Digestion Absorption and Alcohol Protein Vegetarianism Basic Human

Digestion Absorption and Alcohol, Protein & Vegetarianism Basic Human Nutrition Lecture 2

Introduction n All cells require nutrients to provide energy. Hormones and enzymes work with the digestive tract to break complex nutrients from food into smaller ones that can be absorbed through the lining of the intestines into the blood and lymph. These nutrients are then distributed (via blood and lymph) to all cells in the body. 2

Digestion n Process of breaking down foods into nutrients to prepare for absorption. The GI tract is the flexible muscular tube from mouth to anus. Consists of the esophagus, gallbladder, liver, stomach, pancreas, small intestine, large intestine, rectum and anus. 3

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Digestion is both mechanical & chemical n n n Mouth. Teeth and jaws - mastication. Mastication (mashing the food) increases the surface area 5

Secretions of Digestion n Salivary glands n Water, salts, mucus, enzymes 6 Copyright 2005

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Esophagus n n n Tube that leads the bolus to the stomach. The esophageal sphincter is at the upper end. The cardiac sphincter is at the lower end. 8

Stomach n n n The stomach contains gastric glands. The parietal cells of the gastric glands secrete hydrochloric acid Mucosal neck cells secret mucous to protect the mucosal lining. 9

Secretions of Digestion n Stomach n Gastric juice n Gastric glands n Water, enzymes,

Stomach continued n n The stomach contents are churned into an acidic liquid called chyme. It can take 2 to 3 hours to empty the stomach depending on the mixture of nutrients (CHO, protein and fat). 11

Small intestine n n The small intestine consists of duodenum (first 0. 3 m), jejunum (next 1 -2 m, where most of digestion occurs) and ileum (last 1. 5 m). Approximately 90% of digestion takes place in the first 2 sections of the long small intestine. 12

Small intestine continued n n n Chyme release to small intestine through the pyloric valve at the end of the stomach. Rhythmic contractions of the small intestine move the intestinal contents along its length. By the time it reaches the large intestine or colon, digestion and absorption are nearly complete. 13

Large intestine n n n Consists of the ascending and descending colon, transverse colon, sigmoid colon, rectum and anal canal. In the colon, the digested food remnants are further acted upon by bacteria that ferment the remaining undigested food residues. The bacteria synthesize small amounts of vitamin K and the B vitamin biotin that become absorbed. 14

Large intestine continued n n Bacterial fermentation also produces about 500 ml of gas (flatus) each day. The gas is a mixture of hydrogen, nitrogen, methane, hydrogen sulfide and carbon dioxide. The colon absorbs water and compacts the residue into a paste, feces which it moves along to the rectum. The rectum stores feces until eliminated through the anus. 15

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Chemical digestion n n Chemical digestion occurs through digestive enzymes that are secreted by gland cells along the alimentary tract. Enzymes are biological catalysts which speed up chemical reactions. These enzymes are specific in their action and to specific nutrients. Enzymes are manufactured in the salivary glands, the gastric glands, the intestinal glands and the pancreas. 17

Digestive Juices n Salivary glands: n n n secrete saliva to moisten and lubricate food. Amylase - starts the breakdown of starch Amylase is inactivated in the stomach by the acid medium. 18

Digestive Juices n n The gastric glands produce gastric juice which includes hydrochloric acid. The pancreas secretes sodium bicarbonate to neutralize the acids from the stomach. Pancreatic juice contains intestinal enzymes (carbohydrase, lipase and protease). Bile is produced by the liver, stored in the gall bladder and acts as an emulsifier to suspend fat. 19

Disaccharides are digested by. . n Enzymes secreted by the gland cells in the small intestine. n n n Maltase splits maltose into 2 glucose units Sucrase splits sucrose into glucose and fructose Lactase splits lactose into glucose and galactose. 20

Protein digestion begins in the stomach n n n Proteins are amino acids in long chains called polypeptides. Gastric glands secrete the enzyme pepsin in its inactive form pepsinogen. Pepsin is activated by gastric acid. It splits the bonds between proteins (amino acids) into polypeptides of different lengths. 21

