intestinal juice/ digestion and absorption

Digestion breaks down food into smaller molecules, while absorption transfers these nutrients from the digestive tract into the bloodstream for the body to use

1. PUSH BEYOND YOU LIMITS

2. INTESTINAL JUICE Dr. K. Ambareesha ,. PhD Associate Professor, Physiology GMC, Jangaon

3. Learning objectives Composition Mechanism of secretion, Functions Regulation of intestinal juice

4. COMPOSITION

5. Mechanism of secretion Imp components mucus, enzymes and water are secreted by different mechanisms. SECRETION OF ENZYMES : Epithelium of villi contain a large quantity of digestive enzymes, its desquamation releases digestive enzymes as intestinal secretion

6. Secretion of mucus By Brunner’s glands and goblet cells in the crypts of lieberkuhn Protect duodenal wall from gastric juice Secreted due to tactile stimulation of mucosa, vagal stimulation and secretin

7. Secretion of water The enterocytes electrolytes along with end products of digestion. Active secretion of Cl , HCO3 into crypts. Cl ions drag Na through the membrane, all these causes osmotic movement of water.

8. ENZYMES OF THE SMALL INTESTINE

9. REGULATION OF INTESTINAL SECRETION LOCAL STIMULUS  occurs through mechanical [ distention by chyme ]and chemical forms [ irritation caused by chemicals] HORMONAL REGULATION  secretin & cholecystokinin

10. DIGESTION AND ABSORPTION OF NUTRIENTS

11. Introduction The major foods on which the body lives can be classified as  carbohydrates, fats,  and  proteins. (small amounts of vitamins and minerals are also needed by the body) They generally cannot be absorbed in their natural forms through the gastrointestinal mucosa.

12. The processes by which Carbohydrates, fats, and proteins are digested into small enough compounds for absorption The mechanisms by which the digestive end products, water, electrolytes, and other substances, are absorbed.

13. DIGESTION, ABSORPTION AND METABOLISM OF CARBOHYDRATES

14. Carbohydrates in diet Human diet contains three types of carbohydrates: Polysaccharides Disaccharides Monosaccharides

15. Digestion of carbohydrates Enzymes involved in the digestion of carbohydrates are known as amylolytic enzymes. In the mouth : The only amylolytic enzyme present in saliva is the salivary amylase or ptyalin In the stomach: Gastric juice contains a weak amylase , which plays a minor role in digestion of carbohydrates

16. Digestion of carbohydrates In the intestine : Amylolytic enzymes present in the small intestine are derived from pancreatic juice and succus entericus . Amylolytic Enzyme in Pancreatic Juice: Pancreatic amylase Amylolytic Enzymes in Succus Entericus : Maltase, sucrase , lactase, dextrinase and trehalase

17. Digestion of carbohydrates

18. Final products of carbohydrate digestion Final products of carbohydrate digestion are monosaccharides , which are: glucose (80%) fructose galactose.

19. Absorption of carbohydrates Carbohydrates are absorbed from the small intestine mainly as monosaccharides: Glucose galactose fructose.

20. Metabolism of carbohydrates

21. Dietary fiber Dietary fiber or roughage is a group of food particles which pass through stomach and small intestine, without being digested and reach the large intestine unchanged. Major components of dietary fiber: cellulose, hemicelluloses, D­ glucans, pectin, lignin and gums . Source of dietary fiber: fruits, vegetables, cereals, bread and wheat grain

22. Dietary fiber Dietary fiber helps in weight maintenance because it requires more chewing and promotes hunger satisfaction by delaying the emptying of stomach and by giving the person a sense of fullness of stomach . Dietary fiber is suggested to prevent or to treat some disorders such as constipation, bowel syndrome, diabetes etc.

23. DIGESTION, ABSORPTION AND METABOLISM OF PROTEINS

24. Proteins in diet Foodstuffs containing high protein content are meat, fish, egg and milk. Proteins are also available in wheat, soybeans, oats and various types of pulses. Dietary proteins are formed by long chains of amino acids, bound together by peptide linkages.

25. Proteins in diet Proteins present in common foodstuffs: Wheat : Glutenin and gliadin, which constitute gluten Milk: Casein, lactalbumin , albumin and myosin Egg: Albumin and vitellin Meat: Collagen, albumin and myosin.

26. Digestion of proteins Enzymes responsible for the digestion of proteins are called proteolytic enzymes . In the mouth : Digestion of proteins does not occur in mouth , since saliva does not contain any proteolytic enzymes. So, the digestion of proteins starts in the stomach.

27. Digestion of proteins „ In the stomach: Pepsin is the only proteolytic enzyme in gastric juice. „In the small intestine: Most of the proteins are digested in the duodenum and jejunum by the proteolytic enzymes of the pancreatic juice and succus entericus .

