CIE Categories Archives: 9. Transport in Animals

9.4) Blood

9.4) Blood

Red blood cells:

  • they contain haemoglobin – a red protein that combines with oxygen
  • they have no nucleus so they can contain more haemoglobin
  • they are small and flexible so that they can fit through narrow blood vessels
  • they have a biconcave shape (flattened disc shape) to maximise their surface area for oxygen absorption


White blood cells:

  • Two most numerous types are phagocytes and
  • Phagocytes engulfs (ingest) and digest harmful bacteria and cell debris (process called phagocytosis).
  • Lymphocytes produces antibodies.



  • When tissues are damaged and blood vessels cut, platelets clump together and block the smaller capillaries.
  • The platelets and damaged cells at the wound also produce a substance that acts, through a series of enzymes, on the soluble plasma protein called fibrinogen.
  • As a result of this action, the fibrinogen is changed into insoluble fibrin, which forms a network of fibres across the wound.
  • Red cells become trapped in this network and so form a blood clot. The clot not only stops further loss of blood, but also prevents the entry of harmful bacteria into the wound.


The transfer of materials between capillaries and tissue fluid:

  • The fluid that escapes from capillaries is not blood, nor plasma, but tissue fluid.
  • Tissue fluid is similar to plasma but contains less protein, because protein molecules are too large to pass through the walls of the capillaries.
  • This fluid bathes all the living cells of the body and, since it contains dissolved food and oxygen from the blood, it supplies the cells with their needs.
  • Some of the tissue fluid eventually seeps back into the capillaries, having given up its oxygen and dissolved food to the cells, but it has not received the waste products of the cells, such as carbon dioxide, which are carried away by the bloodstream.
  • The tissue fluid that doesn’t return to the capillaries joins the lymphatic system.
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9.3) Blood and lymphatic vessels

9.3) Blood and lymphatic vessels

Arterioles, shunt vessels and venules:

  • The small arteries and arterioles have proportionately less elastic tissue and more muscle fibres than the great arteries.
  • When the muscle fibres of the arterioles contract, they make the vessels narrower and restrict the blood flow (process called vasoconstriction). In this way, the distribution of blood to different parts of the body can be regulated.
  • Shunt vessels, linking the arterioles with venules, dilate to allow the blood to bypass the capillaries. This helps to reduce further heat loss.


Main blood vessels:

  • Pulmonary Veins: This transports oxygenated blood from the lungs to the left atrium
  • Aorta: This transports oxygenated blood from the heart to the rest of the body and the brain.
  • Vena Cava: This transports deoxygenated blood from the rest of the body to the heart.
  • Pulmonary Artery: Transports deoxygenated blood from body to the heart to the lungs.
  • Hepatic Artery: This supplies oxygenated blood to the liver (also pylorus (part of stomach), duodenum and pancreas).
  • Hepatic Portal Vein: This transports blood from the gastrointestinal tract and spleen to the liver, rich in nutrients to be processed by the liver.
  • Renal Artery: This supplies kidney with oxygenated blood.
  • Renal Vein: This transports blood away from the kidney, into the inferior Vena Cava.


The lymphatic system:

  • Not all the tissue fluid returns to the capillaries. Some of it enters blind-ended, thin-walled vessels called lymphatics.
  • The lymphatics from all parts of the body join up to make two large vessels, which empty their contents into the blood system.
  • The fluid in the lymphatic vessels is called lymph.
  • Some of the larger lymphatics can contract, but most of the lymph flow results from the vessels being compressed from time to time when the body muscles contract in movements such as walking or breathing.
  • There are valves in the lymphatics, so that when the lymphatics are squashed, the fluid in them are forced in one direction only: towards the heart.
  • At certain points in the lymphatic vessels there are swellings called lymph nodes.
  • Lymphocytes are stored in the lymph nodes and released into the lymph to eventually reach the blood system.
  • There are also phagocytes in the lymph nodes. If bacteria enter a wound and are not ingested by the white cells of the blood or lymph, they will be carried in the lymph to a lymph node and white cells there will ingest them.
  • The lymph nodes thus form part of the body’s defence system against infection.


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9.2) Heart

9.2) Heart


The heart pumps blood through the circulatory system to all the major organs of the body.



In general, blood flows into the heart from a vein, goes into an atrium, then a ventricle, and out through an artery.