Protein digestion continued n n n Pepsin works best at a p. H of less than 2. This is carefully maintained by the gastric glands to facilitate protein digestion. Protein and polypeptides are further broken down in the intestine at a neutral p. H by the pancreatic enzyme called trypsin. Enzymes from the intestinal glands and the pancreas called peptidases complete the process. 22

Fat digestion occurs mainly in the intestine n n n Tongue produces traces of a fatdigesting enzyme that helps to break down milk fats. Very important to nursing infants. Fat broken down by pancreatic lipase to fatty acids and glycerol. Fats form large globules in the intestinal juices. 23

Fat globules are broken up by Bile salts n n Liver secretes bile (salts), the gallbladder stores it and releases it into the small intestine. Bile salts are not enzymes but emulsifiers which help to break up the fat into smaller fat droplets. The lipase then has a greater surface area to work on. If bile salts are not secreted by the liver, the fat passes undigested into the feces. 24

Absorption of nutrients n n For absorption a large area of contact between the digested food molecules and the intestinal lining is necessary. Small intestine provides a large absorptive area: n n Very long (7 metres in the adult) It has circular folds 25

Absorption continued n n Villi. Microvilli. Folding of the intestinal surfaces greatly increases absorptive capacity. Large supply of blood vessels in small intestine transport the nutrients from the gut to the cells in the body. 26

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The liver – dispatch centre for the refinery n n Nutrients pass through the epithelial cells lining the small intestine and into the capillaries below them. They are then carried away in veins which eventually join one large vein, the hepatic portal vein. This vein carries all blood from the blood vessels of the intestine to the liver. The liver can store the nutrients or change them and release them through general circulation. 28

Maintaining glucose levels n n Liver, along with insulin from the pancreas, maintains fairly constant levels of blood glucose. Large quantities of glucose reach the liver from the alimentary canal via the hepatic portal vein. 29

Maintaining glucose continued The liver can: n 1) break the glucose down as an energy source for liver cells. n 2) convert it to glycogen and store it in liver cells. n 3) convert it into fats which are then sent to fat depots in the body. 30

Liver and proteins & fats n n Amino acids cannot be stored in the body. The liver breaks them down (deamination) and converts them to ammonia and urea. Urea enters the general circulation and is removed by the kidneys. Excess CHO, protein and fats are converted to fat in the liver and sent to fat depots. 31

Liver – the cleansing organ n n The liver also makes bile salts. Stores some vitamins and minerals particularly iron. Removes worn out red blood cells from circulation and destroys them. Inactivates hormones. Detoxifies or inactivates many toxic chemicals and drugs, which can then be eliminated by the kidneys. 32

Digestive Problems Vomiting n n The waves of peristalsis reverse direction. If severe, the contents of the duodenum with its green bile can come up. Solution: drink small amounts liquid as tolerated until nausea subsides. Dehydration can occur. 33

Diarrhea n n Frequent, loose, watery stools. Diarrhea is a symptom of a variety of medical conditions and treatments. It can be the result of disorders of the GI tract – IBS or colitis. Treatment depends on its cause and its severity. 34

Constipation n Is a symptom, not a disease. Often a person’s lifestyle may be the cause. Treatment often involves increasing the fibre content of the diet as well as increasing fluids. 35

Diverticulosis n n Condition in which the intestinal walls develop bulges in weakened areas (most common in the colon). These diverticula can worsen constipation, entrap feces, and become painfully infected and inflamed (diverticulitis). 36

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Heartburn and Acid Indigestion n Occurs soon after eating a meal and can be very painful. The esophageal sphincter allows the stomach contents to reflux into the esophagus. Treatment: eat less at a meal, chew food more thoroughly and eat slow. 38

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Ulcers n n n Ulcer is an erosion of the top layer of cells. The erosion leaves the underlying layers of cells unprotected and exposed to gastric juices. Gastric and duodenal ulcers are a common digestive problem. 40

Ulcers There are 3 major causes of ulcers: n Bacterial infection with Helicobacter pylori n The use of certain anti-inflammatory drugs (aspirin, ibuprofen, naproxen). n Disorders that cause excessive gastric acid secretion. 41

