Human Anatomy: Part 2 - K. A. Dyubenko, A. K. Kolomiysev, Yu. B. Chaykovsky 2008

Special Part
Cardiovascular System, systema cardiovasculare — Venous System
Veins of the Systemic Circulation — Superior Vena Cava System

The SUPERIOR VENA CAVA, v. cava superior* (Fig. 61), is 5–6 cm long and 2.5 cm wide. It is formed by the confluence of the right and left brachiocephalic Veins, vena brachiocephalica dextra et sinistra, posterior to the junction of the first right costal Cartilage with the Sternum. The superior vena cava and its tributaries (the left and right brachiocephalic veins) are located in the superior Mediastinum. Its anterior surface is partially covered by the Thymus, while its posterior surface borders the ROOT of the right lung. The mediastinal Pleura adjoins it on the right, and the ascending aorta lies to its left. At the level of the upper margin of the right pulmonary artery, the azygos vein, v. azygos, along with small mediastinal and pericardial veins, vv. mediastinales et pericardiacae, empties into the trunk of the superior vena cava.

At the level of the junction of the third right costal cartilage with the sternum, the v. cava superior empties into the upper wall of the right atrium. The superior vena cava collects Blood from the VEINS OF THE HEAD and Neck, upper limbs, thoracic wall, and partially from the Abdominal cavity.

Tributaries of the superior vena cava:

1. Vv. brachiocephalicae;

2. V. azygos;

3. V. hemiazygos.

1. The right and left brachiocephalic veins, vena brachiocephalica dextra et sinistra (Fig. 61), are formed by the union of the subclavian vein, v. subclavia, and the internal jugular vein, v. jugularis interna. The right brachiocephalic vein is 2–3 cm long and runs vertically behind the sternoclavicular joint. The left brachiocephalic vein is twice as long as the right; it crosses anteriorly to the Branches of the aortic arch, the left Vagus nerve, and the phrenic nerve. It joins the contralateral vein to form the superior vena cava, v. cava superior.

Tributaries of the brachiocephalic veins:

1. Vv. thyroideae inferiores;

2. V. vertebralis;

3. V. cervicalis profunda;

4. Vv. thoracicae internae;

5. V. intercostalis suprema.

1. The inferior thyroid veins, vv. thyroideae inferiores (Fig. 61), numbering 2 to 3, drain blood from the unpaired thyroid plexus, pl. thyroideus impar, the Trachea, the lower part of the Pharynx, and the Esophagus. Venous blood from the Larynx flows out via the inferior laryngeal vein, v. laryngea inferior, which anastomoses with the superior and middle thyroid veins. In the lower part of The Thyroid Gland, there is A large number of anastomoses forming a plexus from which numerous thyroid ima veins, vv. thyroideae ima, arise and empty into the left and right brachiocephalic veins (O. M. Maksymenkov).

* A variant involving a second superior vena cava, v. cava superior duplex, may occasionally occur (M. A. Tikhomirov, 1900).

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Fig. 61. Azygos vein, v. azygos, hemiazygos vein, v. hemiazygos, and accessory hemiazygos vein, v. hemiazygos accessoria (anterior view) (according to R. D. Sinelnikov)

2. The vertebral vein, v. vertebralis, runs alongside the a. vertebralis within the transverse foramina of the cervical vertebrae, emerges through the foramen of the transverse process of the 6th cervical vertebra, and empties into the v. brachiocephalica.

3. The deep cervical vein, v. cervicalis profunda, accompanies the artery of the same name and drains into the brachiocephalic vein, or occasionally into the vertebral vein.

4. The internal thoracic veins, vv. thoracicae internae, originate from the superior epigastric, superficial epigastric, and musculophrenic veins. These veins anastomose with the intercostal veins and occasionally accompany the internal thoracic artery.

5. The supreme intercostal vein, v. intercostalis suprema, drains venous blood from the II–III intercostal spaces.

In addition to the aforementioned veins, smaller veins empty into each of the brachiocephalic veins: thymic veins, vv. thymicae; pericardial veins, vv. pericardiacae; pericardiacophrenic veins, vv. pericardiacophrenicae; bronchial veins, vv. bronchiales; esophageal veins, vv. oesophageales; and mediastinal veins, vv. mediastinales.

2. The azygos vein, v. azygos*, is a continuation of the right ascending lumbar vein trunk, v. lumbalis ascendens dextra (Fig. 61).

