Water metabolism

The importance of water:

1. Water takes part in reactions of hydrolysis, hydration, dehydration e.c.

2. Water is universal solvent

3. Transport function

4. Thermoregulation

5. Water provides hormonal regulation

Kinds of water and its distribution depend on age:

There are free and coupled (hydrated) water; exogenic and endogenic water.

There are extracellular and intracellular water. By adults extracellular water makes up 1/3 and intracellular water does 2/3. By newborn this correlation is reverse: extracellular water is more than intracellular one. Extracellular water is mobile sector, i.e. this water participates in thermoregulation, transport and hormonal regulation. This is reserve mechanism for newborn.

Distribution of water depend on localization: 1/3 of extracellular water (20%) is divided into extracellular liquid (12%), intravessel’s one (5%), transcellular’s one – 1-3% (water of cavities). The main reserve of water is muscles (50% of total water), then skin and liver.

The way of formation of endogenic water is biologic oxidation. For example, oxidation of 100g of TAG gives 107ml of water; 100g of carbohydrates gives 55 ml of water; 100 g of proteins gives 41 g of water.

The concept of water metabolism (incl. Exchange of water between tissues and blood): sources of water are water that we drink and food stuffs (milk, milk products, watermelon, melon, cucumbers, tomatoes and other vegetables, fruits and food products. Absorption of water begins in gaster and continues in intestine.

The exchange of water between tissues and vessels occurs. This process is promoted by oncotic, ocmotic and hydrostatic pressure. In arterial ends of capillaries the hydrostatic pressure is more than oncotic and osmotic pressure and water exits from vessels into extracellular liquid and then it enters the cells. So the trophic of tissues occurs. In venous ends of capillaries hydrostatic pressure is low, but oncotic and osmotic pressure is more than hydrostatic one and water with final products of metabolism enters the vessels. So excretion occurs. The loss of 10-12% of water results in serious derangement. The loss of 20-25% of water causes the death.

The excretion of water occurs through kidneys (1.5 L), skin (0.5 L), lungs (0.5L), intestine (0.3L).

Biochemistry of erythrocytes

Biochemistry of erythrocytes

The chemical composition of erythrocytes and structure of hemoglobin

Erythrocytes consist of 55 % of water and 45% of dry part. Dry part is 40% of hemoglobin and 5% of other substances (organic and inorganic).

Hemoglobin consists of globin (2 alfa-chains and 2 beta-chains. Each alf-chain contains 141 amino acids; beta chain contains 146 amino acids) and 4 hemes. Heme is 1,3,5,8-tetramethyl;2,4-divinyl; 6,7-dipropionic iron porphyn (should be known by formula):

Metabolism in erythrocytes

1. erythrocytes haven’t got mitochondrions, therefore anaerobic glycolysis is a main pathway of formation of ATP

2. erythrocytes haven’t got nucleus, therefore they don’t synthesize proteins or nucleic acids. These compounds are stored in period of maturation of erythrocytes in bone marrow

3. erythrocytes don’t synthesize glycogen and FFA. They get them during formation in bone marrow

4. glucose enters the erythrocytes independently on insulin

5. the extent of pentose’s cycle in erythrocytes is high and NADPH2 are used for action of MtHb-reductase and NADPH-oxydase of erythrocytes

6. MtHb-reductase reduces MtHb

7. During glycolysis 2,3diphosphoglycerate is formed which is used for deoxygenation

Hemoglobin participates in transfer of oxygen and carbon dioxide.

The transfer of oxygen is named as oxygenation. This process occurs in lungs:

Hb + O2  HbO2 and requires some conditions: 1) high pressure of oxygen; 2) low pressure of carbon dioxide; 3) lower temperature than in tissues; 4) higher pH than in tissues.

So, hemoglobin transfers oxygen from lungs to tissues.

In tissues deoxygenation occurs: HbO2  Hb + O2. This process occurs in conditions which are: 1) high pressure of carbon dioxide; 2) low pressure of oxygen; 3) higher temperature than in lungs; 4) more acidic pH.

The transfer of carbon dioxide occurs by 2 pathways: 1-st is direct one; 2-nd is indirect one)

(should be learned by reaction)

Direct pathway of transfer of carbon dioxide (15-20%) hemoglobin directly interacts with carbon dioxide yielding carbhemoglobin. This process occurs in tissues (venous blood). Carbhemoglobin is saturated by oxygen in lungs, carbon dioxide is released and eliminated from the body.

Indirect pathway of transfer of carbon dioxide (80-85%). This pathway occurs due to the presence of hemoglobin buffer. There are 2 types of hemoglobin buffer: HHb/KHb (in venous blood) and HHbO2/KHbO2 (in arterial blood). Firstly hemoglobin buffer of venous blood interacts with carbon dioxide in the kind of carbonic acid. This acid binds KHb, giving KHCO3 and HHb. KHCO3 interacts with HHbO2 in lungs yielding H2CO3 and KHbO2. Carbonic acid breaks up to CO2 and H2O. CO2 is eliminated from the body.