Overview
This lecture reviews the structure and pathways of the systemic veins, highlighting differences from the arterial system and unique features in venous drainage throughout the body.
Major Veins and Pathways
- Systemic veins return blood to the heart from the body, excluding the pulmonary veins (from the lungs).
- Major entry points to the heart: superior vena cava, inferior vena cava, and coronary sinus.
- Most veins run parallel to arteries and share similar names and locations (e.g., brachial, radial, ulnar, femoral, popliteal, tibial).
- Some veins are unique to the venous system and do not have arterial counterparts.
Head, Neck, and Thorax Drainage
- Brain drains through superior and inferior sagittal sinuses (within the falx cerebri), then into the sigmoid sinus, and finally into the internal jugular vein.
- Internal and external jugular veins run parallel but do not merge; there is no equivalent of the common carotid artery for veins.
- Both sides of the body have short brachiocephalic veins draining into the superior vena cava.
- The median cubital vein, commonly used for blood draws, connects superficial veins in the arm.
- The azygos vein (unpaired) and hemi-azygos vein drain the thorax and empty into the superior vena cava.
Abdomen, Pelvis, and Gonadal Veins
- Hepatic veins drain the liver directly into the inferior vena cava (IVC).
- Renal veins drain the kidneys; lumbar veins are similar to lumbar arteries.
- IVC splits to form common iliac veins, which further divide into internal and external iliac veins.
- Right gonadal vein drains directly into the IVC; left gonadal vein drains into the left renal vein before reaching the IVC.
- The difference in gonadal vein drainage can result in clinical issues such as varicoceles, especially in males.
Hepatic Portal System
- Blood from digestive organs (spleen, colon, intestines) is routed to the liver for detoxification before entering the IVC.
- Major veins: superior mesenteric, inferior mesenteric, splenic, and hepatic portal vein (delivers blood to the liver).
- Hepatic veins return processed blood from the liver to the IVC.
Leg Veins
- Common iliac veins branch into internal and external iliac veins; the femoral vein becomes the popliteal vein at the knee.
- Greater saphenous vein (large, superficial, along the inside of the leg) and small saphenous vein are unique to the venous system.
- Greater saphenous vein is commonly harvested for coronary bypass surgery but is now less used compared to the internal thoracic artery.
Key Terms & Definitions
- Superior vena cava — main vein returning blood from the upper body to the heart.
- Inferior vena cava (IVC) — main vein returning blood from the lower body to the heart.
- Hepatic portal vein — vein carrying blood from digestive organs to the liver for processing.
- Azygos vein — unpaired vein draining thoracic wall and upper lumbar region to the SVC.
- Greater saphenous vein — long, superficial vein in the leg, often used in bypass surgeries.
- Varicocele — varicose vein condition of the scrotum due to gonadal vein drainage patterns.
Action Items / Next Steps
- Review diagrams of systemic veins, especially unique veins not paired with arteries.
- Compare arterial and venous pathways to understand mismatches.
- Study the hepatic portal system and clinical consequences of venous drainage patterns.
- Prepare for practical identification of major superficial and deep veins.