2015-05-26
7285
Blood is a fluid tissue with many various functions. Not only important physiological process takes place in the blood but it determines the activity of widely separated body cells.
Blood is composed of plasma and the corpuscular elements which are called red corpuscles or erythrocytes, white corpuscles or leucocytes and blood platelets or thrombocytes.
It is generally considered that no sex differences exist in the count of white corpuscles or leucocytes. The count of leucocytes in the blood of a healthy person is 4,500 to 9,500 per cu mm (cubic millimetre). When the number of white blood cells (WBC) is counted after mental or physical exertion, meals and mild activity it may increase to 10,000 and more per cu mm.
It is estimated that the erythrocytes are the most numerous cellular elements, ranging from 4,000,000 to 5,000,000 per cu mm. The red blood cell count (RBC) may change with age; when the red blood cell count is done after physical exertion and emotions it may increase.
One knows that red corpuscles have two physical features which are very important in the function of respiration. They have great elasticity and flexibility. These features give them the possibility to pass through very small capillaries. The discoid form of the corpuscle gives it a maximal surface for a given mass.
The most important part of the red cell is its red colouring substance or hemoglobin which on an average forms about 36% of its mass.
The total blood volume is divided into circulating and reservoir volumes.
The average human blood volume is not less than 7.5% but not more than 10% of the body weight. It is generally stated that the circulating volume averages smaller in the females than in the males. The circulating volume of the blood depends on the changes of the air temperature.
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IX. * Закончите предложения, выбрав необходимые словосочетания:
1. The most numerous cellular elements of blood are... (a) white blood corpuscles; 6) red blood corpuscles; в) blood platelets) 2. Blood is... (a) a connective tissue; 6) a muscular tissue; в) a fluid tissue; r) a nervous tissue) 3. The right ventricle discharges out the blood to the lungs... (a) through the aorta; 6) through the pulmonary arteries; в) through the portal vein) 4. The blood is discharged out... (a) of the ventricles; 6) of the atria)
X. * Повторите тексты А, С. Прочтите следующие предложения и скажите, о чем в них говорится:
1. This part of the heart discharges out the blood received from the pulmonary circulation through the aorta to the systemic circulation. 2. This part of the heart discharges out the blood received from the systemic circulation to the lungs through the pulmonary arteries. 3. These corpuscles have great elasticity and flexibility. These features give them the possibility to pass through very small capillaries. 4. The count of these corpuscles in the blood of a healthy person is from 5,000 to 7,000 per cu mm. The number of these corpuscles increases when a person becomes ill.
XI. Прочтите и запомните интересные факты:
Do you know that
1. each erythrocyte lives 120-130 days? 2. each leucocyte lives 4-7 days? 3. every day 200,000,000 erythrocytes are born and the same number dies?
