Circulation In Humans
Bayani Gaba-gaba
Put a finger on the inside of your wrist and wait. That small, regular push is a muscular pump the size of your fist forcing blood out of your chest and down your arm, and it has done so without a single day off since before you were born. Every cell you own is fed and cleaned by that pump. Starve any part of the network for a few minutes and the tissue it serves begins to die.
This lesson takes the whole circulatory system apart and puts it back together: the four chambers of the heart and the order in which they squeeze, the five vessels you have to be able to name, the three kinds of vessel and why each one is built the way it is, and the four components of blood and the jobs they do. By the end you should be able to trace any substance from the place it enters the body to the cell that uses it, explain the shape of every vessel from the pressure it has to survive, and turn an unfamiliar medical situation into biology you already know.
Manufura
- Substances are transported from where they enter the body to the cells, or from the cells to where they are removed from the body, by the circulatory system (the heart, the blood vessels and the blood).
- The heart is an organ that pumps blood around the body in a double circulatory system. Much of the wall of the heart is made from muscle tissue.
- The heart has four main chambers (right and left atria and right and left ventricles).
- Blood enters the atria of the heart. The atria contract and force blood into the ventricles. The ventricles contract and force blood out of the heart. Valves in the heart ensure that blood flows in the correct direction. Knowledge of the names of the heart valves is not required.
- Blood flows from the heart to the organs through arteries and returns through veins. There are two separate circulation systems, one for the lungs and one for all other organs of the body. Knowledge of the blood vessels associated with the heart is limited to aorta, vena cava, pulmonary artery, pulmonary vein and coronary arteries.
- Arteries have thick walls containing muscle and elastic fibres. Veins have thinner walls and often have valves to prevent back- flow of blood.
- In the organs, blood flows through very narrow, thin-walled blood vessels called capillaries. Substances needed by the cells in body tissues pass out of the blood and substances produced by the cells pass into the blood, through the walls of the capillaries.
- Blood is a tissue consisting of a fluid called plasma, in which the white blood cells, platelets and red blood cells are suspended.
- Blood plasma transports: carbon dioxide from the organs to the lungs; soluble products of digestion from the small intestine to other organs; urea from the liver to the kidneys.
- Red blood cells have no nucleus. They are packed with a red pigment called haemoglobin. Red blood cells transport oxygen from the lungs to the organs. In the lungs haemoglobin combines with oxygen to form oxyhaemoglobin. In other organs oxyhaemoglobin splits up into haemoglobin and oxygen.
- White blood cells have a nucleus. They form part of the body’s defence system against microorganisms.
- Platelets are small fragments of cells. They have no nucleus. Platelets help blood to clot at the site of a wound.
- Blood clotting is a series of enzyme-controlled reactions, resulting in the change of fibrinogen to fibrin, which forms a network of fibers trapping blood cells and forming a clot.
- Antigens are proteins on the surface of cells.
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- Which chamber of the heart pumps blood into the aorta? A. The right atrium B. The left atrium C. The right ventricle D. The left ventricle Answer: D
- Which blood vessel carries deoxygenated blood away from the heart? A. The aorta B. The pulmonary artery C. The pulmonary vein D. The vena cava Answer: B
- Which component of the blood has a nucleus? A. The plasma B. A red blood cell C. A white blood cell D. A platelet Answer: C
- Which component of the blood has no nucleus and is packed with haemoglobin? A. The plasma B. A white blood cell C. A red blood cell D. A platelet Answer: C
- Blood plasma transports urea between two organs. Which journey is correct? A. From the kidneys to the liver B. From the liver to the kidneys C. From the small intestine to the liver D. From the lungs to the kidneys Answer: B
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