DIGESTION and ABSORPTION

1. DIGESTION and ABSORPTION Learning Objectives: • Understand the physical and chemical processes of digestion • Learn the function of each organ in the digestive system • Gain an understanding of common Gastrointestinal Disorders

2. TASTE and SMELLThe Chemosenses 1. Olfactory Cells: • Stimulated by odors around us • Found high inside the nose, connect directly to the brain 2. Gustatory Cells: • React to food and beverages • Clustered into taste buds • TASTE: salty, sweet, bitter, sour, and umami

4. TASTE and SMELLThe Chemosenses 3. Common Chemical Sense • Thousands of nerve endings on the moist surfaces of the eyes, nose, mouth, and throat accent our sense of smell and taste • FLAVOR = texture, temperature, common chemical sense, taste, and odor

5. CEPHALIC (preabsorptive) PHASE RESPONSE • In response to sensory stimulation, your body primes its resources to better absorb and use anticipated nutrients • EXAMPLE: Sound (Hearing a description of food) can cause the salivary glands to increase the flow of saliva

6. Important Structures

7. ASSISTING ORGANS

10. PHYSICAL PROCESSES • Chewing • Peristalsis – the wavelike, rhythmic muscular contractions of the GI tract that move chyme down its tract • Segmentation – periodic squeezing and partitioning of the SI which mixes the chyme and promotes close contact with digestive juices and absorbing cells • Sphincters – regulate the flow of food particles

13. CHEMICAL PROCESSES • Enzymes: protein compounds that facilitate chemical reactions but are not altered in the process

14. CHEMICAL PROCESSES • Acid in the stomach (hydrochloric acid) • Base in the small intestine (bicarbonate) • Bile • Mucus

15. MOUTH • Saliva • Amylase – breaks down starches into small sugar molecules (only about 5%) • Lingual Lipase – breaks down fats, but only in a miniscule amount • Epiglottis – guards entrance to the trachea

17. STOMACH GASTRIC JUICE: • Water • Hydrochloric Acid (pH = 2) page 77 • Mucus • Enzymes • Hormones • Intrinsic Factor

18. NUTRIENT ABSORPTION in the STOMACH Only: • Some lipid-soluble compounds • Weak acids, such as alcohol and aspirin

19. SMALL INTESTINE • Almost all digestion of protein, fat, and carbohydrate is performed in the SI Divided into three parts: • Duodenum (the first 10-12 inches) • Jejunum (~ 4 feet) • Ileum (~ 5 feet)

20. NUTRIENT DIGESTION in the SMALL INTESTINE • SECRETIN is released upon the appearance of chyme in the SI  SECRETIN stimulates the release of BICARBONATE from the pancreas  BICARBONATE neutralizes the chyme

21. NUTRIENT DIGESTION in the SMALL INTESTINE • The neutralization is important because the enzymes in the SI need a neutral environment • Pancreatic juice and secretions from the intestinal wall cells contain a variety of digestive enzymes that help to digest fats, carbohydrates, and proteins

22. NUTRIENT DIGESTION in the SMALL INTESTINE • BILE is released from the gall bladder upon the appearance of fat in the SI • BILE acts as an emulsifier, and without it, lipids might not come into contact with pancreatic lipase, and would not be properly digested

23. NUTRIENT DIGESTION in the SMALL INTESTINE • With pancreatic and intestinal enzymes working together, digestion creates smaller compounds of protein, fat, and carbohydrate which can then be easily absorbed • Minerals, vitamins, and cholesterol are not broken down and are generally absorbedunchanged

24. NUTRIENT ABSORPTION in the SMALL INTESTINE • Most absorption occurs in the SI – 90% • Provides the surface area equivalent to a tennis court! • Nutrients are trapped in folds of the intestinal wall and absorbed through the microvilli • Each villus contains blood vessels and a lymph vessel which transport nutrients

26. NUTRIENT ABSORPTION in the SMALL INTESTINE • Water-soluble nutrients are absorbed directly into the bloodstream • Fat-soluble lipid compounds are absorbed into the lymph rather than the blood

