No part of the body is without access to a blood supply. The human heart is a hollow, pulsating muscle located above the diaphragm and slightly left of the midline of the chest. Its rhythmic beating keeps body fluids mixed by constantly forcing blood through the system of blood vessels.
Function
Transportation, protection, and assistance are three main functions of the circulatory system. Transportation moves substances to and from body cells. Prevention defends the body against attack by invading bacteria. Assistance helps regulate body heat. The organs of the human circulatory system are the heart, blood, blood vessels, lymphatic vessels and nodes. The lymphatic system aids the circulatory system in removing cell wastes and transporting nutrients into the cells. The filtering system for lymphatic function uses lymph nodes or glands.
Heart Basics
The pump for blood circulation in humans is the heart. It has a sac-like covering called the pericardium, and the heart muscle itself is called the myocardium. The four chambers in the heart are the right and left atria and the right and left ventricles. The right side pumps used blood to the lungs, where carbon dioxide is replaced by oxygen. The left side receives the fresh blood with oxygen from the lungs and pumps it to all parts of the body. According to Drug Information Online, a normal heart rate, or pulse, averages from 60 beats to 80 beats per minute, and the heart rests between beats. A complete heartbeat is called a cardiac cycle.
Significance of Blood Vessels
In general, blood vessels are divided into groups according to their size, function and characteristics. The distribution route for the fresh blood supply is through the arteries and arterioles to the tiny capillaries. The collection route for used blood starts in the capillaries and goes on to the venules through the veins and back to the right atrium of the heart. Although the capillary is the smallest blood vessel, it serves as the bridge that takes oxygen and food substances to the cells and removes unwanted cell wastes.
Types of Circulation
The heart has its own blood supply, called coronary circulation. Pulmonary circulation is the flow of blood from the heart to the lungs and back to the heart. The hepatic portal circulation system is a special blood route from the intestines, stomach and spleen to the liver. Cerebral circulation refers to the blood route through the brain. Systemic circulation is a general term referring to all of the main blood vessels in the body.
Characteristics of Blood
Blood pressure refers to the pressure that blood exerts on the walls of the blood vessels as the heart moves it along. The National Center for Biotechnology Information reports that the adult human body contains more than six quarts of blood, which is a fluid made up of infection-fighting white blood cells, oxygen-carrying red blood cells, platelets for clot formation and plasma. Blood cells originate as stem cells in the bone marrow. Plasma contains water, proteins, sugars and fats.
