........................... THE CIRCULATORY SYSTEM AND THE CIRCULATION

Activities to do. Read the explanations on the blood and circulatory system and and perform the first Multiple Choice Test . Then read the explanation of the process of circulation and perform the Mute Picture, the second Multiple Choice Test and the Crossword.

1 . The human circulatory system. The circulatory system is responsible to distribute oxygen and nutrients throughout the body, and to collect the carbon dioxide and excretion products from the cells. It is formed of:

• A circulatory liquid called blood,
• A pump that pushes blood called heart, and
• Some tubes called blood vessels (arteries, veins and capillaries) and lymph vessels.

3 . The blood vessels. There are three different types called arteries, veins and capillaries.

• Arteries. They are the vessels that carry blood from the heart to other parts of the body. They are elastic thanks to having a thick middle muscular layer. All of them, except the pulmonary artery, carry blood rich in oxygen.
• Veins. They are the vessels that carry blood to the heart. They are little elastic. For this they need to have internal valves to prevent the blood to move back. All of them, except the pulmonary vein, carry blood low in oxygen.
• Capillaries. They are an extremely thin vessels, originated through the successive branching of arteries and veins, that connect the end of the arteries with the begining of the veins. Their walls are so thin that it allows the exchange of gases in the lungs, the entry of nutrients in the intestine and the exit of the products of excretion in the kidneys.

4 . The circulatory system. The set of all blood vessels form a double circulatory and complete system. It is called double because it includes two circuits, which are the pulmonary and the general. It is called complete because there is no mixing of oxygenated and deoxygenated blood in the heart, specifically the oxygenated blood passes through the left side of the heart and the unoxygenated passes through the right part.

5 . The functioning of the blood circulatory system. Basically it depends on the functioning of the heart. The human heart has four chambers: two who receive blood, the atria, and two to eject blood, the ventricles. Between the left atrium and the left ventricle is the mitral valve which regulates the flow of blood. Between the right atrium and the right ventricle is the tricuspid valve.

The heart functions as a suction pump and impeller. For which it performs movements of relaxation (diastole) followed by movements of contraction (systole). The cardiac cycle (heartbeat) takes 0.8 seconds and has 3 stages:

• Diastole. The walls of the atria and the ventricles relax and aspire blood, which comes through the veins. The blood that fills the arteries does not go backwards thanks to the fact that the semilunar valves (also called sigmoid), which are at its begining, are closed. This phase lasts 0.35 seconds.
• Auricular systole. The walls of the atria contract, the atrio-ventricular valves open (mitral and tricuspid) and blood passes to the ventricles. This phase lasts 0.15 seconds.
• Ventricular systole. The walls of the ventricles contract and the blood from the left ventricle passes through the aorta to the rest of the body, and the blood from the right ventricle passes through the pulmonary artery to the lungs. This phase lasts for 0.3 seconds

AD = Right atrium, AE = Left atrium, VD = Right ventricle, VE= Left ventricle

Multiple Choice Test (Spanish activity. Activity in English is under construction)

7 . The lymphatic system. Is constituted by the lymphatic vessels and lymph nodes. The containing liquid is called the lymph. The lymphatics vessels are blind, ie with no exit. Through its walls it absorbs part of the interstitial fluid and leads it to the blood vessels.

The lymphatic system performs three functions:

• To return to the blood a large portion of the plasma which, due to the pressure, has exited from blood capillaries.
• To transport, absorbed in the intestine, fats and to prevent that blood does not reach the heart with too much fat.
• To produce the antibodies. Within the lymph nodes the lymphocytes, which produce antibodies, are generated. The main lymph nodes are located in the neck, the armpits and in the groins. Its inflammation is a symptom of getting an infection.

• Atherosclerosis. Is due to the deposition of cholesterol plates within arteries.
• Arteriosclerosis. It is a process of hardening of the walls of the arteries due to age.
• Thrombosis. It is a vessel blockage that usually occurs because of the presence of the blood clot which was formed when the platelets broke by being stroked with cholesterol deposits that lay on the inside of the arteries.
• Angina pectoris. Chest pain caused by a strong contraction of the heart which is not receiving enough oxygen, usually due to blockage of the coronary artery.
• Myocardial infarction. This disease has the same symptoms and causes as the angina pectoris but it is a major obstruction that lasts more hours and, therefore, causes the destruction of the part of the heart. If it affects the whole heart, it may end in the death of the individual.
• Heart murmur. Heart failure due to inadequate structure of the heart.
• Tachycardia. Heart rate above 100 beats per minute.
• Hypertension. It is a chronic increase of the arterial pressure.
• Leukemia or blood cancer. It is an abnormal proliferation of white blood cells

 Biology topics Index