Digestive System Honors Anatomy Physiology Unit 6 A

Digestive System Honors Anatomy & Physiology

Unit 6 A Learning Objectives 6. 1 Name & identify the organs of the alimentary canal and accessory organs of digestive system, including wall of alimentary canal and the peritoneum 6. 2 Identify overall function of digestive system and describe how each organ assists this function 6. 3 Describe the 6 digestive processes required for the digestive system to function properly 6. 4 Describe the composition and function of digestive secretions: saliva, pancreatic juices, bile, pepsin, HCl 6. 5 Explain the anatomy of villi and their role in absorption of nutrients 6. 6 Describe the mechanisms of swallowing, vomiting and defecation 6. 7 Describe what happens to foodstuffs as they move along the GI tract 6. 8 Differentiate between how proteins, fats and carbohydrates are digested -where and how 6. 9 Identify some common ailments of the digestive system

Function & Organization Function • The breakdown of food into small enough particles to be digested and absorbed Organization • Alimentary Canal aka GI tract • Accessory Organs

Digestive Processes • Ingestion: bringing food into the system • Mechanical Digestion: the mechanical breakdown of food (chewing, mixing, churning) • Propulsion: movement of food through system

Digestive Processes • Chemical Digestion: breakdown of large food molecules by enzymes • Absorption: transport of digested food materials to the blood or lymph • Defecation: elimination of indigestible material from the body

Peritoneum • The largest serous membrane of the body, lining all organs of the abdominal cavity and the cavity wall – Parietal peritoneum: lines walls – Visceral peritoneum: lines organs – Peritoneal cavity: potential space between membranes; produces serous fluid

Extensions of the Peritoneum • Falciform ligament: connects liver to anterior abdominal wall and diaphragm • Lesser omentum: attaches to medial stomach, attaching it to anterior wall

Extensions of the Peritoneum • Greater Omentum: extends off stomach; contains lymph nodes and holds fatty deposits • Mesentary: suspends coils of small intestine and attaches it to posterior abdominal wall

http: //www. nvcc. edu/home/lmiller/atlas/Digestive%20 System/mesentary 2. gif

Wall Structure of Alimentary Canal • 4 layers – Mucosa/mucus membrane – Submucosa – Muscularis – Serosa http: //www. lab. anhb. uwa. edu. au/mb 140/Core. Pages/Oral/Images/gitplan. gif

Wall Structure of Alimentary Canal 1. Mucosa: lines lumen of alimentary canal – Protects us from microorganisms – Absorbs digested food materials – Secretes mucous & digestive enzymes

Wall Structure of Alimentary Canal 2. Submucosa -Rich in blood vessels, lymphatic vessels and nerve endings -Provides nourishment for tissues and carries away absorbed materials

Wall Structure of Alimentary Canal 3. Muscularis: smooth muscular layer • Induces a propelling action called peristalsis • Has 2 parts: – – Inner layer runs longitudinally Outer layer (constrictor layer) runs circularly

Wall Structure of Alimentary Canal 4. Serosa - Visceral peritoneum -Outermost covering of alimentary canal

Alimentary Canal: Mouth o Function: receives food, starts digestion and prepares it for swallowing - Teeth: performs mastication (chewing) - Uvula: fingerlike extension from archway; works with soft palate to close opening to nasal cavity upon swallowing http: //meltingmama. typepad. com/photos/uncategorized/20 08/01/03/mouth_uvula. gif

Swallowing • Aka deglutition: occurs in 2 phases • Requires coordination from tongue, soft palate, pharynx and esophagus • 1. Buccal phase: food mixed with saliva to form bolus---forced into pharynx by tongue • 2. Pharyngeal-esophageal phase: involuntary, controlled by vagus nerve – Tongue blocks mouth, uvula of soft palate blocks nasal passage, larynx closed by epiglottis so food forced down esophagus

Mouth continued o Salivary Glands: accessory organs around mouth; secretes saliva - saliva: 99. 5% water, 0. 5% solutes - Lysozome: destroys bacteria - Salivary amylase: begins chemical digestion of carbohydrates - Mucus: lubricates and binds food particles to form a bolus

Alimentary Canal: Pharynx o Function: transports food from oral cavity to esophagus -uvula and epiglottis assist pharynx in transporting bolus to the esophagus ONLY

Alimentary Canal: Esophagus Function: 10 inch muscular tube that transports bolus to stomach from pharynx - Peristalsis: alternate waves of muscle contraction & relaxation; moves bolus along alimentary canal

Esophagus continued - Mucosa: made of stratified squamous epithelium to resist abrasion - Cardio-esophageal sphincter: found at distal end; acts as a valve to prevent stomach contents from entering esophagus Sphincter: a circular muscle; acts as valve between organs

Vomiting • Aka emesis • Controlled by emetic center in brain (medulla) • Reverse peristalsis occurring in stomach or small intestine along with contraction of abdominal wall and diaphragm (increases internal pressure) • Causes: irritation of stomach (toxin); disturbance of equilibrium in inner ear

Alimentary Canal: Stomach o Function: c-shaped organ acting as a temporary storage site for food; performs mechanical and chemical digestion -Rugae: deep folds formed by inner lining of stomach when empty -Full stomach: can hold up to 1 gallon of food

