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Digestion Notes (Biology 12) I. Introduction/Overview • Digestion: Breakdown of food into small, soluble molecules • Occurs physically and chemically • Absorption: The process of taking specific compounds into the body • Elimination: Expulsion of materials not absorbed into the body • Excretion: Removal of waste from metabolic processes II. Location of Parts and Function A. Teeth • Type of teeth depends on diet: • Carnivores: Sharp teeth for grasping prey and severing meat • Herbivores: Flat teeth for crushing plant fibers • Omnivores: A combination of tooth types for eating both meat and plants • Structure: • Enamel: Hard outer layer • Dentin: Bony layer under enamel • Pulp: Living part of the tooth (contains nerves and blood vessels) • Teeth are embedded in sockets in the jaw B. Tongue • Functions: • Taste: Detects salt, sour, sweet, and bitter flavors • Positioning food for chewing C. Salivary Glands • Three pairs: • Parotid (side of face; swells with mumps) • Sublingual (under tongue) • Submandibular (lower jaw) • Produce saliva, which contains enzymes for digestion D. Palates • Located at the top of the mouth • Hard palate: Front, separates the mouth from the nasal cavity • Soft palate: Back, ends in the uvula E. Pharynx • Area between mouth and esophagus • Used for both breathing and eating • Epiglottis: Closes over the glottis when swallowing to prevent choking F. Esophagus • Muscular tube that pushes food into the stomach using peristalsis • Composed of five tissue layers: 1. Mucosa (epithelial lining) 2. Submucosa (connective tissue) 3. Muscularis (two muscle layers: circular and longitudinal) 4. Serosa (outer epithelial layer; secretes fluid for lubrication) G. Cardiac Sphincter • Muscle at the junction of the esophagus and stomach • Opens to allow food into the stomach H. Stomach • J-shaped organ, located left of the body’s center • Capacity: About 1 liter • Inner lining contains gastric glands: • Parietal cells → Produce HCl • Chief cells → Produce pepsinogen, activated by HCl into pepsin • Epithelial cells → Produce mucus (protects stomach lining) • Functions: • Storage of food (empties in 2-6 hours) • Digestion using pepsin and salivary amylase • Absorption of water, ethanol • Regulation of pepsin production by the hormone gastrin I. Pyloric Sphincter • Muscle at the junction of the stomach and small intestine • Opens to allow chyme (partially digested food) into the small intestine J. Small Intestine • Length: ~ 3 meters (10 feet) • Highly convoluted to increase surface area for absorption • Interior folds covered with villi (tiny projections that increase surface area) • Divided into three parts: 1. Duodenum (first 25 cm): Produces lactase, peptidase, maltase, nuclease 2. Jejunum 3. Ileum • Functions: • Completes digestion • Absorbs nutrients into the bloodstream K. Liver • Largest organ in the body • Monitors blood composition via the hepatic portal vein L. Pancreas • Produces pancreatic juice (digestive enzymes and sodium bicarbonate to neutralize stomach acid) • Produces insulin (regulates blood glucose) M. Ileo-Caecal Opening • Joins the small intestine to the large intestine N. Caecum • Blind pouch at the end of the small intestine • No function in humans (vestigial), but in herbivores, it helps digest cellulose O. Large Intestine • Parts: 1. Ascending colon 2. Transverse colon 3. Descending colon 4. Rectum (stores feces) 5. Anus (controls feces release) • Functions: • Reabsorbs water (~95% of 10L daily intake) • Forms feces • Produces vitamins B and K using E. coli bacteria III. Digestive Enzymes Enzyme Source pH Digested Food Product Salivary Amylase Salivary Glands 7 Starch Maltose Pepsin Stomach 2 Protein Peptides Pancreatic Amylase Pancreas Basic Starch Maltose Trypsin Pancreas Basic Protein Peptides Lipase Pancreas Basic Fat Glycerol & Fatty Acids Peptidases Small Intestine Basic Peptides Amino Acids Maltase Small Intestine Basic Maltose Glucose Nuclease Pancreas Basic DNA/RNA Nucleotides IV. Swallowing and Peristalsis • Swallowing: Food forms a bolus (food ball) and is moved down the esophagus • Peristalsis: Rhythmic contractions of smooth muscle that push food through the digestive tract V. The 7 Functions of the Liver 1. Detoxifies harmful substances (e.g., alcohol) 2. Stores glucose as glycogen 3. Destroys old red blood cells (recycling heme into bile) 4. Produces urea from amino acid breakdown 5. Makes blood proteins 6. Stores iron and vitamins A, D, E, K 7. Converts amino acids to glucose if needed (gluconeogenesis) VI. Digestive Juices & Hormones Gastric Juice (Stomach) • Contains HCl, pepsinogen (activated into pepsin), and mucus • Helps digest proteins into peptides Pancreatic Juice • Contains sodium bicarbonate (neutralizes acid) • Enzymes: Pancreatic amylase, trypsin, lipase, nuclease Bile (Liver & Gallbladder) • Breaks down fats into small droplets for lipase to act on VII. Control of Digestive Gland Secretions • Nervous Reflex: Presence of food triggers digestion • Conditioned Reflex: External stimuli (e.g
