Life Sciences Glossary: Liver, Nutrition and Nutritional Requirements

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Liver

Liver is the largest gland located above stomach, under the diaphragm. Liver of man weighs about 1,4 kg (4Ib) in the average adult. It is divided into two principal lobes, the right lobe (larger) and the left lobe (smaller) separated by falciform ligament. Liver secretes no digestive enzymes yet its role in digestion is very important.

Principal functions of the liver are:

  • Formation of bile.
  • Carbohydrate storage and release.
  • Formulation of urea.
  • Cholesterol metabolism.
  • Manufacture of plasma proteins
  • Many functions related to metabolism of fat.
  • Inactivation of some polypeptide hormones.
  • Reduction and conjugation of adrenocortical and gonadal steroid hormones.
  • Synthesis of 25-hydroxychole- calciferol.
  • Detoxification of many drugs and toxins.

Jaundice may be caused by retarded function of liver.

Gallbladder

The gallbladder is a sac located along the underside of the liver. It stores bile. Cystic duct conducts bile from liver to gallbladder. The crystallization of cholesterol in bile may produce gallstones or biliary calculi. Surgical removal of the gallbladder is called cholecystectomy.

Bile

  • Bile is made up of bile salts, bile pigments, and other substances dissolved in an alkaline electrolyte solution that resembles pancreratic juice. About 500 ml. Of bile is secreted per day. Some of the components of the bile are reabsorbed in the intestine and then excreted again by the liver (enterohepatic circulation) . The glucuronides of the bile pigments. , bilirubin and biliverdin, are responsible for the golden yellow colour of bile. The bile salts are sodium and potassium salts of bile acids conjugated to glycine or taurine a dewrivave of cysteine.
  • The bile acids are synthesized from cholesterol. In common with vitamin D, cholesterol, a variety of steroid hormones, and the digitalis gluycosides, the bile acids contain the cyclopentano- perhydro phenanthrene nucleus. The 2 principal (primary) bile acids formed in the liver are cholic acid and chenodeoxycholic acid. The bile salts have a number of important actions. They reduce surface tension and, in conjunction with phospholipids, and monoglycerides, are responsible for the emulsification of fat preparatory to its digestion and absorption in the small intestine.
  • In addition, they are amphipathic, i.e.. they have both hydrophilic and hydrophobic domains; one surface of the molecule is hydrophiliuc because the polar peptide bond and the carbodyl and hydroxyl groups are on that surface, whereas the other surface is hydrophobic. Therefore, the bile salts tends to from cylindrical disks called micelles, with the hydrophilic surfaces facing out and a hydrophobic core.

Nutrition and Nutritional Requirements

Nutrition is the procurement of substance necessary for growth, intendancy and activities of a living body. The substance used for nutrition are called nutrients. To keep people healthy, strong energetic and long lived, it is necessary to have a balanced diet.

Components of Food

There are seven essential components of diet. They are carbohydrates, proteins, fats, vitamins, minerals, water and roughage. Major nutrients are carbohydrates, proteins and fats. They are also called as ‘, macronuttients’ . Vitamins and minerals are required in the body only in traces. They are called as ‘microntrients’ . These are as important as macronutrients.

Carbohydrates and fats are energy produces. Protein is a ‘body builder’ proteinds are most essential for body growth and repair of tissues. Vitamins and minerals are mainly metabolic regulators.

Minerals are:

common disaccharides are:

  • Maltose (Glucose + Glucose) ,
  • Sucroise (Glucose + Fructose) and
  • Lactose (Glucose + Galactose) .

Sucrose is the cane sugar found in sugarcane:

  • Sucrose does not reduce Cu ++ to Cu ′ . Maltose or malt sugar is formed during germination of starchy seeds. Lactose or milk sugar is founding in milk. Comparing to the milk of cow, buffalo and goat, lactose is highest in human milk.
  • Starch common in plants and glycogen in animals are two food storage polysaccharides. Both of them can easily be hydrolyzed into their glucose monomers. Cellulose and chitin are two structural polysaccharides. Cellulose is a fibrous polysaccharide with high tensile strength. Cotton fibers contain the largest amount (90 %) of cellulose among natural materials.
  • Cellulose is not found incorporated into asnmimal tissues. Cellulose is digested in ruminants in stomach and rabbit in caecum with the help of intestinal bacteria. Man cannot digest cellulose. Chitin is a polysaccharide found in the exoskeleton of arthropods. Its basic unit is not glucose but Acetylglucosamine.
  • Food storage polysaccharide important to mammals is glycogen. Starch is found abundantly in rice, wheat, legumes, potato, bananas, etc. Excess of carbohydrates in mammals is stored in the form of glycogen in liver and muscles, and also in the form of fat in subcutaneous adipose tissue. Saccharine has a sweet taste, but it is not some sugar.

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