Vascular System Overview

VASCULAR SYSTEM

Chapter 8

Copyright © 2023 by Elsevier, Inc. All rights reserved.

Function of Vascular Structures

  • The vascular system works in concert with the heart and lymphatics to:

    • Transport gases, nutrient materials, and other essential substances to the tissues.

    • Transport waste products from the cells to the appropriate sites for excretion.

Anatomy of Vascular Structures

  • List of major vascular structures includes:

    • Subclavian artery

    • Subclavian vein

    • Cephalic vein

    • Porta

    • Axillary vein

    • Axillary artery

    • Superior vena cava

    • Inferior vena cava

    • Descending aorta

    • Brachial artery

    • Basilic vein

    • Median cubital vein

    • Radial artery

    • Ulnar artery

    • Palmar digital veins

    • Digital artery

    • Basilar artery

    • Internal carotid artery

    • External carotid artery

    • External jugular vein

    • Internal jugular vein

    • Vertebral arteries

    • Common carotid arteries

    • Pulmonary arteries

    • Pulmonary veins

    • Heart

    • Celiac trunk

    • Hepatic veins

    • Renal veins

    • Renal artery

    • Gonadal vein

    • Gonadal artery

    • Common iliac vein

    • Common iliac artery

    • Internal iliac artery

    • Internal iliac vein

    • External iliac vein

    • External iliac artery

    • Great saphenous vein

    • Femoral artery

    • Femoral vein

    • Popliteal artery

    • Popliteal vein

    • Small saphenous vein

    • Anterior tibial artery

    • Posterior tibial artery

    • Peroneal artery

    • Anterior/posterior tibial veins

    • Dorsal venous arch

    • Dorsal digital vein

    • Arcuate artery

    • Dorsal digital arteries

Function of Blood Vessels

  • Arteries: Carry blood away from the heart.

  • Veins: Carry blood towards the heart and back from the tissues.

  • Observations on blood flow:

    • Arteries divide into progressively smaller branches called arterioles.

    • Arterioles lead into capillaries, which branch and form networks for material exchange between blood and tissue fluid.

    • After capillaries, blood collects in small veins called venules.

    • Venules unite to form larger vessels, eventually returning blood to the heart for recirculation.

Anatomy of Blood Vessel Layers

  • Arteries consist of three layered structures:

    1. Tunica intima (inner layer):

      • Composed of several components:

        • A layer of endothelial cells lining the arterial lumen.

        • A delicate connective tissue layer.

        • An elastic layer made of a network of elastic fibers.

    2. Tunica media (middle layer):

      • Composed of smooth muscle fibers mixed with elastic and collagenous tissues.

    3. Tunica adventitia (external layer):

      • Composed of loose connective tissue with smooth muscle fibers and elastic tissue bundles.

  • Vasa vasorum: Refers to the tiny arteries and veins that supply the walls of blood vessels.

Differences Between Arteries and Veins

  • Arteries:

    • Hollow elastic tubes that carry blood away from the heart.

    • Enclosed within a sheath that includes a vein and nerve.

    • Smaller arteries have less elastic tissue and more smooth muscle than larger arteries.

    • Elasticity of larger arteries helps to maintain steady blood flow; e.g., the pulsatile abdominal aorta maintains diameter regardless of respiration.

  • Veins:

    • Hollow collapsible tubes with a diminished tunica media that carry blood toward the heart.

    • Appears collapsed and contains less elastic tissue or muscle in their walls.

    • Typically have larger total diameters compared to arteries and move blood more slowly.

    • Contains valves that prevent backflow, ensuring blood flows only towards the heart.

    • Inferior vena cava (IVC) slightly dilates with suspended respiration.

Aorta Overview

  • The aorta is the largest principal artery in the body, divided into five sections:

    1. Root of the aorta

    2. Ascending aorta and arch

    3. Descending aorta

    4. Abdominal aorta and its branches

    5. Bifurcation into the iliac arteries.

Brachiocephalic Artery

  • Branches include:

    • Aortic arch

    • Ascending aorta

    • Common carotid artery

    • Subclavian artery

    • Thoracic (descending) aorta

    • Abdominal aorta

    • Iliac arteries.

Measurement of the Aorta

  • Transverse Plane:

    • Aorta is a circular structure located anterior to the spine and slightly to the left of the midline.

    • Multiple scans are taken from the xiphoid to the bifurcation for measurement at various levels, including diaphragm, above renal vessels, inferior to renal vessels, and at the bifurcation.

