BioEd Online

Teacher Background

The heart is a relatively small organ—only slightly larger than a person’s fist. Yet it initiates all movement of blood around the body. Why is the movement of blood important? Because blood picks up and carries oxygen and nutrients to all parts of the body. Blood also carries wastes to appropriate places in the body for disposal. This activity, and the two that follow it, will focus on the structure of the heart, its function as a pump, and the circulatory system’s critical role in distributing oxygen and removing carbon dioxide.

The circulatory system consists of the heart, blood and blood vessels. All vertebrates (animals with backbones) have closed circulatory systems, meaning their blood is contained within vessels, separate from the fluid surrounding cells in the body.

At first glance, the heart’s outer surface seems to offer few clues about its important function. However, careful external examination reveals many key structures. For instance, one will notice that the human heart consists of four chambers. Two chambers receive blood from outside the heart, and the other two pump it out of the heart. The receiving chambers are known as atria (the singular form is atrium). The right atrium receives oxygen-depleted blood from the body’s major veins (vessels that bring blood to the heart), and the left atrium receives oxygen-rich blood from the lungs. The two pumping chambers (the ventricles) receive blood from the atria and pump it away from the heart. The right ventricle pumps oxygen-depleted blood via a short loop of blood vessels through the lungs, where it is replenished with oxygen, while the ventricle pumps the oxygenated blood back out into the body through large arteries (vessels that carry blood away from the heart). In short, the left side of the heart works with oxygen-rich blood, and the right side of the heart works with oxygen-depleted blood.

Visible on the exterior of the heart are the coronary arteries, usually surrounded by a layer of fat. These arteries supply blood to the heart muscle itself. It may sound odd, but the heart cannot use the blood contained in its chambers. Instead, it has its own network of blood vessels, called the coronary arteries and coronary veins. Also visible on the exterior of the heart are the let and right auricles (sometimes referred to as “dog ears”), which increase the capacity of the atrium to which they are attached.

Objectives and Standards

Life Science

• Living systems at all levels of organization demonstrate the complementary nature of structure and function. Important levels of organization for structure and function include cells, organs, tissues, organ systems, whole organisms and ecosystems.

• Specialized cells perform specialized functions in multi-cellular organisms. Groups of specialized cells cooperate to form a tissue, such as a muscle.

• Different tissues are, in turn, grouped together to form larger functional units, called organs. Each type of cell, tissue and organ has a distinct structure and set of functions that serve the organism as a whole.

• The human organism has systems for digestion, respiration, reproduction, circulation, excretion, movement, control and coordination, and for protection from diseases. These systems interact with one another.

Science, Health and Math Skills

• Communicating

• Using information

• Interpreting information

• Applying knowledge

Materials and Setup

Materials per Student

• Copy of the student sheet (see Lesson pdf)

Setup

1. Conduct as a class discussion, followed by student working in groups.

2. For the last part of the activity (see Procedure, Item 7), access and view the video, “A Look at the Heart, Part 1,” at www.bioedonline.org. Look under the "Resources" tab and click on "Videos" to access the file.

Procedure and Extensions

1. Ask students, What are the parts of the circulatory system? Encourage student responses by referring to previous lessons, using follow-up questions, and clarifying information until students have provided the following answers: pump (heart), fluid (blood), and tubing (vessels). Explain that in this activity, students will focus primarily on one component of the circulatory system: the heart.

2. Discuss students’ ideas about the human heart by asking questions such as the following.

   • How big is the heart? Tell students to make a ball of one fist. The heart is slightly larger than a fist, and it weighs between 200–425 gm (7–15 oz).

   • Where is the heart located? Explain that the heart is not located on the left side of the chest, as most people think. Instead, it is found in the center of the chest, between the lungs, tilted slightly to the left. Instruct students to sit quietly and try to locate their hearts by feeling for a heartbeat, just to the left of center of the chest.

   • What does the heart look like? Mention that a real heart, which is somewhat conical in shape, looks only somewhat like a valentine.

3. Explain that students will be working in groups to learn more about the circulatory system, especially the heart. Give each student a copy of the student sheet, with labeled diagrams and unlabeled photographs of a heart.

4. Begin by explaining that when looking at the diagram, students should imagine they are facing another person’s heart. This means that the side of the heart to be labeled “right” is on the left side as you face it. You can illustrate this point by having students face each other and raise their right hands.

5. Tell students to locate the right side of the heart on the heart diagram. Next, have them find and label the corresponding area on the photograph. Working in groups, students should continue to find and label on the photograph each part that is identified on the diagram. Explain that this initial focus on appearance of the heart is for orientation only, and not for memorization or testing.

6. Circulate through the class to provide direction, as needed. When students have finished labeling their heart diagrams, let them share their work within their groups to check answers and discuss any discrepancies or questions. Ask students to share any additional observations about the heart. For example, they may notice the fat deposits that surround the blood vessels on the surface of the heart.

7. Show the BioEd Online video, “A Look at the Heart, Part 1.” Lead a class discussion of the similarities and differences between the sheep heart shown in the video and the photo of the heart that students used for this activity. Or, use a model of the human heart to demonstrate the external parts that students identified in the photograph. If you will be conducting the activity, “Examining the Heart,” tell students they will have an opportunity to observe these structures on a real, preserved specimen.

Handouts and Downloads

Download color images from The Science of the Heart and Circulation Teacher's Guide.