BPK 110_Chapter 3.pptx

Learning Objectives Differentiate between digestion, absorption and metabolism. Describe the digestive tract structures. Explain digestion, including the actions and secretions of different digestive tract structures. Outline absorption, including the different absorptive mechanisms. Outline factors...

Learning Objectives Differentiate between digestion, absorption and metabolism. Describe the digestive tract structures. Explain digestion, including the actions and secretions of different digestive tract structures. Outline absorption, including the different absorptive mechanisms. Outline factors that can affect the health of the digestive tract, including the microbiome. Explain cellular respiration, which turns food energy into cellular energy. Digestion Digestion Overview Digestion separates the nutrients in food and breaks larger molecules into smaller ones so they can be absorbed Polysaccharides → sugars Triglycerides → fatty acids Proteins → amino acids Two types of digestion: Mechanical/physical: uses physical process such as chewing to break food apart Chemical digestion: uses enzymes to alter the chemical structure of nutrients Enzymes Enzymes speed up the rate of reaction Provide a location for chemical reactions to occur Enzymes can participate in hydrolysis and condensation reactions Hydrolysis reaction: the input of water helps to break down the molecule: Condensation reactions Hormones Hormones are chemical messengers that are required for many physiological processes, including digestion They are released form one area of the body and travel through the blood to different parts of the body The Digestive System The Digestive Tract Long, tube-like structure Sphincters often separate different parts of the tube Takes ~ 2+ days for material to pass through the entire tract Food spends most time in the large intestine Layers of the Digestive Tract Wall The Mouth Teeth rip food apart Tongue pushes food towards teeth and mixes it with saliva Salivary glands secrete saliva into mouth, which contains: Salivary amylase digests amylose (starch) Lingual lipase digests lipids Mucus lubricates food Lysozyme = antibacterial substance that disinfects food When food leaves the mouth it is a bolus The Pharynx Aka throat Common passageway for food and inspired air No active digestion or absorption The epiglottis directs food from the pharynx into the esophagus instead of down the wrong tube into the trachea (windpipe) How to Dislodge an Object that Enters the Airways and Causes Choking The Esophagus No active digestion or absorption Peristalsis is a type of movement that occurs here and in other parts of the tract The Stomach Temporary reservoir for food Food remains here 4-5 hours Three layers of muscles allow stomach to churn Lower esophageal sphincter and pyloric sphincter close as stomach churns food and mixes it with gastric juice When food leaves the stomach it is in a semi-liquid form = chyme Gastric Juice Cells in the stomach crypts secrete contents of gastric juice: Mucus Lubrication, medium for chemical reactions Gastric lipase Breaks down lipids Hydrochloric acid Unravels proteins, activates pepsinogen Pepsinogen Becomes pepsin, which digests protein The Small Intestine Primary site of digestion and absorption Three sections: duodenum, jejunum, ileum Long length (~6m), large circular folds, villi, microvilli contribute to its large surface area Its total surface area is about the size of a tennis court! Villi of the Small Intestine The villus (plural = villi) is the main functional unit of the small intestine Villi are invaginations of the small intestine wall The cells on their surface have extensions called microvilli (collectively known as the brush border) which secrete enzymes Nutrient subunits are absorbed into the center of the villus where they then enter the blood or the lymph Nutrients Use Different Absorption Mechanisms to Enter the Blood / Lymph Accessory Structures of the Digestive Tract The liver, gallbladder and pancreas secrete material into the duodenum of the small intestine The Pancreas The pancreas secretes pancreatic juice into the small intestine =its exocrine function Pancreatic juice contains: Digestive enzymes Amylase, lipase, proteases Bicarbonate Neutralizes chyme The Liver, Gallbladder and Bile The liver makes bile; the gallbladder stores it. Bile is a lipid emulsifier – it breaks larger lipid globules into smaller ones and allows them to be suspended in a watery environment The Large Intestine Approx 1.5 m in length The colon is the main part of the large intestine Here, any unabsorbed material is either: Packaged for removal Acted upon by bacteria = Microbiota The Microbiome The largest population of non-human cells is found in the large intestine Microbiota = all the non-human organisms found in our body Mostly bacteria 300-500 different species Microbiome = the genetic material of the non-human organisms found in our body The microbiota have roles in: Vitamin synthesis (vitamin K, B2, B12) Energy harvesting Health/disease Appetite Digestive Tract Summary The Digestive Tract in Health and Disease Probiotics and Prebiotics Probiotics = cultures of living organisms (ex. Bacteria) Found in yogurt, kombucha Cannot treat or cure any disease, but may help in the management of certain conditions Prebiotics = carbohydrates that act as food for the microbiota Found in asparagus, garlic, banana… Support the health of the microbiome Ulcers = weakened, damaged parts of the lining of the digestive tract Ex. Canker sores occur in mouth; resolve on own Ex. Peptic Ulcers Occur in esophagus, stomach, small intestine Typically related to infection with H. pylori bacteria Gastroesophageal Reflux Disease Gastroesophageal reflux = when lower esophageal