LESSON 3
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Interacting Body Systems How do your body systems work together? Introduction Suppose you are on a team that is building a robot. You can think of the robot as a system and each part of the robot as a subsystem. The pieces that make up the structure of the robot are one subsystem. The wires that send signals to make the robot move are another subsystem. The remote control that you use to control the robot’s movements is another subsystem. No single subsystem can make the robot perform all its functions, but it can function if all the subsystems work together. How is the robot, and all its interacting parts, like a human being? Like the robot, the human body is a system made up of interacting subsystems that allow it to function. Each part of the human body is part of subsystem called a body system. Each of these body systems performs a certain function for the body. Look at the runner’s heart, blood vessels, and bones. His heart pumps blood through blood vessels and delivers oxygen and nutrients to all parts of his body. His lungs take in oxygen that helps to supply energy to his muscles. Bones that connect to muscles enable him to move. To what body systems do these parts belong? How do you think they interact? What do you think would happen if one of these parts was not working properly? In this lesson, you will learn how parts of the body work together to allow a person to function and move using the example of a person running. You will begin to learn about the subsystems that make up an organism’s body. These body systems exist in humans and many other animals and plants. Finally, you will learn how scientists can use other organisms’ body systems to model human body systems.
Vocabulary skeletal system a body system made up of the framework of bones that supports an organism’s body, protects its internal structures, and allows the body to move muscular system a body system made up of all the muscles of the body that cause movement when they contract, or shorten organ a typically self-contained structure that carries out a particular function for the body digestive system the body system made up of organs that break down food into substances that can be absorbed and used for energy and gets rid of the remaining solid waste that cannot be absorbed respiratory system the body system made up of the organs that bring oxygen into the body and remove carbon dioxide waste circulatory system the body system made up of the heart and blood vessels that circulate blood through the body excretory system the body system made up of the organs that get rid of waste reproductive system the body system made up of the organs that allow adults to produce offspring
Next Generation Science Standards Performance Expectations MS-LS1-3. Use argument supported by evidence for how the body is a system of interacting subsystems composed of groups of cells. Science and Engineering Practices Engaging in Argument from Evidence Use an oral and written argument supported by evidence
to support or refute an explanation or a model for a phenomenon. Crosscutting Concepts Systems and System Models Systems may interact with other systems; they may have subsystems and be a part of larger complex systems. Science is a Human Endeavor
Disciplinary Core Ideas LS1.A. In multicellular organisms, the body is a system of multiple interacting subsystems. These subsystems are groups of cells that work together to form tissues and organs that are specialized for particular body functions.
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1. The Skeletal and Muscular Systems
Figure 3.1A The skeletal system is made up of all the bones in the body. The muscular system is made up of all the muscles in the body. The two systems work together to move the body.
For most of human history, people have had to hunt for meat and search for edible plants to meet their needs for food. Hunting often required running after prey or hiding in trees and carefully throwing weapons at prey as they try to run away. How does the human body allow a person to run, stand, hide, and throw? The skeletal system is an important body system for allowing a person to move. The skeletal system is the framework of bones that supports an organism’s body, protects its internal structures, and allows the body to move. This framework gives the body its overall structure and general shape. The structures that connect bones with other bones are called ligaments. Some bones, such as the skull and ribs, protect soft internal organs. The skull protects the brain, and the ribs form a cage that protects the heart and lungs. Other bones interact with muscles to cause movement. The muscular system is also important for allowing a person to move. All the muscles of the body make up the muscular system. Muscles cause movement when they contract, or shorten. Muscles connect to bones with structures called tendons. Not all muscles are for moving the skeleton, though. The heart is part of the muscular system because it, too, is made of muscle. The heart muscle contracting is what causes the heart to beat. Other muscles in the muscular system help move food or blood through the body.
The Skeletal and Muscular Systems Work Together
Skeletal System
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Muscular System
Bones Move by Muscle Contraction Contracting Biceps
Contracting Triceps
Figure 3.1B Muscles and bones work together to allow for movement, like when picking up an object. When the biceps muscle contracts, the triceps muscle relaxes and the arm bends at the elbow. When the triceps muscle contracts and shortens, the biceps relaxes and the arm straightens at the elbow.
The skeletal and muscular systems are examples of body systems. A body system is a group of organs that works together to perform a particular function in the body. An organ is a typically self-contained structure that carries out a particular function for the body. A bone is an organ of the skeletal system. Tendons and ligaments are other organs in the skeletal system. The brain, heart, and stomach are examples of organs in other body systems. No single organ can do the job of an entire body system. The skeletal and muscular systems work together to help a person move. As an example, Figure 3.1B shows how the biceps and triceps muscles in the upper arm move bones in the arm to bend at the elbow, like when you want to pick up an object. The biceps and triceps are attached to bones in the arm and shoulder by tendons. Starting with a straight arm, when the biceps muscle contracts, it pulls on the bones it is connected to. At the same time, the triceps relax so that the bone is not pulled in two directions at once. Since the lower part of the arm and the upper part of the arm are connected by a hinge, like a door, the lower part of the arm swings up. To straighten the arm at the elbow, the triceps will contract and the biceps relax. Many muscles attached to bones work in pairs like this to move the bones one direction or another. Interacting Body Systems
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2. The Digestive System
Food, like this cheeseburger, provides the body with energy for growth, repair, and life processes. But first, the hamburger must be broken down by the organs in the digestive system into nutrients that the body can use. In the mouth, the large carbohydrates in the bun will be broken down into sugars by chemical digestion.
