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DigestionDigestion

OverviewOverview OrgansOrgans

11 . .Alimentary canalAlimentary canala. Functiona. Function

i. Digestsi. Digests ii. Absorbsii. Absorbs

b. Organsb. Organs i. Mouthi. Mouth

ii. Pharynxii. Pharynx iii. Esophagusiii. Esophagus

iv. Stomachiv. Stomach v. Small intestinev. Small intestine vi. Large intestinevi. Large intestine

Accessory digestiveAccessory digestivea. Organsa. Organs

i. Teethi. Teeth ii. Tongueii. Tongue

iii. Gallbladderiii. Gallbladder b. Glandsb. Glands

i. Salivaryi. Salivary ii. Liverii. Liver

iii. Pancreasiii. Pancreas

Digestive ProcessDigestive Process

Essential activitiesEssential activities1. Ingestion1. Ingestiona. Taking food into digestive system via the moutha. Taking food into digestive system via the mouth2. Propulsion2. Propulsiona. Movement of food through the digestive tracta. Movement of food through the digestive tractb. Swallowingb. Swallowing i. Voluntaryi. Voluntaryc. Peristalsisc. Peristalsis i. Involuntaryi. Involuntary

33 . .Mechanical digestionMechanical digestiona. Chewinga. Chewingb. Mixingb. Mixing i. Salivai. Salivac. Churningc. Churningd. Segmentationd. Segmentation i. Local constriction of the small intestinei. Local constriction of the small intestine4. Chemical digestion4. Chemical digestiona. Mouth through small intestinea. Mouth through small intestine

5. Absorption5. Absorptiona. Movement of digested end products from a. Movement of digested end products from lumen of the GI tract into blood and lymphlumen of the GI tract into blood and lymph6. Defecation6. Defecationa. Elimination of undigested materialsa. Elimination of undigested materials

Histology of the Alimentary CanalHistology of the Alimentary Canal

Four basic layersFour basic layers1. Mucosa1. Mucosa: Innermost layer functions in secretion, : Innermost layer functions in secretion, absorption and protection. It consists of 3 sub-absorption and protection. It consists of 3 sub-layers: lining epithelium, lamina propria & layers: lining epithelium, lamina propria & muscularis mucosae. Epithelium: Simple columnar muscularis mucosae. Epithelium: Simple columnar with goblet cells. Lamina propria: Loose areolar with goblet cells. Lamina propria: Loose areolar connective tissue with capillary beds & lymph connective tissue with capillary beds & lymph nodules. Muscularis mucosae: Thin layer of smooth nodules. Muscularis mucosae: Thin layer of smooth musclemuscle

2. Submucosa2. Submucosa: Composed of dense CT (blood : Composed of dense CT (blood vessels & lymphatic vessels) & elastic fibersvessels & lymphatic vessels) & elastic fibers3. Muscularis externa3. Muscularis externa: Functions in segmentation : Functions in segmentation & peristalsis. It consists of inner circular and outer & peristalsis. It consists of inner circular and outer longitudinal layer of smooth muscle. Sphincters are longitudinal layer of smooth muscle. Sphincters are thickened areas of smooth musclethickened areas of smooth muscle4. Serosa4. Serosa: Areolar connective tissue covered with : Areolar connective tissue covered with mesothelium (single layer of squamous epithelium)mesothelium (single layer of squamous epithelium)

Functional AnatomyFunctional Anatomy

Mouth (oral cavity or buccal cavity) Mouth (oral cavity or buccal cavity) 1. Boundaries: Lips, cheeks, tongue & palate1. Boundaries: Lips, cheeks, tongue & palate2. Palate: Hard palate (rigid & underlain by bone) 2. Palate: Hard palate (rigid & underlain by bone) & Soft palate (formed from muscle)& Soft palate (formed from muscle)

