Food I ntake and Digestion

1. Food Intake and Digestion Will Brown Lecture 3

2. Questions? • Does everyone have a lab manual? • Reminder: Lab worksheets due Thursday at 7PM • Any questions for me? • Subject material • Logistics • Testing/Grading

3. Objectives and Content • Objective: Outline the process of digestion and the major organs and tissues involved • Content • “Eat this: not that!” • Digestive system • Anatomy and physiology of digestive tract • Common digestive issues

4. Which should you eat?

5. McDonald’s: Which one? McDopnald’s Big N’ Tasty

6. Starbucks: Which one? Venti Caramel Latte Venti Caramel Cappuccino

7. Digestive System: Overview • In order to be used, food must be extensively altered for the human body to use • This process has 2 parts • Digestion – the breakdown of food; both mechanical and chemical • Absorption – The uptake of nutrients from the intestine • Takes place in the Gastrointestinal (GI) tract • A long tube that stretches from mouth to anus

8. Digestive system: Overview • Mechanical Digestion – Physical breakdown of food • Chewing • Peristalsis – muscle contractions along the GI tract that move and mix food (process called motility) • Chemical Digestion – The breakdown of food by chemicals secreted by the GI tract • Stomach acid • Pepsin

9. Digestive Tract: Overview • Involved in waste elimination • Houses commensal bacteria • Vitamin K • Biotin • Most processes under autonomic control • Nervous system • Endocrine system

11. Mouth • Responsible for primary mechanical digestion • Teeth • Tongue – to a lesser degree • Taste – allows for sensation of flavors • 5 main flavor components: salty, sweet, bitter, sour and umami; taste buds on tongue • Nose is highly involved in taste sensation • Volatile compounds reach the nasal passages • Signals rest of GI to prepare for food

12. Mouth • Produces Saliva via the salivary glands • Provides lubrication • Acts as a solvent • Produces mucus • Lubricates food and surfaces of GI tract • Produces Salivary Amylase • Enzyme that begins the breakdown of starch

13. Enzymes: A slight digression • Follow “Lock and Key” model • An enzyme only acts on one substrate • Lactase only digests lactose (milk sugar) • Enzymes are diffusion rate limited • Sensitive to pH • Stomach is acidic, small intestine is alkaline • Enzymes designed to work in acidic pH do not work so well in basic conditions

15. Esophagus • Connects the pharynx (the back of the mouth) to the stomach • The epiglottis covers the trachea when food is swallowed • Peristalsis begins at the top of esophagus

16. Esophagus • Esophageal sphincter – muscle at the end of esophagus that prevents stomach contents from entering the esophagus • There are numerous sphincters along the GI; all prevent flow of contents from going backwards • The reason for “heartburn” is stomach contents in the esophagus

17. Stomach • Large sac at the end of the esophagus • Holds ~1 quart of food • This can be different for each person; depends on genetics and diet • Once in the stomach, food mixes with gastric juice • Maintains acidic environment of stomach • Destroys biological activity of foreign enzymes • Activates stomach enzymes • Makes minerals soluble • Release of chyme into small intestine is about 1 tsp at a time

18. Anatomy of Stomach

19. Physiology of Stomach • Mucous producing cells produce mucous that coats the entire stomach and prevents self-digestion • Parietal cells produce hydrochloric acid • Chief cells produce digestive enzymes • Releases gastrin (a hormone) in order to control release of other digestive enzymes and acid • Releases intrinsic factor – required for vitamin B-12 absorption • Can absorb alcohol

20. Small Intestine • Pyloric sphincter joins stomach and small intestine • 3 parts of the SI are the duodenum, jejunum and ileum • ~ 10 ft long • Called small because of narrow diameter; 1 in • More peristalsis to mix food with digestive juices • Enzymes to breakdown carbohydrates, protein, and fat • Prepares vitamins and minerals for absorption • Gastric = stomach; digestive = small intestine

