The Human Body: From Food to Fuel

1. The Human Body: From Food to Fuel BIOL 103, Chapter 4

2. Today’s Topics • Taste and Smell • GI Tract • Digestion and Absorption • Assisting Organs • Circulation of Nutrients • Signaling Systems: Command, Control, and Defense • The Hormonal System • The Immune System • Influences on Digestion and Absorption • Psychological, Chemical, Bacterial Influences • Nutrition and GI Disorders

3. Taste and Smell: The Beginningsof our Food Experience • Sight, smell, thought, taste, and sound • Can trigger a set of responses that prepare the digestive tract to receive food

4. The Gastrointestinal (GI) Tract • Organization • Parts (mouth  anus) • Mouth, esophagus, stomach, small intestine, large intestine, rectum • Accessory organs • Salivary glands, liver, gallbladder, and pancreas

5. Organization of the GI Tract • Functions: • Ingestion (the receipt and softening of food) • Transport of ingested food • Secretion of digestive enzymes, acid, mucus, and bile • Absorption of end products of digestion • Movement of undigested material • Elimination of waste material

6. Organization of the GI Tract • Structural organization of the GI tract • Mucosa (innermost layer) • Glands and absorptive cells • Circular muscle and longitudinal muscle • Mix and move the food • Sphincter: valve that controls the movement of food material so that it travels through the GI tract in only one direction.

7. Overview of Digestion • Mouth • Chewing  break food into smaller pieces • Saliva  lubricates the food  bolus • Down the GI tract: • Physical movement • Peristalsis: waves of muscular contraction that helps push food down the GI tract • Segmentation: a periodic muscle contractions in the small intestine that move the content forward and backward.

8. Overview of Digestion

9. Overview of Digestion • Chemical breakdown: • Bolus  Chyme • Enzymes: are proteins that catalyze (speed up) reactions but are not altered in the process. • Examples: amylase, lipase, etc. • Other secretions: • Stomach Acid • Base • Bile • Mucus

10. Overview of Absorption • 3 Main processes allow nutrients to be absorbed from GI tract  blood/circulation • Passive Diffusion: movement of molecules through cell membrane from high to low concentration gradient without energy use • Facilitated Diffusion: movement of molecules through cell membrane from high to low concentration gradient with a help of a transport protein • Active Transport: movement of molecules through cell membrane requiring both energy (ATP) and protein.

11. Overview of Absorption

12. Assisting/Accessory Organs • Salivary glands • Moisten food • Supply enzymes • Liver • Produce bile (fat emulsifier) • “Detox center:” filters toxins in blood  kidney • “Chemical factory”: >500 chemicals • Produce blood proteins, cholesterol, sugar • “Dynamic Warehouse”: stores hormones, cholesterol, minerals, sugar, etc. • Gallbladder • Stores and excretes bile • Bile’s Enterohepatic circulation: • Liver  Gallbladder  Intestine  Liver • Pancreas • Secretes bicarbonate, digestive enzymes • Secretes hormones (insulin and glucagon)

13. Putting It All Together: Digestion and Absorption • Mouth • Enzymes • Salivary amylase • Lingual lipase • Saliva • Moistens food for swallowing  bolus • Esophagus • Transports food to stomach • Esophageal sphincter (“cardiac sphincter”) • “Heartburn”

14. Putting It All Together:Digestion and Absorption • Stomach Enzymes: • Hydrochloric acid/gastric acid • kills bacteria • prepares protein for digestion • breaks down 3D structure of protein • Pepsinogen (inactive)  Pepsin (active) • Pepsin: breaks down protein into smaller pieces • Gastric lipase: some fat digestion • Gastrin (hormone) stimulates gastric secretion and movement • Intrinsic factor is needed for vitamin B12 absorption.

15. Putting It All Together:Digestion and Absorption • Small intestine (~10ft) • Pyloric Sphincter • Sections of small intestine: • Duodenum • Jejunum • Ileum • Nutrient digestion • Bicarbonate neutralizes stomach acid • Pancreatic and intestinal enzymes to digest carbohydrates, lipids, and proteins.

16. Putting It All Together:Digestion and Absorption • Small intestine • Completes absorption: • Folds, villi, microvilli expand absorptive surface • 600x fold increase/tennis court! • Most nutrients absorbed here • Fat-soluble nutrients  lymphatic system (lymphatic vessel in the intestinal villus) • Water-soluble nutrients bloodstream.

