Digestive System PDF

Week 12 Digestive System Digestive System Functions The digestive system converts food into simpler substances that can be absorbed into the bloodstream and used by cells 1. Ingestion: Taking in food. 2. Mechanical Digestion: Cut...

Week 12 Digestive System Digestive System Functions The digestive system converts food into simpler substances that can be absorbed into the bloodstream and used by cells 1. Ingestion: Taking in food. 2. Mechanical Digestion: Cutting, grinding, and mixing. ⦁ breaking down food into smaller ones without changing chemical composition. 3. Propulsion: Mixing and moving. 4. Chemical Digestion: Breaking food into monomers. 5. Absorption: Movement of nutrients into the bloodstream. 6. Defecation/Elimination: Excretion of indigestible waste. GI Processes 1. Ingestion: Food/liquid into the mouth. 2. Mechanical Digestion: Chewing, churning, segmenting. 3. Propulsion: Swallowing and peristalsis. 4. Chemical Digestion: Enzymes, acids, and secretions breaking down food. ⦁ involves enzymes that work to chemically break down larger food molecules into simpler chemicals (Building blocks; i.e. amino acids from proteins, fatty acids from lipids) 1. Absorption: Digested products absorbed into blood/lymph. 2. Defecation: Elimination of indigestible substances as feces. Week 12 Digestive System 1  Alimentary Canal: Tissue Layers Alimentary Canal: AKA Gastrointestinal (GI) tract. ⦁ Extends from the mouth to the anus and several accessory glands (aids in digestion, includes = salivary glands, liver, gallbladder, and pancreas) ⦁ From beginning to end GI tract include… Mouth, pharynx, esophagus, stomach, small intestines, large intestines, and anal canal. Alimentary canal is a muscular tube about 8m long: passes through the body’s thoracic & abdominoplevic cavities Week 12 Digestive System 2  Innermost to Outermost: 1. Mucosa (mucous membrane): Lines the lumen. Moist, mostly simple columnar. Contains folds. Secretes mucus, digestive enzymes, and hormones. Absorbs nutrients and protects against pathogen 2. Submucosa: Blood vessels, nerve endings, lymphoid tissue (MALT), lymphatic vessels. 3. Muscularis Externa: Smooth muscle layers: Inner circular. Week 12 Digestive System 3  Outer longitudinal. Smooth muscle responsible for segmentation and peristalsis. 4. Serosa: Contains fluid-producing cells: Visceral Peritoneum (innermost, deep). Parietal Peritoneum (outermost, superficial). Peritoneum Largest serous membrane (simple squamous epithelium and areolar connective tissue). Mesentery: Fused sections of peritoneal folds attaching abdominal organs to one another. Omenta: Greater Omentum: Fat, insulates and cushions abdominal organs ("beer belly"). Lesser Omentum: Extends between stomach and liver. Week 12 Digestive System 4  Enteric Nervous System (ENS): "Brain of the Gut" ~100 million neurons between the esophagus and anus. Motor Neurons: Control smooth muscle and secretions. Interneurons: Interconnect and transition signals. Sensory Neurons: Chemoreceptors and stretch receptors. Functions independently but regulated by the Autonomic Nervous System (ANS): Parasympathetic Fibers: Increase peristalsis and gastric juice production. Sympathetic Fibers: Decrease secretion and motility. Gastrointestinal Reflexes Aid in secretion and motility regulation. Respond to stimuli like stretch, pH changes, nutrients, and sight of food. Sensory receptors relay information to ENS, CNS, or ANS. Mouth (Oral Cavity): Site of ingestion and the beginning of digestion. Functions: Mechanical Digestion: Teeth and tongue break food into smaller pieces. Chemical Digestion: Salivary amylase begins carbohydrate digestion. Saliva moistens food and forms a bolus for swallowing. Pharynx and Esophagus: Conduct food from the mouth to the stomach via peristalsis. Esophageal Sphincters: Prevent backflow into the pharynx or regurgitation into the esophagus. Esophagus Week 12 Digestive System 5  ~10 inches long, connecting the pharynx to the stomach. Function: Transport food to the stomach via esophageal sphincters. Stages of Swallowing 1. Buccal Stage: Voluntary. Bolus forced into oropharynx. 2. Pharyngeal-Esophageal Stage: Involuntary. Bolus travels to the stomach. Nasal and respiratory passageways blocked. Stomach C-shaped organ in the LUQ (epigastric and left hypochondriac regions). Functions: Produces chyme by macerating food with gastric juice. Partial digestion via enzymes, acids, and hormones. Secretes hydrochloric acid (HCl), which activates pepsin for protein digestion. Week 12 Digestive System 6  Has protective mucus to prevent self-digestion. Hormones: Gastrin: Released due to stomach distension, pH change, or ACh. Increases gastric juice secretion and motility. Strengthens esophageal sphincter contractions and relaxes pyloric sphincter. Week 12 Digestive System 7  Small Intestine Longest portion of the alimentary canal (7–13 ft.). Subdivided into: 1. Duodenum: Receives chyme, bile, and pancreatic juice. 