Blood and the Circulatory System Help
Introduction to Blood and the Circulatory System
This section discusses the circulatory ( SIR -kyuh-luh- tor -ee) or cardiovascular ( car -dee-oh- VAS -kyuh-lar) system. The circulatory (cardiovascular) system is an organ system including the “heart” (cardi) and “little vessels” (vascul) that carries the blood in a “little circle” that both begins and ends with the heart. Along the way, the blood passes by the main body tissues. In so doing, the blood delivers hormones, glucose, and various other nutrients to the main body tissues. And, as it leaves, the blood picks up a number of waste products from the main body tissues.
How Does the Circulatory Sytem Work?
Glance at Figure 16.1. You will see that if the heart represents a pump for the blood, then the blood vessels represent the pipes carrying it! The arteries ( AR -ter- ees ) are large-diameter vessels that always carry blood away from the heart. Thus, the arteries immediately receive the blood being pumped from the ventricles ( VEN -trih- kls ) – the “little belly”-like lower chambers on either side of the heart. Specifically, the right ventricle (abbreviated as RV) pumps blood out into the common pulmonary ( PULL -mun- air -ee) artery (abbreviated as CPA), which in turn sends blood out towards both “lungs” (pulmon). And the left ventricle (abbreviated as LV) pumps blood out into the aortic (ay- OR -tik) arch. The aortic arch sends the blood from the LV out towards the tissues of the major body systems (other than the lungs) (See Figure 16.2, A).
The Arteries - Arterioles and Cappilaries
As the major arteries (such as the common pulmonary artery and aortic arch) travel farther from the heart, they branch into smaller arteries (Figure 16.2, B). And these smaller arteries, in turn, branch into even smaller arterioles (ar- TEER -ee-ohls) or “little arteries.” As the arterioles approach the cells of the body tissues, they branch into the smallest blood vessels of all, the capillaries ( CAP -ih- lair -ees). Each capillary is very narrow (much like a strand of hair). This characteristic is reflected in the translation of capillary, which “pertains to a hair.”
Since the wall of each capillary is only a single cell thick, nutrients and waste products diffuse across the wall. Nutrients (such as oxygen, O 2 , and glucose) diffuse out of the bloodstream, and into the tissue cells. And waste products (such as carbon dioxide, CO 2 ) diffuse out of the tissue cells, and into the bloodstream.
Venules - Little Veins
After the capillaries run past the tissue cells, several of them merge together to form the venules ( VEN -yewls). The venules are the “little veins,” in the sense that they connect the capillaries to the much larger veins. The veins are all wide-diameter vessels that return blood towards the heart.
Several of the largest veins return blood back to the atria ( AY -tree-ah) – the small “entrance rooms” (atri) or chambers located at the top of the heart. Among the biggest sets of veins are the superior and inferior vena ( VEE -nah) cavae ( KAY -veye), or “upper and lower cave veins.” The superior vena cava (SVC) drains blood down into the right atrium ( AY -tree-um), or RA , from the area above the heart, while the inferior vena cava (IVC) returns blood up into the right atrium from the entire region below the heart.
The four pulmonary veins, as their name suggests, return blood from the lungs and empty it into the left atrium, LA.
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