  • Longitudinal Plane:

    • The aorta is visualized as a long pulsatile tubular structure anterior and to the left of the spine.

    • Landmarks include the left lobe of the liver and the gastroesophageal junction.

    • Imaging should be performed proximal, mid, and distal to the bifurcation, with the transducer positioned perpendicular to the abdomen.

Color Doppler and Aorta Measurement

  • Color Doppler is employed to demonstrate patient lumen of the aorta.

  • Low to medium gain is utilized to visualize the aortic walls.

  • Proper positioning and angulation of the probe may be required to manage fatty tissue or bowel gas artifacts.

Anterior Branches of the Abdominal Aorta

  • Celiac trunk (CT)

  • Common hepatic artery (CHA)

  • Gastroduodenal artery (GDA)

  • Right and left gastric arteries

  • Splenic artery (SA).

Celiac Trunk

  • Visualized sonographically, it arises anteriorly from the abdominal aorta just below the diaphragm.

  • The superior mesenteric artery branches off just inferior to the celiac trunk.

Common Hepatic Artery

  • This small artery branches anteriorly and to the right from the celiac trunk and further divides into the right and left hepatic arteries as it enters the liver.

Left Gastric Artery

  • A small branch of the celiac trunk responsible for supplying blood to the lower third of the esophagus and upper right stomach.

Splenic Artery

  • The largest branch of the celiac trunk that runs along the superior border of the pancreas.

Superior Mesenteric Artery (SMA)

  • Supplies the small bowel via five main branches:

    • Inferior pancreatic artery

    • Duodenal artery

    • Colic artery

    • Ileocolic artery

    • Intestinal artery.

Inferior Mesenteric Artery (IMA)

  • Supplies the descending colon, sigmoid colon, and rectum through three branches:

    • Left colic artery

    • Sigmoid artery

    • Superior rectal artery.

Renal Arteries

  • The right renal artery is longer than the left and courses posterior to the IVC before entering the hilum of the right kidney.

Sonography of the Aorta

  • Imaging is achieved due to acoustic impedance changes between the aorta's elastic walls and its blood-filled lumen.

  • Evaluations include diameter assessment, detecting calcifications, thrombus, or dissection, using various acoustic windows.

Pathology of the Aorta

Arteriosclerosis vs Atherosclerosis

  • Arteriosclerosis: Condition where the arterial walls become thick and stiff, restricting blood flow.

  • Atherosclerosis: A specific subtype of arteriosclerosis, characterized by the build-up of plaque (fats and cholesterol) that restricts blood flow.

Abdominal Aortic Aneurysm (AAA)

  • Defined as a localized dilation of an artery with a diameter increase greater than 1.5 times its normal diameter.

  • Majority are true aneurysms affecting all three layers of the arterial wall.

  • Majority (95%) are infrarenal.

  • Surgical intervention is suggested for aneurysms greater than 5 cm in diameter.

Classification of Aneurysms

True Aneurysm

  • Forms when the tensile strength of the wall decreases due to underlying diseases.

Pseudoaneurysm

  • A pulsatile hematoma resulting from blood leakage into surrounding tissue, encapsulated but not lined by all artery layers.

Rupture of Aortic Aneurysm

  • High risk of mortality associated with a rupture, with a classic presentation of severe abdominal pain, shock, and a palpable expanding abdominal mass.

  • Computed tomography is the preferred imaging modality for evaluating potential ruptures.

Inferior Vena Cava (IVC)

  • Formed by the union of the common iliac veins and ascends through the retroperitoneal space.

  • The IVC serves as a landmark for other abdominal structures and may be visualized using the liver as an acoustic window.

Abnormalities of the Inferior Vena Cava

  • May include congenital variations, IVC dilation, tumors, or thrombosis.

Hepatic Veins

  • These veins drain the liver's unoxygenated blood into the IVC at the diaphragm's level and may show various echogenic features in sonographic imaging.

Portal Venous System

  • The portal vein is formed by the union of the superior mesenteric vein, inferior mesenteric vein, and splenic vein, draining blood from the gastrointestinal tract to the liver.

Portal Venous Hypertension

  • Results from obstruction of the portal vein causing collateral pathways to develop and exhibits several sonographic findings, such as dilated veins and changes in venous flow patterns.

Spontaneous Shunting

  • Occurs through various anastomoses, which allow blood to divert from the obstructed portal system, manifesting in conditions like esophageal varices or umbilical vein distension, indicative of portal hypertension.

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