Anatomy and Physiology of the Cardiovascular System
Introduction
The human heart pumps blood through the arteries, which connect to smaller arterioles and then even smaller capillaries. It is here that nutrients, electrolytes, dissolved gases, and waste products are exchanged between the blood and surrounding tissues. The capillaries are thin-walled vessels interconnected with the smallest arteries and smallest veins Approximately 7,000 L of blood is pumped by the heart every day. In an average person’s life, the heart will contract about 2.5 billion times.Blood flow throughout the body begins its return to the heart when the capillaries return blood to the venules and then to the larger veins. The cardiovascular system, therefore, consists of a closed circuit: the heart, arteries, arterioles, capillaries, venules, and veins (see Figure 5–1). The venules and veins are part of the pulmonary circuit because they send deoxygenated blood to the lungs to receive oxygen and unload carbon dioxide. The arteries and arterioles are part ...of the systemic circuit because they send oxygenated blood ...
(Figure31). The CNS is the body’s control center, consisting of the brain and spinal cord. The brain is responsible for consciousness; its functions include perception, emotion, memory, thought, and language. The lower parts of the brain are also responsible for some unconscious functions, such as regulation of the endocrine (hormonal) and cardiovascular systems. The spinal cord is responsible for simple reflexes; it also serves as a pathway between the brain and the PNS.