EXTRA CREDIT DIGESTIVE SYSTEM - Suggested Answer/Outline

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1 EXTRA CREDIT DIGESTIVE SYSTEM - Suggested Answer/Outline ASSIGNMENT: You have just eaten a balanced meal. The meal contained the macromolecules protein, carbohydrates, and fat as well as a vitamin B12 and a Vitamin D (fat soluble supplement). Describe what will happen to this food and the supplements in the digestive tract. Alimentary canal, also called digestive tract, is the pathway by which food (nutrients for the body) is ingested, broken down, absorbed and excess solid wastes are expelled. The alimentary canal includes the mouth, pharynx, esophagus, stomach, small intestine, large intestine, and anus. 4 LAYERS; (deep to superficial) mucosa, submucosa, muscularis externa & Serosa. 2 CELL TYPES - line the mucosa of the alimentary canal. Stratified squamous epithelial cells line the mouth, pharynx, esophagus and anal canal. Many layers provide better protection of these areas underlying tissue from environmental exposure. Being stratified allows the cells to stretch. Simple columnar cells line the stomach and intestines. This layer contains exocrine and endocrine cells. It also has Tight Junctions between these cells to create a semipermeable seal that very few macromolecules can pass through. MOUTH: or oral cavity where food enters the body. Functions: 1) lubricates the mouth; 2) moistens food; 3) binds food particles; 4) Aides in the ability to taste food; 5) fights foreign microbes with IgA and lysozyme; 6) Keeps a ph to clean mouth and teeth AND ph prevents a build-up of Acids in mouth which can destroy the enamel of teeth and the lining (mucosa) of oral tissues. Secretes: Saliva helps to moisten and soften the food (to prepare to make a bolus ) and begins the digestive process by helping to break down the complex carbohydrates.. ACCESSORY ORGANS: The Salivary Glands, Teeth and Tongue Salivary Glands (exocrine) produce Saliva continuously in the mouth. It s comprised of water (99.4%) and the remaining are electrolytes (Na+, Cl-, HCO3- {bicarbonate}, buffers, glycoproteins, antibodies and enzymes. Controlled by: Parasympathetic stimulation causes production of these watery fluids. (Stimulatory) These secretions are increased by thoughts of the food or in the presence of food. Secretions: Complex carbohydrates are mainly broken down Enzymes: Mucins a glycoprotein used primarily to lubricate the mouth. Amylase - enzyme that helps break down complex carbs before swallowing.

2 Submandibular Gland Located- on the left and right side, below the mandible on the floor of the mouth. Secretes: mostly Mucins (70%) a serous fluid. The rest is mucus and Amylase Parotid Gland Located-- left and right side of face, inferior to zygomatic arch and anterior, inferior to the ear. Secretes --Produces a watery, serous fluid Contains mostly Amylase and about 25% mucins Sublingual Gland Located -- under the tongue. Secretes --ions are contain only about 5% of the serous Mucin. It MOSTLY secretes a very thick, viscous mucus. This is secreted under Sympathetic innervation. You get this when you are nervous or anxious. Teeth and Tongue are the only Accessory organs that have actual contact with food. TEETH: part of mechanical process of digestion. Mastication (chewing) helps to break down sinewy meats and plant fibers and mix them with saliva. Makes food smaller so it is able to be swallowed. TONGUE: Muscular appendage covered by mucous membranes. Functions: Mucus aides in the ability to taste food as it passes over the taste buds that allows us differentiate salty, sweet, bitter, sour and umami sensations of our food. Movements: of tongue mix food in the mouth with saliva, as well as move food towards the throat for swallowing. The rough surface (made of papillae) creates friction as food is moved inside mouth. (FAT Breakdown) Secretes: Lingual lipase - enzyme to break down triglycerides. 3 PHASES OF SWALLOWING: 1 st step is voluntary, the others are involuntary. Buccal Phase. Getting ready to swallow food. Mixed by tongue and chewed into small pieces by teeth for saliva to moisten and add its enzymes to food. Now the food is called a BOLUS. The tongue pushes the Bolus the posterior of the oral cavity into the oropharynx. Pharyngeal Phase As the bolus is pass and the rising the tongue aids the soft palate and uvula to elevate thus sealing off the Nasopharynx. Reflexes signal the hyoid bone and larynx to elevate and the epiglottis seals of the glottis so food won t go down the wrong pipe. Now muscles of pharynx contract and push the bolus towards the esophagus. Note: at this point breathing stops to accommodate the swallowing action.

