DIGESTION & ABSORPTION OF CARBOHYDRATES AND THEIR DISORDERS Dr Sara Mariyum

Nutrition It is a process by which organisms obtain and utilize their food It has two parts: 1. Ingestion- process of taking food into the digestive system so that it may be hydrolyzed or digested. 2. Digestion- the breakdown of food (either chemically or mechanically) in order to utilize nutrients

Nutrients Micronutrients- vitamins, minerals, & water Macronutrients- proteins, lipids, carbohydrates

Water, vitamins, and minerals are small molecules that can be absorbed without digestion. (Hydrolysis) Large molecules like carbohydrates (starch), lipids, and proteins require digestion.

Digestion Digestion – The process of changing food into simple components that can be absorbed by the body. Digestive tract or Gastrointestinal tract- where digestion & absorption take place Mouth->esophagus->stomach->small intestine->large intestine

Types of Digestion Chemical Digestion Mechanical (Physical) Digestion

Mechanical Digestion Food is crushed, broken or cut into smaller pieces (ingestion into MOUTH) It INCREASES the surface area of the food in order to aid in chemical digestion Is accomplished by PERISTALSIS and by the churning of the stomach.

Chemical Digestion Is carried out by the digestive ENZYMES Example: Saliva -breaks down starch into disaccharides (contains the enzyme amylase) Stomach acid (HCL or Hydrochloric Acid) - breaks down gastric protease which digests proteins BILE -produced by the liver and stored in the gall bladder breaks down fats

MECHANISM FOR CHEMICAL DIGESTION Hydrolysis - the splitting of large, insoluble molecules into small, soluble molecules with the addition of water

This process is regulated by hydrolytic (digestive) enzymes and is illustrated by the following: 1. Maltose + water ----> simple sugars (glucose) 2. Proteins + water ---> amino acids 3. Lipids + water ---> 3 fatty acids + glycerol

Carbohydrates Carbohydrates are made of carbon, hydrogen and oxygen atoms. These atoms form chemical bonds that follow the laws of nature.

Digestion of Carbohydrates Monosaccharides Do not need hydrolysis before absorption Di- and poly-saccharides Relatively large molecules Must be hydrolyzed prior to absorption Hydrolyzed to monosaccharides Only monosaccharides can be absorbed

Carbohydrates Ingestion Polysaccharides (starch and dextrin's) Disaccharides ( lactose, sucrose, maltose, trehalose) Monosaccharide's ( glucose and fructose)

Starch

Carbohydrate Digestion Mouth Salivary amylase Breaks starches down to maltose, maltotriose, alpha dextrins Plays only a small role in breakdown because of the short time food is in the mouth

Carbohydrate Digestion Pancreas Pancreatic amylase Hydrolyzes alpha 1-4 linkages Produces monosaccharides, disaccharides and oligosaccharides Major importance in hydrolyzing starch to maltose Amylase Polysaccharides Disaccharides

Act on uncooked starch too Intestinal amylase

Digestion in Small Intestine Digestion mediated by enzymes synthesized by cells lining the small intestine (brush border) Brush Border Enzymes Disaccharides Monosaccharides

Digestion in Small Intestine Sucrase Sucrose Glucose + Fructose Maltase Maltose Glucose + Glucose Lactase Lactose Glucose + Galactose

Isomaltose isomaltase 2 mol of glucose Maltotriose maltase 3 mol of glucose Alpha dextrins maltase n mol of glucose

Resistant starch Small intestine….colon Fermentation by bacteria Form short chain fatty acids

Food Containing Resistant Starch Oats Cooked and Cooled Rice Legumes  Potato Starch. Cooked and Cooled Potatoes Green Bananas Hi-Maize Flour

CELLULOSE No digestive enzyme

Sources of Monosaccharide in Small Intestine Diet Hydrolysis of Starch Hydrolysis of Disaccharides

Overview Carbohydrate Digestion Location Enzymes Form of Dietary CHO Mouth Salivary Amylase Starch Maltose Sucrose Lactose Stomach (amylase from saliva) Dextrin→Maltose Small Intestine Pancreatic Amylase Maltose Brush Border Enzymes Glucose Fructose Galactose + + + Glucose Glucose Glucose Large Intestine None Bacterial Microflora Ferment Cellulose

Absorption & Transport Absorption occurs in the small intestine 1. Wall of small intestine covered with 100s of folds 2. Each fold covered with 1000s of villi 3. Each villi contains 100s of microvilli

Nutrient Absorption - Carbohydrate Transport for glucose and galactose Sodium-glucose transporter 1 (SGLT1) Glucose transporter (GLUT 2)

Facilitated transport for fructose GLUT 5 GLUT 2

Distributed to tissue through circulation Small Intestine Monosaccharides Carbohydrates Portal Vein Active Transport Liver Distributed to tissue through circulation

In the liver, galactose and fructose are converted to glucose. Monosaccharides, the end products of carbohydrate digestion, enter the capillaries of the intestinal villi. Small intestine In the liver, galactose and fructose are converted to glucose. Figure 4.11: Absorption of Monosaccharides. Monosaccharides travel to the liver via the portal vein.

Factor Affecting Glucose Absorption Intestinal factors Thyroid Adrenal cortex Vitamins

Summary of Carbohydrate Digestion and Absorption Polysaccharides broken down to monosaccharides Monosaccharides taken up by active transport or facilitated diffusion and carried to liver

Lactose Intolerance Inability to digest significant amounts of lactose, which is the predominant sugar in milk A result of lactase insufficiency, the enzyme essential for the conversion of lactose into glucose and galactose

Types of Lactose Intolerance Congenital: Absence from birth of lactase due to a mutation in the gene responsible for creating lactase. Secondary: Due to diseases that destroy the lining of the small intestine along with the lactase. Developmental: A decrease in the amount of lactase that occurs after childhood and persists into adulthood Of the three types of lactose intolerance, secondary is the type observed most often in infants participating in the WIC program. Congenital lactose intolerance in infants is very rare. Primary lactose intolerance usually develops after two years of age. Secondary lactose intolerance is usually temporary, perhaps due to illness, and resolves within one to two weeks.

Symptoms of lactose intolerance Intolerance does not involve the immune system Nausea, cramping, bloating, abdominal pain, gas, diarrhea Symptoms may begin from 15 minutes to several hours after eating food with lactose For both children and adults, if your body reacts to food, you may have a food intolerance – not an allergy. Unlike food allergies, food intolerances usually don’t involve the immune system. However, they prompt many of the same symptoms and are often mislabeled as allergies. In persons with lactose intolerance, undigested lactose produces uncomfortable symptoms. Most common are nausea, cramping, bloating, abdominal pain, gas and diarrhea. Symptoms may begin anytime from 15 minutes up to several hours after consuming foods or drinks containing lactose. The severity of symptoms varies from person to person and how much and when lactose is consumed in relation to other foods.

Infants with lactose intolerance Breastfeeding Alternatives to breastfeeding Lactose free formula Most infants produce the lactase enzyme to digest lactose from birth. The body may produce less lactase as it gets older. For the formula fed infant sensitive to lactose, a soy or lactose free formula is most appropriate.

Children and Women with Lactose Intolerance Eat or drink small servings Eliminating milk and other dairy foods may lead to nutritional risks

Glucose Galactose Malabsorption Congenital defect Lack of transporter Diarrhea