Page 398 - Atlas of Histology with Functional Correlations

CHAPTER 10 Circulatory System

The mammalian circulatory system comprises two major systems: the
cardiovascular system and the lymphatic vascular system.

CARDIOVASCULAR SYSTEM

The cardiovascular system consists of the heart, major arteries, arterioles,
capillaries, venules, and veins that form a closed system of blood vessels that
carry blood. Within this system are two major circuits that distribute blood, the

systemic circulation and the pulmonary circulation. Both circuits depend on
the pumping action of the heart for blood distribution. The systemic circulation
carries the blood from the heart to all organs, tissues, and cells via arterial

vessels and then back to the heart via the venous vessels. The pulmonary system
carries deoxygenated blood from the heart to the lungs for gaseous exchange and
the oxygenated blood back to the heart for distribution via the systemic
circulation.

The main functions of the blood vascular system are gaseous exchange;

temperature control; and transport of oxygen, carbon dioxide, nutrients,
hormones, metabolic products, cells of immune defense system, and many other
essential products. The histology of the heart muscle has been described in detail
in Chapter 8 as one of the four main tissues. In this chapter, heart histology is

illustrated only as part of the cardiovascular system.

Types of Arteries

There are three types of arteries in an organism: elastic arteries, muscular

arteries, and arterioles. Arteries that leave the heart with the oxygenated blood
become smaller as they exhibit progressive branching. With each branching, the
luminal diameters of the arteries gradually decrease until the smallest vessel, the

capillary, is formed.

Elastic arteries are the largest blood vessels and include the pulmonary

397