Alcohol n n n Alcohol is a drug Provides energy (7 kcal/ml), but is not a nutrient. Small molecule, easily diffuses in and out of cells, therefore rapidly absorbed. 42

Alcohol and Nutrition 43 Copyright 2005 Wadsworth Group, a division of Thomson Learning

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Absorption of Alcohol continued n n n Alcohol dehydrogenase (enzyme in Liver) breaks down small to moderate amounts of alcohol to acetaldehyde. This can reduce the amount of alcohol entering the blood by about 20%. Alcohol is rapidly absorbed in the small intestine. It gets absorbed and metabolized before most nutrients. 45

Absorption of Alcohol continued n n The liver possesses an enzyme system that metabolizes alcohol and several types of drugs. This is called the Microsomal ethanoloxidizing system (MEOS). Chronic alcohol abusers use this pathway more frequently and may develop an increased tolerance to alcohol. 46

Alcohol absorption continued n n Liver can process only a certain amount of alcohol per hour (1/2 oz ethanol/hr). When amount of alcohol exceeds capacity, spills over into all bodily fluids including the cerebrospinal, brain, (in pregnancy, placenta and fetus). 47

Alcohol absorption continued n n n 10% of circulating alcohol is lost through urine, breath and skin. Excess alcohol deprives brain of oxygen, brain shuts down functions that regulate breathing and heart rate. Lose consciousness. Alcohol poisoning due to rapid ingestion of large amounts of alcohol; body shuts down, but processing of alcohol continues causing death. 48

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Absorption of Alcohol continued n n n Acetaldehyde in GI tract not completely converted to acetate. Damages gut lining. Alcohol digestion takes priority over fats, protein and carbohydrates. Liver cells detoxify alcohol and uses products to make fatty acids which are further made into fats. 50

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Hangover n n Ethanol competes with methanol for absorption and processing in the liver. Methanol metabolite formaldehyde builds up. Dehydration occurs, leading to headache and dry mouth. Alcohol irritates stomach and intestinal lining causing diarrhea and vomiting. 53

Hangover n n n Vomiting/diarrhea causes further loss of electrolytes and dehydration. Processing of alcohol diverts liver from glucose production which leads to hypoglycemia. Effects can last up to one day. 54

Treatment of hangover n n Only time is an effective treatment combined with fluids and some carbohydrates to replace losses and reverse hypoglycemia. Caffeine compounds dehydration. More alcohol continues process. Type of alcohol and mixes not responsible for hangover. Total amount of alcohol responsible. 55

Not all individuals handle alcohol the same. n n Women – produce 40% less of ADH in stomach than men Smaller body size equals smaller liver, less enzymes. Less water more body fat than men, get drunk quicker and stay drunk longer than men on same amount of alcohol. Seniors – less body water. 56

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University and alcohol n n Accepted means of stress relief among students. Binge drinking common more negative effects; property destruction, drunk driving, accidents, missed classes, etc. Greater risk of rape for women. Acceptable alcohol intake is 1 drink per day for women and 2 per day for men. 59

Low-Risk Drinking Guidelines n Zero n Two n n Being alcohol free provides the lowest risk of alcoholrelated problems. Have no more than 2 standard drinks on any one-day. 60

Low-Risk Drinking Guidelines… n Nine n n Fourteen n Women may have up to 9 standard drinks a week. Men may have up to 14 standard drinks a week. 61

Low-risk drinking guidelines n n n One standard drink = 13. 6 grams of alcohol One standard drink = 5 oz/142 ml of wine (12% alcohol) One standard drink = 1. 5 oz/43 ml of spirits (40% alcohol) One standard drink = 12 oz/341 ml of regular strength beer (5% alcohol) Higher alcohol beers and coolers have more alcohol than one standard drink! 62

Alcohol and Malnutrition n n In moderate drinkers alcohol may stimulate appetite. Alcohol can contribute to body fat and weight gain. Heavy drinkers usually consume alcohol as substituted energy. Chronic alcohol abuse displaces nutrients from the diet and interferes with the body’s metabolism of nutrients. 63