28. Digestion of proteins Proteolytic Enzymes in Pancreatic Juice : Trypsin, chymotrypsin and carboxypeptidases . Trypsin and chymotrypsin are called endopeptidases, as these two enzymes break the interior bonds of the protein molecules. Proteolytic Enzymes in Succus Entericus : Final digestion of proteins is by the proteolytic enzymes present in the succus entericus . It contains dipeptidases , tripeptidases and aminopeptidases.

29. Digestion of proteins

30. Final products of protein digestion Final products of protein digestion are the amino acids , which are absorbed into blood from intestine.

31. Absorption of proteins Proteins are absorbed in the form of amino acids from small intestine . Absorption of amino acids is faster in duodenum and jejunum and slower in ileum .

32. Metabolism of proteins

33. DIGESTION, ABSORPTION AND METABOLISM OF LIPIDS

34. Lipids in diet Lipids are mostly consumed in the form of neutral fats , which are also known as triglycerides . Triglycerides are made up of glycerol nucleus and free fatty acids. Triglycerides form the major constituent in foods of animal origin and much less in foods of plant origin .

35. Lipids in diet Apart from triglycerides, usual diet also contains small quantities of cholesterol and cholesterol esters . Dietary fats are classified into two types: 1. Saturated fats 2. Unsaturated fats.

36. Saturated fats Saturated fats are the fats which contain triglycerides formed from only saturated fatty acids. The fatty acids having maximum amount of hydrogen ions without any double bonds between carbon atoms are called saturated fatty acids.

37. Unsaturated fats Fats containing unsaturated fatty acids are known as unsaturated fats. Unsaturated fatty acids are fatty acids formed by dehydrogenation of saturated fatty acids. Unsaturated fats are classified into three types: 1. Monounsaturated fats 2. Polyunsaturated fats 3. Trans fats.

38. Digestion of lipids Lipids are digested by lipolytic enzymes . „ In the mouth: Saliva contains lingual lipase . This enzyme is secreted by lingual glands of mouth and swallowed along with saliva. So, the lipid digestion does not commence in the mouth. In the stomach: Gastric lipase or tributyrase is the lipolytic enzyme present in gastric juice. „ In the intestine: Almost all the lipids are digested in the small intestine because of the availability of bile salts , pancreatic lipolytic enzymes and intestinal lipase .

39. Final products of fat digestion Fatty acids , cholesterol and monoglycerides are the final products of lipid digestion.

40. Digestion of lipids

41. Absorption of lipids Monoglycerides , cholesterol and fatty acids from the micelles enter the cells of intestinal mucosa by simple diffusion. In the mucosal cells, most of the monoglycerides are converted into triglycerides. Triglycerides are also formed by re-esterification of fatty acids with more than 10 to 12 carbon atoms. Some of the cholesterol is also esterified.

42. Absorption of lipids Triglycerides and cholesterol esters are coated with a layer of protein, cholesterol and phospholipids to form the particles called chylomicrons. Chylomicrons cannot pass through the membrane of the blood capillaries because of the larger size. So, these lipid particles enter the lymph vessels and then are transferred into blood from lymph.

43. Absorption of lipids Fatty acids containing less than 10 to 12 carbon atoms enter the portal blood from mucosal cells and are transported as free fatty acids or unesterified fatty acids. Most of the fats are absorbed in the upper part of small intestine. Presence of bile is essential for fat absorption.

44. Storage of lipids Lipids are stored in adipose tissue and liver. Fat stored in adipose tissue is called neutral fat or tissue fat.

45. Transport of lipids in blood – lipoproteins Free fatty acids are transported in the blood in combination with albumin . Other lipids are transported in the blood, in the form of lipoproteins.

46. Lipoproteins Lipoproteins are the small particles in the blood which contain cholesterol, phospholipids, triglycerides and proteins. Proteins are beta­globulins called apoproteins .

47. Classification of Lipoproteins Lipoproteins are classified into four types on the basis of their density: 1. Very-low-density lipoproteins (VLDL) 2. Intermediate-density lipoproteins (IDL) 3. Low-density lipoproteins (LDL) 4. High-density lipoproteins (HDL)

48. Functions of Lipoproteins

49. Adipose tissue Adipose tissue or fat is a loose connective tissue that forms the storage site of fat in the form of triglycerides. It is composed of adipocytes, which are also called fat cells or lipocytes . Adipose tissue is of two types: 1. white adipose tissue 2. brown adipose tissue

50. White adipose tissue White adipose tissue is distributed through the body beneath the skin, forming subcutaneous fat. White adipose tissue has three functions: 1. Storage of energy 2. Heat insulation 3. Protection of internal organs

51. Brown adipose tissue The coloration of this adipose tissue is due to high vascularization and large number of iron-rich mitochondria. Brown adipose tissue does not store lipids but generates heat by burning lipids. In infants and hibernating animals, brown adipose tissue plays an important role in regulating body temperature via non-shivering thermogenesis.

52. Brown adipose tissue Heat production in brown fat is very essential for survival of infants and small animals in cold environment. It is because, the lipid in this tissue releases energy directly as heat.

53. Metabolism of lipids

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