Test questions

1. Which factor is the driving force for the interconversion of proteins, fats, carbohydrates, and the integration of energy?

2. Enumerate the main energy sources of the organism.

3. What processes occur in the absorptive and postabsorbtive periods?

4. Enumerate the hormones that regulate metabolism of proteins, fats and carbohydrates, specify their influence on the metabolic processes in different tissues

5. Which hormones excess can reduce the concentration of glucose? Explain the answer.

6. Prove why overeating of digestible carbohydrate is a risk factor in atherosclerosis and obesity development.

7. What are the changes in metabolism occur in the organism during starvation?

8. What are the causes of Addison's disease? What are metabolic disorders observed in this disease?

9. Enumerate the major manifestations of diabetes.

10. What kind of diabetes do you know? How can they be differentiated with respect to blood tests, urine tests?

6. Mineral and water and salt metabolism

6.1. Water in the human body

Water plays an important role in life processes, not only as a necessary component of all cells and tissues of the organism, but also as a medium in which all chemical transformations connected with the life of the organism occur. Salt metabolism is intimately connected with the water metabolism. Most of the mineral compounds in the organism are in water solutions. Salts, like water, are not sources of energy to the organism, but they are a part of all cells and tissues and are a necessary part of it.

The water content in the human organism is about two thirds of organism weight, decreased slightly with age. Higher water content is in newborns. Some of the water, part of the organism tissues, is in a bound form in them. For example, such compact tissues and organs, like muscles, skin, kidneys, heart, include 70-80% of water.

Water has a number of specific chemical and physical properties. Clean water is a neutral liquid, which dissolve well various inorganic and organic substances. Due to the large dielectric coefficient water facilitates the electrolytic dissociation of dissolved electrolytes. A small viscosity of water, which depends on the speed of movement of fluids in the blood and lymphatic vessels, tissue crevices, etc., is also one of its important properties.

All chemical reactions and physico-chemical processes in the human organism occur in the aqueous environment. This is hydrolysis reactions, where the water is directly involved in the reaction, many oxidation reactions, hydration, colloids swelling and other.

Water plays an important mechanical role in facilitating the sliding of the friction surfaces (joints, ligaments, muscles, etc.). Evaporation of the water through the skin is an ability by which a person maintains a constant organism temperature during the formation of strong heat in the organism or at high ambient temperature.

The main parameters of the liquid medium of the organism are the osmotic pressure, pH and volume. Osmotic pressure and pH of the extracellular fluid and blood plasma are the same. The pH inside the cells of different types may be different depending on the characteristics of metabolic mechanisms of active transport, selective permeability of membranes. Maintaining constant intracellular environment is provided by the constancy of the osmotic pressure, pH and volume of extracellular fluid and blood plasma, and they, in turn by the action of the kidneys and hormones that regulate their function.

Man can not stand any significant dehydration and die from lack of water much faster than from lack of food. Adult daily requirement of water is about 40 grams of water per 1 kg body weight. Water requirement is met by the intake of various liquids (drinking water, beverages, soups) – 1-1.5 liters; water of foods – about 1-1.5 liters; water that forms in tissues of the oxidation of various substrates of tissue respiration – about 400 ml.

The amount of water formed during the oxidation of 100 g of various nutrients is expressed by the following figures: the lipid – 107 ml, carbohydrate – 55 ml, protein – 41 ml; 12 ml of water is formed from 100 calories during the usual mixed diet.

The water coming from outside should fully compensate for the constant loss of water through the kidneys (urine), skin (sweat), lungs (breathing), intestine (feces). This loss of water is linked to the implementation of a number of important physiological functions. The main part of the end products of nitrogen metabolism in humans is excreted through the kidneys into the urine. In humans, depending on body weight and sex, in this way about 1.2-1.5 liters of water are excreated during the day. By drinking plenty of fluids, the diuresis is increased, and conversely, urine amount is decreased at the restriction of drinking. Condensation of the urine is possible only to a certain limit. Excessive restriction of water intake inevitably leads to violation of excretion of metabolism products, in particular nitrogen waste products. A large part of mineral salts (sodium chloride, phosphates, etc.) is excreted in soluble form in urine from an organism. The retention in the body of these salts, as well as various nitrogenous constituents of urine quickly would lead to incompatible with life changes of plasma blood osmotic pressure, interstitial fluid and intracellular contents.

Maintaining the concentration of water in various tissues of the human body at a certain level is done by the special mechanisms of the regulation, in particular a sense of thirst. Thirst is the result of reflex excitation of certain parts of the cerebral cortex at the first sign of changes in osmotic pressure of blood plasma. Absorption of water entering the body through the mouth, begins in the stomach, but most of it goes into the blood capillaries and and partly lymphatic vessels in the gut. The osmotic pressure of blood is usually higher than the osmotic pressure of the chyme; the absorption of water does not require any energy consumption. Absorbed water is partly retained in the liver; part of it enters the systemic circulation. However, no significant liquefaction of the blood (hydremia) was observed even after absorption of large quantities of water (at once 1.5 liters). This is explained by the fact that the large mass of absorbed water is immediately transferred from the blood into the intercellular fluid, as well as the abdominal cavity. The skin and liver play a particularly important role as the organs that hold the excess of absorbed water.

Water metabolism is not isolated and independent from the metabolism of other substances. This relationship is most significant with mineral metabolism. Sodium salts cause water retention in the tissues. Potassium and calcium salts help to remove water from the body. The water balance is also depends on the content of proteins, lipids and carbohydrates in food. The diet rich in carbohydrates provides a significant increase in body weight; but especially children become a kind of "loose" due to the retention of large amounts of water in their bodies. The lipopexia in the body, by contrast, is not accompanied by water retention, but rather leads to a negative water balance.

If more water is introduced into the body than it can be excreted through the kidneys; sweating starts, accompanied by headache, nausea and general weakness.

Excretion of water from the body is controlled by several mechanisms; the most important of which is a mechanism for the regulation of uropoiesis. It will be reviewed in the section "Biochemistry of the kidneys".