Proteins n n n Proteins have a unique structure that consists of carbons, oxygen, hydrogen and nitrogen. Amino acids are the building blocks of protein. They are linked together by peptide bonds in strands that may consist of up to 1000 amino acids. About 20 amino acids are required by the body. 64

Amino Acids 65 Copyright 2005 Wadsworth Group, a division of Thomson Learning

Essential amino acids n n The body can make up about half of the 20 amino acids Essential amino acids must be obtained from food. 66

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Recycling amino acids n n The body can reuse its amino acids. Both food proteins after digestion and body proteins after use are dismantled to release their amino acids. Cells can use the amino acids as energy and discard the nitrogen as waste. By reusing amino acids to build proteins, the body recycles and conserves a valuable nutrient while easing its burden of disposing nitrogen. 68

The variety of proteins… n The unique shapes of proteins perform different tasks: n n n Globular shape—blood proteins, are water soluble; hollow balls can carry and store materials in their interiors. Some form rope fibers that lend support and elasticity to body parts. Enzymes are proteins which act on other substances to change them chemically. 69

DNA & protein n Heredity and DNA. Any mistake in the sequence leads to disease. Example sickle cell anemia. Each person is different because of differences in body proteins that is determined by their genetic code or DNA. 70

Protein digestion n n Denaturation of proteins begins in the stomach acid. Enzymes in the intestine break down the protein strands into single amino acids, dipeptides, tripeptides polypeptides. Intestinal cells further break down the smaller strands into amino acids and absorb them into the bloodstream. A few dipetides and tripeptides cross into the bloodstream without further digestion. 71

Absorption of amino acids n n Different sites in small intestine absorb different types of amino acids. Amino acids of the same type compete for absorption. n n A large intake of a single amino acid may limit absorption of other amino acid of its general type. In the bloodstream, amino acids can be used by any cell in the body. 72

Functions of proteins n n Growth & maintenance of body tissues. Enzymes facilitate needed chemical reactions Hormones – regulate body processes. Some hormones are proteins and some are made from amino acids. Antibodies – proteins form the immune system molecules that fight disease. 73

Function of proteins continued n n n Fluid & electrolyte balance. Acid-base balance. Energy. 74

Function of proteins continued n n n Transportation. Blood clotting. Structural components. 75

Protein Quality n n n High quality proteins contain all the essential amino acids. These are obtained from meat, fish poultry, milk, cheese, eggs, milk and many soybean products. Plant proteins are diverse in amino acid content and offer less protein. Combining plant foods that together contain all the essential amino acids is considered complementary. 76

Complementary proteins n n Need not be eaten together as long as they are eaten in the same day and the diet supplies adequate energy and a total protein from other sources. Vegetarians need to eat a variety of grains, legumes, seeds, nuts, and vegetables. 77

Recommended Intakes n RDA n 0. 8 g/kg/day n 10% - 35% of energy

Vegetarianism Main Types: Vegan: Includes foods only from plant sources, vegetables, grains, legumes, fruits, nuts. Lacto-ovo: includes plant foods, dairy foods and eggs. No flesh or fish. Lacto-vegetarian includes plant foods and dairy foods. No eggs, flesh or fish. 79

Vegetarian diet in general n n n Less fat and protein More complex carbohydrate from whole grains, fruits and vegetables More fibre Vegetarians need to select calcium-rich foods. Vitamin D supplements may be required. Vegans must rely on vitamin B 12 frotified sources. 80

Benefits of vegetarian diet in general n n n Less obesity from fewer calories. Lower blood pressure. Less heart disease – less saturated fat, high intake of phytochemicals and antioxidants from fruits & vegetables. Less constipation and diverticular disease – due to high fibre. Less cancer – (reasons similar to heart disease). 81

Vegetarian diets throughout the lifespan n Diet planning during pregnancy, lactation, infancy, childhood and adolescence must provide for the increases in energy and nutrients needed. Fortified foods or supplements for Vitamin D, Calcium and Vitamin B 12 may be required. http: //www. nutrispeak. com/foodguides. htm 82