Final answer:
Red blood cells, or erythrocytes, deliver oxygen throughout the body and remove carbon dioxide. They travel through arteries, capillaries, veins, and the heart in a coordinated manner. The cardiac cycle links the circulatory system with the nervous system.
Step-by-step explanation:
Red blood cells, or erythrocytes, play a crucial role in delivering oxygen to cells throughout the body. The journey of a red blood cell starts in the red marrow of certain bones, where they are produced. Once released into circulation, they lack a nucleus and other organelles, allowing them to carry more hemoglobin and oxygen. As red blood cells travel through arteries, capillaries, and veins, they deliver oxygen and pick up carbon dioxide. When they reach the lungs, they exchange the carbon dioxide for fresh oxygen. To return to the lower leg, the red blood cells travel through the heart and vessels in a coordinated series of contractions and relaxations known as the cardiac cycle.
The events in the cardiac cycle link the circulatory system with the nervous system through the control of the heart's contractions. The heartbeat is regulated by the sinoatrial (SA) node, also known as the natural pacemaker, which receives signals from the autonomic nervous system. The sympathetic division of the autonomic nervous system stimulates the SA node to increase the heart rate, while the parasympathetic division slows it down. This connection ensures that the circulatory system functions appropriately in response to changes in the nervous system.