2. Jejunum: Absorbs nutrients 3. Ileum (ends at the ileocecal valve): Absorbs remaining nutrients and transfers undigested material to the large intestine Week 12 Digestive System 8  Specialized Structures: Circular Folds: Mucosa and submucosa folds. Villi: Mucosal projections for absorption. Microvilli: Plasma membrane extensions increasing surface area. Chemical Digestion and Absorption: Completed by pancreatic juice, bile, and intestinal juice. Nutrient and water absorption. Accessory Digestive Organs 1. Liver: largest gland in the body Produces bile for emulsifying fats. Performs metabolism, detoxification, and glycogen storage. 2. Gallbladder: Stores, concentrates, and releases bile. Releases bile into the small intestine through the bile duct 3. Pancreas: Produces pancreatic juice (enzymes for all food groups, sodium bicarbonate). Mixed gland with exocrine and endocrine functions: Exocrine: Produces pancreatic juice containing digestive enzymes and bicarbonate to neutralize stomach acid. Endocrine: Secretes insulin and glucagon to regulate blood glucose. Large Intestine Subdivided into: 1. Cecum (with appendix). Week 12 Digestive System 9  2. Colon (ascending, transverse, descending, sigmoid). 3. Rectum & Anus: Terminal end of the digestive system Functions: Water and vitamin absorption. Feces formation and expulsion. Propulsion: Haustral churning (moving chyme between pouches). Peristalsis. Mass movements (transverse colon to rectum). Metabolism 1. Carbohydrate Metabolism: Preferred fuel for ATP production. Glucose converted to ATP via: Glycolysis. Citric acid cycle. Electron transport chain. 2. Fat Metabolism: Provides twice the energy of carbs/proteins. Excess stored in adipose tissue. 3. Protein Metabolism: Used for ATP only when overabundant or carb/fat reserves are low. Regulation of Digestion 1. Neural Regulation: Parasympathetic Stimulation: Enhances digestive activity. Week 12 Digestive System 10  Sympathetic Stimulation: Reduces digestive activity. 2. Hormonal Regulation: Gastrin: Stimulates gastric juice production. Secretin: Promotes bicarbonate secretion from the pancreas. Cholecystokinin (CCK): Stimulates bile release and pancreatic enzyme secretion. Digestive Enzymes 1. Carbohydrate Digestion: Begins in the mouth with amylase. Continues in the small intestine with maltase, sucrase, and lactase. 2. Protein Digestion: Begins in the stomach with pepsin. Continues in the small intestine with enzymes like trypsin. 3. Lipid Digestion: Begins in the small intestine with bile and lipase. 4. Nucleic Acid Digestion: Enzymes like nucleases break DNA and RNA into nucleotides. Absorption and Transport Carbohydrates: Absorbed as monosaccharides into the blood. Proteins: Absorbed as amino acids into the blood. Lipids: Absorbed as fatty acids and glycerol into the lymphatic system. Feces and Defecation Composed of undigested food residues, bacteria, water, and mucus. Defecation Reflex: Week 12 Digestive System 11  Triggered by the stretching of rectal walls. Involves voluntary and involuntary muscle contractions. Notes from Digestive SUPP Mouth and Associated Structures Mucous Membrane lined Lips: Protect anterior opening Cheeks: Lateral Walls Lips and cheeks help keep food between teeth during chewing. Functions: Partial digestion of starches by salivary amylase. Begins mechanical breakdown of food. Forms a soft, flexible bolus for swallowing. Manipulates food with tongue, grounds with teeth, and mixes with saliva. Palate Hard Palate: Anterior Roof Separates oral and nasal cavities, enabling simultaneous chewing and breathing. Acts as a rigid shelf for the tongue to push food against. Formed by maxillary and palatine bones. Soft Palate: Posterior Roof Located in the posterior oral cavity; composed mainly of skeletal muscle. Manipulated during yawning, swallowing, or singing. Moves upward with the uvula during swallowing to close off the nasopharynx. Week 12 Digestive System 12  Tongue Skeletal muscle covered with mucous membrane. Functions: Moves food within the mouth for swallowing. Contains papillae, which house taste buds. Closes off nasopharynx to prevent food/drink from entering nasal cavity Attachments: Mandible, styloid