21. Small intestine • Lining folded numerous times – creates villi • Villi are fingerlike projects • Trap food as it moves to enhance absorption • Covered with absorptive cells that have a highly folded cap called microvilli • Creates a surface area 600 times greater than if it were a normal tube

23. Absorptive cells • Responsible for transporting nutrients and digestive food across the intestinal barrier and into the body • Short lived – rapidly turned over and renewed • Dead cells are sloughed off, digested and reabsorped • Have a highly folded cap, called microvilli, further increases surface area of SI

24. Absorption • Passive diffusion – Higher concentration in lumen than in body so nutrients move with a gradient • Fats, water, some minerals • No energy required • Facilitated diffusion – Compounds require carrier to assist in diffusion • Fructose • No energy required

25. Absorption • Active absorption – Nutrients in low concentration in lumen are taken up into the body, usually with carrier • Glucose, and amino acids • Requires energy input • Phagocytosis/pinocytosis – Cell membrane creates a fold that closes off to create a vessicle which can move things from lumen to dorsal side of cell • Phago=eat or devour; pino=sip or drink • In infants, Immune substances from mothers milk • Requires energy; highest energy requirements

26. Absorption • Water soluble compounds enter blood stream via capillaries • Glucose • Amino acid • Most vitamins • Some minerals • Fat and fat soluble compounds enter the lymph system and then enter the blood stream later • Once absorbed into the blood, goes directly to the liver • Hepatic portal • Detoxifies blood • If pregnant, then heads directly to uterus

27. Large Intestine • Transition from SI to LI is called the ileocecal sphincter – prevents LI contents from re-entering the SI • Very little nutrient absorption occurs in LI • Anatomically different from SI • No villi • No digestive enzymes • High number of mucous producing cells • Mucous protects LI from bacteria and helps hold feces together

28. Large Intestine • Nutrients absorption does occur • Water - ~10-30% of total • Some fatty acids • Sodium and potassium • Some vitamins • Houses numerous commensal bacteria • Most are beneficial – probiotic • Recent studies have demonstrated that there are over 2000 types of bacteria that can live in the LI • Most people have between 200-500 different species • After birth the colon is rapidly colonized; usually from the mother • Another term to know – prebiotic; substances that help probiotics grow

30. Rectum and Anus • Last portion of LI • Feces held in rectum until pushed into the anus for elimination • The anus contains 2 sphincters • Internal anal sphincter – autonomic control • External anal sphincter – voluntarily controlled

31. Accessory organs • Not part of GI tract but play important role in aiding digestion • Gall Bladder • Houses bile (which is made in the liver) • Bile release under hormone control • Released due to presence of fat in stomach • Bile acts as “soap” to emulsify fat for absorption • Components of bile can be recirculated and reused – process known as enterohepatic circulation • Bile can also house substances for excretion that are to large to exit via the kidneys

33. Accessory organs • Pancreas • Makes hormones and pancreatic juices • Hormones: insulin and glucagon; both act on blood sugar levels • Pancreatic juices: bicarbonate, water, and digestive enzymes • Bicarbonate is a basic substance that neutralizes acidity of chyme as it moves from stomach to SI • Important because not as much mucous in SI compared to stomach; low pH would cause ulceration of SI • Liver: makes bile and cleans blood after absorption

34. Digestion Review • Mouth • Esophagus - ~10 in • Stomach – Holds ~1 quart • Food held 2-4 hours • Small Intestine – 3-10 hours • Duodenum – 10” long • Jejunum – 4’ long • Ileum – 5’ long • Large intestine – up to 72 hours • 3.5 ft long • Cecum, ascending, transverse, descending, and sigmoid colon

35. From Figure 3-10 pg 97

36. Important Secretions and Products of GI Table 3-3 pg.99

37. Common Digestive Issues • Lactose intolerance – inability to digest lactose (milk sugar); More on this in carbohydrate lecture • Diverticulosis – Inflammation of intestinal tract; more on this in carbohydrate lecture

