Digestive System

The digestive system is made up of the digestive tract—a series of hollow organs joined in a long, twisting tube from the mouth to the anus—and other organs that help the body break down and absorb food.

Organs that make up the digestive tract are the mouth, esophagus, stomach, small intestine, large intestine—also called the colon—rectum, and anus. Inside these hollow organs is a lining called the mucosa. In the mouth, stomach, and small intestine, the mucosa contains tiny glands that produce juices to help digest food. The digestive tract also contains a layer of smooth muscle that helps break down food and move it along the tract.

Two “solid” digestive organs, the liver and the pancreas, produce digestive juices that reach the intestine through small tubes called ducts. The gallbladder stores the liver’s digestive juices until they are needed in the intestine. Parts of the nervous and circulatory systems also play major roles in the digestive system.

Respiratory System

The primary function of the respiratory system is to supply the blood with oxygen in order for the blood to deliver oxygen to all parts of the body. The respiratory system does this through breathing. When we breathe, we inhale oxygen and exhale carbon dioxide. This exchange of gases is the respiratory system's means of getting oxygen to the blood.

Respiration is achieved through the mouth, nose, trachea, lungs, and diaphragm. Oxygen enters the respiratory system through the mouth and the nose. The oxygen then passes through the larynx (where speech sounds are produced) and the trachea which is a tube that enters the chest cavity. In the chest cavity, the trachea splits into two smaller tubes called the bronchi. Each bronchus then divides again forming the bronchial tubes. The bronchial tubes lead directly into the lungs where they divide into many smaller tubes which connect to tiny sacs called alveoli. The average adult's lungs contain about 600 million of these spongy, air-filled sacs that are surrounded by capillaries. The inhaled oxygen passes into the alveoli and then diffuses through the capillaries into the arterial blood. Meanwhile, the waste-rich blood from the veins releases its carbon dioxide into the alveoli. The carbon dioxide follows the same path out of the lungs when you exhale.

The diaphragm's job is to help pump the carbon dioxide out of the lungs and pull the oxygen into the lungs. The diaphragm is a sheet of muscles that lies across the bottom of the chest cavity. As the diaphragm contracts and relaxes, breathing takes place. When the diaphragm contracts, oxygen is pulled into the lungs. When the diaphragm relaxes, carbon dioxide is pumped out of the lungs.

Circulatory System

The Circulatory System is the main transportation and cooling system for the body. The Red Blood Cells act like billions of little UPS trucks carrying all sorts of packages that are needed by all the cells in the body. Instead of UPS, I'll call them RBC's. RBC's carry oxygen and nutrients to the cells. Every cell in the body requires oxygen to remain alive. Besides RBC's, there are also White Blood Cells moving in the circulatory system traffic. White Blood Cells are the paramedics, police and street cleaners of the circulatory system. Anytime we have a cold, a cut, or an infection the WBC's go to work.

The Heart

The heart is located in the chest cavity. It is surrounded by a covering called the pericardium. The heart itself is divided into four chambers, called the right and left atria and the right and left ventricles.
The heart is connected to the rest of the body by means of VEINS which return to the lungs and the ARTERIES which pump blood to the body. The AORTA is the main artery coming out of the heart and receives blood under great pressure from it.
It is important to note is that the heart itself needs a constant supply of oxygen and nutrients to work (much as a car needs gas to run). This is supplied by the CORONARY ARTERIES which run on the surface of the heart. They come out of the root of the aorta.

The Brain

Making sense of the brain's mind-boggling complexity isn't easy. What we do know is that it's the organ that makes us human, giving people the capacity for art, language, moral judgments, and rational thought. It's also responsible for each individual's personality, memories, movements, and how we sense the world.

All this comes from a jellylike mass of fat and protein weighing about 3 pounds (1.4 kilograms). It is, nevertheless, one of the body's biggest organs, consisting of some 100 billion nerve cells that not only put together thoughts and highly coordinated physical actions but regulate our unconscious body processes, such as digestion and breathing.