3 Esophageal Phase The inferior constrictor muscles of the esophagus relax and opens the esophagus. Now in the esophagus, the bolus is propelled by Peristaltic waves (The contraction of the longitudinal and circular muscles in the muscularis externa in a rhythmic fashion) to the stomach. ESOPHAGUS: Located: a muscular tube located deep to the trachea. It connects the laryngopharynx to the stomach. Function: is to move food from the pharynx to the stomach. Cardiac sphincter. A ring of circular muscle at the end of the esophagus. Keeps the contents of the stomach from going backwards. Stomach acids can erode any lining outside of the stomach and cause ulcers. Controlled by: signals from the ANS. Parasympathetic stimulation opens (relaxes) it. Sympathetic Stimulation and presence of GASTRIN contracts (closes) it. STOMACH : Alimentary canal structure is a little different here. The mucosal layer is ridged or rippled: Called RUGAE the surface flattens out to accommodate all the food that has been swallowed. In the ripples are deep depressions called GASTRIC PITS. A second change is the muscularis externa layer has an EXTRA layer of muscles called ---Oblique muscles: --- helps the mixing and churning of food. The bolus will be called Chyme by the time it is ready to leave the stomach. Functions: 1) mixing chamber for the bolus. 2) Mainly to digest proteins. 3) reservoir to hold food. 4) Stomach releases Acids and 5) Enzymes will begin chemical breakdown of food and add juices to help liquefy it. 6) Very low ph helps to kill foreign organisms (except H.pylori) 7) Secretes Intrinsic Factor to bind to Vit B12 to be absorbed in ileum. ABSORPTION: very limited Some H2O; certain salts; aspirin (lipid soluble drug); ETOH (slowed by presence of fats) Gastric Secretions - - from gastric pits Mucus: Located: On surface of Mucosa, secrete an alkaline mucus that protects (blankets) the epithelium against stress and acid. Gastric Glands: Located: Fundus & Body Secrete: (exocrine) Chief Cells: pepsinogen; an inactive proenzyme.

4 Parietal Cells: 1) HCl- ( H+ and Cl- are excreted into the lumen of gastric gland) & converts pepsinogen to make PEPSIN. Proteolytic Protein-digesting enzyme. 2) Intrinsic factor; glycoprotein --helps Vit B12 to be absorbed in ileum. Pyloric Glands: Located: pyloric region Secrete: (endocrine) G Cells: Gastrin Stimulatory hormone; stimulates chief & parietal cells & contractions of gastric wall D Cells : Somatostatin Inhibitory hormone; inhibits release of gastrin Constantly produced but is over-ridden by hormonal & neural stimuli when stomach is getting ready for digestion or is digesting. 3 Phases of Stomach Control: Cephalic phase: (Stimulatory) taste, smell, sight, thought of food stimulates (via parasympathetic nerves) salivary glands to secrete saliva, gastric glands to secrete gastric juices and the muscularis of stomach to begin churning Gastric Phase: (Stimulatory) food enters the stomach the wall is distended, triggering stretch receptors. This reinforces the cephalic phase - gastric glands are stimulated, stomach churning is stimulated and the hormone gastrin (produced in gastric glands) stimulates the lower esophageal sphincter (aka cardiac sphincter) to contract. Gastrin also stimulates the gastric glands and muscularis of stomach and it inhibits (so they relax and open) the pyloric sphincter and the ileocecal sphincter. This allows food to be moved along the digestive tract. Intestinal phase: when acid chyme enters duodenum & ph changes (acidic) inhibits parasympathetic nerve stimulation of stomach via submucosal plexus (secretions, blood flow) & Myenteric Plexus ( GI motility/sphincters) PYLORIC SPHINCTER: opens (relaxes) when Chyme exerts enough pressure. Controlled by : Parasympathetic stimulation and Gastrin (hormone from G Cells) Keep it closed from stomach. Sympathetic stimulation & Somatostatin (hormone from D Cells) - once in duodenum to slow down stomach motility.(motility & gastrin) SMALL INTESTINE: major region of chemical digestion and absorption. Wall of Small Intestine - mucosa is made of simple columnar epithelium. ---muscularis is composed of longitudinal (for peristalsis) and circular smooth muscle (for segmentation)

