The human body is a complex system with structures ranging from cells to organ systems and functions ranging from waste removal to protection and defense. The structures and functions are dedicated to maintaining a state of health in the body.
Comparing the Human Body and Cities
Think about a city you visit frequently and the complex structure of that city. You might consider the buildings, the streets, or all the rooms within those buildings, or people within those rooms. Now think about the roadways, waterways, sewers, parks, power plants, even the railways that go in and out of the city moving millions of people a day to their jobs and homes at night. A complex city needs a highly complex system of government administration to attend to all the demands placed upon it.
There is a complex web of discrete units within that administration system to attend to each of these needs at once, functioning at their designated roles but cooperating together at the same time - law enforcement, traffic and transportation guidance, sewer and garbage pickup, as well as education and power systems.
Let's think about our bodies in the context of a system. In the same way, the human body functions a lot like a city, with separate units designated for specific functions, but all working together for a common purpose.
A city as an example of a system.
Structures of the Human Body
Most people are familiar with the functions of the major organs in the human body, but cells are where the magic happens. Starting from a single cell, the human organism ends up with over 200 different kinds of cells. A cell is a membrane-enclosed compartment containing molecular machinery dedicated to carrying out metabolic reactions and maintaining the genetic material. Each kind of cell is specialized to carry out a task within the body. Some cells carry oxygen through our bloodstream (red blood cells); some contract and power our movements (muscle cells); and some process and transmit information about our environment and our bodies (brain cells). That is, of course, just to name a few.
These hardworking little cells end up organizing and grouping together to form the four tissue types in the body. A tissue is a specialized group of cells and their products that function together. The four tissue types in the human body are as follows: epithelial, muscle, nervous, and connective tissue. Epithelial tissue is great for building structures with walls and passageways and compartments. Muscle tissue has cells organized and coordinating together to contract and move. Nervous tissue consists of neurons linked together in vast networks for transmitting and receiving information. Finally, connective tissue provides much of the physical structures and supports within the body and includes materials like cartilage, fat, bone, and blood.
If you take some tissues and combine them into a larger structure that has a dedicated function, you have created an organ. You are probably familiar with organs - things like the heart, lungs, liver, and kidneys. We think of the heart as contracting and providing the force necessary to pump our blood. It is dedicated to that task. We don't expect that sometimes the kidneys will do the pumping, and sometimes the brain will do the pumping, and so on. We expect that the heart will carry out that function our entire lives.
If you take a collection of organs that are all geared towards accomplishing a specific larger function within the body, then you have an organ system. We have eleven of these, ranging from the digestive system to the immune system. If you think about the digestive system, the organs (mouth, liver, stomach, intestines, etc.) included in it each play a crucial but distinct role in digesting our food and allowing absorption of nutrients to fuel metabolism. Each organ individually would not be able to achieve that overarching task.
The human body depicting major organs and structures.
The Functions of the Human Body
Now that we have a general understanding of the hierarchical structure of the human body, let's think about the large-scale functions taking place. At any given time, the body is dedicated to maintaining the stable internal conditions that we associate with health. This ability to constantly sense and correct changes within the body is termed homeostasis. The most basic example of homeostasis is regulation of body temperature. From a young age, we know that our temperature is supposed to be 98.6 degrees Fahrenheit. A healthy human body works to keep the temperature within a narrow range, despite changes in our environment. When our bodies are unable to properly regulate our temperature, we recognize that something is wrong.
We can place our organ systems into some broad categories based on the kinds of things they do to help us maintain homeostasis:
- For movement and support, the muscular system and the skeletal system provide the body with movement, support, and protection - functions crucial for survival and interaction with our environment.
- For protection, the body is under constant environmental assault and also must deal with internal housekeeping of fluids, old cellular material, and malfunctioning cells. The integumentary (protective layer) and lymphatic/immune systems are dedicated to these tasks.
- For maintenance, this is probably the category most associated with homeostasis. Nutrients and oxygen are brought into our bodies for fuel (digestive and respiratory system) and waste, in terms of carbon dioxide and body fluids, are disposed (urinary, digestive, and respiratory system).
- For transport, the cardiovascular system is dedicated to moving materials around the body, both the delivery of essential cellular materials and removal of waste materials.
- For control, the nervous and endocrine systems provide the crucial controls of all the organs carrying out the diverse functions in the body.
- For reproduction, the reproductive system ensures the survival of our species and plays a major role in our development into functioning and healthy adults.
Interactions of Human Body Organs
How important the division of labor is between the organs of the human body cannot be overstated. It is impossible for one organ system to take over all of the bodily functions while the rest of the systems just take a break. You don't expect organ systems to swap functions. Your kidneys will always do the waste handling of the bloodstream. Your thyroid gland will (hopefully) always make thyroid hormones. Your heart will always pump your blood. If any one organ or organ system ceases to function properly in terms of contributing to the health of the human body, we would typically become quite sick and require outside intervention to help temporarily replace the lost function.
The human body is a system of interacting parts with divisions dedicated to carrying out specific tasks to ensure its smooth operation and maintenance of internal conditions. Its organization is structurally hierarchical from molecules and cells up to organs and organ systems. These biological structures have specific jobs, or bodily functions. Functions are typically not interchangeable, and organ systems depend on the functions of other systems to keep them going. When every structure is doing its job, we consider the body to be in a state of health, or homeostasis.
Human Body Analogy
In this writing activity, students will be creating an analogy for the six categories of functions in the human body. Analogies are comparisons that challenge student's creativity and writing skills. For example, a student might compare the human body to a city. The protection of the human body, like the integumentary system, is analogous to the walls of a city. The maintenance of the human body, carried out by homeostasis, might be like the city workers, like garbage men, construction workers, and plumbers that keep the city running. The transport, or cardiovascular system, is like a highway in the city, and the control, the nervous and endocrine system is like the mayor or the government. The reproductive system might be like city planners, who help build suburbs and new additions to the city.
In this activity, you'll be creating an analogy for the human body and the six categories of functions in it as explained in the lesson: movement and support, protection, maintenance, transport, control, and reproduction. You should choose a system with many different parts, just like the human body has. For example, you might choose to compare the human body to a city, a sports team, or a school. You should include how each of the six categories of function relate to your analogy. To make sure you meet all the requirements, check out the criteria for success below.
Criteria for Success
- Analogy compares the human body to another system
- All six of the main functions of the human body are explained
- Analogy is at least 500 words
- Analogy is scientifically accurate