Circulation and Respiration CHAPTER 23 Circulation and Respiration

Biology and Society: Doped Up The 1998 Tour de France Was marred by alleged use of performance-enhancing drugs by some teams. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings

Figure 23.1

The drug at the center of the controversy was erythropoietin (EPO), A natural hormone that boosts the production of red blood cells and that can be harmful if used as a supplement.

Unifying Concepts of Animal Circulation Every organism must exchange materials with its environment. The purpose of the circulatory system is to facilitate this exchange.

Open and Closed Circulatory Systems All but the simplest animals have circulatory systems with three main components: A central pump A vascular system The circulating fluid

Open circulatory system The heart pumps blood into large open-ended vessels. Fluid circulates freely among cells. Many invertebrates, such as molluscs and arthropods have open circulatory systems.

Figure 23.2a

Closed circulatory system Blood is confined to vessels and is distinct from the interstitial fluid. Earthworms, octopuses, and vertebrates have closed circulatory systems.

Figure 23.2b

The closed circulatory system in vertebrates is called a cardiovascular system. This system includes the heart and blood vessels.

The Human Cardiovascular System In the human cardiovascular system, The central pump is the heart. The vascular system is the blood vessels. The circulating fluid is the blood.

The Path of Blood In humans and other vertebrates, the three components of the cardiovascular system are organized into a double circulation system. There are two distinct circuits of blood flow.

The pulmonary circuit carries blood between the heart and the lungs.

Figure 23.3a

The systemic circuit carries blood between the heart and the rest of the body.

Figure 23.3b

A trip through the human cardiovascular system Path of Blood Flow in Mammals

Figure 23.4

The human heart is a muscular organ about the size of a fist. How the Heart Works The human heart is a muscular organ about the size of a fist. It is located under the breastbone. It has four chambers.

The path of blood flow through the human heart

Figure 23.5

The heart relaxes and contracts regularly: The Cardiac Cycle The heart relaxes and contracts regularly: Diastole is the relaxation phase of the heart cycle. Systole is the contraction phase.

Figure 23.6

The Pacemaker and the Control of Heart Rate The pacemaker, or SA (sinoatrial) node, sets the tempo of the heartbeat. The pacemaker is composed of specialized muscle tissue in the wall of the right atrium.

Figure 23.7a

The impulses sent by the pacemaker produce electrical currents that can be detected by electrodes placed on the skin. These are recorded in an electrocardiogram (ECG or EKG).

In certain kinds of heart disease, the heart’s electrical control fails to maintain a normal rhythm. The remedy is an artificial pacemaker.

Figure 23.7b

Blood Vessels If the heart is the body’s “pump,” then the “plumbing” is the system of arteries, veins, and capillaries. Arteries carry blood away from the heart. Veins carry blood toward the heart. Capillaries allow for exchange between the bloodstream and tissue cells.

All blood vessels are lined by a thin layer of tightly packed epithelial cells. Structural differences in the walls of the different kinds of blood vessels correlate with their different functions.

Figure 23.8

Blood Flow Through Arteries The force that blood exerts against the walls of your blood vessels is called blood pressure. Blood pressure is the main force driving the blood from the heart to the capillary beds. A pulse is the rhythmic stretching of the arteries caused by the pressure of blood forced into the arteries during systole.

Optimal blood pressure for adults is below 120 systolic and below 80 diastolic. High blood pressure is persistent systolic blood pressure higher than 140 and/or diastolic blood pressure higher than 90. It is also called hypertension.

Blood Flow Through Capillary Beds At any given time, about 5–10% of your capillaries have a steady flow of blood running through them.

Figure 23.9a

The walls of capillaries are thin and leaky. As blood enters a capillary at the arterial end, blood pressure pushes fluid rich in oxygen, nutrients, and other substances into the interstitial fluid. At the venous end of the capillary, CO2 and other wastes diffuse from tissue cells and into the capillary bloodstream.

Figure 23.9b

Blood Return Through Veins After chemicals are exchanged between the blood and body cells, blood returns to the heart via the veins. By the time blood exits the capillaries and enters the veins, the pressure originating from the heart has dropped to near zero.

Blood still moves through the veins against the force of gravity. As skeletal muscles contract, they help squeeze the blood along.

Figure 23.10

Blood The circulatory system of an adult human has about 5 L (11 pints) of blood. Just over half of this volume is plasma. Suspended within the plasma are several types of cellular elements.

Figure 23.11

Red Blood Cells and Oxygen Transport Red blood cells are by far the most numerous type of blood cell. They are also called erythrocytes. Carbohydrate-containing molecules on the surface determine the blood type.

Figure 23.12a

Each red blood cell contains large amounts of the protein hemoglobin. Hemoglobin contains iron and transports oxygen throughout the body. Anemia is an abnormally low amount of hemoglobin or a low amount of red blood cells.

White Blood Cells and Defense White blood cells fight infections and cancer. They are also called leukocytes. There are about 700 times fewer white blood cells than red blood cells.

Figure 23.12b

Platelets and Blood Clotting Blood contains two components that aid in clotting: Platelets (thrombocytes) are bits of cytoplasm pinched off from larger cells in the bone marrow. Fibrinogen is a membrane-wrapped protein found in plasma.

Platelets release molecules that convert fibrinogen into fibrin. Fibrin is a threadlike protein. Fibrin forms a dense network to create a patch.

Figure 23.12c

Stem Cells and the Treatment of Leukemia New blood cells are continually formed from unspecialized stem cells found in red bone marrow. Stem cells differentiate into red and white blood cells and the cells that produce platelets. Bone marrow cells show great promise for the treatment of disease.

Leukemia is cancer of the white blood cells. A person with leukemia has an abnormally high number of white blood cells, most of which are defective. Leukemia is usually fatal unless treated. Not all cases respond to treatment.

The Role of the Cardiovascular System in Homeostasis The cardiovascular system performs several homeostatic functions: Controlling chemical balance Controlling the composition of the blood Regulating body temperature Distributing hormones Defending against foreign invaders Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings

Cardiovascular Disease Cardiovascular disease accounts for 40% of all deaths in the United States. The leading cause of death in the United States is heart attack.

When blood exits the heart, several coronary arteries immediately branch off to supply the heart muscle. If one or more of these arteries is blocked, the heart muscle cells will quickly die. This is called a heart attack.

Figure 23.13

Atherosclerosis is a chronic cardiovascular disease. The blood vessels become impaired gradually. Vessels are narrowed by plaques of cholesterol and other substances that form in the inner walls of arteries.

Figure 23.14

How can you avoid becoming a heart disease victim? Don’t smoke. Exercise. Eat a heart-healthy diet.