6th-Chapter 2: Lesson 2.2 Moving and Exchanging Substances Pg.45-53

Circulatory System

The (also called the cardiovascular system) is formed by all the structures that move blood through the body (Figure 2.8). The consists of the heart, blood vessels, and blood. The heart pumps the blood that the transport to every cell in the human body. Functions of the circulatory system include the following:

• transporting and other nutrients to cells in the body

• removing and other waste products

• regulating body

• assisting with function

Caring for the circulatory system through healthy eating and physical activity supports these functions. In the next sections, you will learn more about the heart and how blood circulates in the heart. You will also learn more about blood vessels and blood.

Heart The is a hollow, located in the center of the chest. The heart is a steadily working muscle. It beats around times per year and pumps about of blood each day.The heart contains four hollow spaces called . The top two chambers are called atria. The bottom two chambers are called . Valves control the of blood flow in the heart. Like doors that open only one way, the valves make sure blood flows in the right direction. For example, one makes sure that blood flows from an atrium to a ventricle. It will not let blood flow from a ventricle to an . Other valves make sure that blood leaving a ventricle does not flow backward into the ventricle.

The you feel and hear is caused by the contraction of the heart chambers and closing of valves. The first heart sound is the atria squeezing blood into the ventricles. The second sound is the pumping blood out of the heart.

Blood Circulation

Blood follows a path that provides the body with a continual supply of blood. You can trace this path in Figure 2.9.

Oxygen-poor blood flows from around the body into the , which passes this blood into the right ventricle. The right ventricle pumps oxygen-poor blood out of the heart to the lungs, where this blood obtains .

Then oxygen-rich blood is returned from the into the left atrium of the heart, which passes blood into the left ventricle. Finally, the pumps oxygen-rich blood into the aorta. The oxygen-rich blood is then pumped around the body. After oxygen is used up, the oxygen-rich blood becomes blood and flows back into the right atrium. The process then begins again.

Blood Vessels

are an extensive network of pipes that carry blood throughout the entire body (Figure 2.10). There are three types of blood vessels. These vessels are the , , and .

carry oxygen-rich blood. The largest artery is the , which carries blood from the left ventricle of the heart to other . Most arteries carry blood from the heart to the rest of the body. These arteries have muscular walls that can handle the pressure created by the heart’s pumping. Arteries branch into smaller , and these branch into even smaller ones.

The smallest arteries are the capillaries. have very thin walls with no muscle. They deliver oxygen and nutrients to body cells and pick up cells’ waste. Capillaries lead into tiny veins, which lead into larger veins.

carry oxygen-poor blood. Two large veins, called the vena cavae, carry blood into the right atrium of the heart. One vena cava brings blood from the head and upper body. The other brings blood from the lower body.

Blood

plays an important role in maintaining a person’s and sustaining life. As you already learned, blood carries oxygen and nutrients through the body, while also removing carbon dioxide and waste. a person’s body temperature, similar to how a regulates the temperature in a room. Blood also protects the body against infection.

Because of blood’s vital role in the , many people donate blood to organizations such as the American Red Cross. In fact, one pint of donated blood can save up to three lives. For this reason, people who donate blood are actually giving the gift of life.

Blood is made up of both parts (Figure 2.11). The liquid part of blood is called plasma. Plasma makes up at least half of blood's content. It is responsible for carrying all parts of blood throughout the body.The solid parts of blood consist of blood cells, blood cells, and platelets.

Red blood cells make up one-half the blood’s volume. Red blood cells contain a red substance called hemoglobin, which can carry and . As a result, red blood cells transport oxygen throughout the body.

cells move through the blood and live in various organs of the body. They help defend the body against infections.

Platelets are responsible for blood clotting. stops blood from flowing outside the wall of a blood vessel. This action helps prevent blood loss when blood vessels are injured.

Respiratory System

The cannot deliver oxygen to the body’s cells without the help of the respiratory system. The respiratory system includes that obtain vitally important oxygen from the outside world (Figure 2.12). This body system draws oxygen into the and delivers it to blood vessels. It also takes —another gas—out of the blood and sends it outside the body. Since the body’s cells require oxygen, a healthy respiratory system enables all other body functions. Respiratory organs can be divided into the respiratory systems.

Upper Respiratory System

The system allows air containing oxygen to enter the body. Air enters the nose and mouth and passes down through the throat to the and then through the trachea to the lungs. You can feel the as a bump in the front of your throat. It vibrates when you speak, as air passes across the . A small structure covers the larynx when you swallow and prevents food from entering the .

The walls of the make a sticky substance called mucus. This mucus traps bacteria and dust particles so they cannot enter the lungs. Extra is made when someone has an infection or an allergic reaction. The passage behind the nose is also lined with mucus and with that warm and moisten air. You see evidence of this on cold days when you exhale. The warm, exhaled air forms water vapor as it contacts the cold outside air.

Lower Respiratory System

The branches into two bronchi, which are air passages that lead to each lung. The bronchi branch into smaller passages called inside the lungs. These smaller airways end as sacks called . When you inhale, air fills the alveoli. The alveoli are important for oxygen exchange in the lungs. If they fill with fluid, as in , air and oxygen cannot enter them. This can disrupt the vital process of .

Respiration

is the exchange of oxygen and carbon dioxide in the respiratory system. It includes two steps: . When you inhale, you take in air, which reaches the lungs. Air fills the alveoli, and oxygen moves into the blood in tiny . These capillaries then deliver oxygen-rich blood to the heart.

At the same time, moves from the blood into the . This air travels back into the respiratory passages. When you exhale, you push the air with carbon dioxide out of the body (Figure 2.13).

help the lungs take in and push out air. During , muscles enlarge the chest. This draws air in through the mouth and nose. The chief muscle doing this work is the diaphragm. The is a sheet of muscle beneath the lungs and above the . As the diaphragm moves down, the chest expands. Other muscles of the chest, especially those between the ribs, also help the chest expand. happens when these muscles relax. The chest collapses and squeezes air out the mouth and nose.