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

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

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

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

Organization of the GI Tract Functions: 1.Ingestion (the receipt and softening of food) 2.Transport of ingested food 3.Secretion of digestive enzymes, acid, mucus, and bile 4.Absorption of end products of digestion 5.Movement of undigested material 6.Elimination of waste material

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.

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.

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

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.

Overview of Absorption

Assisting/Accessory Organs 1.Salivary glands – Moisten food – Supply enzymes 2.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. 3.Gallbladder – Stores and excretes bile – Bile’s Enterohepatic circulation: Liver  Gallbladder  Intestine  Liver 4.Pancreas – Secretes bicarbonate, digestive enzymes – Secretes hormones (insulin and glucagon)

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”

Putting It All Together: Digestion and Absorption Stomach Enzymes: – Hydrochloric acid/gastric acid 1.kills bacteria 2.prepares protein for digestion 1.breaks down 3D structure of protein 2.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.

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.

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.

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

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

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

Circulation of Nutrients Vascular System 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. 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

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

Summary of Digestion and Absorption of Nutrients in the Human Body

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: 1.Enteric nervous system: nerves located in the GI wall. 2.Autonomic nervous system: part of CNS that controls organ function. – Responses to sight, smell, thought of food by enhancing GI movement and secretion

Signaling Systems: Command, Control, Defense

Hormonal system – Hormones: chemical messengers that travel in the bloodstream 1.Increases or decreases GI motility and secretions 2.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.

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.

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.

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

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

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

Nutrition and GI Disorders Colorectal cancer: cancer in colon or rectum – 3 rd 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.

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

Summary