The heart contains valves to prevent the blood flowing backwards:

  • the right side has a tricuspid valve (a valve with three flaps)
  • the left side has a bicuspid valve (a valve with two flaps)
  • Both sides have semi-lunar valves (at the entrances to the pulmonary artery and aorta).



  • The left ventricle has thicker walls than the right because it needs to pump blood to most of the body while the right ventricle fills only the lungs.
  • The ventricles of the heart have thicker muscular walls than the atria. This is because blood is pumped out of the heart at greater pressure from these chambers compared to the atria.
  • The septum keeps blood from the right (deoxygenated) and left (oxygenated) sides of the heart from mixing. This is important because the blood in the left ventricle is loaded with oxygen for the rest of the body to use.
  • In pumping the blood, the muscle in the walls of the atria and ventricles contracts and relaxes. The atria walls contract first and force blood into the ventricles. Then the ventricles contract and send blood into the arteries.
  • Valves prevent blood flowing backwards during or after heart contractions.


The activity of the heart may be monitored by:

  • ECG (electrocardiogram)
  • Pulse rate
  • Heart sound using a stethoscope, ‘lub-dub’ sound caused by the closure of the valves


The effect of physical activity on the pulse rate:

  • At rest, the heart beats about 70 times a minute, but varies according to age, gender and fitness.
  • An increase in physical activity increases the pulse rate, up to 200 beats per minute.
  • After exercise has stopped, the pulse rate gradually drops to its resting state, the rate depends on the fitness of the person.
  • During exercise, the muscle cells need more energy than usual. They therefore need to respire more and, as a consequence, need more oxygen and glucose, and they produce more waste, carbon dioxide.
  • If the muscle does not get enough oxygen, it will start to respire anaerobically, producing lactic acid, which cause muscle fatigue, leading to cramp.


Coronary heart disease:

  • The coronary arteries supply blood to the heart muscle. These may become blocked by a buildup of fatty plaques containing cholesterol, resulting in coronary heart disease.
  • If a coronary artery is blocked, the blood supply to part of the heart muscle is cut off. That part of the heart cannot continue to contract, causing a heart attack.


Possible Causes:

  • Lack of exercise
  • Diet high in fat and cholesterol
  • Diabetes
  • High Blood Pressure
  • Genetics
  • Stress
  • Smoking



  • Maintaining a healthy, balanced diet will result in less chance of a person becoming obese. Also be a low intake of saturated fats, so the chances of atheroma and thrombus formation are reduced.
  • Exercising increases muscle tone, good heart muscle tone leads to an improved coronary blood flow and the heart requires less effort to keep pumping.



  • Regular dose of aspirin (salicylic acid). Aspirin prevents the formation of blood clots in the arteries, which can lead to a heart attack.
  • Angioplasty and stent. Angioplasty involves the insertion of a long, thin tube called a catheter into the blocked blood vessel. A wire attached to a deflated balloon is then fed through the catheter to the damaged artery. The balloon is then inflated to widen the artery wall, freeing the blockage. Stent can be used. This is a wire-mesh tube that can be expanded and left in place.

By-pass surgery. The surgeon removes a section of blood vessel from a different part of the body, such as the leg. The blood vessel is then attached around the blocked region of artery to by-pass it, allowing blood to pass freely.

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9.1) Transport in animals

9.1) Transport in animals


The blood, pumped by the heart, travels all around the body in blood vessels. It leaves the heart in arteries and returns in veins. Valves, present in the heart and veins, ensure a one-way flow for the blood, as blood enters an organ, the arteries divide into smaller arterioles, which supply capillaries. In these vessels the blood moves much more slowly, allowing the exchange of materials such as oxygen and glucose, carbon dioxide and other wastes. Blood leaving an organ is collected in venules, which transfer it onto larger veins.


Single circulation of fish:

  • Simplest circulatory systems of all vertebrates.
  • A heart, consisting of one atrium (collecting chamber) and one ventricle (ejection chamber), sends blood to the gills where it is oxygenated. The blood then flows to all the parts of the body before returning to the heart.
  • Known as a single circulation because the blood goes through the heart once for each complete circulation of the body.
  • This system is inefficient because blood pressure is lost when the blood passes through capillaries in the gills


Double circulation of mammals:

  • The blood passes twice through the heart during one complete circuit.
  • Once on its way to the lungs (pulmonary circulation) and again on its way to the body (systemic circulation)
  • Advantage of maintaining a high blood pressure to all the major organs of the body.
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