Test Questions

1. Describe the metabolism of calcium and phosphorus in the body.

2. What hormones are involved in the regulation of phosphorus-calcium metabolism?

3. What kind of reception predominates in hormones that regulate calcium and phosphorus metabolism?

4. What is the mechanism of conversion of vitamin D to calcitriol?

5. List the symptoms observed during hypo-and hypercalcemia.

6. What are the main organic components of bone?

7. What inorganic compounds are parts of the bone?

8. Describe the process of bone formation.

9. What factors influence the formation of bone tissue and its metabolism?

II. Laboratory workshop Laboratory work 1. Lipid metabolism

Experiment 1. Emulsification of fats.

The emulsification of fats is essential for speeding up the digestion of fats in the intestinal canal by the enzyme lipase, because it enlarges the contact surface of the fat with the lipase aqueous solution. The emulsifiers are surface-active substances such as proteins, bile acid salts and soaps. They are adsorbed on the surface of fat drops, forming a very thin layer, and the hydrophilic groups of emulsifiers are turned towards the aqueous phase while the hydrophobic radicals are directed to the fat. Thus, the surface tension between the two phases (water / fat) is decreased, which leads to the dissociation of the fat drops into smaller ones.

Take five test tubes. Fill the first tube with 1 ml of distilled water, the second one with 1 ml of bile (twice diluted), the third one with 1 ml of protein solution, the fourth one with 1 ml of 1% solution of sodium oleate, the fifth one with 1 ml of 1% solution of sodium carbonate. Then add 3-4 drops of vegetable oil to each tube simultaneously shaking them and then placing into a tube rack.

After that the stability of emulsions and the degree of their dispersion are noted.

Experiment 2. Digestion of fats. Bile acid influence on pancreatic lipase activity

The breakdown of fats to glycerol and higher fatty acids in the intestine occurs mainly with the participation of pancreatic lipase. Triglycerides are split into glycerol and fatty acids. Fatty acids can be detected by titration with alkali. Bile acids emulsify fats, increasing their contact surface with the lipase, as well as activate the lipase.

Pour 20 ml of milk in the flask. Neutralize it in the presence of 2 drops of phenolphthalein solution with 4 drops of 10% sodium hydroxide solution. Then add 0.1 n. sodium hydroxide solution drop by drop until it becomes light pink. From the neutralized milk prepare experienced samples according to Table 3. Pancreatin drug is used as a source of lipase. The samples are left at room temperature.

Table 3

Hydrolysis of milk fat by lipase

Sample number	Milk volume, ml	Pancreatine mass, mg	Bile volume, ml	Water volume, ml	Results of titration (in ml) of 0.1n. NaOH solution at time intervals, min:
					15	30	45	60	75	90
1	5	100	-	1
2	5	100	1	-
3	5	-	1	-

Titrate the samples with 0.1 n. NaOH solution at given time intervals from the beginning of the incubation until they become light pink. Then again leave them at room temperature. Write down the amount of used alkali in the table. Each time the amount of fatty acids released from the milk fat during the hydrolysis by lipase at a time interval (15 minutes) is titrated.

Write the equation of triglyceride splitting by lipase.

Depict graphically the dynamics of the splitting of fat by lipase for each sample by plotting on the x-axis time in minutes, and the y-axis – volume of 0.1 n. solution of NaOH (in ml) used to neutralize the fatty acids formed in a given time.

Express the lipase activity as a concentration of fatty acid carboxyl groups formed in 100 ml of milk during the whole experiment, using the following formula:

,

where C is the concentration of COOH-groups formed in 100 ml of milk (g/100 ml); m_e is equivalent mass of carboxyl group; 0,1 is the normality of the solution NaOH; V (ml) is the volume of 0.1 n. NaOH solution used for the titration of 5 ml of milk for the whole incubation period (the sum of all titrations); 5 (ml) is the volume of milk in the titrated sample.

On the basis of the curves on the graph and the received data of the concentration of carboxyl groups draw a conclusion about the dependence of lipase activity on the presence of bile acids.

Experiment 3. The role of serum albumin in the transport of fatty acids in the blood.

The blood always contains a certain amount of nonesterified (free) higher fatty acids that appear in the enzymatic cleavage of nutrition lipids and lipids from the body fat depots by lipase. Higher fatty acids, insoluble in water, are transported in plasma mainly as complexes with albumins. An albumin molecule contains a cavity formed by hydrophobic amino acid radicals. The hydrocarbon chain of fatty acids may be placed in this cavity (see Fig).

Fig. Transport of fatty acids by blood serum albumin

Pure 0,5 ml of sodium oleate solution in two test tubes. Add 1,5 ml of blood serum to the first test tube and the same amount of water to the second one. Then add the hydrochloric acid solution drop by drop to the second test tube until the first signs of higher fatty acid residue are observed. Repeat the procedure with the first test tube. Describe and explain the observed phenomena.