TongueTongue1. Bundles of skeletal muscle1. Bundles of skeletal muscle2. Function2. Functiona. Mix food with salivaa. Mix food with saliva i. Bolusi. Bolusb. Position bolus for swallowingb. Position bolus for swallowing

Salivary glands Salivary glands 1. Function of saliva: Cleanses mouth, dissolves 1. Function of saliva: Cleanses mouth, dissolves tastants, moistens & initiates chemical breakdowntastants, moistens & initiates chemical breakdown2. Types: Extrinsic (3 pairs: parotid, subman-2. Types: Extrinsic (3 pairs: parotid, subman-dibular & sublingual) & intrinsic (buccal glands)dibular & sublingual) & intrinsic (buccal glands)3. Secretory cells: Serous cells (watery secretion 3. Secretory cells: Serous cells (watery secretion with enzymes) & mucous cells (viscous) with enzymes) & mucous cells (viscous)

Teeth Teeth 1. Classification: Incisors, canines, premolars & 1. Classification: Incisors, canines, premolars & molarsmolars2. Dental formula:2. Dental formula:

(2I, 1C, 2PM, 3M/2I, 1C, 2PM, 3M) X 2 = 32(2I, 1C, 2PM, 3M/2I, 1C, 2PM, 3M) X 2 = 32

Pharynx: Oropharynx to Laryngopharynx Pharynx: Oropharynx to Laryngopharynx

EsophagusEsophagus1. Laryngopharynx into esophagus1. Laryngopharynx into esophagus2. Pierces diaphragm & joins stomach via cardiac 2. Pierces diaphragm & joins stomach via cardiac orifice gated by cardiac sphincterorifice gated by cardiac sphincter3. Four layers: Mucosa, submucosa, muscularis 3. Four layers: Mucosa, submucosa, muscularis (skeletal and smooth regionally distributed) & (skeletal and smooth regionally distributed) & adventia (not serosa: entirely connective tissue)adventia (not serosa: entirely connective tissue)

Digestive processes in mouth, pharynx & Digestive processes in mouth, pharynx & esophagusesophagus1. Mastication: Mechanical breakdown by teeth 1. Mastication: Mechanical breakdown by teeth and tongueand tongue2. Deglutition: Complicated process of swallowing2. Deglutition: Complicated process of swallowing(two phases which involves 22 muscles)(two phases which involves 22 muscles)

StomachStomach1. Expansion of the GI tract1. Expansion of the GI tract2. Sack for storage and chemical breakdown in 2. Sack for storage and chemical breakdown in which food is converted to chymewhich food is converted to chyme

StomachStomach

Gross anatomy Gross anatomy 1. Four regions: Cardiac (region where food 1. Four regions: Cardiac (region where food enters), fundus, body & pyloric. Terminates at the enters), fundus, body & pyloric. Terminates at the pylorus & connects with small intestine via pyloric pylorus & connects with small intestine via pyloric sphincter.sphincter.2. Greater curvature (lateral convex surface)2. Greater curvature (lateral convex surface)3. Lesser curvature (medial concave surface)3. Lesser curvature (medial concave surface)

Microscopic anatomy Microscopic anatomy 1. Four tunics1. Four tunics2. Lining epithelium: Simple columnar (entirely 2. Lining epithelium: Simple columnar (entirely goblet cells) with gastric pits (gastric glands that goblet cells) with gastric pits (gastric glands that produce gastric juice)produce gastric juice)

3. Secretory cells of gastric glands: 3. Secretory cells of gastric glands: Mucous neck Mucous neck cellscells (produce acidic mucus), (produce acidic mucus), parietal cellsparietal cells (secrete (secrete HCl and intrinsic factor), HCl and intrinsic factor), chief (zymogenic) cellschief (zymogenic) cells (produce pepsinogen which is converted initially by (produce pepsinogen which is converted initially by HCl into pepsin which will catalyze conversion HCl into pepsin which will catalyze conversion thereafter) & thereafter) & enteroendocrine cellsenteroendocrine cells (produce (produce hormones that regulate digestive function) hormones that regulate digestive function)

