Organ System Structure and Function

All living things are systems, made up of smaller, interacting parts that work together to support the functioning of the organism. As the number of cells increases in a multicellular organism, each cell becomes better able to perform one particular function. In this lesson, students model the relationships between cells, tissues, organs, and organ systems within the human body. 

• Multicellular organisms are made up of more than one kind of cell and groups of these specialized cells are designed to do one job very well. 
• Humans are so complex that the body is made up of subsystems composed of interacting parts.
• Each system interacts with and depends on the other systems to function properly.
  
  

• Why do multi-celled organisms benefit from having specialized cells?
• What kinds of jobs do the cells in the human body have to carry out?
• How are tissues organized in the human body?
• How are cells related to organ systems?
• How does the immune system interact with the digestive system in ways that may protect some people from getting the flu?
• How can the heart be part of both the circulatory system and the muscular system?
• How are all of the systems, organs, tissues, and cells able to work together?
  
  

Misconception: Humans are made up of one kind of cell.

Fact: Humans have about 200 different kinds of cells, which are specialized for specific functions.

Misconception: Body systems are independent of one another, and so a change to one system won’t affect other systems.

Fact: Each body system is made up of smaller parts, but the systems all interact with and depend on each other for the body to function properly.

Circulatory System : a group of organs that distribute blood, oxygen, and nutrients to the body’s cells and carry away waste products

Digestive System : a group of organs that break down food into energy that can be used by cells in the body

Excretory System : a group of organs that remove waste from the body

Immune System : a group of organs that defend the body against infectious organisms and other harmful invaders

Organ : a structure composed of two or more tissue types that work together to carry out a specific function

Organ System : a group of closely interacting organs that carry out a specific function

Respiratory System : a group of organs that enable an organism to collect oxygen and dispose of carbon dioxide

Getting the Flu

Every year in the fall and winter, many people get the flu. But Lamar Johnson never seems to get sick. Lamar is 44 years old, and he doesn’t think he’s ever had the flu. He eats a lot of fruits and vegetables. He wonders if this is why he seems to stay healthy when people around him get sick.

Scientists don’t know for sure what makes one person catch the flu while another person stays healthy. In 2011, a team of scientists designed an experiment to help them answer this question. They infected 17 healthy people with the flu virus. They then used different tools to study how each person’s body responded to the virus.

The scientists wanted to see how each person’s immune system reacted to the flu virus. The immune system defends the body against infectious organisms and other harmful invaders.

Study Results

About half of the 17 people who were infected with the flu virus got sick. The results showed that the immune systems of people who didn’t have flu symptoms responded in different ways from the immune systems of those people who got sick. Scientists hope that their results will eventually lead to therapies that could one day prevent everyone from getting the flu.

Understanding how and why people get sick is complicated. One of the reasons it is complex is that the human body is made up of many different parts. For example, it is made up of about 200 different kinds of cells. Each kind of cell has a specific function that contributes to the overall functioning of the body. Some cells digest food. Others attack harmful substances. Still others carry substances such as nutrients or oxygen around the body.

Cell Specialization

This is called specialization. Instead of every cell trying to do every job, groups of cells are specialized to do one job very well. Each group of specialized cells is more efficient than if each cell worked on its own.

For example, white blood cells are part of the immune system. They play an important role in its defensive strategy. There are different kinds of white blood cells, each with a specific function. One kind of white blood cell surrounds and breaks down anything it believes does not belong in the body. It does this in one of two ways. It either absorbs the invader or releases a chemical called an enzyme that will destroy it.

Cells that are similarly specialized for a specific function group together to form tissues. Animals including humans generally have four kinds of tissues: epithelial, connective, muscular, and nervous tissues.

In this lesson, students create a model to investigate the hierarchical organization within the phenomena of a human organ system and analyze how different organ systems rely on each other for an organism to function. Students use the body system model they develop and analysis to explain how the body is a system of smaller interacting systems, which are themselves composed of groups of specialized cells.