Texts: the blood system. Blood. Pre-reading and reading tasks

1. Study the vocabulary to avoid difficulties of understanding:

affect (v)	[q'fekt]	воздействовать
clot (v)	[klPt]	свертываться
invade (v)	[In'veId]	вторгаться
survive (v)	[sq'vaIv]	выживать, продолжать существовать
withstand (v)	[wID'stxnd]	противостоять
clot	[klPt]	сгусток
germ	[dZE:m]	микроб, бактерия
liquid	['lIkwId]	жидкость
mammal	['mxm(q)l]	млекопитающее
means	[mi:nz]	средство
particle	['pQ:tIk(q)l]	частица
platelet	['pleItlIt]	тромбоцит
removal	[rI'mu:v(q)l]	удаление
rupture	['rAptSq]	разрыв
scab	[skxb]	корка
web	[web]	сеть
pulsatile	['pAlsqtaIl]	пульсирующий
sufficient	[sq'fIS(q)nt]	достаточный

2. Try to guess the meaning of the following words and word combinations:

pumping action	aquatic environment
pathogenic organism	self-preservation system
alkalinity	to propel
non-aqueous surroundings	circulatory system
acidity	watery medium
bleeding	right ventricle
fibrin	carbon dioxide
capillary	left atrium

3. Read the text carefully to fulfil the tasks that follow. 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.