Examples of Autonomic Nervous System Pathways
Main veins of the body
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Veins are the vessels that carry blood from the periphery to the heart. Most veins carry deoxygenated blood, except for the pulmonary veins, which carry oxygenated blood from the lungs to the heart.
The venous blood is intended to be carried into the heart, from which it will be pumped to the lungs in order to get oxygenated. All the venous pathways of the body essentially end up in either the superior vena cava or the inferior vena cava, which convey the blood into the right atrium of the heart. As a rule of thumb, the superior vena cava drains the venous blood from the upper half of the body (above the diaphragm), while the inferior vena cava drains the lower half of the body (below the diaphragm).
This article will give you an overview of the main veins of the body.
Head and neck
The head and neck are drained by three major, paired veins:
- Internal jugular vein, which drains the majority of the face, brain, and neck
- Subclavian vein, which primarily drains the upper limb, but also collects some blood from the neck
- Brachiocephalic veins, which arise from the confluence of the same-sided internal jugular and subclavian veins
The left and right brachiocephalic veins merge to form the , which then carries all the venous blood from the head and neck directly into the right atrium of the heart.
Thorax
The major veins of the thorax are the following:
- The azygos vein collects the blood via its tributaries (hemiazygos and accessory hemiazygos veins) from the intercostal spaces, esophagus, bronchi, pericardium, mediastinum, and diaphragm. It drains directly into the superior vena cava.
- The pulmonary veins are the only veins that carry oxygenated blood. They deliver the oxygen-rich blood from the lungs into the left atrium of the heart.
- The internal thoracic veins drain a part of the thoracic wall and breasts and they drain into the same-sided brachiocephalic vein, which then drains into the superior vena cava.
- The cardiac veins, namely the great, middle, and small cardiac veins, convey the venous blood from the myocardium of the heart and drain into the coronary sinus. The coronary sinus is a small venous container that drains directly into the right atrium of the heart.
Master your knowledge of blood vessel structure with these diagrams and arteries and veins quizzes.
Abdomen and pelvis
The abdomen, as well as the pelvis and lower limbs, essentially drain into the inferior vena cava (IVC). The inferior vena cava is created by the union of the left and right common iliac veins. It passes through the diaphragm coursing towards the heart, and it empties into the right atrium of the heart.
The direct tributaries of the inferior vena cava in the abdomen and pelvis are the phrenic, lumbar, suprarenal, renal, and gonadal veins, which carry the blood from the diaphragm, posterior abdominal wall, adrenal glands, kidneys, and gonads, respectively.
The remainder of the venous blood from the abdomen is delivered to the inferior vena cava through the hepatic portal vein. This vein is made by the union of the superior mesenteric and splenic veins, which deliver the blood from the following organs and regions:
- Superior mesenteric vein collects the blood from the foregut and midgut: small intestine and a part of the large intestine, pancreas
- Splenic vein collects the blood from the spleen, parts of the pancreas and stomach, and hindgut (distal transverse colon, descending colon, sigmoid colon, and rectum)
The pelvis is mostly drained by the tributaries of the internal iliac veins. The internal iliac veins merge with the external iliac veins (carrying the blood from the lower limb) and create the common iliac veins. The left and right common iliac veins merge to form the inferior vena cava.
Upper limb
The veins of the upper limb are grouped into superficial and deep venous systems. The superficial veins are found just beneath the skin. The main superficial veins are the cephalic and basilic veins. The cephalic vein drains the superficial layer of the lateral (radial) aspect of the upper limb, while the basilic vein drains the medial (ulnar) side. The cephalic vein empties into the axillary vein, while the basilic vein drains into the brachial vein.
The deep veins of the upper limb begin from the deep palmar arches of the hand. These venous vessels continue into the radial and ulnar veins, which drain the forearm. These veins then merge to form the brachial veins, which course through and drain the arm. The brachial veins unite with the basilic vein to form the axillary vein. The axillary vein then continues as the subclavian vein, which drains the entire upper limb. It joins the internal jugular vein to form the brachiocephalic vein on the same side of the body, which then joins the brachiocephalic vein from the opposite side to create the superior vena cava.
Lower limb
The pattern of venous drainage of the lower limb is similar to that of the upper limb. The veins are also grouped into superficial and deep veins. The major superficial vein is the greater saphenous vein, which collects the venous blood from the subcutaneous tissue of the lower limb.
The deep veins collect the blood from the remainder of the lower limb. This system begins with the plantar and dorsal veins of the foot. These veins then convey the blood into the fibular vein and anterior tibial and posterior tibial veins. These three veins drain the leg and merge to form the popliteal vein, which also drains the knee region. The popliteal vein continues into the femoral vein, which is the main vein of the thigh. The femoral vein courses beneath the inguinal ligament, after which it becomes the external iliac vein.
The external iliac vein then joins with the internal iliac vein from the same side to create the common iliac vein. The left and right common iliac veins merge to form the inferior vena cava, which conveys blood from the lower limbs to the right atrium of the heart.
References
- Open Anatomy. (n.d.). TA2 Viewer. Retrieved April 5, 2023, from https://ta2viewer.openanatomy.org/
- Betts, J. G., Young, K. A., Wise, J. A., Johnson, E., Poe, B., & Kruse, D. H. (2022). Anatomy and Physiology (2nd ed.). OpenStax. https://openstax.org/details/books/anatomy-and-physiology-2e
- Moore, K. L. (2018). Clinically Oriented Anatomy (8th ed.). Philadelphia, PA: Wolters Kluwer.
- Drake, R. L., Vogl, A. W., & Mitchell, A. W. M. (2015). Gray’s Anatomy for Students (3rd ed.). Edinburgh, Scotland: Churchill Livingstone.
- Standring, S. (2021). Gray’s Anatomy (42tst ed.). Edinburgh: Elsevier Churchill Livingstone.