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Pancreatic Juice
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Chapter 9 – Skeletal Muscles 1. Connective Tissue Surrounding a Skeletal Muscle: • Epimysium: Surrounds the entire muscle. • Perimysium: Surrounds bundles of muscle fibers (fascicles). • Endomysium: Surrounds individual muscle fibers. 2. Histology and Function of Sarcomeres: • Histology: Sarcomeres are the structural and functional units of skeletal muscles, composed of repeating units between two Z-lines. • Function: They enable muscle contraction through the sliding filament mechanism. 3. Main Components: • Thin Filaments: Actin, tropomyosin, and troponin. • Thick Filaments: Myosin. 4. Function of Transverse Tubules and Sarcoplasmic Reticulum: • Transverse Tubules (T-tubules): Transmit action potentials deep into the muscle fiber. • Sarcoplasmic Reticulum: Stores and releases calcium ions for muscle contraction. 5. Motor Unit: A motor neuron and all the muscle fibers it innervates. 6. Neuromuscular Junction: The synapse where a motor neuron meets a muscle fiber, allowing for signal transmission. 7. Synapse: A junction between two neurons or a neuron and a muscle cell where communication occurs. 8. Actions of Acetylcholine (ACh): • Initiates muscle contraction by binding to receptors on the sarcolemma. • Degraded by: Acetylcholinesterase. 9. Neurotransmitter Released at Motor Axon Terminals: Acetylcholine. 10. Steps in Excitation-Contraction Coupling: • Action potential travels along sarcolemma. • Calcium is released from the sarcoplasmic reticulum. • Calcium binds to troponin, causing tropomyosin to move, exposing binding sites on actin. • Myosin heads form cross-bridges and initiate contraction. 11. Order of Muscle Fiber Contraction: • Action potential → Calcium release → Cross-bridge formation → Power stroke → ATP binding → Cross-bridge detachment. 12. Mechanism of Muscle Contraction: • Sliding filament theory: Actin and myosin filaments slide past each other. 13. Interaction of Actin, Myosin, and Calcium: • Calcium binds to troponin, shifting tropomyosin to expose myosin-binding sites on actin, enabling cross-bridge cycling. 14. Cross-Bridges: Myosin heads that bind to actin during contraction. 15. Contraction Types: • Isotonic: Muscle length changes. • Eccentric: Muscle lengthens under tension. • Isometric: Muscle tension without length change. • Concentric: Muscle shortens under tension. 16. Force of Muscle Contraction: • Controlled by motor unit recruitment. • Partial Tetany: Incomplete relaxation. • Fused Tetany: Sustained contraction without relaxation. 17. Bones and Muscles as Levers: • Fulcrum: Pivot point of the lever. 18. Synergist and Antagonist: • Synergist: Assists the primary mover. • Antagonist: Opposes the primary mover. 19. Muscle Atrophy: Wasting of muscle due to disuse or disease. 20. Myasthenia Gravis: Autoimmune disorder causing muscle weakness by targeting ACh receptors. 21. Linea Alba: A fibrous structure running down the midline of the abdomen. 22. Origin, Insertion, and Actions of Specific Muscles: (Let me know which specific ones you’d like to focus on.) Chapter 17 – Digestive System 1. Alimentary Canal: A continuous muscular tube extending from the mouth to the anus. 2. Functions of the Digestive System: • Ingestion, digestion, absorption, and elimination. 3. Breakdown and Absorption: • Carbohydrates: Begin in the mouth (amylase). • Proteins: Start in the stomach (pepsin). • Fats: Start in the small intestine (lipase, bile). 4. Layers of Alimentary Canal Walls: • Mucosa, submucosa, muscularis, serosa. 5. Accessory Organs: • Liver, pancreas, gallbladder. 6. Sympathetic vs. Parasympathetic Effects: • Sympathetic: Decreases digestion. • Parasympathetic: Enhances digestion. 7. Hormones: • Gastrin: Stimulates gastric juice secretion. • Cholecystokinin (CCK): Stimulates bile and pancreatic juice. • Secretin: Stimulates bicarbonate secretion. 8. Peristalsis vs. Segmentation: • Peristalsis: Wave-like contractions. • Segmentation: Mixing movements. 