Human Anatomy Part 2 - K. A. Dyubenko A. K. Kolomiytsev Yu. B. Chaykovsky 2008

Special Part
Cardiovascular system, systema cardiovasculare - Venous system

Class="center">Veins, venae (Greek phlebs, hence phlebitis, inflammation of a vein wall). These are efferent Blood Vessels that transport (return) venous blood from the most remote Organs and Tissues of the body to the right atrium. An exception is the Pulmonary veins, which carry oxygen-rich arterial blood from the Lungs to The Heart (left atrium).

Together, all venous vessels form The Human Body's Venous system (Fig. 59), which is part of The Cardiovascular system. Veins are a vital component of the SYSTEMIC AND PULMONARY Circulation, completing the circulatory loop by draining blood from the capillary bed and performing a drainage function. Veins transport not only BLOOD AND Lymph, but also CEREBROSPINAL FLUID. They evacuate Metabolic waste products from organs and tissues, distribute Hormones produced by Endocrine glands throughout the body, and supply nutrients (via the PORTAL VEIN SYSTEM). The venous system acts as a blood reservoir, primarily due to venous plexuses, holding 70% of the total blood volume at any given moment. Along with these Functions, vein walls serve as major reflexogenic zones involved in the Regulation of Blood circulation, as they contain numerous nerve endings, chemoreceptors, and baroreceptors (B. A. Dolgo-Saburov).

The venous compartment of the vascular bed is characterized by a larger cross-sectional area and diameter, lower blood flow velocity, and lower blood pressure, all of which significantly influence hemodynamics. In the venular segment, blood flows more slowly and at a lower pressure than in capillaries. Consequently, interstitial fluid and metabolic waste pass from tissues into the blood through the venous segment of the microcirculatory bed. Naturally, this process is facilitated by hemodynamic conditions in larger veins that return blood to the heart.

Compared to the Arterial System, the venous compartment of the vascular bed has the following Anatomical Features:

1. A greater number of veins and their significant width. Because veins are capacious vessels, they contain 70–80% of the total blood volume.

2. The presence of deep paired companion veins, vv. comitantes, which accompany main arterial trunks and facilitate blood outflow from the extremities. Large-diameter Arteries are accompanied by a single vein (for example, the subclavian, common carotid, renal, and splenic vessels are each accompanied by one vein).

3. The preservation of bilateral Symmetry or segmental features (for example, in the VEINS OF THE trunk).

4. The presence of superficial (subcutaneous) veins In addition to deep veins.

5. The Location of A number of venous trunks within neurovascular bundles (sometimes alongside arteries and lymphatic vessels).

6. The arrangement of veins corresponding to skeletal structures (along THE Vertebral Column—the INFERIOR VENA CAVA; the Ribs—intercostal veins; and the BONES OF THE limbs—brachial, ulnar, radial, femoral, etc.).

7. The passage of several veins along a short pathway to the main venous trunk.

8. The presence of venous plexuses in specific blood drainage systems and anastomoses between different systems (e.g., porto-caval and cavo-caval anastomoses).

9. The presence of Dural Venous Sinuses within the cranial cavity and diploic veins (venae diploicae) within the cranial bones.

10. The presence of Valves in small (at least 0.5 mm in diameter) and medium-sized veins that prevent the backflow of blood.

11. The presence of arteriovenous anastomoses in The Vascular System capable of diverting blood directly from arterioles to venules, bypassing the capillary bed.