Most people no longer hunt for their food, but humans still need to eat multiple times a day. All animals need food to survive. Food gives a person energy to run, throw, move, and even sleep. An organism’s body runs on the energy stored in food. How does the body get energy from food? The body cannot directly use the energy found in food. To be used by the body, food must first be broken down, or digested, into simpler substances. The digestive system is the body system that breaks down food into substances that can be absorbed and used for energy and gets rid of the remaining solid waste that cannot be absorbed. Food is mostly made up of substances called carbohydrates, proteins, and fats. These are broken up into simpler substances that can be absorbed and used throughout the body for energy. The digestive system forms a long tube from the mouth to the rectum. Hollow, muscular organs make up different parts of the tube. The main organs of the digestive system are the mouth, esophagus, stomach, small intestine, large intestine, and rectum. Each one has an important role in digesting food. The Mouth and Esophagus Digestion occurs in the mouth in two different ways. Large food particles are split into smaller pieces by chewing, grinding, and mashing with the teeth. Food is also broken down chemically by digestive juices in the saliva. Chemical digestion changes the food into different substances through chemical reactions. Saliva specifically breaks down large carbohydrates into simpler sugars. Say, for example, you are eating a hamburger. Your teeth break up the pieces of the bun, meat, lettuce, and tomato. Your saliva breaks down the carbohydrates in the bun into sugars. Your tongue helps by moving the food around in the mouth and then pushing it into the throat. Swallowing moves the food into the next organ, the esophagus. The esophagus is the part of the digestive tube that connects the mouth to the stomach. Muscles in the esophagus push the food into the stomach.
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The Stomach The stomach is a bag-like organ made of strong muscles. As the muscles in the stomach contract and relax, food is mixed and broken down. When the food is in smaller pieces, it is easier to digest. Here, all the pieces of your hamburger are being broken apart. Additionally, several digestive juices made in the stomach chemically digest proteins in the hamburger. From the stomach, the partially digested food moves into the small intestine.
Parts of the Digestive System
Mouth Esophagus
The Intestines and Solid Organs The small intestine is the longest organ of Liver the digestive system, measuring more than six meters long in humans. Most of the digestion of proteins and carbohydrates takes place here. The small intestine Small Intestine absorbs most of the digested nutrients Large Intestine that have been broken down and transfers those nutrients to the blood stream. Blood transports the nutrients to all parts of the body, where the energy stored in the nutrients is released. There are two organs that are not part of the hollow tube that makes up most of the digestive system, but they help in digestion by making digestive juices flow into the small intestine. The liver produces digestive juices that break down fats, like the fat in the hamburger meat. The pancreas produces digestive juices that continue to break down fats, carbohydrates, and proteins into even smaller substances. Material that has not been absorbed in the small intestine passes into the large intestine. Here, water is removed. Most of what remains is waste. Waste is stored in the lower part of the large intestine, called the rectum, before it is eliminated from the body. The trip your hamburger has made through your digestive system has lasted many hours and involved the interaction of many organs and systems. The digestive system breaks down food and the other organ systems transport this digested food to be used for energy all over the body. The muscles in the digestive system move food all the way through the tube, from the mouth to the rectum. Without the aid of muscles, blood, and other parts of the body, the digestive system would not be able to provide energy to the body.
Stomach
Rectum
Figure 3.2 The digestive system forms a long hollow tube from the mouth to the rectum. Different organs with different functions make up the parts of the tube, but they all work together to create a functional digestive system.
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3. The Respiratory and Circulatory Systems You probably don’t pay much attention to the breaths you take every day or whether your heart is beating. If you are a runner, however, you may have noticed that your heart beats faster and you begin to breathe more rapidly when you start to run. Why does this happen? The Respiratory System When you are running, you start breathing rapidly to take in more oxygen, and push out more carbon dioxide. Your body requires oxygen for the process of releasing energy from broken down food. Running uses a lot of energy, so more oxygen Figure 3.3 is needed. During these chemical reactions, carbon dioxide waste is The main organs of the respiratory formed. Too much carbon dioxide is toxic, so it must be removed from system are the lungs. The circulatory the body before it can cause harm. This causes you to breathe out more system is made up of the heart and to release that carbon dioxide. the blood vessels. Together these two The respiratory system is the body system that brings oxygen into systems transport blood, oxygen, and the body and removes carbon dioxide waste. The main organs of the nutrients throughout the body. Oxygen respiratory system are a pair of lungs. When you inhale, air containing helps to release energy from broken oxygen passes from the environment through your nose and mouth down food, which is essential for and into your lungs through tubes. At the end of the tubes, deep within running or even just surviving. the lungs, are many tiny air sacs that have very thin walls. Oxygen entering the lungs The Respiratory and Circulatory Systems passes from the tubes and through the walls of the air sacs. Here is where the respiratory Heart system interacts with the circulatory system.
Trachea
Lungs Blood Vessels
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The Circulatory System As you run, your heart begins to beat faster. The oxygen that was in your lungs moves into your blood, where it is carried all over the body. The circulatory system, consisting of the heart and blood vessels, circulates blood throughout the body. The pumping action of the heart muscle is what moves the blood all around the body. Oxygenated blood near the lungs gets to the heart through a vein, a type of blood vessel. Veins carry blood to the heart from the rest of the body. The heart then pumps that blood all over the body through arteries, another type of blood vessel. Arteries carry blood away from the heart. As you run, your heart beats faster to pick up more oxygen from the lungs and transport it to where it is needed. In addition to oxygen, blood can transport nutrients and waste from all over the body to where it can be used or removed.