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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.

Additional text

Read the text carefully to fulfil the tasks that follow.

BLOOD

Like muscle, bone, cartilage, and nerves, blood is a type of tissue, a collection of similar types of cells and the associated intercellular substances that surround them. Tissues are categorized into four main types: 1) epithelium, 2) muscle, 3) nervous, and 4) connective. Connective tissue includes blood, lymph, bone, and cartilage. In the case of blood and lymph, the base substance, or matrix, is a liquid. What differentiates these two from other tissue types is that they are not stationary. Blood is a fluid flowing through blood vessels throughout the body (lymph runs through the lymph vessels).

Blood accounts for about 8 percent of a human’s total body weight, amounting to an average of four to six liters per adult (over a gallon), depending on individual size. Blood is thicker (more viscous) and slightly heavier than water. And, depending on the organism, blood is usually slightly warmer than the animal’s body temperature. While the core body temperature of most humans is 37oC (98.6oF), their blood is about 38oC (100.4oF). Blood pH is slightly alkaline, ranging from about 7.35 to 7.45. Its salt (NaCl) concentration normally varies from about 85 to 90 ppt (parts per thousand), or two to three times the concentration of sea water.

Plasma is the fluid portion of both blood and lymph. Fifty to sixty percent of the blood volume consists of plasma. When the proteins involved in clotting are removed from blood plasma, the remaining liquid is called serum. The plasma, which is over 90 percent water, carries a variety of ions and molecules. In addition to salts and proteins, there are many nutrients such as amino acids, fats, and glucose. There are also dissolved gases such as carbon dioxide, as well as antibodies, hormones, enzymes, and certain waste products such as urea and uric acid. The relative amount of plasma in the blood depends upon the species, the sex, the organism’s health when being examined, and on a host of other variables. The remaining 40 to 50 percent of the blood volume is composed of cells and cell fragments that can be divided into three main categories: red blood cells, or erythrocytes; white blood cells, or leukocytes; and platelets, or thrombocytes, which are fragments of cells.

Post-reading tasks

  1. Define the following concepts: blood, plasma, serum.

  2. Name: a) the main types of tissue, b) the kinds of connective tissue, c) the constituents of plasma, d) types of blood cells.

  3. Explain what differentiates: a) blood and lymph from other tissue types, b) blood from lymph, c) blood from water.

  4. Write an essay describing the structure of blood.