compendium 3

• What is another Name for the digestive tract?

  Alimentary Canal
• What is an accessory organs and provide an example.

  Primarily glands that secrete fluids into the digestive tract.

  Eg. liver, gallbladder, pancreas
• What are the 6 functions of the digestive system and their definitions?

  1. Ingestion: Introduction of food into stomach (via mouth)

  2. Mastication: Chewing. Chemical digestion requires large surface area so breaking down large particles mechanically facilitates chemical digestion.

  3. Secretion: Lubricate, liquefy, digest (e.g. Mucus: Secreted along entire digestive Tract, lubricates food, coats and protects lining).

  4. Digestion: Mechanical and chemical digestion of food into nutrients.

  5. Absorption: Movement of nutrients out of digestive tract into cells.

  6. Elimination: Waste products removed from body; faeces. Defecation.
• Histology: What is the mucosa and what does it contain?

  The Innermost Layer, secretes mucus.

  
  

  Contains mucous epithelium, lamina propria (loose CT) and muscularis mucosae (smooth muscle)
• Histology: What is the Submucosa and what does it contain?

  Thick connective Tissue Layer

  
  

  Contains blood vessels, nerves, lymphatic vessels, small glands etc.
• Histology: What is the Muscularis and what is it's function?

  2/3 smooth muscle layers, movement & secretion.
• Histology: What is the Serosa/Adventita and what is it's function?

  Outermost layer, connective tissue, stability.
• What is the Peritoneum? What are mesenteries (2 of them)?

  Peritoneum: Serous membrane that is located in the abdominopelvic cavity. The walls and organs of the abdominal cavity are lined with this serous membrane.

  · Visceral Peritoneum: Covers Organs

  · Parietal Peritoneum: Covers interior surface of body wall.

  
  

  Mesenteries: Peritoneum (epithelial tissue) which connects organs together. Routes by which blood vessels and nerves pass from body wall to organs.

  
  

  1. Greater Omentum: Mesentery that connects stomach to transverse colon.

  2. Lesser Omentum: Mesentery that connects stomach to liver and diaphragm.
• Oral Cavity: What are the 4 types of teeth and what is the dentition formular?

  1. Incisors - Biting, cutting and stripping

  2. Canines - Seizing, piercing and tearing

  3/4. Premolars and molars - Grinding and crushing

  
  

  Formula: 2123
• What does Saliva do? What are the 3 salivary glands and what enzymes do they secrete and it's function?

  Saliva: Protects oral cavity, moistens, lubricates and digests food.

  
  

  1. Parotid glands

  2. Submandibular glands

  3. Sublingual glands

  
  

  Salivary Amylase: Enzyme found in saliva that breaks down carbohydrates into smaller sugars.

  
  

  Lingual Lipase: Enzyme that digests lipids
• What is Lysozyme?

  Antibacterial Enzyme = reduces bacteria present in oral cavity.
• The 4 functions of the Oral Cavity.

  Ingestion and Mastication - Movement of mandible causes teeth to break down food. Tongue and cheeks place food between teeth. Food mixed with saliva which allows food to be tasted.

  
  

  Propulsion and Mixing - Tongue forms food into bolus and pushes it into the pharynx to begin swallowing reflex.

  
  

  Secretion - Saliva contains mucin, bicarbonate and water which lubricate the oral cavity and lysosome which kills microorganisms. Amylase and lingual lipase are secreted in saliva.

  
  

  Digestion - Amylase in saliva begins carbohydrate digestion.
• What is the Pharynx and Uvula?

  The pharynx connects oral cavity to Esophagus.

  
  

  Uvula (soft palate) prevents food/drink from entering the nasopharynx.
• What are the 2 functions of the pharynx?

  Propulsion and Mixing - Swallowing moves bolus into oesophagus. Materials prevented from entering nasal cavity by the soft palate and kept out of lower respiratory tract by epiglottis and vestibular folds.

  
  

  Secretion - Mucus provides lubrication.
• What is the esophagus and epiglottis?

  Esophagus is a tube that connects pharynx to stomach. 25 cm long, lies posteriorly to the trachea.

  
  

  Epiglottis prevents food/drink from entering the trachea.
• What are the 2 functions of the Esophagus?

  Propulsion and Mixing - Peristaltic contractions moves bolus from pharynx to stomach. The lower Esophageal sphincter limits reflux of the stomach contents into the esophagus.

  
  

  Secretion - Mucus provides lubrication and protects inferior esophagus from stomach acid.
• What are the 3 Phases of Swallowing?

  1. Voluntary Phase: Tongue pushes bolus to back of oral cavity towards pharynx (oropharynx).

  
  

  2. Pharyngeal phase: Soft palate (uvula) close off the nasopharynx. Bolus touches receptors on oropharynx and swallowing reflex moves bolus down pharynx and into Esophagus. Epiglottis covers trachea.

  
  

  3. Esophageal Phase: Bolus is moved down Esophagus towards stomach by peristalsis.
• What does the stomach produce?

  Mucus, hydrochloric acid, protein digesting enzymes (pepsin).
• What does the stomach churn food into?

  Chyme
• What are the two sphincters and where are they located?

  Gastroesophageal (cardiac): to esophagus

  
  

  Pyloric: To duodenum
• Rugae


  Folds in stomach wall that allow stomach to stretch after eating.
• What are the layers of the stomach?

  Visceral Peritoneum: Serosa

  
  

  Muscularis: Three Layers

  o Outer Longitudinal

  o Middle Circular

  o Inner Oblique

  
  

  Submucosa

  
  

  Mucosa
• Describe the 4 functions of the stomach

  Propulsion and Mixing - Mixing waves churn ingested materials and stomach secretions into chyme. Rugae allow the stomach to expand and store food. This allows further mixing in the stomach prior to propulsion of small amounts of chyme into the small intestine by peristaltic waves.