5 ---Needs to increase Surface area for absorption by as a series of permanent folds, plicae circulares, ---Each plicae circularis has villi on its outer surface and each Villus has a Brush Border of Microvilli. (lower duodenum and jejunum) --- Each villus contains a capillary bed (merge into hepatic portal vein) and a large lymph capillary --lacteal. -Lacteal: MOVE FATS: Transports molecules too large for Blood capillaries. Absorbed fatty-acids are put together with protein-lipids called Chylomicrons. Moved venous circulation via lacteals thoracic duct subclavian vein superior vena cava to heart into systemic circulation to reach the Hepatic artery. 3 Regions of Small Intestine: Plicae circulares do not expand like rugae in stomach - duodenum: Mixing Chamber receives Chyme & neutralizes its ph; separated from the stomach by the pyloric sphincter ; - ducts from pancreas and liver deliver secretions from these glands (see accessory organ) - glands secrete thick alkaline mucus(buffers) to neutralize chyme - jejunum: -most chemical digestion and absorption occurs here - ileum: an area of some absorption (vit B12 only when bound to Intrinsic Factor) - the ileocecal valve is a sphincter that closes the distal end of the small intestine & separates it from Large Intestine. Controlled by: Parasympathetic activity (Increase in secretory activity) Acidic Chyme as it enters the duodenum stimulates Secretin. Stimulates production CCK (After chyme arrives) Local reflexes- myenteric plexuses Distention of the duodenum stimulates parasympathetic nerves that stimulate segmentation and peristalsis Gastroenteric reflex- stimulated by stretch receptors in stomach, stimulate motility and secretion along entire sm. Intestine Parasympathetic stimulation via Vagus nerve (secretes this during Gastric Phase) The proteins and fats in the chyme stimulate the production of the hormone CCK (cholecystokinin) which stimulates the 1) pancreas to secrete digestive enzymes, 2)the gallbladder to contract forcing bile into the duodenum, 3) the pyloric sphincter to contract. 4) CCK also inhibits the gastric glands and stomach churning. Gastroileal reflex relaxes ileocecal valve to move mostly undigested material to Lg. Intestine. SYMPATHETIC INNERVATION - inhibits the secretions of duodenal Glands. (too much like stress can cause duodenal ulcers) Secretions: Digestive enzymes are located within membrane of Microvilli.

