By Andrew Golin,
Simply put, the cardiovascular system is a set of connected tubes with varying sizes that circulate blood around the body. Physiological systems can be classified as open or closed. Systems where substances can easily enter or exit, such as the digestive tract, are referred to as open. Conversely, blood is unable to escape the cardiovascular system so it labelled a closed system.
Blood is a necessary liquid medium for human life because it is the major route of transporting substances in the body. Whether substances come from exogenous or endogenous origins, the body must be able to transport matter from compartment to compartment. When separated by density, blood contains three main components: plasma, buffy coat, and red blood cells. Plasma contains water, ions (atoms or molecules that contain an electric charge), proteins, and compounds. The buffy coat mainly consists of white blood cells, elements of the immune system primarily involved in defending the body from infection and disease. The last component, red blood cells, are essentially bags of hemoglobin molecules which bind and transport oxygen around the body.
The cardiovascular system is made up of two major circulatory pathways, the systemic and pulmonary circuit. In order to satisfy the body’s requirement of oxygen, the lungs and heart function together via the pulmonary circulatory system. In this system, the lowest-right chamber of the heart, the right ventricle, pumps oxygen-poor blood through the pulmonary artery to the lungs. As one inhales, oxygen enters the lungs and diffuses into the deoxygenated blood. The now oxygenated blood, reenters the left atrium of the heart through the pulmonary vein.
The pulmonary circulatory system then feeds into the systemic circuit, where newly oxygenated blood in the lowest left chamber of the heart, the left ventricle, pumps oxygen-rich blood throughout the body. As blood travels throughout the body, oxygen and nutrients are transported from blood into tissues. After oxygen and other nutrients are utilized to satisfy the cells’ needs for metabolism, carbon dioxide and other waste products are released from bodily tissues and enter the blood stream. The deoxygenated blood which now contains carbon dioxide returns to the heart and re-enters the pulmonary system once again. The carbon dioxide-rich blood then passes through the lungs where it exchanges carbon dioxide for oxygen. The cycle then repeats to satisfy the body’s constant need for oxygen.
Blood vessels can be divided into two broad classes, arteries and veins. Arteries carry blood away from the heart and veins return blood to the heart. Arteries generally carry oxygenated blood away from the heart, whereas the pulmonary artery, the vessel that carries blood away from the heart to the lungs, carries deoxygenated blood. Conversely, the far majority of veins return deoxygenated blood to the heart. The pulmonary vein is the exception, which returns oxygenated blood from the lungs to the heart.
Arteries and veins have different anatomical features in addition to their differing direction of blood transport. As the heart pumps blood through arteries, arterial blood vessels must be able to withstand great pressure experienced when blood is pushed against arterial walls as a result of the heart’s pumping. Because of this, arteries have relatively thicker vessel walls compared to veins1. As arteries travel along the body, arteries branch off into smaller blood vessels called arterioles. Arterioles further branch into even smaller blood vessels, capillaries, where a collection of many small capillaries form a capillary bed. Arteries and veins chiefly transport blood, whereas capillary beds function as regions of nutrient, gas, and waste exchange between blood and tissue.
As blood passes through the capillary bed, small veins called venules funnel blood into larger veins. Arteries are acting as a high pressure system which transport energy in the form of pressure, where nutrients and gasses exit the higher pressure vessel and enter the lower pressure tissue via the capillary bed. As pressure decreases once nutrients, gasses, and energy are exchanged, blood vessels situated past the capillary network, veins, are lower pressure vessels. As a water hose loses pressure (and therefore energy) over large distances, veins analogously are transporting blood under low pressure. To overcome this, veins contains valves which prevent blood from flowing away from the heart, and ensures blood is only moving in one direction, towards the heart.
Transportation, exchange, and oxygenation, are only a few of the important functions the cardiovascular system is involved with. A major risk factor in cardiovascular disease is a sedentary lifestyle2. It is therefore important to allocate time exercising in order to improve or maintain a healthy cardiovascular system. Exercise has been shown to decrease the chances of having cardiac events such as heart attacks, reduce body weight, blood pressure and bad (LDL) cholesterol, and increase good (HDL) cholesterol and insulin sensitivity2.
But how much exercise should one do? The aforementioned benefits can be achieved by performing 30 minutes (or more) of modest activity on most days of the week2. The Surgeon General’s Report and the National Institutes of Health report define modest activity as any activity performed with an intensity similar to brisk walking. Activities can include anything from walking to yard work, as long as the minimum intensity is met.
- 20.1 Structure and Function of Blood Vessels | Anatomy and Physiology. Opentextbcca. 2017. Available at: https://opentextbc.ca/anatomyandphysiology/chapter/20-1-structure-and-function-of-blood-vessels/. Accessed March 29, 2017.
- Myers J. Exercise and Cardiovascular Health. Circulation. 2003;107(1). doi:10.1161/01.cir.0000048890.59383.8d.
Fig 1. 20.1 Structure and Function of Blood Vessels | Anatomy and Physiology. Opentextbcca. 2017. Available at: https://opentextbc.ca/anatomyandphysiology/chapter/20-1-structure-and-function-of-blood-vessels/. Accessed March 29, 2017.
Fig 2. Obtained from public domain, Wikimedia commons.