Human Anatomy and Physiology - I. V. Gayvoronsky 2011

Cardiovascular system
Venous system

Veins ensure the outflow of Blood from Organs back to The Heart. Their walls are thinner and less elastic than those of Arteries. Blood movement through these vessels is driven by the suction effect of The Heart and the thoracic cavity, where negative pressure is created during inhalation. A certain role in blood transport is also played by the contractions of surrounding Muscles and the BLOOD FLOW IN adjacent arteries. The walls of venous vessels contain Valves that prevent the backward movement of blood (in the direction away from the heart). Veins originate from small, branching venules, which in turn stem from a network of capillaries. They then converge into larger vessels, ultimately forming major trunk veins.

According to the number of major venous collectors, the systemic VEINS OF THE Greater Circulation are divided into four separate systems: the coronary sinus system, the SUPERIOR VENA CAVA system, the INFERIOR VENA CAVA system, and the hepatic portal system.

Coronary sinus system. Blood from the heart walls is collected into the great, middle, and small cardiac veins. The great cardiac vein runs in the anterior interventricular sulcus and continues into the coronary sinus. It is located on the posterior surface of the heart within the coronary sulcus (between the left atrium and left ventricle). The middle and small cardiac veins drain into the coronary sinus. From there, blood flows directly into the right atrium. Smaller cardiac veins open directly into the right atrium as well.

Superior vena cava system. The superior vena cava, vena cava superior, is formed by the junction of the right and left brachiocephalic veins (Fig. 12.15). The superior vena cava collects blood from the HEAD, neck, upper limbs, and the walls of the thoracic and partially abdominal cavities. It empties into the right atrium.

The azygos vein, v. azygos, empties into the superior vena cava, collecting blood from the walls of the thoracic cavity and partly the Abdominal cavity. It is located to the right of THE Vertebral Column. It receives the right posterior intercostal veins and the hemiazygos vein (lying to the left of the vertebral column), which in turn receives the left posterior intercostal veins. In addition, tributaries of the azygos vein carry blood from the Diaphragm, Pericardium, and mediastinal organs—the Esophagus and Bronchi. The bronchial veins collect deoxygenated blood from the bronchi and lung parenchyma.

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Fig. 12.15. Venous system (diagram):

1 — internal jugular vein; 2 — brachiocephalic vein; 3 — External Jugular Vein; 4 — subclavian vein; 5 — Thoracic duct; 6 — internal thoracic vein; 7 — superior vena cava; 8 — intercostal veins; 9 — hemiazygos vein; 10 — hepatic veins; 11 — inferior vena cava; 12 — lumbar veins; 13 — left ascending lumbar vein; 14 — portal vein; 15 — common iliac vein; 16 — internal iliac vein; 17 — rectal venous plexus; 18 — femoral vein; 19 — external iliac vein; 20 — azygos vein

The brachiocephalic veins, w. brachiocephalicae (right and left), are formed by the union of the subclavian and internal jugular veins. The junction point of the subclavian and internal jugular veins is called the venous angle. The thoracic duct empties into the left venous angle, while the Right lymphatic duct empties into the right one. The brachiocephalic veins receive blood from The Thyroid Gland, vertebral column, Mediastinum, and partially from the intercostal spaces.

The internal jugular vein, v. jugularis interna, begins at the jugular foramen as a direct continuation of the sigmoid sinus of the dura mater. It is the largest vein in the neck region. It runs within the carotid neurovascular bundle of the neck, alongside the common carotid artery and Vagus nerve. It drains blood from the cranial cavity, face, and neck organs into the brachiocephalic vein. The tributaries of the internal jugular vein are divided into intracranial and extracranial.

Intracranial tributaries include: cerebral veins; meningeal veins, which collect blood from the Meninges; emissary and diploic veins from the cranial bones; superior and inferior ophthalmic veins, which collect blood from the orbital organ complex and partially from the Nasal cavity; and labyrinthine veins from the Inner ear. They carry blood into the Dural Venous Sinuses. The dural venous sinuses (superior and inferior sagittal, transverse, straight, cavernous, superior and inferior petrosal, sigmoid, etc.) are channels whose walls are formed by the dura mater. A distinctive feature of these sinuses is that their walls are rigid and do not collapse. This facilitates a continuous outflow of blood from the cranial cavity. At the same time, if they are injured, it can lead to dangerous bleeding that is difficult to stop.

Extracranial Tributaries of the internal jugular vein include: the facial vein, which collects blood from the face and Oral Cavity; the retromandibular vein, which receives blood from the scalp, External ear, Muscles of Mastication, deep facial Tissues, nasal cavity, and the Maxilla and Mandible; and the pharyngeal, lingual, and superior thyroid veins, which collect blood from the corresponding organs.

The external and anterior jugular veins belong to the superficial veins of the neck. They collect blood from the Skin of the lateral and anterior surfaces of the neck, forming prominent anastomoses with each other. Blood from these veins flows primarily into the internal jugular vein.

The external jugular vein is better developed than the anterior one and is clearly visible through the skin.

It should be specifically noted that Blood flow through the Veins of the Head and Neck occurs primarily due to the action of gravity. These veins lack valves. Owing to the suction action of the heart and the ongoing outflow of blood from the head, a negative venous pressure is maintained within them. Consequently, if they are damaged, air may be sucked into the wound. The greatest danger in this case is not the Hemorrhage itself, but rather The entry of air into the lumen of the vascular bed.

The subclavian vein, v. subclavia, runs above the 1st rib anterior to the scalene muscles. It is a direct continuation of the axillary vein and collects blood from the upper limb.