The right ascending lumbar vein originates in the abdominal cavity (lumbar and sacral regions) and anastomoses with the veins of the external vertebral plexus and the lumbar veins. It enters the thoracic cavity through the aperture between the medial and intermediate crura of the Diaphragm, where it becomes known as the azygos vein, v. azygos. In the thoracic cavity, it is situated in the posterior mediastinum along the right side of THE Vertebral Column; the Thoracic duct and the Thoracic Aorta lie to its left, and the esophagus lies anterior to it. At the level of the IV–V vertebrae, the v. azygos arches forward over the root of the right lung to empty into the superior vena cava. At its termination, the v. azygos features a bicuspid valve. The azygos vein serves as an important anastomotic bridge between the inferior and superior venae cavae and the hepatic portal system.

* V. azygos acts as a venous reservoir collecting blood from the right intercostal veins.

Tributaries of the azygos vein:

1. V. subcostalis,

2. Vv. phrenicae superiores,

3. Vv. pericardiacae,

4. Vv. mediastinales,

5. Vv. oesophageales,

6. Vv. bronchiales,

7. Vv. intercostales posteriores dextrae,

8. V. intercostalis superior dextra

1. The subcostal vein, v. subcostalis, is located below the XII rib. It empties into the ascending lumbar vein as the latter passes through the diaphragm.

2. The superior phrenic veins, vv. phrenicae superiores, drain into the azygos vein as it passes through the diaphragm.

3. The pericardial veins, vv. pericardiacae, numbering 3-4, empty into the initial segment of the azygos vein.

4. The mediastinal veins, vv. mediastinales, 5-6 short, slender branches that empty into various segments of the azygos vein.

5. The esophageal veins, vv. oesophageales, 4-7 veins emptying into the azygos vein

6. The bronchial veins, vv. bronchiales, 2-3 veins draining into the azygos vein at the level of the IV-V thoracic vertebrae.

7. The right posterior intercostal veins, vv. intercostales posteriores dextrae IV-XI, empty into the azygos vein at the level of the rib heads.

8. The right superior intercostal vein, v. intercostalis superior dextra, empties into the terminal part of the azygos vein. It anastomoses with the venous plexuses of the vertebral column.

Fig. 61 A. Variations of the azygos and hemiazygos veins (after V. H. Frautschi).

1 - bimain variant; 2 - transitional single-outlet variant; 3 - transitional two-outlet variant; 4 - transitional three-outlet variant; 5 - monomain variant

3. The hemiazygos vein, v. hemiazygos (Fig. 61), is the largest tributary of the azygos vein. It originates in the abdominal cavity from the left ascending lumbar vein, v. lumbalis ascendens sinistra, which anastomoses with the lumbar veins. The hemiazygos vein serves as a venous collection basin for the lower left posterior intercostal veins.

The hemiazygos vein enters the thoracic cavity through an opening in the diaphragm between the muscular bundles of the left crus of the diaphragm and reaches the VII-XI thoracic vertebrae. Here it turns to the right, crosses the vertebral column, thoracic aorta, and ductus thoracicus, and empties into the azygos vein*.

Tributaries of the hemiazygos vein:

1. Left posterior intercostal veins, vv. intercostales posteriores sinistrae;

2. Accessory hemiazygos vein, v. hemiazygos accessoria;

3. Esophageal veins, vv. oesophageales;

4. Mediastinal veins, vv. mediastinales.

* The crossing of the vertebral column by the hemiazygos vein occurs in several variants: at the level of the VIII, IX, X, or XI thoracic vertebrae (B. V. Ognev, V. H. Frauchi).

Fig. 62. Venous plexuses of the vertebral column. A — on a sagittal section; B — on a transverse section

Along with the aforementioned tributaries of the azygos and hemiazygos veins, the largest ones are considered to be:

1. Posterior intercostal veins, vv. intercostales posteriores, which run in the costal groove and drain blood from the walls of the thoracic cavity and, partially, from the anterior abdominal wall, as well as from the Skin and Muscles of the back, vertebrae, and Spinal Cord.

2. Venous plexuses of the vertebral column — the anterior and posterior internal vertebral plexuses, plexus venosi vertebrales interni anterior et posterior (Fig. 62). They extend from the foramen magnum to the sacrum. They receive the spinal veins and the veins of the spongy substance of the vertebra. The anterior and posterior external venous plexuses, plexus venosi vertebrales externi anterior et posterior, are located on the anterior surface of the vertebrae. Venous blood from the external plexus drains directly into the v. azygos, v. hemiazygos, and v. hemiazygos accessoria, as well as into the posterior intercostal, lumbar, and sacral veins.

Various morphological Variants of the azygos and hemiazygos veins are observed (B. V. Ognev, V. H. Frauchi, 1960) (Fig. 61 A).