Module 3: Metabolism and Digestive System PDF

Module 3: Metabolism and Digestive System Part I: Metabolism and Overview of Digestion Part II: Organs of the Digestive System Part I: Metabolism and Overview of Digestion and the Digestive System Energy All cells need energy for growth, repair, and movement. Energy is released by breaking t...

Module 3: Metabolism and Digestive System Part I: Metabolism and Overview of Digestion Part II: Organs of the Digestive System Part I: Metabolism and Overview of Digestion and the Digestive System Energy All cells need energy for growth, repair, and movement. Energy is released by breaking the bonds in our food That energy is used to make ATP ATP can then supply energy to cells where it is needed ATP molecules are like batteries for cells ATP “charged battery” ADP “drained battery” Metabolism Metabolism describes the biochemical reactions that take place within a living organism to maintain life Catabolic reactions release energy when larger molecules are broken into smaller subunits Anabolic reactions synthesize larger molecules from smaller ones and require energy Catabolic and anabolic reactions are coupled Metabolic Rates A metabolic rate is the amount of energy (calories) spent in a certain time Metabolic rates can vary greatly between individuals. Basal Metabolic Rate (BMR): the number of calories you burn as your body performs basic (basal) life-sustaining function. Resting Metabolic Rate (RMR): the number of calories burned if you stayed in bed all day. Metabolic Rates Weight, height, age, and sex are factors in the BMR formula. The higher the BMR, the more calories you need/burn per day. Genetics and hormones also account for variations in BMR but those are too individual to be included in general formula. Note: You don’t need to memorize the formulas for BMR. There are easy online calculators.  Summary of the Major Structures and Digestion Organs of the Digestive System Before our cells can use food molecules, they must be broken down into small subunits (digestion) and then enter the bloodstream or lymph. This takes place in the digestive system (or gastrointestinal tract) The digestive system is a long muscular tube which provides space for digestion followed by selective absorption for molecules (nutrients) Functions of the Digestive System: 1. Digestion - process by which large molecules from plants and animals we ate are mechanically (e.g., chewing) and chemically (e.g., enzymes or acid) broken down to into their building blocks, or subunits 2. Absorption - process by which these basic building blocks are taken up through the cells lining the GI tract and enter blood or lymph 3. Excretion – elimination of non-absorbed waste from the body 4. Elimination of microbes that enter with food (assisted by immune system) Mechanical Digestion Biting and chewing in the mouth Contractions, mixing in the stomach Peristalsis squeezes food as it move through the GI tract Chemical Digestion Enzymes are proteins that speed up the chemical reactions Names of major digestive enzymes and their substrate Amylase - starch (carbohydrate) Lipase - lipids (fats) Peptidase, protease, pepsin – peptides (proteins) Lactase - lactose (milk sugar, a carbohydrate) Sucrase - sucrose (table sugar) Gastrointestinal Tract Major parts Mouth Esophagus Stomach Small intestine Large intestine Rectum Anus Different molecules are broken to small components that are absorbed in different parts of the digestive system For example, fats are broken down into their components in the small intestine Accessory Organs of the GI Tract For chemical breakdown of food molecules, we need acid, such as the hydrochloric acid found in the stomach and enzymes that are made and secreted to gastrointestinal tract by accessory organs such as: Salivary glands- lubrication, amylase and lipase Liver – secretes bile; purifies blood coming from small intestine Gallbladder – stores bile Pancreas – digestive enzymes; peptidase Movement of Food Through the GI tract Food moves from mouth to anus by peristalsis – waves of contractions that propel food along the GI tract The movement is regulated by presence of sphincters – muscular rings that prevent the backflow or early release of food through the GI tract Food moves through GI tract in chunks that change as secretions are added and food is partially digested Bolus – mass