21  •  Circulation and Respiration 827

Transporting fuel, raw materials, and gases into, out of, and around the body

The circulatory system is the chief route of distribution in animals. 828

21.1

What is a circulatory system, and why is one needed? 828

21.2

Circulatory systems can be open or closed. 829

21.3

Vertebrates have several different types of closed circulatory systems. 831

The human circulatory system consists of a heart, blood vessels, and blood. 834

21.4

Blood flows through the four chambers of the human heart. 834

21.5

Electrical activity in the heart generates the heartbeat. 836

21.6

Blood flows out of and back to the heart in blood vessels. 838

21.7

This is how we do it: Does thinking make your head heavier? 841

21.8

Blood is a mixture of cells and fluid. 842

21.9

Blood pressure is a key measure of heart health. 845

21.10

Cardiovascular disease is a leading cause of death in the United States. 847

21.11

The lymphatic system plays a supporting role in circulation. 849

The respiratory system enables gas exchange in animals. 852

21.12

Oxygen and carbon dioxide must get into and out of the circulatory system. 852

21.13

Oxygen is transported while bound to hemoglobin. 854

21.14

Gas exchange takes place in the gills of aquatic vertebrates. 857

21.15

Respiratory systems of terrestrial vertebrates move oxygen-rich air into and carbon-dioxide-rich air out of the lungs. 858

21.16

Birds have unusually efficient respiratory systems. 860

21.17

Muscles control the flow of air into and out of the lungs. 862

Evolutionary adaptations maximize oxygen delivery. 863

21.18

Animals living at high elevations have special adaptations to the low-oxygen conditions. 863

21.19

Humans become acclimated to low-oxygen conditions. 864

StreetBIO: KNOWLEDGE YOU CAN USE

“Contents under Pressure”: recognizing and avoiding the bends. 866