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In this article we will discuss about the Water Metabolism:- 1. Distribution of Water in the Body 2. Factors Influencing the Distribution of Body Water 3. Intake and Loss 4. Physiological Functions 5. Regulation of Passage.
Contents:
- Distribution of Water in the Body
- Factors Influencing the Distribution of Body Water
- Intake and Loss of Body Water
- Physiological Functions of Water
- Regulation of Passage of Water
1. Distribution of Water in the Body:
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Water is the largest constituent of the body. The average body water is 60 to 70 per cent of the total body weight. Females contain a little less amount of water than males.
Body water is distributed as follows:
a. Intracellular Fluid:
Intracellular fluid (the fluid within the cells) contains 50 per cent of the total body weight.
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b. Extracellular Fluid:
Extracellular fluid (all of the fluid outside the cell) contains 20 per cent of the total body weight.
This 20 per cent can be further divided into the following compartments:
(i) Plasma (the extracellular fluid of the blood): 4.5 per cent.
(ii) Interstitial and lymph fluids: 8 per cent.
(iii) Dense connective tissue, cartilage and bone: 6 per cent.
(iv) Trans-cellular fluid (found in salivary glands, pancreas, liver, thyroid gland, gonads, skin, mucous membranes of the respiratory and gastrointestinal tracts and the kidneys as well as the fluids in spaces within the eye, CSF, etc.): 1.5 per cent of the body weight.
2. Factors Influencing the Distribution of Body Water:
The distribution of water is continuously changing. Osmotic forces are the principal factors for controlling the amount of fluid in the various compartments of the body. These are maintained by the solutes in the body water.
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The solutes are divided into three categories:
a. Organic Compounds of Small Molecular Size (Glucose, Urea, and Amino Acids etc.):
Since these substances diffuse freely across the cell membrane, they are not important in the distribution of water. But if they are present in large amounts, they can help in retaining water.
b. Organic Substances of Large Molecular Size (Proteins):
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These substances can throw effect in the transfer of fluids from one compartment to the other.
c. The Inorganic Electrolytes:
These inorganic electrolytes are the most important both in the distribution and in the retention of body water.
3. Intake and Loss of Body Water:
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a. Water Intake:
Water is supplied to the body by the following processes:
i. Water taken orally.
ii. Along with food.
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iii. Oxidation of foodstuffs: Fats, proteins and carbohydrates yield water after combustion. Fats produce 107 ml/100 gm., proteins 41 ml/100 gm. and carbohydrates 56 ml/100 gm.
b. Water Losses:
Water is lost from the body by 4 routes:
i. Evaporation from skin and lungs.
ii. Kidneys, as urine.
iii. The intestines, in the the feces.
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iv. Perspiration.
C. Additional Water Losses in Disease:
i. Water loss is more in diarrhea and vomiting and these losses can be fatal in infants.
ii. In kidney disease, renal water loss is more.
iii. In fever, insensible losses may rise much higher than normal.
iv. Patients in high environmental temperatures also sustain extremely high external water losses.
Water Balance:
An equilibrium persists between the intake and output of water in the body. In addition to other factors, certain hormones, such as ADH, vasopressin, oxytocin and aldosterone influence the regulatory mechanism of body water. The balance sheet of water is given above.
There is a continuous excretion of water in the form of digestive juices from the body into the alimentary canal and that water is reabsorbed along with the water of food and drink. The amount of this internal secretion is 7 to 10 litres per day. All of this amount is reabsorbed except about 100 ml which is excreted in feces. The secretion of saliva experiences the fact when we have a sore throat.
4. Physiological Functions of Water:
a. Specific Heat:
More heat is required to raise the temperature of 1 gram of water through 1°C than almost any other solid or liquid. This clearly explains that heat produced as a result of chemical reactions in the cell can cause the minimum rise in body temperature.
b. Latent Heat of Evaporation:
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Water has the highest latent heat of evaporation than any other liquid. A certain amount of water can cause maximum cooling by evaporation so that the body temperature does not rise.
c. Solvent Power:
Water can form true solutions as well as colloidal solutions. Even the water insoluble substances are made water soluble by the hydrotropic action. Therefore, it is the most suitable solvent for cellular components, water thus brings various substances in contact for chemical reactions to proceed.
d. Dielectric Constant:
Oppositely charged particles can coexist in water. Therefore, it is a good ionizing medium. This increases the chemical reactions.
e. Catalytic Action:
A large number of chemical reactions in the body are accelerated by water due to its ionizing power. All chemical reactions in the body proceed in presence of water only.
f. Lubricating Action:
Water acts as a lubricant in the body to prevent friction in-joints, pleura, conjunctiva and peritoneum.
5. Regulation of Passage of Water:
a. If the capillary pressure is increased, more water will flow into the tissues.
b. A fall in blood pressure helps the passage of water from the tissues to the blood.
c. If the plasma proteins are decreased, water will flow into the tissues.
d. Dilution of blood by excessive ingestion of water can lower the osmotic pressure of the plasma proteins and thus may increase capillary pressure.