  
  

  Secretion - Release of hydrochloric acid creates acidic stomach environment. Acid kills most microorganisms and activates the precursor of the proteolytic enzyme pepsin. Gastric lipase and intrinsic factor are secreted. Mucus provides lubrication and prevents digestion of stomach wall.

  
  

  Digestion - Mechanical digestion occurs as food is churned. Protein digestion begins as result of the actions of hydrochloric acid and pepsin. Gastric lipase and lingual lipase digest a small amount of lipids.

  
  

  Absorption - Water, alcohol and aspirin absorption takes place in the stomach.
• Describe the movements of the stomach?

  1. Mixing wave initiated towards the pyloric sphincter

  2. Fluid part is pushed towards pyloric sphincter and solid part pushed back towards body of stomach

  3. Peristaltic and mixing waves

  4. Fluid part is pushed towards pyloric sphincter and solid part pushed back towards body of stomach

  5. Peristaltic waves force fluid part of chyme through pyloric sphincter into duodenum. Solid part is further churned.
• Why does the small intestine have a large Surface area?

  For efficient absorption of nutrients.
• What are the divisions of the small intestine?

  Duodenum: First 25cm beyond the pyloric sphincter.

  
  

  Jejunum: 2.5m

  
  

  Ileum: 3.5m
• What is the function of the duodenum? What enzymes are being used to breakdown nutrients?

  Chyme mixes with various digestive enzymes.

  
  

  Bile enters via bile duct from liver/gallbladder to emulsify fats.

  
  

  These enzymes enter via the pancreatic duct.

  1. Pancreatic Lipase: Breakdown lipids

  2. Pancreatic amylase: Breakdown carbohydrates

  3. Trypsin:Breakdown proteins (from pancreas)
• What are the fold in the small intestine and its function? Villi are also present; what is their function?


  Plicae circulares: Circular folds in the wall of small intestine.

  
  

  Villi: Folds of the mucosa that contain capillaries and lacteals (vessels by which macromolecules move out of the small intestine and are picked up the lacteals and blood vessels to move back into the blood and travel to cells that need them.
• What are the 4 functions of the small intestine?

  Propulsion and Mixing - Segmental contractions mix the chyme, and peristaltic contractions move the chyme into large intestine.

  
  

  Secretion - Bicarbonate ions from pancreas and bile from liver neutralize stomach acid to form pH environment suitable for pancreatic and intestinal enzymes. Mucus provides lubrication, prevents digestion of the intestinal wall, and protects the small intestine from stomach acid. Bile eliminated.

  
  

  Digestion - Segmental contractions aid digestion. Enzymes from pancreas and small intestine lining breakdown food molecules. Bile salts emulsify lipids to allow for lipid digestion.

  
  

  Absorption - Nutrients are actively or passively absorbed. Most water is absorbed.
• What are the functions of the liver and what is the secretion?

  Makes bile (100ml/day).

  Stores Glucose (as glycogen) and lipids for energy.

  Detoxification.

  
  

  Bile: Bile salts in by emulsify lipids, making them available to lipases, and help make and product soluble and available for absorption by the intestinal mucosa; many of the other buyer contents of waste products, such as bile pigments
• Gall Bladder


  Stores concentrated bile.
• Function of the Pancreas and name its products.

  Produces digestive enzymes (pancreatic amylase, lipase). Produces insulin and glucagon for blood sugar homeostasis
• Function of the Large Intestine

  Propulsion and Mixing - Movements propel faeces towards the anus, and defecation eliminates the faeces.

  
  

  Secretion - Mucus provides lubrication; mucus and bicarbonate ions protect against acids produced by bacteria.

  
  

  Absorption - The proximal half of the colon absorbs salts (eg. NaCl), water and vitamins (eg. K) produced by bacteria.

  
  

  Elimination - The distal half of the colon holds faeces until they are eliminated.
• List the basic histological layers of the digestive tract. (Label)

  1. Mucosa

  2. Submucosa

  3. Muscularis

  4. Serosa/Adventitia
• Explain the difference between digestion and absorption

  Digestion - Mouth, stomach, small intestine

  o Breakdown of food molecules for absorption into circulation.

  o Mechanical: Breaks down large food particles to small.

  o Chemical: Breaking of covalent bonds by digestive enzymes,

  
  

  Absorption - Nutrients from the small intestine, water from the large intestine

  o Molecules are moved out of digestive tract and into circulation for distribution throughout the body.
• What are nutrients and what is their function?

  Nutrients: Chemicals taken in to body to

  · Produce energy

  · Provide building blocks to build other molecules
• What are the 6 classes of nutrients and their recommenced intake?

  carbohydrates (60%), proteins(10%), lipids(30%), vitamins, minerals, water
• Carbohydrates building blocks


  Disaccharides and monosaccharides other largest building blocks for carbohydrates. Monosaccharides include glucose, fructose and galactose. When two monosaccharides come together and form a covalent bond, they create Disaccharides. A long chain of disaccharides form polysaccharides.
• What is a polysaccharide and what are 2 examples?


  Long chains of 3000+ monosaccharides

  
  

  Glycogen and Starch/Cellulose
• Describe carbohydrate absorption

  Polysaccharide chain e.g. glycogen. Digested by saliva in oral cavity & pancreatic amylase in duodenum.

  
  

  Disaccharide chain e.g. sucrose. Digested by sucrase in the intestine

  
  

  Monosaccharide chain (e.g. glucose). Glucose absorbed into blood via villi / microvilli in intestine. Transported to liver via hepatic portal vein.