Introduction to the Vascular System: Vascular Anatomy

Vascular Anatomy: An Introduction to the Vascular System

Glossary Terms

  • Artery: A blood vessel that carries blood away from the heart.

  • Arteriole: A small artery with a muscular wall; a terminal artery, which continues into the capillary network. Arterioles are the main control of blood flow (vascular resistance) in the circulatory system.

  • Capillary: A small blood vessel with only endothelium and basement membrane through which exchange of nutrients and waste occurs. Exchange of oxygen, carbon dioxide, waste, and nutrients mainly occurs at this level.

  • Collateral: A vessel, adjacent or parallel to another vessel, that can enlarge to aid in carrying blood flow around a blockage.

  • Venule: A small vein that is continuous with a capillary. The venous side of the capillaries is drained by venules.

  • Vein: A blood vessel that carries blood toward the heart.

Blood Vessel Structure and Function

General Structure of Blood Vessels

Blood vessels typically consist of three main layers or tunics:

  • Tunica Intima: The innermost layer, composed of endothelium and a basement membrane. It also forms the projections that create venous valves.

  • Tunica Media: The middle layer, primarily composed of smooth muscle cells, allowing for vasoconstriction and vasodilation. In arteries, it may contain internal and external elastic membranes.

  • Tunica Adventitia: The outermost layer, composed of connective tissue.

Key Differences Between Arteries and Veins

  • Arteries: Generally have thicker walls overall with more muscle and elastic fibers, especially large elastic arteries like the aorta, common carotid, and common iliac arteries. Arteries are classified not only by size but also by the composition of their walls.

  • Veins: Have thinner walls overall with less muscle compared to similarly sized arteries. They often contain valves.

Capillary Permeability and Exchange

  • Nutrient and oxygen exchange is simultaneous with carbon dioxide and waste exchange at the capillary level.

  • Capillary permeability to large molecules varies depending on the characteristics of the tissue bed; it is not the same in all tissues.

Arterioles and Resistance

  • Arterioles are the primary site of vascular resistance and control blood flow into the capillary beds.

  • They regulate tissue perfusion and systolic blood pressure by constricting or dilating, due to their concentric layers of smooth muscle cells.

Venous Valves

  • Venous valves are formed by projections of the intima layer.

  • They have only two leaflets (bicuspid) and normally allow for unidirectional flow, preventing bidirectional flow.

  • They are more numerous in the veins of the lower extremities due to gravity.

  • They are usually absent from veins in the thorax and abdomen.

Arterial Anatomy

Head and Neck Arteries

  • Brachiocephalic Artery (Innominate Artery): The first and largest branch off the aortic arch on the right side. It divides into the right subclavian artery and the right common carotid artery.

  • Left Common Carotid Artery: Typically arises directly from the aortic arch.

  • Subclavian Arteries: Supply the brain and neck, and the thoracic wall and shoulder. Branches include the thyrocervical trunk and costocervical trunk.

  • Common Carotid Arteries: Bifurcate into the internal carotid artery (ICA) and external carotid artery (ECA).

    • Internal Carotid Artery (ICA): Runs from the carotid bifurcation to the base of the skull without branching off (cervical segment). The petrous segment passes through the carotid canal. The intracranial segment includes cavernous, clinoid, ophthalmic, and communicating segments, giving off branches that contribute to the Circle of Willis.

      • The ophthalmic artery is usually the first branch of the internal carotid artery at the intracranial level.

    • External Carotid Artery (ECA): Has several branches, including:

      • Anterior Branches: Superior thyroid artery, lingual artery, facial artery.

      • Posterior Branches: Occipital artery, posterior auricular artery.

      • Terminal Branches: Superficial temporal artery, maxillary artery.

Intracranial Arteries and the Circle of Willis

  • Vertebral Arteries: Ascend via the cervical vertebrae, enter the cranium, and join to form the basilar artery.

  • Basilar Artery: Formed by the junction of the two vertebral arteries. Gives off branches like superior cerebellar artery, anterior inferior cerebellar artery, pontine arteries.

  • Posterior Cerebral Arteries: Terminal branches of the basilar artery.

  • Circle of Willis: A critical arterial anastomosis at the base of the brain, formed by branches of the internal carotid and vertebral arteries.

    • Components include: Anterior cerebral arteries, anterior communicating artery, internal carotid arteries, posterior communicating arteries, posterior cerebral arteries.

    • Collateral Pathway Example: If the left internal carotid artery is occluded, blood can be supplied from the right internal carotid artery through the anterior communicating artery to the left anterior cerebral artery, perfusing the brain.

Upper Extremity Arteries

  • Axillary Artery: Continuation of the subclavian artery.

  • Brachial Artery: Deep brachial artery is a branch.