38. Common Digestive Issues: Ulcers • Erosion of stomach lining, esophagus, or duodenum • Loss of protective mucous layer • In younger people, primarily in SI; older is stomach • Millions will develop ulcers sometime in their life resulting in lots of health care $ spent • Symptoms include pain ~2 hours after eating • Causes;originally thought to be caused by high stomach acid • H. pylori infection found in 80% of ulcers • Stress • Smoking is a complicating factor • Treatments • Antibiotics for H. pylori • Proton pump inhibitors (Prilosec, Nexium, and Prevacid) block acid formation • H2 blockers (Tagamet, Zantac, and Axid) block histamine related acid secretion • Reduce smoking • Limit use of NSAIDs

39. Common Digestive Issues: Heartburn • ~50% of Americans experience heart burn occasionally • AKA: acid reflux • Recurrent form called gastroesophageal reflux disease (GERD) • Esophagus has limited mucous protection so easily eroded causing pain • Symptoms-For GERD must occur >2 times/week • Pain • Coughing • Nausea • Long term untreated GERD can lead to Barrett’s Esophagus • Treatments • OTC antacids – short term quick releif • Proton pump inhibitors (Prilosec, Nexium, and Prevacid) block acid formation • H2 blockers (Tagamet, Zantac, and Axid) block histamine related acid secretion

40. Common Digestive Issues: Constipation • Difficult or infrequent evacuation of bowels • Common causes • Ignoring “urges” for prolonged periods • LI muscle spasms • Ca and Fe supplements • Medications and antacids • Treatments • High fiber foods and plenty of water; good for mild constipation • Develop more regular bowel habits • Laxatives

41. Common Digestive Issues: Irritable Bowel Syndrome • Not to be confused with IBD (Inflammatory Bowel Disease) • ~25 million adults report IBS symptoms • Cramps and pain • Gassiness and abdominal distention • Bloating • Irregular bowel function – diarrhea, constipation or both, mucous in feces • Worth noting that 50% of IBS patients report some type of abuse – verbal or sexual are the most common • Treatments – very individualized • High fiber foods • Elimination diets which focus on dairy, caffeine and gas-forming foods • Herbal supplements • Probiotics • Low fat diet and more frequent small meals • Aside from discomfort and upset there are no other health concerns

42. Common Digestive Issues: Diarrhea • Usually lasts a few days • Symptoms • Very loose or liquid stool • Increased frequency of bowel movements • Causes • Usually infection in intestine – mostly due to bacteria or virus • Less common is consumption of foods not readily absorbed – sorbitol or very high fiber foods such as bran • Treatment • Lots of fluids during affected stage – first 24 to 48 hours • Important for those at high risk of dehydration – infants & elderly • If lasting longer than 7 days – seek medical help

43. Common Digestive Issues: Gallstones • Affects 10-20% of adults in US • Results from formation of solid crystal particles of bile that form in gallbladder • Causes • Excess weight – especially in women • Genetic background – Native Americans have increased risk • Advanced age - >60 years • Reduced gallbladder activity – reduced contraction • Altered bile composition • Diabetes • Diet – low fiber food • Rapid weight loss or prolonged fasting

44. Common Digestive Issues: Gallstones • Symptoms • Pain in upper right abdomen • Gas • Bloating • Nausea and/or vomitting • Treatment – surgical removal of gallbladder is most common • Prevention • Avoid becoming overweight – especially for women • Avoid rapid weight loss - >3lbs/week • ↓ animal protein and ↑ plant protein; ie: nuts • High fiber diet

45. Less Common Digestive Disorders • Cystic Fibrosis • Inherited disease caused by overproduction of mucous • Usually affects upper respiratory tract • Pancreas produces thick mucous that blocks ducts which causes cell death – result is ↓digestive enzymes • Celiac disease • Allergic reaction to gluten • Gluten is common in certain cereals like wheat and rye • Damages Absorptive cells reducing surface area in SI • Removing gluten from diet usually results in amelioration of disease