The body systems
The human body is made up of numerous systems. A system is made up of different organs. The main systems are the skeletal and muscular systems, the digestive system, the circulatory system, the respiratory system, the nervous system and the reproductive system. Other systems are the urinary and endocrine systems.
Below is a brief account of what each system does:
1 The skeletal and muscular system
The skeletal system is all of the bones in your body. Your bones give you your shape and enable you to move. The average, full-grown adult has 206 bones in his/her body. Inside most bones, there is a material called bone marrow, which produces red blood cells. When you are a baby and a toddler, your bones are gelatin like. Because you fall down a lot, this way you don’t break all your bones. The skeletal system works closely together with the muscular system to allow us to move. The human body contains more than 650 individual muscles.
2 The digestive system
The digestive system is the system that digests (or breaks down) food. The digestive process starts in the mouth. There, chewing + saliva helps break down the food into smaller pieces. Then, you swallow the food and it goes down the esophagus (or food tube). At the end of the esophagus is the stomach. In the stomach, stomach acids break down the food even more into a milky liquid. The acids do not burn through the stomach wall because it is lined with mucus. After the stomach twists and turns to digest your food, the food is sent in to the small intestine. The small intestine is about 32 ft. long. It is lined with tiny finger like objects called villi. Little bits of food are sucked into the villi and put into the blood stream where your cells are fed with that food. Also, the pancreas, liver, and many other tiny glands in your small intestines discharge secretions and help digestion. It takes about 3 hours for food to pass through the small intestine. Next, the food goes into the large intestine. The large intestine is about 5 ft. long. Food stays in the large intestine for about 1 or 2 days. The solid waste “bladder”, as you could call it, is the rectum that sticks out horizontally from the rest of the large intestine. Then, it goes out of the anal canal.
3 The circulatory system
This system is the system that circulates your blood. Blood carries different nutrients around the body. The parts of the circulatory system are the arteries, veins, capillaries, liver, and the heart. The arteries are tubes that lead blood away from the heart. The veins lead blood back to the heart. Capillaries are tiny tubes that connect the arteries and veins so blood can go back to the heart. Finally, the heart. This is the hardest working organ in the body. It has to squeeze and relax, squeeze and relax, about 70 times a minute. Your body has 100,000 miles of blood vessels. Your heart is about the size of your fist. The sole function of the heart is to pump blood from the veins into the arteries at the rate of 5 liters every minute at rest, but quicker during exercise or movement.
4 The nervous system
The nervous system controls your body. The nervous system is a network that carries information in the form of nerve impulses to and from all parts of the body in order to bring about bodily activity. The key organs in the nervous system are the nerve cells and the brain. The brain is the most important organ in your body. The brain sends signals throughout your body to tell it what to do. These signals go through the nerves. Some of these signals you control, some go automatically. For instance, if you want to move, you make the brain send out signals. The brain sends out signals to make your heart pump and many other vital functions automatically. Finally, the spine plays a significant role in the nervous system; all of the nerves come from the brain and down the spine, then they branch off.
5 The reproductive system
There are two different kinds of reproduction: sexual and asexual. Sexual happens when a male and female have sex, and asexual happens without sexual intercourse. Humans reproduce by sexual reproduction.
The male reproductive organs are mainly outside of the body. One of the organs is called the penis. Behind and below the penis is a small sack named the scrotum. Inside the scrotum are two oval shaped objects called the testicles or testes. These testicles produce sperm. The sperm look like microscopic tadpoles.
In-between the female’s legs is the vulva, which is made of tiny folds of skin. The vulva covers the opening to a canal inside the female’s body called the vagina. The vagina leads up into the uterus, which is a hollow, oval shaped reproductive organ. Around the bottom of the female abdomen, are two oval shaped objects called the ovaries, which produce the human egg. About every 28 days, the ovaries ovulate, or release an egg. The egg enters a tube nearby that is called the fallopian tube, or the oviduct. The tubes carry the egg to the uterus to be fertilized. If there are no sperm to fertilize the egg, the lining that has been forming, ready to receive a fertilized egg (an embryo), is released through the vulva. This lining contains about 60cc of blood. This can cause pains and cramps for the female. This periodic bleeding is called menstruation, or a ‘period’. A woman who is pregnant will not have menstruation.
6 The respiratory system
The respiratory system is the system that allows you to breathe. It is made up of the trachea, diaphragm, and lungs. Your diaphragm is a muscle. Inside the lungs are the bronchial tubes and the alveoli, or air sacks. In your throat, there is a flap of skin called the epiglottis, which covers the trachea when you swallow, and covers up the esophagus when you breathe. This is to control the food and air that goes down. When you inhale, your diaphragm forces your ribs expand. The opposite happens when you exhale. Also, there are veins in your lungs where red blood cells pick up oxygen.