  • Radial Artery:

    • The radial collateral artery and radial recurrent artery create a lateral vascular arcade for potential collateral flow.

    • Branches include the superficial palmar branch of the radial artery.

  • Ulnar Artery:

    • Branches include the interosseous artery and the recurrent ulnar artery.

    • The radial artery is NOT typically a branch of the ulnar arteries.

  • Palmar Arches:

    • Superficial Palmar Arch: Formed predominantly by the ulnar artery, which connects with the superficial palmar branch of the radial artery.

    • Deep Palmar Arch: Formed by the radial artery.

  • Collateral Pathway for Hand Perfusion: If the radial artery is harvested (e.g., for coronary artery bypass grafting), the hand would remain perfused by the ulnar artery via the superficial palmar arch, which connects with the superficial palmar branch of the radial artery, ensuring continuous blood flow.

Abdominal Arteries

  • Abdominal Aorta: Descends through the abdomen.

    • Celiac Trunk (or Celiac Artery): A major anterior branch, typically branching into the splenic artery, left gastric artery, and common hepatic artery.

      • The hepatic artery is part of the portal system.

    • Superior Mesenteric Artery (SMA): A major anterior branch.

    • Renal Arteries: Supply the kidneys (right and left).

    • Gonadal Arteries (Ovarian/Testicular): Typically arise from the abdominal aorta.

    • Inferior Mesenteric Artery (IMA): A major anterior branch.

  • Aortic Bifurcation: At the level of the 4^{th} lumbar vertebra, the abdominal aorta bifurcates into the right and left common iliac arteries.

  • Common Iliac Arteries: Each divides into an external and internal iliac artery.

    • External Iliac Arteries: Become the common femoral arteries after passing the inguinal ligament.

    • Internal Iliac Arteries: Also known as hypogastric arteries.

  • Collateral Pathways for Mesenteric Arteries: The superior and inferior mesenteric arteries are typically linked via the marginal artery of Drummond and the arc of Riolan, which can provide collateral flow in case of occlusion.

Lower Extremity Arteries

  • Common Femoral Artery: Formed by the external iliac artery passing the inguinal ligament.

  • Profunda Femoral Artery (Deep Femoral Artery): A major branch of the common femoral artery, often providing most collaterals that bypass superficial femoral or popliteal artery occlusions.

  • Superficial Femoral Artery (SFA): Delineated from the popliteal artery by the adductor canal.

  • Popliteal Artery: Located behind the knee.

    • Its terminal branches are the anterior tibial artery, posterior tibial artery, and peroneal artery.

    • The popliteal artery bifurcates into the anterior tibial artery and the tibioperoneal trunk, which then divides into the posterior tibial and peroneal arteries.

    • Gives off genicular arteries (e.g., descending genicular artery, inferior lateral genicular artery).

  • Anterior Tibial Artery: Continuous with the dorsalis pedis artery on the foot.

Venous Anatomy

Head and Neck Veins

  • Internal Jugular Veins: Drain into the brachiocephalic veins.

  • External Jugular Veins: Drain into the subclavian veins (not the brachiocephalic veins).

  • Vertebral Veins: Formed by a dense venous plexus and drain the posterior portion of the head and neck.

  • Transverse Sinus, Lateral Sinus, Cavernous Sinus: Intracranial venous sinuses.

  • Retromandibular Vein, Facial Vein, Anterior Jugular Vein, Superficial Temporal Vein, Occipital Vein.

Upper Thorax Veins

  • Brachiocephalic Veins (Right and Left): Formed by the confluence of the internal jugular and subclavian veins.

  • Superior Vena Cava: Formed by the confluence of the right and left brachiocephalic veins; drains blood from the head, neck, and upper extremities to the heart.

  • Internal Thoracic Veins.

Upper Extremity Veins

  • Superficial Veins:

    • Cephalic Vein

    • Basilic Vein

    • Median Cubital Vein

    • Median Antebrachial Vein

    • Interosseous veins are NOT superficial veins.

  • Deep Veins: Generally mirror the arteries (e.g., radial veins, ulnar veins, brachial veins, axillary vein).

    • Deep palmar venous arch, palmar digital veins.

Abdominal Veins

  • Inferior Vena Cava (IVC): The largest vein in the body; formed by the confluence of the common iliac veins.

    • Renal Veins: Drain kidneys into IVC (left and right).

    • Suprarenal Veins: Drain adrenal glands (left and right).

    • Gonadal Veins (Ovarian/Testicular): Right gonadal vein drains into the IVC; left gonadal vein typically drains into the left renal vein.

    • Inferior Phrenic Veins: Drain diaphragm (left and right).

    • Hepatic Veins: Drain the liver directly into the IVC.

