diameter – vasoconstriction – and blood volume to a particular area.
The walls of the veins are composed of the same three layers, but are thinner as they are not subjected to as much pressure as the artery’s wall and do not distribute blood to the tissues but collects blood from the tissues. The vein walls are less muscular with a reduced tunica media but a relatively thick tunica externa.
C. Major Blood Vessels
Outlined below are the main vascular circuits by which blood travels to and from the heart. For arteries, begin with the heart, work distally. For veins, start peripherally and trace the venous return to the heart. Names of blood vessels often reflect their location.
Outline of Major Systemic Arteries
A. Aorta and its Branches
Aortic semilunar valve
Ascending aorta left coronary artery
right coronary artery
Brachiocephalic Right Common Carotid* right side of head and neck
Right Subclavian → right upper extremity (see section B.)
Left Common Carotid* left side of head and neck
Left Subclavian left upper extremity (see section B.)
Intercostals intercostals and chest muscles, pleurae
Superior Phrenics posterior and superior surfaces of diaphragm
Bronchials bronchi of lungs
Inferior Phrenics inferior surface of diaphragm
Celiac Common Hepatic liver
Left Gastric stomach and esophagus
Splenic spleen, pancreas, stomach
Superior Mesenteric small intestine, cecum, ascending and transverse colon
Suprarenals → adrenal (suprarenal) glands
Renals → kidneys
Gonadals Testiculars testes
Inferior Mesenteric Transverse, descending, sigmoid colon, rectum
Common Iliacs (see section C.)
B. Arteries of the Upper Limb
Brachial Artery arm
Radial Artery* (lateral) forearm
Ulnar Artery (medial) forearm
Palmer Arches hand
C. Arteries of the Lower Limb
Common Iliac Artery
Internal Iliac Artery pelvis and perineum
External Iliac Artery lower limb, lower abdominal wall
Femoral Artery* thigh region
Popliteal (behind the knee) Artery* knee joint and popliteal region
Anterior Tibial Artery Dorsalis Pedis Artery* dorsum of foot
Tibioperoneal trunk posterior leg
Posterior Tibial Artery plantar region of foot
Peroneal Artery (lateral) lateral leg region
*Blood vessels where pulse can be taken.
Outline of Major Systemic Veins
A. Veins of the upper limb
Venous Networks of Hand
Medial Basilic Vein Cephalic Vein (Lateral)
(superficial arm and forearm)
Internal Jugular Veins (large) drains blood from the veins
of brain, head and neck, these veins are medial.
External Jugular Veins (small) drains blood from veins
of superficial regions of head and neck, these veins are
Superior Vena Cava
B. Veins of the Lower Limb
Dorsal / Plantar Venous Arches of Foot
Small Saphenous Vein Deep Veins
(posterior leg) (peroneal, anterior and posterior
tibialis draining the leg)
Great Saphenous Vein
(medial leg, anterior thigh)
Femoral Vein Popliteal Vein
(thigh) (knee joint and popliteal region)
External Iliac Vein Common Iliac Vein Inferior Vena Cave
(testes or ovary)
Arteries of the Brain - Circle of Willis
The major cerebral arteries form the circle of Willis. The circle of Willis surrounds the infundibulum of the pituitary.
The anterior cerebral arteries are branches of the internal carotid arteries, the posterior cerebral arteries are branches of the vertebral arteries. The vertebral arteries run through the transverse foramen of the cervical vertebrae.
From internal carotid arteries there are the;
Anterior cerebral arteries, connecting the 2 anterior cerebral arteries is the
anterior communicating artery
Middle cerebral arteries
Posterior communicating arteries
From vertebral arteries the basilar artery branches off. The basilar artery then gives off the cerebellar arteries along the base of the cerebellum.
From the basilar artery the posterior cerebral arteries branch off. Connecting the posterior cerebral arteries to the anterior cerebral arteries are the posterior communicating arteries. These 4 arteries form the circle of Willis.
D. Portal Circulation
For the most part venous blood follows a direct route to the right atrium. However, blood leaving the stomach and intestines contain nutrients absorbed from the gastrointestinal tract. The hepatic portal vein shunts this blood to the liver, to enable the liver to remove nutrients for later use by the body’s cells and to detoxify harmful substances.
A portal system is one that begins and ends in capillaries. The hepatic portal system begins in the capillaries of the gastrointestinal tract and ends in capillaries of the liver.
The hepatic portal vein forms from a merger of the superior mesenteric and splenic veins. The splenic vein receives branches of the inferior mesenteric, pancreatic and short gastric vein. The right and left gastric veins drain directly into the portal vein near the stomach’s pyloric region.
Hepatic veins drain the blood from the liver into the inferior vena cava, which returns the blood to the heart.
E. Lymphatic System
Lymphatic vessels collect excess tissue fluid and return it to the venous system. The lymphatic system begins as blinded-ended capillaries within the intestinal villi. These lymphatic capillaries are called lacteals. From the lacteals the lymph fluid flows into larger and larger lymphatic veins. Along the path of the lymphatic veins are lymph nodes. The lymph nodes house lymphocytes and macrophages that defend the body against foreign substances. The nodes are in a strategic position to engulf and destroy antigenic materials and so “sterilize” the lymph before it is returned to the blood circulatory system.
The large lymphatic veins then lead into two collecting ducts. The right lymphatic duct drains the upper right side of the body and empties into the right subclavian vein. The major collecting duct, the left lymphatic or thoracic duct, drains the rest of the body and empties into the left subclavian vein.