processes, and hyoid bone. Lingual Frenulum: Limits posterior movement of the tongue. Site of tongue-tie. Pharynx Extends from internal nares to esophagus and larynx. Features: Skeletal muscle lined with mucous membrane. Stratified squamous epithelium with mucous-producing glands. During swallowing: Muscles of the pharynx raise and expand to receive the food bolus. Soft palate and uvula rise to close off the nasopharynx. Larynx is pulled superiorly, and the epiglottis folds over the glottis. Esophagus Propels food to the stomach via peristalsis. Peristalsis: Alternating contractions of longitudinal and circular muscles. Gravity does not assist food transport once it leaves the mouth. Week 12 Digestive System 13  Peristaltic Waves moves food through the esophagus to the stomach. Small Intestine Hormones Cells in the duodenum respond to food and partially digested material. Hormones are primarily meant to turn off stomach activity. Hormones and Hormone-like Products that Act in Digestion Hormone Source Stimulus for secretion Action Food in the stomach, particularly partially, - stimulates release of gastric Gastrin Stomach digested proteins, juice - Stimulates stomach ACh released by emptying nerve fibers. - Stimulates gastric secretion Intestinal gastrin Duodenum Food in the stomach and emptying Increase output of pancreatic Acidic chyme and juice rich in bicarbonate ions Secretin Duodenum partially digested - increase bile output by liver foods in Duodenum - inhibits gastric mobility and gastric gland secretion Cholecystokinin Duodenum Fatty chyme and Increases output of enzyme- (CCK) partially digested rich pancreatic juice - proteins in duodenum stimulates gallbladder to expel stored bile - relaxes sphincter of duodenal papilla Week 12 Digestive System 14  to allow bile and pancreatic juice to enter the duodenum - inhibits secretion of gastric Gastric inhibitory Duodenum Food in duodenum juice - stimulates insulin peptide (GIP) release Cells Secretion Effects: + pancreatic Juice; + Bile (liver); - S Cells Secretin gastric mobility + pancreatic Juice; + bile CCK cells CCK (Cholecystokinin) (gallbladder); Relax duodenal (cholecystokinin) sphincter GIP (glucose-dependent K Cells Inhibit gastric juice; + insulin insulinotropic peptide) Key Processes Digestion: Physical and chemical breakdown of food for absorption and assimilation. Chemical digestion involves enzymatic activity. Metabolism: Physical and chemical processes for energy production and substance maintenance. Cellular Respiration 1. Glycolysis: Splitting glucose into pyruvic acid in the cytoplasm. Yields 2 ATP and 2 energized coenzymes per glucose molecule. 2. Anaerobic Respiration: Pyruvate converts to lactic acid when oxygen is limited. Effective for short bursts of ATP production. Week 12 Digestive System 15  3. Krebs Cycle: Occurs in the mitochondrial matrix. Converts pyruvate to acetyl CoA and produces ATP, CO₂, and coenzymes. 4. Electron Transport Chain: Final stage of cellular respiration. Uses coenzymes to generate ATP via oxidative phosphorylation. Digestive Organ Functions Mouth: Ingests food; begins carbohydrate and lipid digestion. Moistens, cleans, and lubricates food and the oral cavity. Pharynx: Propels food to the esophagus. Lubricates food and passageways. Esophagus: Propels food to the stomach. Stomach: Mixes and churns food to form chyme. Begins protein digestion; absorbs some substances (e.g., alcohol, aspirin). Secretes intrinsic factor for vitamin B12 absorption. Small Intestine: Mixes chyme with digestive juices from the pancreas, gallbladder, and intestinal glands. Absorbs nutrients and water. Large Intestine: Absorbs water, electrolytes, and vitamins from bacterial activity. Week 12 Digestive System 16  Concentrates food residue into feces for defecation. Accessory Organs Liver: Produces bile to emulsify lipids. Gallbladder: Stores, concentrates, and releases bile. Pancreas: Produces digestive enzymes and bicarbonate-rich juice to neutralize acidic chyme. Digestive System Integration Cardiovascular: Blood supplies digestive organs with nutrients and oxygen. Endocrine: Hormones regulate gland secretion. Integumentary: Skin protects organs and synthesizes vitamin D for calcium absorption. Lymphatic: Defends against pathogens and absorbs lipids. Muscular: Supports and protects abdominal organs. Nervous: Regulates muscle contractions and secretions. Respiratory: Provides oxygen for energy production. Skeletal: Protects and supports digestive organs. Urinary: Activates vitamin D for calcium absorption. Week 12 Digestive System 17