The blood system

Our blood acts as a transport system, carrying substances around the body. It is rather like a road network, with large arteries as main roads and very small vessels as lanes. Blood itself is made up of a liquid called plasma and two main types of cell – red cells and white cells. Red cells contain a chemical called hemoglobin, which is responsible for carrying oxygen to all the body’s cells. White cells are far fewer in number than red cells. Their job is to attack invading germs. There are also small particles in blood called platelets, which help the blood to clot when we cut ourselves.

When we cut ourselves, blood vessel walls break. The bleeding stops when enough platelets have stuck to the broken walls and signalled other substances to come. These substances form strands called fibrin, which form a web over the red blood cells to create a clot. The scab is the clot on the skin.

The walls of arteries and veins are made up of three layers. Arteries carry blood away from the heart and are thicker than veins because they must withstand the heavy pumping action of the heart. Veins carry blood back to the heart. Small arteries and veins are linked by tiny tubes called capillaries.

The heart is the muscular organ that causes the blood to circulate in the body. The heart of birds and mammals is a pulsatile four-chambered pump composed of an upper left and right atrium and a lower left and right ventricle. The atria function mainly as entryways to the ventricles, whereas the ventricles supply the main force that propels blood to the lungs and throughout the body.

All cells, in order to survive, must obtain the necessary raw materials for metabolism, and have a means for the removal of waste products. In small plants and animals living in an aquatic environment, these needs are provided for by simple diffusion. The cells of such organisms are very near the external watery medium, and so nutrients and wastes do not have a large distance to travel. However, as the size of the organism increases, more and more cells become further removed from the media bathing the peripheral cells. Diffusion cannot provide sufficient means for transport. In addition, without internal transport, organisms are restricted to watery environments, since the movement to land requires an efficient system for material exchange in non-aqueous surroundings. Therefore, larger animals have developed a system of internal transport, the circulatory system. This system, consisting of an extensive network of various vessels, provides each cell with an opportunity to exchange materials by diffusion.

Blood is the vital tissue in the circulatory system, transporting nutrients and oxygen to all the cells and removing carbon dioxide and other wastes from them. Blood also serves other important functions. It transports hormones, the secretions of the endocrine glands, which affect organs sensitive to them. Blood also acts to regulate the acidity and alkalinity of the cells via control of their salt and water content. In addition, the blood acts to regulate the body temperature by cooling certain organs and tissues when an excess of heat is produced (such as in exercising muscle) and warming tissues where heat loss is great (such as in the skin).

Some components of the blood act as a defense against bacteria, viruses, and other pathogenic (disease-causing) organisms. The blood also has a self-preservation system called a clotting mechanism so that loss of blood due to vessel rupture is reduced.

2. COMPREHENSION CHECK.

1. Provide evidence from the text to support or disprove the following statements:

a) The blood system is like a road network.

b) Hemoglobin is responsible for carrying oxygen to the lungs.

c) The main function of white cells is to destroy germs.

d) Arteries are thinner than veins.

e) The ventricles propel blood to the lungs.

f) Metabolism and the removal of waste products are provided for by simple diffusion in plants and animals.

g) The circulatory system of larger animals is an efficient system for material exchange.

h) Blood regulates the body temperature.

2. Use the information from the text to answer the questions:

a). What is blood made up of?

b). What are platelets and what do they help to do?

c). When does the bleeding stop?

d). How is a clot created?

e). What are capillaries?

f). What does the heart of mammals consist of?

g). What must all cells have in order to survive?

h). What is the circulatory system?

i). What are the main functions of blood?

j). How is blood loss reduced?

3. Restore the logical order of the main subtopics of the text:

a). Material exchange in organisms of different types.

b). Different kinds of blood vessels.

c). The main components of blood and their role.

d). Important functions of blood.

e). A clotting mechanism.

f). The role of the heart in the blood circulation.

3. LANGUAGE FOCUS.

1. In each box below match the words which are: a) similar or b) opposite in meaning:

a)		b)
to link	to propel	aquatic	to reduce
main	sufficient	thick	lower
to move	basic	to increase	far
job	various	upper	thin
environment	to get	left	internal
enough	work	small	large
to obtain	surroundings	few	right
to provide	to name	external	non-aqueous
different	to connect	near	many
to call	to supply

2. Match the following words with the right definitions:

platelets	the muscular organ that causes the blood circulation
arteries	small particles helping the blood to clot
capillaries	blood vessels carrying blood away from the heart
circulatory system	secretions of the endocrine glands
hormones	tiny tubes linking small arteries and veins
hemoglobin	a system of internal transport
heart	a chemical responsible for carrying oxygen to all the body’s cells

3. Change the words in capital letters to fit the context of the sentence:

a) These substances form a web over the red cells ……. a clot (CREATION).

b) The heart causes the blood ……… in the body (CIRCULAR).

c) In order to survive all cells must have a means for the ……. of waste products (REMOVE).

d) The cells of small plants and animals are very near the external …. medium (WATER).

e) …… cannot provide sufficient means for transport (DIFFUSE).

f) The ….. to land requires an efficient system for …. exchange in non-aqueous …… (MOVE, MATER, SURROUND).

g) This system consists of an ……. network of …… vessels (EXTEND, VARY).

h) Blood acts to regulate the …… and ….. of the cells (ACID, ALKALINE).

4. Try to say this in English using the vocabulary of the Unit:

а). Кровь состоит из жидкости, называемой плазмой, и двух основных типов клеток: красных и белых кровяных клеток.

б). В крови содержатся небольшие частицы – тромбоциты, которые помогают крови сворачиваться.

в). Эти вещества образуют нити, называемые фибрином.

г). Артерии несут кровь от сердца, а вены - обратно к сердцу.

д). Все клетки должны получать необходимое сырье для метаболизма.

е). Клетки небольших растений и животных расположены близко к внешней водной среде, таким образом питательным веществам и отходам не приходится перемещаться на большое расстояние.

4. FOLLOW-UP ACTIVITIES.

1. Name: a) the main components of the blood system and describe their functions, b) the most important functions of blood.

2. Talk about: a) the main blood vessels and their role, b) the difference in the raw materials supply and the removal of waste products in small plants and animals and larger animals.

3. Write a paragraph describing the blood system.