17. Putting It All Together:Digestion and Absorption • Large Intestine • Ileocecal valve • Sections • Cecum, colon, rectum, and anal canal • Digestion • Peristaltic movement is slow, taking 18-24 hours for material to travel • Some bacterial activity (e.g. fiber digestion)

18. Beans, Beans, Beans! • Beans are made up of oligosaccharides (e.g. raffinose and stachyose), a component of fiber. • They are ignored until they are met by 700+ species of bacteria in your large intestine. • Bacteria digests these sugars  gases accumulate  flatulence

19. Putting It All Together:Digestion and Absorption • Large Intestine: • Absorption • Water • Na, K, Cl • Vitamin K (produced by bacteria) • Elimination at anal sphincter • Feces: 60% solid (bacteria, dietary fiber, digestive secretions), 40% water

20. Circulation of Nutrients Vascular System Lymphatic system Vessels that drain lymph (clear fluid formed in the spaces between cells) Fat soluble-vitamins are absorbed into lymph vessels in the intestine. Bypasses liver and delivers nutrients to veins in the neck  enter blood • Veins and arteries • Water soluble nutrients are absorbed into the capillaries of the intestines. • Blood carries nutrients through portal vein to the liver before dispensing them through the body.

21. Circulation of Nutrients

22. Circulation of Nutrients • Excretion and Elimination • Lungs • Excrete water and carbon dioxide (metabolic wastes) • Kidneys filter blood • Excrete digestive wastes • Urine: urea + salts + water • Maintain water and ion balance

23. Summary of Digestion and Absorption of Nutrients in the Human Body

24. Signaling Systems:Command, Control, Defense • Nervous system • Nerves carry info back and forth between tissues and the brain using chemical signals known as neurotransmitters. • The Central Nervous System (CNS) regulates GI activity in 2 ways: • Enteric nervous system: nerves located in the GI wall. • Autonomicnervous system: part of CNS that controls organ function. • Responses to sight, smell, thought of food by enhancing GI movement and secretion

25. Signaling Systems:Command, Control, Defense

26. Signaling Systems:Command, Control, Defense • Hormonal system • Hormones: chemical messengers that travel in the bloodstream • Increases or decreases GI motility and secretions • Influence your appetite by sending messages to your CNS. • Thus, your CNS and hormones work together to coordinate movement and secretions of the GI tract.

27. Signaling Systems:Command, Control, Defense • Immune System • Purpose: protects us from foreign invaders • Role of GI tract • Immune Response • Macrophages: “big eaters” engulf and kill pathogens and old-cells • Natural killer cells: attack virus-infected cells or cancerous cells • Location of lymphoid tissues • Lymphocytes: white blood cells present in blood and lymph • Some types produce antibodies – protein molecules that tag, neutralize, and help destroy bacteria/viruses or toxins.

28. Influences on Digestion and Absorption • Psychological influences • Positive: Taste, smell, presentation of food • Negative: Stress, fear, depression • Example: Stress  activate autonomic NS  reduced gastric secretion, reduced blood flow to stomach, inhibition of peristalsis  upset stomach • Chemical influences • Cooking  protein changes + produce chemicals that may influence digestion  easier food digestion/absorption processes • Bacterial influences • HCl acid kills most bacteria • If lives  food borne illnesses, gastritis, ulcer, etc.

29. Nutrition and GI Disorders • Constipation (< 3x/week) • Hard, dry, infrequent stools • Reduced by high fiber, fluid intake, and exercise • Diarrhea (> 3x/day) • Loose, watery, frequent stools • Symptom of diseases/infections  peristalsis • Can cause dehydration • Broth, tea, toast, and other low-fiber foods can help reduce diarrhea

30. Nutrition and GI Disorders • Diverticulosis • Pouches along colon develop as people age • 10-25% people  pouches become infected • High-fiber diet reduces formation: • Low-fiber diet  harder stools  more pressure on colon  weak spots bulge outwards and form pockets • Heartburn and GERD • Chronic heartburn  GERD • Reduced by smaller meals, less fat • Smoking weakens the esophageal sphincter • Being overweight often worsens symptoms

31. Nutrition and GI Disorders • Irritable Bowel Movement (IBS) • Causes abdominal pain, diarrhea, or constipation and cramps • Stress and certain foods aggravate the symptoms • Examples: milk, beans, chocolate, alcohol • Associated with reproductive hormones • Can usually be controlled by diet and lifestyle modifications • Stress management

32. Nutrition and GI Disorders • Colorectal cancer: cancer in colon or rectum • 3rd leading cause of cancer-related deaths in the US • Eating a lot of red meat and low fiber food can increase risks • Fiber-rich diet may reduce risk: • Hypothesis: more fiber  goes down the GI tract faster, dilution of carcinogens in a bulkier stool, etc… • BUT, human/animal studies do not support those theories.

33. Nutrition and GI Disorders • Ulcers • Pain in the upper abdomen • Sore is in duodenum: duodenal ulcer • Sore is in stomach: gastric ulcer • Can cause nausea, vomiting, loss of appetite, and weight loss • Cause: Bacteria (H. pylori) and over-usage of NSAIDS (aspirin, ibuprofen) • Functional dyspepsia • Chronic pain in the upper abdomen with no obvious physical cause • Treat with medicine and stress reduction

34. Summary