Circulatory System - Anterior View
The circulatory system is responsible for transporting blood throughout the body. The circulatory system includes the heart, arteries, arterioles, capillaries, venules and veins. The system is responsible for delivering oxygen and nutrients to organs, tissues and cells of the body, and for removing carbon dioxide and other waste products.
The heart is the central pump for the system. The human heart at rest beats on average 72 beats per minute. This equals approximately 2.5 billion beats in a lifetime. Each heart beat, or contraction, pumps blood into the circulatory system.
The circulatory system can be thought of as two separate system connected by the heart. These are the pulmonary circulation system and the systemic circulation system. Pulmonary circulation system pumps blood through the lungs to pick up oxygen. This oxygen rich blood then returns to the heart for its next journey. Systemic circulation delivers oxygen-rich blood to the body organs, tissues and cells. Some people also include a coronary circulation system that provides blood to nourish the heart cells. This system is part of the systemic circulation.
Each beat of the heart pumps blood into both the pulmonary and system circulation system. This provides a continuous flow of oxygenated blood to the body's organs, tissue and cells. It also provides a continuous flow of deoxygenated blood to the lungs where the red blood cells pick up oxygen.
Circulatory System - Anterior View
Blood is circulated through the body in blood vessels. There are five types of blood vessels in the human body. Arteries carry blood away from the heart. As the arteries get smaller in diameter they are called arterioles. Arterioles lead into very small capillaries. The capillaries enable the exchange of water, oxygen, carbon dioxide, and many other nutrient and waste chemical substances between the blood and surrounding tissues. From the capillaries, the blood flows into venules which then flow into larger veins returning blood to the heart.
As can be see in the diagram to the right, there are many large blood vessels carrying blood throughout the body. Most blood vessels operate as artery-vein pairs. For each artery carrying blood to a region, there is a vein returning the blood to the hear. For example, the common carotid artery delivers blood to the head and brain, and the jugular vein returns the blood to the heart. Sometimes the matching artery and vein have the same name, such as the pulmonary artery and pulmonary vein that deliver blood to and from the lungs, respectively.
The aorta is the largest artery in the body. It is connected to the heart and delivers blood to all arteries in the systemic circulation system. The aorta branches into smaller arteries such as the carotid artery, subclavian artery, axillary, brachial, gastric, renal and common iliac. These arteries branch into even smaller arteries, such as the common iliac branching into the superior vesical artery supplying blood to the bladder, and the femoral artery delivering blood to the legs.
Similarly the veins appear as branches of a tree, collecting blood from various parts of the body and returning it to the heart. The superior vena cava carries deoxygenated blood from the upper half of the body to the heart. It collects blood from the upper limbs, head and neck through the left and right brachiocephalic veins that that collects blood from the subclavian vein and jugular vein. The inferior vena cava returns blood from the lower body through a series of veins including the left and right common iliac veins.