The Cardiovascular System
The cardiovascular system consists of the heart and an extensive network of arteries and veins throughout the body. Oxygenated blood is pumped by the heart to the rest of the body and deoxygenated blood returned to the heart. Prior to the heart pumping the blood into the arteries it needs to go to the lungs to pick up oxygen. After the blood has successfully delivered the oxygen to all of the cells throughout the body it then transports the deoxygenated blood back to the heart by the veins and repeats the process.
The heart continuously pumps at around 70-75 beats per minute, sending out 5.25 Litres of blood (stroke volume) around the body. Oxygenated blood will also contain the essential nutrients required to support the body's metabolism. Stroke volume will change dependent upon age, gender, body temperature, emotions and activity level.
There are three types of blood cells;
This enables the body to carry out a number of functions;
Blood also contains plasma. The contents of plasma include; Albumin, which helps maintain osmotic pressure, Carrier molecules for lipids and steroid hormones, Globulins which transport antibodies, and Lipoproteins which carry triglycerides and cholesterol.
Erythrocytes contain haemoglobin which enables it to carry oxygen. It requires B12, folic acid, and haem (iron). Red blood cell numbers need to be controlled to a certain constant. The lifespan of a red blood cell is 120 days, When old or damaged, they are removed from the circulation by the spleen and broken down in the liver. Haemoglobin is broken down into Haem and Globin, which is further broken down into amino acids. The Haem is broken down into iron and bilirubin. The iron can be stored by the liver and then transported to the bone marrow where new haemoglobin is produced. The bilirubin is transported to the gall bladder where it forms bile, and is eventually excreted in the faeces.
In situations of hypoxia (low oxygen levels in the blood) the kidneys release Erythropoietin which stimulates the production of new red blood cells in the bone marrow. Excess Carbon Dioxide will result in the sympathetic nervous system being increased resulting in more rapid breathing as the body responds to eliminate the excess through the lungs.
Leucocytes are important in protecting the body from any foreign invasions that may cause damage. They are specialised cells that have different functions which enables them to to deal with microbes, parasites, and fungi. Some patrol the body within the blood responding to cytokines (chemical messengers) produced by distressed cells of the body, as a result of damage or infection. They also have the ability to learn from the experience of the infection and produce antibodies to that threat, and will respond quicker the next time it encounters the same pathogen. They also help to remove damaged or infected cells.
Platelets also responds to damaged cells and tissue. They produce blood clots that stops bleeding and helps to fix the damage.
An important measure of the heart's functioning is its blood pressure. If too high, blood vessels may be damaged causing clots or bleeding from the site of rupture. If it is too low, blood flow would be inadequate for the essential organs to function as they are not receiving sufficient quantities of blood to work effectively. Therefore blood pressure is constantly monitored. Hypertension is when there is an increase in blood pressure, often from an unknown cause. However there are identifiable risk factors, such as; Family history, smoking, sedentary lifestyle, high intake of salt or alcohol, stress, and obesity. Hypertension can also be due to kidney disease resulting in water and salt retention, or as a result of an endocrine disorder, again leading to the retention of excess sodium and water. Hypotension, low blood pressure, which usually occurs as a complication of other conditions, for example, shock or Addison's disease. This may lead to in an inadequate blood supply to the brain causing fainting or longer states of unconsciousness.
The control of blood pressure is achieved through;