2 Blood Vessels and Blood
Blood Vessels and Blood Word Parts
Click on prefixes, combining forms, and suffixes to reveal a list of word parts to memorize for the Cardiovascular System – Blood.
Blood pumped by the heart flows through a series of vessels known as arteries, arterioles, capillaries, venules, and veins before returning to the heart.
- 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 capillary is 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
- 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 (see Figure 13.3). 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.
| 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
Concept Check
- 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?
Cardiov