The Cardiovascular System
In order to carry out its functions, the cardiovascular system pumps blood through the blood vessels. This is done by the pumping of the heart. Furthermore, the circulatory system is associated with other systems in the body, for example the lymphatic system.
Blood and Blood Vessels
Blood consists of white blood cells, red blood cells, platelets and liquid plasma. Plasma accounts for about 50% of the total blood content and consists mainly of which has glucose, proteins such as enzymesand hormones and waste products dissolved in it. Oxygen and carbon dioxide are also present in the blood and are carried by the red blood cells .
Within the human body, blood is carried in blood vessels which can differ in size and makeup .
Innitiate from the heart and carry blood to organs and tissues where oyxgen and nutrients are needed. Therefore, they carry blood which is rich in these components. The diameter of the larger arteries can be altered by smooth muscle contraction and relaxation in order to maintain blood pressure, keeping the blood flowing. Thick walls, muscular (see cardiac muscle), and elastic layers ensure that the strain due to the blood flow and the contraction of the heart does not damage the walls, which on average are only 1mm thick .
In contrast to the arteries, veins have thinner walls and are therefore more flexible. These properties arise from the low blood pressure within veins, causing the blood flow to be much slower. A further characteristic of veins are the valves they contain, which are made from endothilium tissue and restrict the blood flow into one direction. Valves contain of two cusps that only open into the direction of blood flow due to pumping of the heart.
This is especially important regarding their function, as this is to return deoxygenated blood to the heart. The main two veins doing this are called superior and inferior venae cavae.
As the distance of the blood vessels to the heart increases, the amount of branching increases and the blood vessels become smaller and finer in order for the blood to reach every part of the body. Starting with large arteries, these blood vessels then further divide into little vessels called capillaries (0.01 mm in diameter). Not only the size decreases but also the thickness of the walls decreases to a layer of only one cell so that a maximum exchange of gases with cells and tissues can be achieved.
The capillaries carrying waste products away from the cells and tissues eventually enlarge into veins which carry the blood back to the heart.
The wall of the heart consists of myogenic muscle which is called myocardium. Just like all other tissues in the body, this muscle requires nutrients and oxygen which are supplied by blood vessels called coronary arteries. These originate from the right and the left artery which in turn divide from the aorta. Naturally, waste products must be removed as well which is done by the coronary sinus. 
Inside the heart, hollow chambers can be found which are filled with blood and emptied again during each contraction cycle. The top chambers are called right and left atrium and receive blood from the body. They are located above the right and left ventricle respectively which pump blood into the arteries to the body. The upper and lower chambers are seperated by valves and the right and left side are seperated by the septum.  Valves allow blood to flow into the ventricles from the system during diastole and again close during ventricular systole in oder to avoid the blood flowing back when the heart contracts.
The muscle wall of the left hand side of the heart is much thicker and stronger due to the fact that it has to pump blood into the whole system that supplies the body with blood and therefore has to supply more powerful contraction.
(see also Heart)
Coronary Heart Disease
This type of disease is caused by insufficient nutrient and oxygen supply to the heart muscle as a consequence of damaged or malfunctional coronary arteries.
CHD includes common conditions like Atherosclerosis, Angina or Heart attack. 
This disease is due to fatty deposits that lign and eventually clog the arteries, causing them to narrow and become inflexible. Sources of the fatty deposits are excess fat and cholesterol in the blood, which settles on the artery walls as the blood flows through. These deposits are then known as atheroma. These structures in turn form plaques as they start to accumalate. As these plaques build up, the lumen of the diseased artery narrows and consequently blood flow is restricted. In fatal cases, blood flow is not possible beyond the plaque, so blood supply becomes insufficient and body parts like the brain may suffer oxygen starvation can result in a stroke (also see Angina).
Major factors that influence fatty deposits are smoking, saturated fat rich diet, lack of exercise and overweight.
Angina is a condition that can also be desbribed as chest pain and results from insufficient blood supply to the heart muscle. This insufficient blood supply means the heart muscle lacks oxygen, which in turn stresses the heart when it works at increased rate. This might occur during exersice, stress, cold weather or large food intake but can be relieved by relaxation and subsequent decrease in rate of activity of the heart muscle. As explained in the above section, the insufficient blood supply may result from atherosclerosis where the arteries are narrowed.
Due to oxygen starvation, the heart muscle may be damaged over time (see Heart Attack).
This type of condition is also called Myocardial Infarction and results from oxygen starvation in an area of the heart muscle where blood flow was restricted or lacking. The restriced blood flow results from blockage or narrowing of the arteries in the heart muscle (as described in Atherosclerosis) and leads to the formation of blood clot or thrombus. The lack of oxygen and the accumulation of waste products then causes tissue death within this specific area of the cardiac muscle.
Symptoms of a heart attack are sweating, shortness of breath, nausea and loss of consciousness.
- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 1.14 1.15 1.16 1.17 1.18 Parker S. (2007) The Human Body Book, 1st edition, London: Dorling Kindersley Limited.
- ↑ http://stayhealthier.wordpress.com/2010/03/30/cardiovascular-system-understand-it-to-stay-healthy/
- ↑ Brown H. (1997) Physiology and Pharmacology of the Heart, 1st edition, Oxford: Blackwell Science Limited.