Nutrition and Digestion BIOL 1306 SU23 PDF

Nutrition and Digestion BIOL 1306 Biology for Majors 1 Jenifer Gifford, Ph.D. [email protected] 1. Describe the 4 modes of feeding and the difference between the incomplete and complete digestive tracts 2. Order the process that food takes from the mouth to the anus while explaining the role of each...

Nutrition and Digestion BIOL 1306 Biology for Majors 1 Jenifer Gifford, Ph.D. [email protected] 1. Describe the 4 modes of feeding and the difference between the incomplete and complete digestive tracts 2. Order the process that food takes from the mouth to the anus while explaining the role of each major organ 3. Compare and contrast the digestive systems of mammals, birds, and ruminants 4. State the specific locations of biomolecule digestion and which enzymes are responsible 5. Discuss the roles of transport and osmosis during the absorption process of nutrients and water 6. Describe an example of nutritional homeostasis Animals that Ingest Other Organisms are Heterotrophs Animals consume other organisms in order to obtain 1. Chemical Energy for Synthesizing ATP 2. Carbon containing compounds for building molecules Animals that obtain the energy and nutrients they need from ingesting other organisms are called heterotrophs. 1 Adaptations Resulted in Diverse Strategies for Feeding Biologists assign animal feeding techniques to 1 of 4 strategies: 1. Suspension feeders filter small organisms or bits of organic debris from water by means of cilia, mucus-lined “nets,” or other structures 2. Deposit feeders swallow organic-rich sediments and other types of deposited material 3. Fluid feeders suck or lap up blood, nectar, or other fluids 4. Mass feeders seize and manipulate chunks of food Natural selection has matched animal mouthpart structures to their method of obtaining food: Nutritional Requirements • Energy stored in food is measured in kilocalories • Chemical energy and building blocks come from nutrients, which includes carbohydrates, proteins, and fats • Essential Nutrients cannot be synthesized and must be obtained from diet • Essential amino acids (9/20 amino acids) • Essential fatty acids (2 fatty acids) • Vitamins: Organic compounds vital for health but required only in minute amounts. Some are coenzymes • Minerals: inorganic substances used as components of enzyme cofactors or structural materials Some Nutritional Requirements Vitamin or Mineral Source Function Consequences of Deficiency 2 Structure and Function of Digestive Tracts • The digestive system handles the extraction and absorption of nutrients and elimination of solid wastes • There are two main types of digestive tracts: Structure and Function of Digestive Tracts Advantages of a Complete Digestive Tract: 1. Different chemical and physical processes can be confined to different compartments within the tract 2. Due to a one-way flow of food and wastes, material can be ingested and digested without interruption Several vital organs and glands are connected to the digestive tract as accessory structures. These contribute digestive enzymes and other products that play a key role in digestion Incomplete Digestive Tracts have one opening for both ingestion and elimination that leads directly into the gastrovascular cavity. Complete Digestive Tracts have two designated openings for ingestion and elimination Digestion is a Catabolic Process Ex. Pancreas, gall bladder, liver Digestion is a Catabolic Process Carbohydrates à Tri-/Di- saccharides à Monosaccharides Proteins à Polypeptides à Amino acids Distinct chemical changes occur as food moves through each compartment in the digestive tract: 1. In the mouth, enzymes in saliva begin chemical breakdown of carbohydrates and lipids 2. Chemical digestion of protein begins in the acidic environment of the stomach. Some lipid digestion can occur in the stomach 3. Chemical digestion of carbohydrates, proteins, and lipids is completed in the small intestine 4. The small molecules that result are absorbed in the small intestine along with water, vitamins, and ions 3 The Mouth and Esophagus • In the mouth, chewing makes food particles smaller and softer and enzymes in saliva and on the tongue breakdown starches and lipids: 1. 2. Salivary glands in the mouth secrete amylase and mucus which cleaves bonds in starch to release dextrins and disaccharides Cells in the tongue synthesize and secrete lingual lipase, which begins the digestion of lipids. • Once food is swallowed, it enters the esophagus, which connects the mouth and stomach • The food is propelled down the esophagus by a wave of muscle contractions called peristalsis • The system is a reflex—an automatic reaction to a stimulus—that is stimulated by the act of swallowing The Stomach A Modified Esophagus in Birds • In bird species, the esophagus has a prominent, widened segment called the crop where food can be stored and, in some cases, digested • The crop allows individuals to eat a large amount in a short time and then retreat to a safe location while digestion occurs. • Some birds store food in their crops and then regurgitate it into the mouths of their young. • In the enlarged crop of these species, bacteria that are capable of breaking down cellulose perform digestion. Protein Digestion • The stomach is a tough, muscular pouch bracketed on both ends by ringlike muscles called sphincters, which control the passage of material • Protein digestion begins in the stomach and is finished in the small intestine • When food enters the stomach, muscular contractions result in churning that mixes and breaks down the food mechanically while enzymes digest proteins and some lipids • The lumen of the stomach is highly acidic (pH= 1.5) due to hydrochloric acid (HCl) • Parietal cells secrete HCl when stimulated buy the hormone gastrin • Proteases break down proteins • Pepsinogen is the inactive form of pepsin and is stored in Chief cells. Upon release into the stomach, Pepsin digests protein. • This yields individual amino acids that can enter the bloodstream and be transported to cells in the body • Mucous cells secrete mucus, which lines the gastric epithelium and protects the stomach from damage 4 A Modified Stomach in Birds and Ruminants Food in the Stomach Stimulates the Pancreas • Cattle, sheep , goat, and deer are classified as Ruminants • Their chambered stomach is specialized for digesting cellulose instead of proteins • Bacteria and protists