There was a time when I didn’t know much more about the human body than that my wife’s was beautiful!
How strange, I thought. We only get one body. It has to last a lifetime. And the better it works, the better we feel. Why wouldn’t we want to know everything about how it works and how to maintain it?
Yet most of us don’t. We know more about the insides of our car than how our body functions.
Maybe that’s because cars come with owner’s manuals, but your body doesn’t.
Well, problem solved.
This article introduces a 12-part series that will explain how your body works. This series is the instruction manual for your body that you never got.
This initial article will briefly describe the 11 human body systems.
Articles about each of the body systems will follow, one a day. Each article will answer these questions . . .
- What Does The System Do?
- What Makes Up The System?
- How Does The System Work?
- What Can Go Wrong With The System?
- How Do You Keep The System Healthy?
And each article will include “5 Interesting Facts About The System.”
Before starting this discussion of our body systems, however, you must understand that dividing your body into 11 systems for the purpose of studying them does not mean that they are independent systems. Far from it, they are interconnected and dependent on each other.
In fact, some body parts are part of multiple systems. For example, the long bones (like the femur) are not only part of the skeletal system, but they are also part of the circulatory system because they manufacture blood cells. And the ovaries are part of the endocrine system as well as the reproductive system. More about all of this later . . .
These are the 11 main human body systems, presented in alphabetical order.
The circulatory system is made up of your heart, blood vessels and blood. Your heart pumps oxygen-rich blood from your left ventricle into your biggest artery, the aorta. From there, the aorta branches into smaller arteries, which then branch into even-smaller arteries that travel all over the body. When blood reaches the smallest blood vessels, called capillaries, an exchange occurs. Oxygen, nutrients and hormones are deposited into the cells and waste material from the cells, such as carbon dioxide, is collected for the return trip to the heart.
Veins carry the blood back to the heart where it enters the right atria, passes through the right ventricle and is sent to your lungs where, in capillaries in the lungs, the waste carbon dioxide is deposited and oxygen is picked up. The newly oxygenated blood returns to the heart and, this time, it enters the left atria. From there it goes to the left ventricle and, from there, it is pumped again .
Click here to learn more about your circulatory system.
Your digestive system consists of organs that break down food into the protein, vitamins, minerals, carbohydrates and fats that your body uses for energy and for building and repairing cells and tissues.
Food passes from your mouth down through a muscular tube called the esophagus, and into the stomach, where food continues to be broken down. The partially digested food passes into the small intestines where it is broken down into nutrients which enter the bloodstream through tiny hair-like projections called villi. The liver, the gallbladder and the pancreas produce enzymes and substances that help with digestion in the small intestine.
The last section of the digestive tract is the large intestine, which includes the cecum, colon, and rectum. Indigestible remains of food are eliminated through the anus.
Click here to learn more about your digestive system.
The endocrine system is made up of a group of glands that produce the body’s long-distance messengers, or hormones. Hormones are chemicals that control body functions such as metabolism, growth, and sexual development. The glands, which include the pituitary gland, thyroid gland, parathyroid glands, adrenal glands, pineal body, pancreas, ovaries, and testes, release hormones directly into the bloodstream, which transports the hormones to organs and tissues throughout the body.
Click here to learn more about your endocrine system.
The immune system is our body’s defense system against infections and diseases. Organs, tissues, cells, and cell products work together to respond to dangerous organisms (like viruses or bacteria) and substances that may enter the body from the environment.
An anatomic response physically prevents threatening substances from entering your body. Examples of the anatomic system include the mucous membranes and the skin. If substances do get by, the inflammatory response goes on attack.
The inflammatory system works by excreting the invaders from your body. Sneezing, runny noses, and fever are examples of the inflammatory system at work.
When the inflammatory response fails, the immune response goes to work. This is the central part of the immune system and it is made up of white blood cells, which fight infection by gobbling up antigens. About a quarter of white blood cells, called the lymphocytes, migrate to the lymph nodes and produce antibodies which fight disease.
Click here to learn more about your immune system.
The lymphatic system has three main purposes. It removes excess fluid and waste products from the spaces between the cells and returns them to the blood stream. It aids the immune system in destroying and removing waste, debris, dead blood cells, pathogens, toxins, and cancer cells. And it also absorbs fats and fat-soluble vitamins from the digestive system and delivers these nutrients to be used by the cells of the body.
Click here to learn more about your lymphatic system.
The muscular system is made up of tissues that work with the skeletal system to control movement of the body. Some muscles—like the ones in your arms and legs—are voluntary, meaning that you decide when to move them. Other muscles, like the ones in your stomach, heart, intestines and other organs, are involuntary. This means that they are controlled automatically by the nervous system and hormones—you often don’t even realize they’re at work.
Muscles also generate heat to help regulate your body’s temperature and maintain your posture.
Click here to learn more about your muscular system.
The nervous system is the control system and the network of communication for your body.
Think of your brain as a central computer that controls all voluntary and involuntary bodily functions.
Your “computer” acts through a network that relays messages back and forth from the brain to different parts of the body.
This “network” consists of the spinal cord and nerves. The spinal cord runs from the brain down through the back to nerves which branch out to every organ and part of your body.
When a message comes into the brain from anywhere in the body, the brain tells the body how to react. For example, if you accidentally touch a hot stove, the nerves in your skin shoot a message of pain to your brain. The brain then sends a message back telling the muscles in your hand to pull away. Fortunately, all of this occurs lightning fast.
Click here to learn more about your nervous system.
The reproductive system allows humans to produce children. Sperm from the male, which is produced in the testes, fertilizes the female’s egg, or ovum, in the fallopian tube. The fertilized egg travels from the fallopian tube to the uterus, where the fetus develops over a period of nine months.
Click here to learn more about your reproductive system.
The respiratory system brings air into the body and removes carbon dioxide. It includes the nose, trachea, and lungs.
When you breathe in, air enters your nose or mouth and goes down a long tube called the trachea. The trachea branches into two bronchial tubes, or primary bronchi, which go to the lungs. The primary bronchi branch off into even smaller bronchial tubes, or bronchioles. The bronchioles end in the alveoli, or air sacs. Oxygen follows this path and passes through the walls of the air sacs and blood vessels and enters the blood stream. At the same time, carbon dioxide passes into the lungs and is exhaled.
Click here to learn more about your respiratory system.
The skeletal system has a number of functions, some obvious and some less so. Of course, it supports your body and gives it structure.
However, in addition, your skeletal system works with the bones to allow movement, protects your internal organs, produces blood (in the bone marrow) and stores minerals such as calcium and phosphorous which it releases into the blood when necessary.
Click here to learn more about your skeletal system.
The urinary system eliminates waste from the body, as urine. The kidneys remove waste from the blood. The waste combines with water to form urine. From the kidneys, urine travels down two thin tubes called ureters to the bladder. When the bladder is full, urine is discharged through the urethra.
Click here to learn more about your urinary system.
Oh . . . if you want to learn more from the world’s greatest personal trainer, my wife Kathie Lamir, this is her website.