sphincter weakens; acidic stomach contents spill into esophagus Aka “heart burn” Can lead to gastroesophageal reflux disease (GERD) Can then lead to ulcers, Barrett’s esophagus Irritable Bowel Syndrome(IBS) Cause unknown Symptoms of IBS include abdominal pain, bloating, cramping, diarrhea, constipation, flatulence Treatment focuses on alleviating symptoms: Avoiding trigger foods, managing stress, drinking plenty of fluids… Diverticulitis Diverticula = weakened walls of the large intestine form outpouchings Diverticula can become inflamed = diverticulitis Diverticula can blead = diverticulosis Age, obesity, smoking, physical inactivity increase risk Diets low in fibre and high in animal fat increase risk Gallstones Hardened bile deposits that form stones in the gallbladder Can be painful, especially when fat is consumed and gallbladder contracts to release bile Diets high in simple sugars, saturated fat and energy increase risk Gallbladder may need to be removed Digestive Tract Cancers Cancer = uncontrolled multiplication of our cells Can occur anywhere in digestive tract; most common in colon Colorectal cancer has both genetic and lifestyle risk factors Physical inactivity, obesity increase risk Diets high in red and processed meats increase risk, those high in vegetables, fruits and fibre decrease risk Constipation = bowel movements that are difficult to pass or less frequent Stools tend to be dry, hard and can be painful to excrete Increases risk for hemorrhoids Risk factors include age, female sex, genetics, physical inactivity, the use of certain medications and IBS Diet low in fruits, vegetables and water also increases risk Diarrhea Occurs when matter passes too quickly through the large intestine Stools are loose and have a liquid-like consistency Typically due to bacterial and viral infections. Can be caused by food poisoning Delivering Absorbed Nutrients Delivery of Nutrients to the Liver Nutrients that enter the blood capillaries at the villi will then enter veins that lead to the liver = All nutrients except large lipids and fat-soluble vitamins At the liver, material is stored, used, detoxified or sent off to the rest of the system The material that enters the cardiovascular system can then be transported to where it is needed Dietary Toxins and Detoxification Recall that toxins are substances that can be found in food that can cause damage to the body. Ex. Persistent organic pollutants (POPs) Levels of toxins in a well-balanced diet are typically below the threshold for harm Also, the liver, kidneys and lungs remove toxins form the body Lack of evidence to support the use of commercial detox diets for detoxification/ improved health Energy Metabolism Metabolism Metabolism = sum of chemical reactions that occur in our bodies Anabolism smaller molecules come together to form larger ones requires an input of energy Catabolism Larger molecules are broken down into smaller ones Leads to a net release of energy The catabolism of the energy-yielding nutrients (carbs, fats, proteins) leads to the release of energy This energy is captured within ATP: the energy currency of the body Capturing and Releasing Energy via ATP Cellular Respiration Cellular respiration = the catabolism of the energyyielding nutrients leading to the production of ATP Primarily occurs in the mitochondria (“powerhouse”) of the cell It occurs in several steps, collectively known as a metabolic pathway The cellular respiration of glucose is summarized by the equation: Once this is understood, the metabolism of triglycerides Summary of Glucose Metabolism Glucose Metabolism Step 1: Glycolysis Glycolysis = breakdown of glucose Anaerobic; produces minimal ATP Glucose Metabolism Step 2: The Breakdown of Pyruvate Pyruvate catabolism depends on whether oxygen is present (aerobic conditions) or not (anaerobic conditions) Aerobic conditions – acetyl CoA is formed Anerobic conditions- pyruvate is formed Some ATP is formed Cannot be sustained Reversible back to pyruvate when oxygen is again available Glucose Metabolism Step 3: Citric Acid Cycle Citric Acid Cycle= complex set of reactions that begins when acetyl CoA combines with oxaloacetate Produces CO2 , water, and the capture of energy in GTP (≈ATP) Most notably, electron transporters (NADH + H+, FADH2) capture electrons and move to the mitochondrial membrane to begin the electron transport chain Glucose Metabolism Step 4: The Electron Transport Chain Electrons are exchanged between the electron transporters (NADH + H+, FADH2) and membrane-bound proteins This leads to a build up of protons (H+) on one side of the membrane These protons will move through a protein pump that is associated with an enzyme called ATP synthase. This process leads to the production of more than 30 molecules of ATP. Lipid Metabolism Triglycerides have three fatty acids attached to a glycerol backbone Majority of energy is derived from fatty acids Beta-oxidation splits the fatty acid two carbon atoms at a time Each two-carbon molecule of a fatty acid can be used to form acetyl CoA Proceeds through remaining stages of cellular respiration Ketogenesis Can occur when diet is high in fat and very low in carbohydrates The citric acid cycle requires carbohydrates On a very low carb diet, fatty acids cannot enter citric acid cycle, instead form ketones Amino Acid Metabolism First, the nitrogen group of the amino acid must be removed (deaminated) There are 21 amino acids – each with a unique side chain Therefore there are 21 possibilities for what remains Deaminated amino acids will either be used to form: Pyruvate Acetyl CoA Citric Acid Cycle Intermediates Non-Energy Uses of Sugars, Lipids and Amino Acids When we consume more energy than we need, most of the excess is stored as lipid in our fat tissue