in the stomach chambers ferment cellulose to produce food for themselves; meanwhile, other byproducts of the fermentation, as well as some of the microbes themselves, are used as food by the ruminant • Birds do not have teeth and cannot chew food into small pieces. Instead, most species swallow sand and small stones that lodge in the gizzard. As this muscular sac contracts, food is pulverized by the grit. The Small Intestine: Digestion and Absorption • Peristalsis in the stomach moves small amounts of material through the sphincter at the base of the stomach and into the small intestine, A long tube folded into a compact space in the abdomen 1. The arrival of food in the stomach stimulates secretion of secretin hormone in the small intestine • This induces the flow of bicarbonate ions into the small intestine to neutralize stomach acid. 2. Cholecystokinin is released by the small intestine which stimulates pancreatic enzyme secretion The Small Intestine: Digestion and Absorption • The small intestine has an enormous surface area for absorption of nutrients and water due to epithelial tissue covered with projections called villi, which have projections called microvilli • Because each villus contains blood vessels and a lymphatic vessel called a lacteal, nutrients pass quickly from epithelial cells into the body’s transport systems • Food mixes with secretions from the pancreas, liver, and gallbladder and begins to move through the tube • As food is digested in the small intestine, nutrients are absorbed across the epithelia of the small intestine. 5 The Pancreas Secretes Digestive Enzymes • The pancreas is a soft fleshy organ nestled near the liver in the abdominal cavity • Main functions include: • Secretion of hormones such as insulin into the bloodstream • Secretion of digestive enzymes including proteases/ amylases/ lipases into the small intestine • Secretion of bicarbonate into the small intestine to neutralize stomach acids Carbohydrate Digestion and Absorption The Pancreas Secretes Digestive Enzymes • Pancreatic enzymes that can digest proteins are stored in an inactive form in the pancreas • After secretion, enzymes in the small intestine activate the previously inactive pancreatic enzymes • Enteropeptidase (in the SI) cuts a pancreatic enzyme called trypsinogen, resulting in the active enzyme trypsin • Trypsin, in turn, activates other enzymes that were synthesized by the pancreas and secreted in an inactive form Lipid Digestion Pancreatic amylases continue carbohydrate digestion: • Pancreatic lipase completes digestion of lipids, which results in release of fatty acids and monoglycerides Two general principles apply to monosaccharide and amino acid absorption: 1. It is highly selective; proteins in microvilli transport specific nutrients into epithelial cells 2. It is active transport • Fats tend to enter the small intestine in large globules that are broken up by emulsification so that pancreatic lipase can act on them • Emulsification results from the action of small molecules called bile salts that are synthesized in the liver and secreted in bile, which is stored in the gallbladder • Glucose enters intestinal cells using a glucose/sodium cotransporter. • Glucose exits intestinal cells and diffuse into nearby blood vessels using a glucose carrier. 6 Lipid Absorption • After the monoglycerides and fatty acids are released by lipase activity, they enter the small intestine epithelial cells by simple diffusion • Once inside the cells, they are processed into protein-coated globules called chylomicrons: • These move into lacteals by the process of exocytosis • The lacteals merge with larger lymph vessels that merge with veins • In this way, fats enter the bloodstream without clogging small blood vessels Absorption of Water in the Small Intestine When solutes from digested material are absorbed into the epithelium of the small intestine, water follows passively by osmosis This is an important mechanism for: 1. Absorbing water that has been ingested 2. Reclaiming liquid that was secreted into the digestive tract in saliva, mucus, and pancreatic fluid The Large Intestine Water What type of biomolecules are in this meal? Carbs? Protein? Lipids? Large amounts of water and almost all nutrients are absorbed before digested material reaches the large intestine: • In the colon, feces is formed in the large intestine by absorbing additional water and compacting remaining wastes • The feces are held in the rectum, the final part of the large intestine, until they can be eliminated Solutes What is the path a bite of this burger takes through your body? Where is each biomolecule digested? Where/how is each one absorbed? Molecule Digested Where? How? Absorbed Where 7 The Human Microbiome Nutritional Homeostasis When digestion is complete, amino acids, fatty acids, ions, sugars, vitamins, and minerals enter the bloodstream and are delivered to the cells that need them Nutritional Homeostasis: Glucose Regulation The Pancreas produces the hormones insulin and glucagon in the Islets of Langerhans These hormones are responsible for blood glucose regulation 8 Blood Sugar Rises Beyond Set Point • The hormone insulin is produced in the pancreas when blood glucose levels are high: • It binds to receptors on cells and causes them to increase their rate of glucose uptake and processing • Insulin stimulates cells in the liver and skeletal muscle to import glucose from the blood and synthesize glycogen from glucose monomers • As a result, blood glucose levels decline Blood Sugar Falls Below the Set Point • If blood glucose levels fall too low, cells in the pancreas secrete a hormone called glucagon: • In response to glucagon, cells in the liver catabolize glycogen and produce glucose via gluconeogenesis • As a result, glucose levels in the blood rise • Insulin and glucagon form a negative feedback system Diabetes Mechanisms Homeostasis is Maintained People with diabetes mellitus experience abnormally high levels of glucose in their blood because cells cannot import the glucose Type 1 diabetes mellitus is an autoimmune disease: The body’s immune system mistakenly targets cells for destruction Insulin-producing cells are destroyed Type 2 diabetes mellitus occurs when receptors for insulin no longer functioning correctly or are fewer in number: The primary risk factors for this form are obesity, high-sugar diets, lack of exercise, and genetic predisposition 9