This section describes the central vasculature and its structures.

Arterial Circulation

The Aorta: The systemic vessel that ascends from the left ventricle of the heart is called the ascending portion of the aorta. The aorta arises from the left ventricle, behind the lower border of the third left costal cartilage and passes up and to the right to curve backwards behind the upper border of the second left costal cartilage. The ascending aorta is closely related to both the pulmonary trunk and the superior vena cava. At its base are attached the three cusps of the aortic valve. Just above the cusps are three dilations, the aortic sinuses, from which arise the coronary arteries. It is within the fibrous pericardium and bound together with the pulmonary trunk in a layer of serous pericardium. Within the pericardial sac it is possible to pass an instrument between the aorta and superior vena cava, around the back of the aorta and pulmonary trunk. This is the transverse sinus.

The aortic arch:  The arch passes backwards and to the left behind the right half of the munubrium. Crossing the arch anterolaterally are the left phrenic, left vagus, left vagal cardiac branch and left sympathetic cardiac branch. As the vagus reaches the inferior border of the arch it gives off the left recurrent laryngeal nerve which passes backwards around the ligamentum arteriosum, to ascend between the trachea and esophagus. The upper part of the arch gives rise to the brachiocephalic trunk, left common carotid and left subclavian arteries.

The thoracic aorta:  The thoracic aorta lies in the posterior mediastinum closely applied to the left anterolateral aspect of the vertebral column. It begins as a continuation from the aortic arch at the lower border of the fourth thoracic vertebra. As it descends in the thorax the aorta moves to the right so as to lie directly anterior to the mid line as it passes behind the median arcuate ligament into the abdomen. In the upper half of its course the aorta lies behind the left primary bronchus, left pulmonary artery and left pulmonary veins. The esophagus at first lies to the right, but at the diaphragm comes to lie anterolateral and to the left.  Two types of vessels arise from the thoracic aorta - the visceral arteries which supply the pericardium, lungs, bronchi and esophagus, and the parietal arteries which supply the thoracic wall. The esophagus receives four or five branches which arise from the anterior surface of the aorta, to pass down wards and laterally to the esophagus forming an anastomosing plexus. The esophageal arteries anastomose with branches of the inferior thyroid above, and the left gastric below. The bronchial arteries are variable in number and pass along the primary brochi to reach the lungs. Nine pairs of posterior intercostal arteries arise from the posterior aspect of the descending aorta. These arteries come to lie the the subcostal grooves below the the third to eleventh ribs. The arteries are separated from the pleural cavity by the parietal pleura, but may easily be rutured and bleed into the pleural cavity. The upper two intercostal spaces are supplied by the superior intercostal artery from the costocervical trunk of the subclavian artery.

Brachiocephalic Artery: The first vessel to branch from the aortic arch is the brachiocephalic artery. It is very short and branches at the level of the clavicle to form the right common carotid artery.

Left and Right Coronary Arteries: The right and left coronary arteries are the only branches that arise from the ascending aorta. The coronary arteries supply blood to the cardiac muscle.

Internal and External Carotids: The common carotid artery bifurcates into the internal and external carotid arteries slightly below the angle of the mandible. By pressing gently on this area, you can palpate your pulse.

Left and Right Common Carotids: The common carotid arteries course upwards in the neck along either lateral side of the trachea. Several small vessels arise from the common carotid artery to supply blood to the larynx, thyroid, anterior neck muscles and lymph glands of the neck. The right common carotid artery transports blood to the right side of the head and the neck, and the right subclavian artery, which transports blood to the right upper limb.  The second and third branches of the aortic arch are the left common carotid artery which transports blood to the left side of the head and the neck, and the left subclavian artery, which transports blood to the left upper limb.

Left and Right Vertebral Artery: From each subclavian artery arise a vertebral artery that carries blood to the brain as well as a short thyrocervical trunk and an internal thoracic artery.

Left and Right Subclavian: the right subclavian artery branches off the brachiocephalic trunk, and the left subclavian artery arises directly from the aortic arch. Each subclavian artery passes laterally deep to the clavicle, carrying blood toward the arm.

Axillary: The subclavian artery becomes the axillary artery as it passes into the axillary region. Several small branches arise from the axillary artery and supply blood to the tissue of the upper thorax and shoulder region.

Deep Brachial: A deep brachial artery branches from the brachial artery and curves posteriorly near the radial nerve to supply the triceps brachii muscle.

Brachial: The brachial artery is the continuation of the axillary artery through the brachial region. The brachial artery courses on the medial side of the humerus, where it is a major pressure point and the most common site for determining blood pressure.

Radial and Ulnar Arteries: The brachial artery bifurcates into the radial and ulnar arteries, which supply blood to the forearm and a portion of the hand and digits.

Celiac: The celiac trunk arises from the abdominal aorta and divides into three arteries: the splenic, left gastric, and the common hepatic arteries.

Right Renal: Arterial blood enters the kidney at the hilum through the renal artery, which divides into interlobar arteries that pass between the renal pyramids through renal columns.

Abdominal Aorta: The abdominal portion of the aorta is the segment of the aorta between the diaphragm and the level of the fourth lumbar vertebra. The first branches of the abdominal aorta are the paired inferior phrenic arteries.

