The Eight Major Systems
The digestive system The excretory system The muscular system The respiratory system
The skeletal system The nervous systemThe circulatory system The immune system
The Circulatory System
Another very major system of the human body that we will be visiting is the Circulatory System. It is responsible for moving nutrients and oxygen to all parts of the body, and for removing waste products. It works closely with all other body systems, including the skeletal system, believe it or not. Both red and white bloodcells are produced in part by the bone marrow. White blood cells are also produced by the spleen and a few other tissues. The circulation of the blood in the human body is divided into two sections, the pumonary circulation and the systemic circulation. The purpose of pulmonary circulation is to oxygenate the blood, and clear the carbon dioxide out. It is then pumped back out to systemic circulation, where it picks up nutrients, delivers oxygen and nutrients, collects waste products, and passes through the kidneys to remove urea and other waste. Blood flows into the heart from the systemic circuits in the right atrium, then flows out into the pulmonary through the right ventricle. After it gets out of the pulmonary circuits it enters the left atrium, and is pumped back out to the systemic circuits by the left ventricle. As you can see from this, the blood on the left side of the heart contains much more oxygen than the blood on the right side.
The beat of the heart is controlled by the sinoatrial node, which is also known as the pacemaker. The pacemaker is located on the right side of the heart on the atrium just below where the superior vena cava enters the heart. It is a small area of specialized
cardiac cells that can spontaneously initiate their own electrical impulse. When the pacemaker sends out a pulse, it travels rapidly through the cells of the atria, assisted by the intercalated disks. About 100 milliseconds after this, the pulse reaches the atrioventricular node which transmits the pulse to the ventricles, causing them to contract and thus completeing the heartbeat.
Another importand thing to know about the circulatory system is what blood pressure is. Blood pressure is a measure of the force per unit area with which blood pushes against the walls of the blood vessels. There are two numbers used to indicate a person's blood pressure. The systolic pressure is measured when the ventricles are contracting. The diastolic pressure is measured when the ventricles are relaxed. They are usually displayed Systolic/Diastolic.