Portal Venous System

  • The portal system includes the hepatic artery and portal vein, but the main portal vein is formed by other veins.

  • Main Portal Vein: Formed by the confluence of the splenic vein and the superior mesenteric vein (SMV), posterior to the neck of the pancreas.

  • Inferior Mesenteric Vein (IMV): Typically drains into the splenic vein or the confluence of the splenic and superior mesenteric veins.

  • Gastric Veins (Left and Right): Drain into the portal vein.

  • Esophageal Veins: Can be involved in portal hypertension.

  • Pancreaticoduodenal Arcade.

Lower Extremity Veins
Deep Venous System

  • The deep venous system starts at the deep plantar arch (which includes the plantar venous arch, plantar metatarsal veins, and plantar digital veins) and the deep veins of the foot.

  • Posterior Tibial Veins, Anterior Tibial Veins, and Peroneal Veins unite to form the popliteal vein.

  • Popliteal Vein: As it ascends through the adductor canal, the vein typically moves from medial to lateral of the artery.

  • Femoral Vein: Formed by the continuation of the popliteal vein.

  • Profunda Femoral Vein (Deep Femoral Vein): Joins the femoral vein to form the common femoral vein.

  • Common Femoral Vein: Continues as the external iliac vein above the inguinal ligament.

  • External Iliac Vein and Internal Iliac Vein join to form the common iliac vein.

  • Right and Left Common Iliac Veins unite to form the inferior vena cava.

Superficial Venous System

  • The superficial system originates from the dorsal venous arch of the foot (which includes dorsal metatarsal veins, dorsal digital veins, lateral marginal vein, and medial marginal vein).

  • Great Saphenous Vein: The longest vein in the body, ascends medially up the leg and thigh, dumping into the common femoral vein.

  • Small Saphenous Vein: Ascends posterior-laterally up the calf, typically draining into the popliteal vein.

  • Lateral Accessory Saphenous Vein, Medial Accessory Saphenous Vein.

  • Perforating Veins: Connect the superficial and deep venous systems (e.g., perforating veins of Dodd, Boyd, Sherman, Cockett).

Vascular Anatomy Practice Test

  1. Which layer of a blood vessel is primarily composed of smooth muscle cells, allowing for vasoconstriction and vasodilation?
    A) Tunica Intima
    B) Tunica Media
    C) Tunica Adventitia
    D) Endothelium

  2. Venous valves are formed by projections of which layer of the blood vessel wall?
    A) Tunica Adventitia
    B) Tunica Media
    C) Tunica Intima
    D) Basement membrane

  3. The first and largest branch off the aortic arch on the right side is the:
    A) Left Common Carotid Artery
    B) Right Subclavian Artery
    C) Brachiocephalic Artery
    D) Vertebral Artery

  4. The ophthalmic artery is usually the first branch of which artery at the intracranial level?
    A) External Carotid Artery
    B) Vertebral Artery
    C) Basilar Artery
    D) Internal Carotid Artery

  5. If the left internal carotid artery is occluded, which component of the Circle of Willis can provide collateral blood flow from the right internal carotid artery to the left anterior cerebral artery?
    A) Posterior Communicating Artery
    B) Middle Cerebral Artery
    C) Anterior Communicating Artery
    D) Posterior Cerebral Artery

  6. The superficial palmar arch is formed predominantly by which artery?
    A) Radial Artery
    B) Ulnar Artery
    C) Brachial Artery
    D) Axillary Artery

  7. At what vertebral level does the abdominal aorta typically bifurcate into the right and left common iliac arteries?
    A) L2 B) T{12}
    C) L4 D) S1

  8. Which artery is a major branch of the common femoral artery and often provides most collaterals that bypass superficial femoral or popliteal artery occlusions?
    A) Superficial Femoral Artery
    B) Anterior Tibial Artery
    C) Profunda Femoral Artery
    D) Peroneal Artery

  9. The main portal vein is formed by the confluence of which two veins?
    A) Right and Left Gastric Veins
    B) Splenic Vein and Inferior Mesenteric Vein
    C) Hepatic Veins and Superior Mesenteric Vein
    D) Splenic Vein and Superior Mesenteric Vein

  10. The left gonadal vein typically drains into which other vein?
    A) Inferior Vena Cava
    B) Left Renal Vein
    C) Superior Mesenteric Vein
    D) Splenic Vein

Answer Key:

  1. B) Tunica Media

  2. C) Tunica Intima

  3. C) Brachiocephalic Artery

  4. D) Internal Carotid Artery

  5. C) Anterior Communicating Artery

  6. B) Ulnar Artery

  7. C) L_4

  8. C) Profunda Femoral Artery

  9. D) Splenic Vein and Superior Mesenteric Vein

  10. B) Left Renal Vein