6 ----Intestinal Glands Secrete intestinal juices which contain mucus and water (1.8 liters/day). ----Keeps digestive enzymes and Chyme in Solution. ----Duodenal Glands secrete thick alkaline mucus to protect epithelium from acids, enzymes, chyme. Gastrin stimulatory hormone of stomach acid Somatostatin inhibitory hormone of stomach acid Secretin stimulates release of bile from GB; release of Pancreatic Juices (both incr. ph) CCK (cholecystokinin) - causes GB Contraction to release Bile, stimulate pancreas to release proenzymes & relax Hepatopancreatic Sphincter to release bile & pancreatic proenzymes into duodenum. CCK also inhibits the gastric glands and stomach churning. VIP (Vasoactive Intestinal Peptide) stimulates secretions of intestinal glands; dilates regional capillaries (helps with absorption of nutrients in sm. Intestine) ----INHIBITS acid production in stomach. GIP (Gastric Inhibitory Peptide) Inhibits gastric activity when Fats & Carbohydrates (esp. Glucose) is present in small intestine. Stimulates release of insulin from pancreatic Islets. Macromolecules that are broken down Carbohydrates Sucrose, Maltose, Lactose into monosaccharides Intestinal Lipase fats to fatty acids & glycerol Vitamin b12 - bound to intrinsic factor absorbed in distal ileum absorbed by active transport Proteins Proteases & Peptidases breakdown Di & Tripeptides into amino acids BY: Enzyme Enterokinase from Brush Border converts Trypsinogen (pancreas) Trypsin (active) Trypsin activates (proenzymes from pancreas) Chymotrypsinogen Chymotrypsin; Procarboxypeptidase carboxypeptidase, Proelastase Elastase Nutrients ABSORBED in Small Intestine by: : Thru Diffusion: H2O, electrolytes, water soluble vitamins B, C (except B12) Absorbed by blood: H2O, electrolytes, monosaccharides, amino acids Facilitated Diffusion: monosaccharides, amino acids Active transport: Vitamin B12, H2O, electrolytes, monosaccharides, amino acids Fats the Long Road 1) as fatty acids by simple diffusion thru phospholipid Bilayer. 2) to the E.R. in cell for synthesizing into fats. 3) Fats cluster together with a Protein covering form Chylomicrons. 4) Chylomicrons leave Epithelial cells for Lacteals of lymph system, in lamina propria of inststinal villi.

7 5)Lymph transports chylomicrons away to the thoracic duct Lt. Subclavian Vein (bloodstream) Accessory Organs: Aid in digestion PANCREAS: Function: Produces an HCO3- and several digestive enzymes to break down all types of food molecules. Organ that is and mostly exocrine glands (ie. Pancreatic Juice) part endocrine glands(produces Insulin). -Exocrine - the enzymes secreted in inactive form and are activated in the duodenum. -secreted into small ducts that merge to larger ducts. pancreatic duct & common bile duct Duodenal Ampulla controlled by the Hepatopancreatic sphincter to enter the duodenum. Secretions: Pancreatic amylase breaks down glycogen & starches into Mono, Di & tripeptides Lipase digests fats to monoglycerides and fatty acids. Pancreatic Nucleases: break down RNA, DNA to nucleotides. Bicarbonate Ions: make alkaline pancreatic juice (ph 8) to neutralize acidic chyme & protect intestinal lining. Pancreatic Proteolytic Enzymes: when activated breaksdown Proteins to Dipeptides, Tripeptides & Amino Acids Tripsinogen Chymotrypsinogen Procarboxypeptidase Proelastase See activation in Small Intestine, Secretions Controlled By: 1) acidic chyme stimulates the production of the hormone secretin which stimulates the release of watery buffer solution (ph 8). 2) CCK stimulates increase in the production & secretion of Pancreatic Enzymes. 3) Vagus Nerve stimulates pancreatic secretions. 4) Cepahlic Phase of gastric regulation stimulates to synthesize enzymes Before food enters duodenum.