of food mixed with saliva that moves from the mouth through the esophagus to the stomach Chyme – watery mixture of partially digested food and secretions from liver and pancreas that moves through intestines Feces – mass of undigested fiber, tough connective tissues, bacteria, and old intestinal cells formed in the large intestine and excreted Module 3 Part 2: Organs of the Digestive System Functions of the Mouth Taste analysis Mechanical digestion Chewing Swallowing Lubrication by saliva Limited chemical digestion by saliva Salivary amylase – digestion of starch Salivary lipase – digestion of fat No absorption yet, food is not digested enough to be absorbed Esophagus A tube from pharynx (back of mouth) to stomach Epiglottis - prevents food from entering trachea (windpipe) Lower esophageal sphincter prevents backflow of stomach contents (which are acidic!) into esophagus Stomach Mechanical and chemical digestion Mucus Protects stomach from acid Hydrochloric acid (HCl) Breaks proteins Activates some digestive enzymes Enzymes Pepsin - protein digestion Intrinsic factor Involved in vitamin B-12 absorption Gastrin Stimulates mucus and HCl production Small Intestine Site of most chemical digestion and absorption High surface area due to folded villi Three segments Duodenum- mixing of food with pancreatic juices and bile Jejunum – site of nutrient and water absorption Ileum – absorbs nutrients and water not previously absorbed Molecules Absorbed in the Small Intestine Glucose Amino acids Fats Vitamins Most minerals (e.g., calcium, magnesium, iron) Water (70% to 90% of total) Alcohol (80% of total) Bile acids Pancreas Large gland associate with the digestive system Produces hormones and enzymes Proteases break proteins Trypsin - most important protease from pancreas Pancreatic amylase: breaks down starches Pancreatic lipase: breaks down fats Nucleases: break down nucleic acids Large Intestine, Rectum, Anus Absorption of water, some minerals, vitamins Feces compaction Whatever is not absorbed will be excreted Water Undigested fiber Tough connective tissues (from animal foods) Bacteria Dead intestinal cells Rectum collects and holds feces, absorbs any remaining water and electrolytes (minerals) Anus Common Diseases of the GI Tract: GERD Gastroesophageal Reflux Disease Stomach acid or bile flows into the food pipe and irritates the lining. Symptoms include burning pain in the chest that usually occurs after eating and worsens when lying down. Relief from lifestyle changes and over-the-counter medications is usually temporary. Stronger medication may be needed. Common Diseases of the GI Tract: Peptic Ulcers Stomach acid erodes the lining of the stomach, or esophagus or duodenum Pain Bleeding Perforation Most common causes Helicobacter pylori infection, NSAIDs which impair mucus formation Symptoms Stomach pain ~2 hours after eating Weight loss Lack of appetite Nausea/vomiting Common Diseases of the GI Tract: Diarrhea Increased fluidity, Treatment frequency, or amount of Prevent dehydration bowel movements Fluid Electrolytes Causes Dietary changes Infections, microorganisms Decrease fat, fiber, poorly Malabsorption (e.g., absorbed carbohydrates lactose, sugar alcohols) When to seek medical Excessive fiber attention Prolonged (>7 days for adults) Dehydration Blood in stool Common Diseases of the GI Tract: Constipation Difficult or infrequent bowel movements Causes Ignoring the urge to defecate Low fiber diet Muscle or nerve problems Lifestyle changes Dietary supplements Diet (e.g., calcium, iron) Increase fluid Increase fiber Increase physical activity Regular bowel habits Common Diseases of the GI Tract: Diverticulosis and diverticulitis Some people have weak intestinal walls – formation of balloon-like structures – diverticuli Formation of these abnormal diverticuli is called diverticulosis When food gets stuck in diverticuli they become inflamed and rupture – diverticulitis, which can be fatal Most dangerous is corn and other small not-so-easily- digestible foods like nuts Fiber helps by speeding movement and not allowing food to get stuck Antibiotics Common Diseases of the GI Tract: Celiac disease Chronic, immune response to dietary gluten Flattens villi of small intestine Results in nutrient malabsorption Sources of gluten Wheat Barley Rye Symptoms Diarrhea Cramps, bloating, flatulence Fatigue Weight loss Anemia