Stomach continued o Divided into 4 regions: 1. cardia: receives bolus from -esophagus 2. fundus: expanded region, temporarily holding food

Stomach continued 3. body: main part of stomach - greater curvature: convex lateral margin -lesser curvature: concave medial margin 4. pyloris: inferior region with thickened walls -pyloric sphincter: valve that controls movement of food from stomach into small intestine

Stomach Wall • 4 basic layers: mucosa, submucosa, muscularis and serosa • Mucosa & muscularis is functionally and structurally different – Mucosa: gastric pits work to produce and secrete gastric juices • HCL, digestive enzymes and mucus

Stomach Wall – Muscularis • Stomach has an additional layer of muscle fibers • Allows stomach to churn and mix stomach contents

Stomach Functions • Mechanical Digestion: churning and mixing of stomach contents to aid digestion • Chemical Digestion: pepsin: breaks down proteins (works only in acidic environments-HCl in stomach!)

Stomach Functions • Absorption: limited absorptive abilities (water, salts, glucose, alcohol, aspirin and some lipid-soluble drugs) • Propulsion: propels food into small intestine in the form of CHYME (mixture of food particles & gastric juice) – Chyme presses against pyloric sphincter causing it to relax and allows chyme to pass

Carbohydrate Digestion • Carbohydrate: nutrient; main source of energy in the body – Glucose: a simple sugar; the end product of carbohydrate digestion • Takes place in the mouth & small intestine • Enzymes: – salivary amylase: starch to double sugars – pancreatic enzymes, intestinal enzymes (maltase, sucrase, lactase): double sugars to simple sugars

Protein Digestion • Protein: basic nutrient; used in anabolism (tissue building) – Amino Acid: the building blocks of proteins; the end product of protein digestion • Takes place in the stomach & small intestine • Enzymes: – Pepsin in gastric juices – Trypsin in pancreatic juice – Peptidases in intestinal juice

Fat Digestion • Basic food type; used for energy and insulation – Fatty acids and glycerol: end products of fat digestion • Takes place in the small intestine • Enzymes: – Bile in duodenum: fat droplets into smaller fat droplets – Pancreatic lipase: small fat molecules into fatty acids and glycerol

Time to Digest • Carbohydrate-rich meal: moves through the stomach rapidly • Fat-rich meals: may take up to 6 hours to pass through the stomach

Alimentary Canal: Small Intestine • Completes mechanical and chemical digestion & is the main site of nutrient absorption • Propels food through with peristaltic waves • 20 feet long, highly coiled • Takes ~ 3 -10 hours to move chyme through • Suspended to posterior abdominal wall via mesentary

Small Intestine continued 3 Segments: 1. Duodenum: receives chyme from stomach & digestive enzymes from accessory organs; about 10 inches long 2. Jejunum: site of absorption; about 8 feet long

Small Intestine continued 3. Ileum: about 12 feet long; the end of digestion and absorption of nutrients Ileocecal valve: the junction at which the small & large intestine join; sphincter muscle controlling the flow of material between organs

Wall of Small Intestine • Highly convoluted mucosa for better absorption through increased surface area – Intestinal villi: tiny projections of mucosa – Microvilli: even smaller projections on the intestinal villi

http: //www. biog 1105 -1106. org/demos/105/unit 6/media/villus. structure. jpg

Wall of Small Intestine • Within each villi is: – Blood capillaries – Lacteals (lymphatic vessels) - Act to carry absorbed nutrients away

Alimentary Canal: Large Intestine • Final segment of alimentary canal • ~5 feet long but larger in diameter than small intestine • Function: to dry out indigestible material by absorbing water; eliminate unwanted materials

Large Intestine continued • 5 main segments of large intestine – Cecum: sac-like pouch receiving material from ileum – Vermiform appendix: worm-like extension holding lymphatic tissue – Colon: ascending, transverse, descending, sigmoid – Rectum – Anus

Large Intestine continued Anus: has 2 sphincters 1. Internal: involuntary; told to relax when fecal matter stimulates the defecation reflex in the rectum 2. External: voluntary; if relaxed, elimination occurs

Fecal Formation • Fecal matter: 75% water, 25% indigestible material, mucus and bacteria – Color: produced by bile – Gas: produced by the metabolism of bacteria or from swallowing air – Movement of matter is very slow ~ 1824 hours

Mass Movement & Defecation • Food residue moves through large intestine via peristalsis and mass movement • Mass movements: slow moving powerful contractile waves over colon – Occurs 3 -4 X per day (oftentimes just after eating) • Defecation Reflex: feces stretching out rectum walls which contract while sphincters relax – Communication between rectum and brain to decide if “now is the time”

Digestion Mishaps • Heartburn: the damage to esophageal mucosa due to presence of stomach acids because of a weak cardio-esophageal sphincter • Gastric ulcer: when the mucus layer of the stomach is not strong enough to withstand gastric acids; burns a hole in stomach wall

Digestion Mishaps • Diarrhea: the decreased absorption of water and electrolytes in the small & large intestine leading to watery stool • Constipation: the increased absorption of water and electrolytes in the large intestine; leads to hard, impacted stool