8 LIVER: large organ involved in many metabolic, hematologic and functions. (over 200). Vitamin D That was eaten earlier is absorbed by capillaries in the small intestine and delivered via Hepatic Portal vein to be absorbed and stored in hepatocytes. Functions: Synthetic: Produces bile needed for Digestion. The liver detoxifies blood from intestines that it receives via the hepatic portal vein. Metabolic: Stores glycogen, lipids, iron, Vit A, B12, D, E, K Metabolizes vitamins & minerals Drug Inactivation removes from blood & breaksdown; limiting how long they re effective. Carbohydrate Metabolism: stabilize blood glucose levels. Low levels hepatocytes Breakdown glycogen reserves and convert to glucose for the blood stream. Lipid Metabolism: regulates circulating levels of triglycerides, fatty acids & cholesterol. Low levels hepatocytes breakdown reserves for the bloodstream. Amino Acid Metabolism: removes excess from bloodstream. To be used for synthesizing proteins or can be converted to lipids or glucose for energy storage. Waste product removal: Ammonia(NH3) /Ammonium (NH)4 produced by the DEAMINATION of proteins (amino acids -NH2) is converted to a less toxic compound (urea) by the liver and excreted by the kidneys. Hematologic: Synthesize plasma proteins ( ie. albumins) Removal of old RBC s by phagocytic Kupffer cells; Converts Hgb to bilirubin & biliverdin which are components of bile. Removes or stores toxins Removes circulating hormones (absorbs too) E, NE, Insulin, Thyroid hormones, steroid homones ( estrogen & androgen) & corticosteroids. Secretions: - BILE is a break down product of hemoglobin from the destruction of old red blood cells. Contains bile salts is used to emulsify fats in the intestines. Breaksdown fat droplets to increase surface area to enzymatic action. GALLBLADDER: Anatomy: Fundus (furthest away from cystic duct, body, and neck Functions: - the gall bladder stores excess bile until needed. Made in liver. Under influence of CCK bile is released into cystic duct commom bile duct hepatopancreatic sphincter duodenum. Concentrates it when not in use H2O absorbed, Bile salts concentrated Secretions: under CCK, bile is released from storage.

9 LARGE INTESTINE: Little or no digestion happens here. NO digestive glands and NO villi Divided into 3 major regions Cecum; Colon; Rectum ---Cecum connects to the ileum separated by the ileocecal valve; a short section that receives chyme from the small intestine. ---Vermiform appendix is a blind pouch that connects to the cecum. ---Colon has 4 sections Ascending; Transverse; Descending; Sigmoid (s-shaped) ---Anal canal is the last portion of the rectum that ends at the anus Functions: ---Absorbs water and electrolytes and bile salts(in ascending colon) ---Stores and forms fecal matter (rectum), ---Eliminates waste (defecation) (via anus) ---Bacterial digestion by-product of Gas, (flatus) ---Minerals, and some vitamins (K, B5, Biotin) are recovered from the mostly indigestible material Secretes: ---Mucus for lubricating lumen as, protection from bacteria, maintaining ph Absorption: --- mostly Water absorbed from more solid indigestible materials. --- bile salts (enterohepatic circulation) ---Minerals, and some vitamins (vitamin K) are recovered from the indigestible material by the intestinal bacteria (flora) good bacteria. Movements: ---3 thin bands of longitudinal muscle run along either side of the cecum and colon, called the taenia coli. Taenia coli pull the colon into pouches called Haustra. (Peristaltis) ---circular muscles ring around each haustra. (Segmentation) ---movements are slower & less frequent in Lg. Intestine than in the sm. Intestine ---Segmentation Haustral Churning movements happen in Haustra about every 30 min. ---Peristalsis mass movement moves food from haustra to haustra forward. (1-3x p/day), usually follows large meals. Controlled By: can be triggered by reflex from stomach distension (gastrocolic reflex)or duodenal distension (duodenalcolic reflex) Stimulatory reflexes that move waste from transverse colon to the rectum.

10 Rectum: --- the last portion of the circular muscle of the anal canal forms the internal anal sphincter - this is smooth muscle under Involuntary control. --- skeletal muscle of the abdominal floor forms the external anal sphincter - this is muscle that is under Voluntary Control. Defecation Reflex as feces move into rectum it is the first time one can have the urge to defecate. -- mass movement of feces into rectum causes stretch receptors to send signals to the spinal cord. --- spinal reflex contracts the rectum. --- spinal reflex relaxes internal sphincter relaxation (open) --- Voluntary control and impulses from brain keep external sphincter contacted (closed) until one is ready to defecate (voluntary relaxing the External Sphincter). ***voluntary relaxation of external sphincter control of muscle is learned behavior (potty training).