28. NUTRIENT ABSORPTION in the SMALL INTESTINE • Duodenum and Upper Jejunum: most minerals (except sodium, chloride, and potassium) • Jejunum and Upper Ileum: carbohydrates, amino acids, water-soluble vitamins • Jejunum: lipids and fat-soluble vitamins • Terminal Ileum: Vitamin B12

29. LARGE INTESTINE • Is ~ 5 feet long and includes the cecum, colon, rectum, and anal canal

31. NUTRIENT DIGESTION in the LARGE INTESTINE • Little digestion occurs in the large intestine • The large population of bacteria digests small amounts of fiber • This bacterial activity forms: Vitamin K, Vitamin B12, Thiamin, Riboflavin, Biotin, and gases

32. NUTRIENT ABSORPTION in the LARGE INTESTINE • Little absorption occurs in the large intestine • However, it does absorb: water, sodium, potassium, chloride, and some of the Vitamin K produced by bacteria • It does not absorb Vitamin B12

33. Healthy Bacteria Probiotics are live microorganisms (in most cases, bacteria) that are similar to beneficial microorganisms found in the human gut. Probiotics are available to consumers mainly in the form of dietary supplements and foods. Look for “live and active cultures”. The good bacteria most often comes from two groups: Lactobacillus or Bifobacterium.

34. Prebioticsare not digested in the SI, and are used as food by bacteria

35. NUTRITION and GI DISORDERS CONSTIPATION • Occurs when the colon absorbs too much water, or if the colon’s muscle contractions are slow and sluggish • CAUSES: • Not enough liquids in the diet • Not enough fiber in the diet • Sedentary lifestyle • Some medications • Abuse of laxatives • TREATMENT?

36. NUTRITION and GI DISORDERS DIARRHEA • Occurs when the colon absorbs too little water • CAUSES: • Most common: infection from bacteria, viruses, or parasites • Antibiotics • Chronic diarrhea may signal a more serious medical problem (Inflammatory Bowel Disease) • TREATMENT • BRAT diet (bananas, rice, applesauce, toast) • Rehydrate and replace electrolytes

37. NUTRITION and GI DISORDERS Gastroesophageal Reflux Disease • Basically, chronic “heartburn” CAUSES: • Hiatal Hernias • Foods that relax the lower esophageal sphincter (LES) • Frequently occurs in people with asthma, irritable bowel syndrome, and developmental disabilities • Concern because of increased risk of esophageal cancer

40. TREATMENT • Avoid foods that relax the LES • Don’t lie down or exercise too soon after eating, raise the head of the bed • Wear loose fitting clothing • Medications

41. NUTRITION and GI DISORDERS DIVERTICULOSIS • Result of rising pressure in the colon, believed to be caused by low-fiber diet and constipation DIVERTICULITIS • Infected or inflamed diverticulum (fecal matter or bacteria gets trapped) • May experience abdominal pain, indigestion, fever • Diverticulum may rupture causing infection, or can form scar tissue and create an obstruction

43. Diverticulosis/itis • TREATMENT • Diverticulosis – high fiber diet • Diverticulitis – low fiber diet

44. NUTRITION and GI DISORDERS IRRITABLE BOWEL SYNDROME • Disorder that interferes with normal functions of the colon. Symptoms are abdominal pain, bloating, constipation, and diarrhea • People with IBS have more sensitive colons and react more strongly to: stress, large meals, certain foods, caffeine, or alcohol • Diagnosed by symptoms and the absence of other diseases • TREATMENT • Reduce stress • Change diet • Medications

45. NUTRITION and GI DISORDERS ULCERS CAUSES: • Helicobacter pylori infection (most common), chronic use of anti-inflammatory drugs, and disorders that cause excessive gastric acid secretion • Not caused by spicy foods or stress

47. TREATMENT • Antibiotics • Medications (acid suppressors)

48. NUTRITION and GI DISORDERS LACTOSE INTOLERANCE CAUSES: • Inability to digest lactose, caused by a shortage of lactase • Symptoms: nausea, cramps, bloating, gas, and diarrhea • TREATMENT • Don’t eat dairy products! Or eat less, and more processed types (ex. Yogurt vs. milk )