This is a diagram of the skeletal system (left), respiratory system, digestive system (middle), and the circulatory system (right)
Circulatory system
The circulatory system is probably the most important organ system in our body; it deals with sending our blood throughout our body, thus nourishing our body cells. The main organ of the circulatory system is our heart; what the heart does is it pumps all the blood to the lungs and then to the body. The heart has four parts within itself; a left atrium, a right atrium, a left ventricle, and a right ventricle. Their are two major blood circulations; the pulmonary circulation and the systemic circulation. The pulmonary circulation deals with sending the blood to the lungs to get oxygenated. Without oxygen, our cells wouldn't have energy, and without energy, we would die. The pulmonary circulation consists of pulmonary veins and pulmonary arteries. The pulmonary arteries send the blood to the lungs to get them oxygenated, and are sent back through the pulmonary veins. From the pulmonary veins, blood is sent to the left atrium to the left ventricle and then to the aorta starting systemic circulation (circulation between the body and heart). The Aorta is the biggest artery in our body, and it sends oxygenated blood throughout our body. After going through our entire body, deoxygenated blood goes to the Vena Cava, the largest vein in our body, and then back to the right atrium, making the cycle continue for years on end.
nervous system
The nervous system, alongside the Circulatory system, is the most important system in our body. It is responsible for allowing us to do the greatest things ever: Move around. The Nervous system consists of the Brain, the Spine, and Neurons. There are two parts of nervous systems: The Central Nervous System (CNS) and the Peripheral Nervous System (PNS). The PNS is the system that sends neurons throughout your body. 'The main function of the PNS is to connect the CNS to the limbs and organs (Wikipedia).' It also is responsible for sending neurons to the rest of the body and to the brain. A neuron is made up of a nucleus, an axon, and a dendrite. The CNS consists of the brain and the spine. The Brain receives and sends information to the body. The Brain is also divided into 5 parts; the Cerebrum, the Cerebellum, and the Brain Stem. The spinal cord is what sends the neurons to the body and to the brain; it acts as a passageway. Without the nervous system, the body can not give or receive information and all will be disrupted (Christopher and Dana Reeve foundation).
digestive system
To get energy, not only do we need to send oxygenated blood to our body cells, but we also need to digest food, and that's exactly what the digestive system is all about. The digestive system is important for providing our body with proteins, carbohydrates, vitamins and fats (NIH Publication). There are many organs in the digestive system such as the intestines and the pancreas, but all the food gets digested in a specific order: The food first enters through the mouth, where you must begin to chew your food and swallow it. While you chew your food, your mouth begins to produce saliva which starts a chemical digestion of carbohydrates and helps break down your food (986). After the mouth, the food goes down the pharynx, an open part that begins at the back of your mouth. The food travels down the esophagus and into the stomach. The stomach is the organ located in your upper abdomen, and its main function is to process and transfer food to the next organ; the liver. The liver is the second biggest organ in our body, and it holds the responsibility of checking every nutrient we consume and sees whether it can move forward. If the nutrient is good, it is moved forward. The liver helps digest food and create proteins (Dr. Oz). After that, food goes into the small intestine and then the large intestine where it is processed, and then it is taken out through the anus.
skeletal system
The skeletal system consists of our bones and skeleton. In fact, the reason humans are classified as vertebrates is mainly because we have a back bone. Some bones include the skull and the ribs. The most obvious function is to hold our bones and body together, and it also meant to protect your body. Bones also serve as a reservoir for calcium and protein (Cliffnotes). Ax we grow, our exoskeleton grows with us. The ligaments and joints connect our bones together.
respiratory system
The respiratory system stands along side as one of the most important systems in our body. It serves the function of inhaling oxygen and getting the oxygen for us to survive. We breathe in through our nose and mouth, and the air we get is sent down through the trachea. The trachea is then divided into 2 tubes called bronchial tubes (WebMD). From there the air is sent to the lungs where it oxygenates the blood and sends it back to the blood stream to give to the rest of the body. The function of the alveoli is to hold oxygen and Carbon Dioxide during respiration (Janmohammad).