A solution with a big osmotic pressure is called hypertonic, with a small osmotic pressure – hypotonic. At division of these solutions by semipermeable membrane water will transfer into more concentrated (with a greater osmotic pressure) hypotonic solution till osmotic pressures become identical.
A constancy of osmotic pressure is called isoosmoticity. Osmotic pressure has a great meaning for living organism functioning. It plays a great role in processes of food assimilation, metabolism, water and salts between cells and their environment. In normal conditions osmotic pressure of internal environments of a human body is constant.
Osmotic pressure of blood maintains within the limits of 7,71-8,12 atm (781,2-622,76 kPa) at body temperature 37°C. Such a great value of osmotic pressure is caused by presence of ions of low-molecular compounds in a big quantity. The part of blood osmotic pressure due to proteins (albumins, globulin) is called oncotic pressure or colloid osmotic pressure. Oncotic pressure makes 0,03-0,04 atm (3,04-4,05 kPa). A greater part of blood osmotic pressure is due to sodium chloride.(Table 3).
Table 3 The concentration of various components in lymph and plasma
|
Concentration, mg/100 ml |
Plasma |
Lymph |
|
Protein |
6,85 |
2,61 |
|
Sugar |
123 |
1,24 |
|
Calcium |
10,4 |
9,2 |
|
Chloride |
3,92 |
4,13 |
Reffering to data in Table 3 we can calculate the total pressure in blood capillary as a difference of hydrostatic pressure produced by heart work and colloid osmotic pressure. As a result of heart contraction hydrostatic blood pressure in arterial capillaries is equal to 44 cmH2O (43,12 kPa) and in venous capillaries – 17 cmH2O (16,66 kPa). Colloid pressure due to concentration of penetrating and nonpenetrating components of a solution is equal to 36 cmH2O (35,28 kPa). Thus, the total pressure in the area of arterial end of the blood capillary is equal to 6 cmH2O (7,64 kPa) and is directed outside and in the area of venous end – 19 cmH2O (16,62 kPa) and directed inside.
Owing to the fact that cells’ surfaces and tissues of organism have got characteristics of semipermeable membranes osmotic pressure is a great factor inside of an organism determined water distribution between various parts of organism. Osmotic pressure of the cell content (turgor or turgor pressure of a cell) balances by elastic tension of cellular walls. Many functions of cell and first of all their ability to maintain certain shape, support turgor, to accomplish the metabolism with environment etc. depend on osmotic pressure of both cell content and intercellular fluid.
The leading role in maintaining and supporting of osmotic pressure at certain and constant level in a human body apparently plays conjunctive tissue, absorbing excess of water from blood or viceversa giving away its water in the case of increase of salt in blood. Thus, in normal healthy cells its content should be hypertonic toward the external environment.
At contact with hypertonic solution cell lose water and compress, there comes the plasmolysis of a cell. The return phenomenon hemolyses is observed at mixing blood with hypertonic solution. In this case water penetrates into erythrocytes, last ones swells and explode. Hemoglobin transforms to a solution and tincture it into the red colour. According to this, solutions of medical products, entered hypodermically and intravenously, should be isotonic, that is to have identical osmotic pressure with osmotic pressure inside of erythrocytes. Otherwise as a consenquence of absorbing of dissolvent inside of erythrocytes will either swell till they explode as a result of turgor that is hemolyses will occur; or diminish in its volume, wince due to osmotic return of water – plasmolysis.
Isotonic in relation to blood physiological solution contains 0,9% (0,15 mol/L of sodium chloride). Isotonic solutions enter at great losses of blood and use for study isolated organs and tissues from organism. Now more modern physiological solutions are being created which contain salt mixing: KCI, CaCI2, MgCI2, MgSO4 and others. At their creation attention has been paid that salt structure of water is similar to sea water that, probably, is caused by beginnings of a life in the water environment.
In medical practice hypertonic solutions are used ( in a form of gauze bandage, wetted in hypertonic solutions NaCI) for wound cleansing from pus. The current of a liquid in such gauze bandages is directed outside of a gauze ( in direction of solutions with a great osmotic pressure).
Measurement of osmotic pressure in biological environment is a very labor-intensive object. That’s why for its calculation is used familiar to us and easier determinate values, for example ∆tf. The following ratio is used for calculation:
P=8,3 * T * C ≈ 8,3 * T * (∆tf/K)
(because ∆tf = K * Cm and C ≈ Cm)
If we know that a freezing point of blood is -0,56°C (Table 2), then osmotic pressure of blood at 37°C will be equal to:
P = 8,3(273+37)*(0,56/1.86)=780,2 kPa
2. WATER SOLUTIONS OF NONELECTROLYTES
ELECTROLYTES NAME THE SUBSTANCES WHICH ARE BREAKING APART IN SOLUTIONS OR LIQUID MELTS ON IONS. Electrolytes can be divide into 2 groups: weak and strong electrolytes. Weak electrolytes dissociate only partly in water solutions, and dynamic balance between ions and nondissociated molecules in the solution is being established. Strong electrolytes in water solutions dissociate almost completely.
Уважаемый посетитель!
Чтобы распечатать файл, скачайте его (в формате Word).
Ссылка на скачивание - внизу страницы.