The veins of the upper limb are subdivided into deep and superficial (subcutaneous) veins. Deep veins accompany the Arteries of the same name. As a rule, each artery is accompanied by two veins. Exceptions are the axillary vein and the veins of the fingers. The axillary vein is a continuation of the two brachial veins and transitions into the subclavian vein.

Two major subcutaneous veins run along the upper limb—the basilic and cephalic veins of the arm, v. basilica et v. cephalica (Fig. 12.16). They originate in the HAND FROM THE dorsal venous network. The first begins in the region of the little finger, runs along the medial margin of the forearm, and empties into the brachial vein. The second begins in the region of the thumb, runs along the lateral surface of the forearm and arm, then passes through the groove between the deltoid and pectoralis major muscles to empty into the axillary vein. The anastomosis between the subcutaneous veins in the cubital fossa is called the median cubital vein. It connects with the deep veins of the forearm. Intravenous injections are commonly administered into this vessel.

System of the inferior vena cava. The inferior vena cava, v. cava inferior, is the largest vein in The Human Body (its diameter ranges from 22 to 34 mm). It is formed by the confluence of the right and left common iliac veins, which in turn are formed by the union of the external and internal iliac veins. The inferior vena cava lies slightly to the right of the median plane, with the aorta positioned to its left. It passes through the diaphragm at the level of its central tendon. The inferior vena cava empties into the right atrium.

Blood enters the inferior vena cava system from the lower limb (external iliac vein), the walls and Organs of the pelvis (internal iliac vein), the lower part of the trunk (lumbar veins), and certain abdominal organs: the testicular (in males) and ovarian (in females) veins carry blood from the Gonads; the renal vein drains blood from the Kidney; the suprarenal (adrenal) vein drains the Adrenal gland; and the hepatic veins (3–4) drain the Liver. It should be noted that blood enters the liver via the hepatic artery (arterial blood) and the portal vein (containing substances absorbed in the gastrointestinal tract). Due to the unique vascular Structure OF THE liver, these two blood streams merge. The outflow of blood that has passed through the organ is carried out via the hepatic veins into the inferior vena cava.

Fig. 12.16. Superficial veins:

1 — facial vein; 2 — superficial temporal vein; 3 — external jugular vein; 4 — anterior jugular vein; 5, 13 — cephalic vein of the arm; 6 — median cubital vein; 7 — palmar venous network; 8 — basilic vein of the arm; 9 — superficial epigastric vein; 10 — great saphenous vein; 11 — dorsal venous network of the FOOT; 12 — dorsal venous network of the hand

The internal iliac vein, v. iliaca interna, collects blood from the walls and Internal Organs of the lesser pelvis. From the pelvic walls, the obturator veins (accompanying the artery of the same name) and the superior and inferior gluteal veins, which carry blood from the gluteal muscles, drain into the internal iliac vein. The veins collecting blood from the pelvic organs form numerous anastomoses known as venous plexuses. Venous plexuses are well developed in the region of the internal genitalia, Urinary Bladder, and rectum. In males, these plexuses are located near the prostate and Seminal Vesicles, while in females they are situated near the Uterus, Vagina, and external genitalia.

The external iliac vein, v. iliaca externa, is a continuation of the femoral vein and carries blood from the lower limb as well as partially from the anterior abdominal wall.

The veins of the lower limb are divided into superficial (subcutaneous) and deep. All deep veins of the lower limb run alongside the corresponding arteries of the same name. In most cases, an artery is accompanied by two veins; however, the femoral vein, popliteal vein, and deep femoral vein are single vessels. The largest of the deep veins is the femoral vein, which passes through the vascular lacuna and continues as the external iliac vein.

The superficial veins originate from the dorsal venous arch of the foot. The great saphenous vein, v. saphena magna, starts on the medial side of the foot, ascends along the medial aspect of the leg and thigh, and empties into the femoral vein. The small saphenous vein, v. saphena parva, originates on the lateral margin of the foot, crosses behind the lateral malleolus to the posterior aspect of the leg, and drains into the popliteal vein. Numerous anastomoses connect the superficial and deep veins.

Knowledge of the angioarchitecture of the lower limb veins helps surgeons perform Procedures to treat one of the most common conditions — varicose veins.

The PORTAL VEIN SYSTEM. The portal vein, v. portae, collects blood from the unpaired abdominal organs: The Stomach, Pancreas, Gallbladder, small and large intestines, and Spleen (Fig. 12.17). Its largest tributaries are the superior and inferior mesenteric veins, as well as the splenic vein.

A unique feature of the portal vein is that it transports blood not toward the heart, but to the liver. Within this organ, the portal vein branches extensively. These branches, together with those of the hepatic artery, form a specialized type of capillaries known as sinusoids. These microscopic vessels within the liver lobule converge into central veins. The central veins subsequently unite to form the hepatic veins, which empty into the inferior vena cava.

Fig. 12.17. The portal vein system (diagram):

1 — inferior vena cava; 2 — splenic vein; 3 — inferior mesenteric vein; 4 — left common iliac vein; 5 — superior mesenteric vein; 6 — portal vein

Venous anastomoses. Like arteries, veins communicate extensively with one another. The major types include cavacaval anastomoses (between the superior and inferior vena cava systems) and portacaval anastomoses (between the portal vein and the inferior or superior vena cava). The portal and caval veins feature numerous anastomoses located within the retroperitoneal adipose tissue, the walls of the esophagus and rectum, and along the round ligament of the liver. The anastomoses running along this ligament connect the portal vein with the superficial veins of the anterior abdominal wall. The most clinically significant cavacaval anastomoses are located in the vertebral canal and on the anterior abdominal wall. When blood outflow through one of the venous systems is impaired, these anastomoses become severely dilated. The venous walls may even rupture, leading to massive hemorrhages (such as esophageal-gastric, hemorrhoidal, etc.).