10.2 – Anatomy of the Blood Vessels
Blood pumped by the heart flows through a series of vessels known as arteries, arterioles, capillaries, venules, and veins before returning to the heart.
Overview of Blood Vessels
- Arteries transport blood away from the heart and branch into smaller vessels, forming arterioles.
- Arterioles distribute blood to capillary beds, the sites of exchange with the body tissues.
- A capillaryis a microscopic channel that supplies blood to the tissues themselves, a process called perfusion.
- Exchange of gases and other substances occurs in the capillaries between the blood and the surrounding cells and their tissue fluid (interstitial fluid).
- For capillaries to function, their walls must be leaky, allowing substances to pass through.
- Capillaries lead back to small vessels known as venules.
- Venules are small veins that converge into larger veins.
- A vein is a blood vessel that conducts blood toward the heart.
- Compared to arteries, veins are thin-walled vessels with large and irregular lumens.
- Larger veins are commonly equipped with valves that promote the unidirectional flow of blood toward the heart and prevent backflow toward the capillaries caused by the inherent low blood pressure in veins as well as the pull of gravity.
- Other ways in which the body assists the transport of venous blood back to the heart involve contractions of skeletal muscles in the extremities (see figure below), as well as pressure variations caused by breathing motion in the chest.
Concept Check 1
- Select the correct bolded word: arteries always carry blood away from/towards the heart.
- Select the correct bolded word: veins always carry blood away from/towards the heart.
Both arteries and veins have the same three distinct tissue layers, called tunics, for the garments first worn by ancient Romans. From the most interior layer to the outer, these tunics are the tunica intima, the tunica media, and the tunica externa. The smooth muscle in the middle layer, the tunica media, provides the vessel with the ability to vasoconstrict and vasodilate as needed to ensure sufficient blood flow.
The table below compares the features of arteries and veins.
| Characteristic | Arteries | Veins |
|---|---|---|
| Direction of blood flow | Conducts blood away from the heart | Conducts blood toward the heart |
| General appearance | Rounded | Irregular, often collapsed |
| Pressure | High | Low |
| Wall thickness | Thick | Thin |
| Relative oxygen concentration | Higher in systemic arteries
Lower in pulmonary arteries |
Lower in systemic veins
Higher in pulmonary veins |
| Valves | Not present | Present most commonly in limbs and in veins inferior to the heart |
The Major Arteries and Veins in the Human Body
Many arteries and veins share the same names, parallel one another throughout the body, and are very similar on the right and left sides of the body. For example, you will find a pair of femoral arteries and a pair of femoral veins, with one vessel on each side of the body. In contrast, some vessels closer to the midline of the body, such as the aorta, are unique and not paired. Names of vessels may change with location. Like a street that changes name as it passes through an intersection, an artery or vein can change names as it passes an anatomical landmark. For example, the left subclavian artery becomes the axillary artery as it passes into the axillary region, and then becomes the brachial artery as it enters the upper arm. The next two diagrams illustrate the major arteries and veins in the human body.
Concept Check 2
- Without looking back at the images of the main arteries and veins of the body, can you name and locate 3 arteries and 3 veins in your body?
Image Descriptions
Figure 10.1 image description: The left panel shows the structure of a skeletal muscle vein pump when the muscle is relaxed, and the right panel shows the structure of a skeletal muscle vein pump when the muscle is contracted.[Return to Figure 10.1].
Figure 10.2 image description: The top left panel of this figure shows the ultrastructure of an artery (labels read from top: tunica externa, tunica media, tunica intima, smooth muscle, internal elastic membrane, vasa vasorum, external elastic membrane, nervi vasorum, endothelium, elastic fiber), and the top right panel shows the ultrastructure of a vein (labels read from top: tunica exerna, tunica media, tunica intima, vasa vasorum, smooth muscle, endothelium). The bottom panel shows a micrograph with the cross sections of an artery and a vein. [Return to Figure 10.2].
Figure 10.3 image description: The major arteries in the human body. Labels read (from top, clockwise) right common carotid, left common carotid, axillary, pulmonary trunk, descending aorta, diaphragm, renal, superior mesenteric, gonadal, inferior mesenteric, common iliac, internal iliac, deep femoral, femoral, descending genicular, doraslis pedis, plantar arch, fibular, anterior tibial, posterial tibial, popliteal, palmer arches, exernal iliac, ulnar, radial, brachial, celiac trunk, ascending aorta, aortic arch, brachiocephalic trunk, right subclavian, vertebral. [Return to Figure 10.3].
Figure 10.4 image description: The major veins in the human body. Labels read (from top, clockwise) internal jugular, brachiocephalic, superior vena cava, intercostal, inferior vena cava, gonadal, lumbar, right and left common iliac, external iliac, internal iliac, deep femoral, femoral, posterior tibial, anterior tibial, dorsal venous arch, plantar venous arch, fibular, small saphenous, popliteal, great saphenous, digital, palmar venous arches, ulnar, median antebrachial, medial cubital, hepatic, basilic, brachial, cephalic, axillary, subclavian, externa jugular. [Return to Figure 10.4].
Attribution
Except where otherwise noted, this chapter is adapted from “Cardiovascular System – Blood Vessels and Blood” in Building a Medical Terminology Foundation by Kimberlee Carter and Marie Rutherford, licensed under CC BY 4.0. / A derivative of Betts et al., which can be accessed for free from Anatomy and Physiology (OpenStax). Adaptations: dividing Cardiovascular System – Blood Vessels and Blood chapter content into sub-chapters.
Blood vessels that transport blood away from the heart.
A very small artery that leads to a capillary
A microscopic channel that supplies blood to the tissues through perfusion
The delivery of blood to an area/tissue/organ
Extremely small vein
Blood vessels that carry blood back to the heart.
The smooth muscle layer in the blood vessel wall contracts, causing the vessel diameter to narrow. This increases blood pressure in the vessel.
The smooth muscle layer in the wall of the blood vessel relaxes, allowing the vessel to widen. This decreases blood pressure in the vessel.