9. Epiglottis Function: Prevents food from entering the trachea. 10. Heartburn: Caused by stomach acid reflux into the esophagus. 11. Stomach Parts: Fundus, body, pylorus. 12. Secretions: • Parietal Cells: Hydrochloric acid, intrinsic factor. • Chief Cells: Pepsinogen. 13. Digestive Enzymes and Substances: • Amylase: Breaks down starch. • Pepsin: Digests proteins. • Trypsin: Protein digestion. • Lipase: Fat digestion. • Bile Salts: Emulsify fats. 14. Liver, Gallbladder, Pancreas Functions: • Liver: Produces bile. • Gallbladder: Stores bile. • Pancreas: Produces enzymes and bicarbonate. 15. Anatomy of Bile Ducts: • Common hepatic, cystic, and pancreatic ducts form the common bile duct. 16. Functions of Large Intestine: • Absorption of water, vitamin production, and feces formation. 17. Defecation Reflex: Triggered by rectal wall distension. Chapter 18 – Nutrition 1. Excess Glucose Storage: As glycogen in the liver and muscles. 2. Tissue Requiring Glucose: Nervous tissue (brain). 3. Triglyceride Components: Glycerol and three fatty acids. 4. Essential Amino Acids: Cannot be synthesized by the body
Updated 119d ago
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Digestive System Notes Alimentary Canal (Gastrointestinal Tract) The continuous tube through which food passes, allowing digestion and absorption of nutrients. Organs Included: 1. Mouth: • Entry point for food. • Mechanical digestion via chewing (teeth). • Chemical digestion begins with saliva containing amylase. 2. Pharynx: • Passageway for food, fluids, and air. 3. Esophagus: • Propels food to the stomach using peristalsis. 4. Stomach: • Function: Temporary storage tank for food. • Mixes food with gastric juices for breakdown into chyme. • Secretes pepsin (breaks down proteins). 5. Small Intestine: • Divisions: • Duodenum. • Jejunum. • Ileum. • Primary site of nutrient absorption. • Receives bile (from liver) and pancreatic juices (from pancreas) to aid digestion. 6. Large Intestine: • Divisions: • Cecum, appendix, colon (ascending, transverse, descending, sigmoid), rectum, anal canal. • Functions: • Absorbs water. • Houses bacterial flora for vitamin synthesis. • Forms and eliminates feces. 7. Rectum and Anal Canal: • Stores feces for elimination. Accessory Digestive Organs These organs assist the alimentary canal by producing or storing substances necessary for digestion. Organs Included: 1. Teeth: • Primary Teeth: 20 deciduous teeth erupt between 6 and 24 months. • Permanent Teeth: 32 permanent teeth appear between 6 and 12 years. • Classifications: • Incisors: For cutting and nipping. • Canines: Fang-like for tearing and piercing. • Premolars (Bicuspids) and Molars: Broad crowns for grinding and crushing. 2. Tongue: • Mostly skeletal muscle. • Functions: • Contains taste buds to analyze nutrient content of food. • Mixes food with saliva to form a bolus. • Aids in swallowing. 3. Salivary Glands: • Function: Produce and secrete saliva (water-based liquid containing amylase) for chemical digestion. • Types: • Parotid glands. • Submandibular glands. • Sublingual glands. • Fun Fact: Mumps infect the parotid glands. 4. Liver: • Secretion: Produces bile, a greenish liquid (pH 7.6–8.6) essential for fat digestion. • Functions of Hepatocytes: • Produce bile. • Process nutrients from blood. • Store fat-soluble vitamins. • Detoxify harmful substances. 5. Gallbladder: • Thin-walled muscular sac on the liver’s ventral surface. • Functions: • Stores and concentrates bile. • Releases bile into the duodenum to emulsify fats. • Disorders: • Gallstones causing blockages and pain. • Extreme cases can result in gallbladder rupture. 6. Pancreas: • Exocrine Function: • Produces pancreatic juice containing enzymes for digesting carbohydrates, proteins, and lipids. • Endocrine Function: • Secretes insulin to regulate blood glucose levels. • Disorders: Malfunction can cause diabetes. Important Notes About Digestive System Processes 1. Ingestion: Intake of food through the mouth. 2. Propulsion: • Swallowing. • Peristalsis (waves of muscle contractions moving food through the tract). 3. Mechanical Digestion: • Chewing (mouth). • Churning (stomach). • Segmentation (small intestine). 4. Chemical Digestion: • Breakdown of food molecules by enzymes. 5. Absorption: • Movement of nutrients into blood or lymph via small intestine. 6. Defecation: • Elimination of indigestible substances and waste products as feces.
Updated 140d ago
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Pancreatic juice
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