Common Iliac: The abdominal aorta terminates in the posterior pelvic area by dividing into the right and left common iliac arteries. These vessels pass downward and divided approximately 5cm and terminate by dividing into the internal and external iliac arteries.

Internal Iliac: The internal iliac artery has extensive branches to supply arterial blood to the gluteal muscles and the organs of the pelvic region.

External Iliac: The external iliac artery gives off two branches before exiting the pelvic cavity beneath the inguinal ligament. Once through the inguinal canal, the external iliac artery becomes the femoral artery.

Common Femoral: The femoral artery passes through an area called the femoral triangle on the upper medial portion of the thigh. At this point, the femoral artery is close to the surface and is an important arterial pressure point.

Popliteal Artery: The femoral artery becomes the popliteal artery as it passes across the posterior aspect of the knee.

Central Venous Circulation

External Jugular: blood from the scalp, portions of the face, and the superficial neck regions is drained by the external jugular veins. These vessels descend on either lateral side of the neck and drain into the right and left subclavian veins. The external jugular veins are more superficial and usually drains blood primarily from the posterior head, neck, and drain into the subclavian vein.

(Seeley, 1997)

Internal Jugular: The paired internal jugular veins drain blood from the brain, meninges, and deep regions of the face and neck. The internal jugular veins are much larger and deeper than the external jugular veins. They drain blood from the cranial vault and the anterior head, face, and neck. The internal jugular vein is formed primarily as the continuation of the venous sinuses of the cranial vault. Once the internal jugular veins exit the cranial vault, they receive several venous tributaries that that drain the external head and face. The internal jugulars join the subclavian veins on each side of the body to form the brachiocephalic veins.

(Seeley, 1997)

Subclavian: The axillary vein becomes the subclavian vein at the margin of the first rib. The subclavian veins receive blood from the external jugulars. The left and right subclavian veins are located behind the clavicles. The internal jugular veins join the subclavian veins on each side of the body to form the brachiocephalic veins.

Superior Vena Cava: One of the three major veins returning blood from the body to the right atrium, the superior vena cava returns blood from the head, neck, thorax, and upper limbs. It is formed by the union of the two brachiocephalic veins.

Hepatic portal veins (superior mesenteric vein & splenic vein): Blood from the liver is drained by hepatic veins that empty into the inferior vena cava. Blood from the cystic vein also enters the hepatic veins. The hepatic vein joins the inferior vena cava. (Figure 21-18). The blood entering the liver through the hepatic portal vein is rich with nutrients collected from the intestines, but it can also contain a number of toxic substances harmful to the tissues of the body. The hepatic portal vein, the largest vein of the system, is formed at the union of the superior mesenteric vein, which drains the small intestine, and the splenic vein, which drains the spleen.

(Neeter, 1997)

Inferior Vena Cava: The right atrium receives venous blood from the superior vena cava, which drains the upper potion of the body, and from the inferior vena cava, which drains the lower portion such as the abdomen, pelvis, and lower limbs.

Veins of the Lower Limb: The veins of the lower limb consist of superficial and deep groups. The distal deep veins are paired and follow the same path as the arteries, whereas the proximal deep veins are unpaired. The anterior and posterior tibial veins are paired and accompany the anterior and posterior tibial arteries. The unite just inferior to the knee to form the single popliteal vein, which ascends through the thigh and becomes the femoral vein. The femoral vein becomes the external iliac vein. (Figure 21-19)

(Neeter, 1997)

Small and Great Saphenous veins: The superficial veins of the lower extremity are the small and great saphenous veins. The small saphenous vein arises from the lateral side of the foot and empties into the popliteal vein behind the knee. The great saphenous vein, the longest in the body, originates over the dorsal and medial side of the foot and ascends along the medial side of the leg and thigh to empty into the femoral vein (figure 21-19).  

Veins of the Thorax: Three major veins return blood from the thorax to the superior vena cava: The right and left brachiocephalic veins and the azygos vein. The thoracic drainage to the brachiocephalic veins is through the anterior thoracic wall by way of the internal thoracic veins. They receive blood from the anterior intercostals veins. Blood from the posterior thoracic wall is collected by posterior intercostals veins that drain into the azygos vein on the right and the hemiazygos or accessory hemiazygos vein on the left. The hemiazygos and accessory hemiazygos veins empty into the superior vena cava (figure 21-16).

(Neeter, 1997)

Ascending Lumbar Veins: Blood from the posterior abdominal wall drains into the ascending lumbar veins. These veins are continuous superiorly with the hemiazygos on the left and the azygos on the right. Blood from the rest of the abdomen, pelvis, and lower limbs returns to the heart through the inferior vena cava (figure 21-16).

Basic Study Questions

1.  Describe the major arteries and veins of the upper and lower extremities

2.  What type of vessel has the most impact upon blood pressure and why?

3.  Describe the general function and structure of arteries, arterioles, veins, venules and capillaries.

4.  For what purpose is the Allen's test performed?

5.  Where is the blood pressure the lowest?

Additional Study Questions