Digestive processes occurring in stomachDigestive processes occurring in stomach1. Enzymatic digestion: Protein digestion is 1. Enzymatic digestion: Protein digestion is initiated in stomach (pepsin)initiated in stomach (pepsin)2. Lipid soluble substances can pass through 2. Lipid soluble substances can pass through stomach mucosa (alcohol and aspirin)stomach mucosa (alcohol and aspirin)3. Production of intrinsic factor: Required for 3. Production of intrinsic factor: Required for absorption of B12 absorption of B12

Regulation of gastric secretionRegulation of gastric secretion1. Three phases: 1. Three phases: Cephalic, gastric & intestinalCephalic, gastric & intestinal2. 2. Cephalic phaseCephalic phase: Occurs prior to food entering : Occurs prior to food entering stomach (brain response to food) via hypothalamic stomach (brain response to food) via hypothalamic stimulation of the vagus nerve (parasympathetic stimulation of the vagus nerve (parasympathetic enteric ganglionic neurons stimulate the stomach enteric ganglionic neurons stimulate the stomach glands)glands)

3. 3. Gastric phaseGastric phase: Local signaling within stomach : Local signaling within stomach due to the presence of food (distension, peptides or due to the presence of food (distension, peptides or low acidity) lead to HCl release (gastrin is released low acidity) lead to HCl release (gastrin is released in response to chemical stimuli & stimulates the in response to chemical stimuli & stimulates the release of HCl by parietal cells)release of HCl by parietal cells)

4. 4. Intestinal phaseIntestinal phase: : Excitatory phaseExcitatory phase: Duodenum : Duodenum releases a gastrin-like substance that promotes releases a gastrin-like substance that promotes additional activity of gastric glands. additional activity of gastric glands. Inhibitory Inhibitory phasephase: Enterogastric reflex inhibits vagal nuclei, : Enterogastric reflex inhibits vagal nuclei, inhibits local reflexes, activates sympathetic fibers inhibits local reflexes, activates sympathetic fibers that tighten pyloric sphincter & causes the release that tighten pyloric sphincter & causes the release of enterogastrones.of enterogastrones.5. Enterogastrone are secretin, cholecystokinin 5. Enterogastrone are secretin, cholecystokinin (CCK), vasoactive intestinal peptide (VIP) & (CCK), vasoactive intestinal peptide (VIP) & gastric inhibitory peptide (GIP)gastric inhibitory peptide (GIP)

Small IntestineSmall Intestine

Gross anatomy Gross anatomy 1. Pyloric sphincter to ileocecal valve1. Pyloric sphincter to ileocecal valve2. Subdivisions: Duodenum, jejunum & ileum2. Subdivisions: Duodenum, jejunum & ileum

Microscopic anatomyMicroscopic anatomy1. Expanded surface area for absorption1. Expanded surface area for absorption2. Structural modifications: 2. Structural modifications: Circular folds Circular folds (deep (deep folds of the mucosa and submucosa), folds of the mucosa and submucosa), VilliVilli (finger- (finger-like projections of the mucosa) & like projections of the mucosa) & MicrovilliMicrovilli or or brush border (projections of plasma membranes) brush border (projections of plasma membranes)

HistologyHistology1. Simple columnar epithelium1. Simple columnar epithelium2. Submucosa includes lymphatic tissue: 2. Submucosa includes lymphatic tissue: Peyer’s patchesPeyer’s patches

Liver and gallbladder Liver and gallbladder

D. Liver and gallbladder D. Liver and gallbladder 1. Accessory organs associated with small intestine 1. Accessory organs associated with small intestine 2. Liver has a role in digestion in addition to its 2. Liver has a role in digestion in addition to its other functions: Bile production and export other functions: Bile production and export (emulsification of fat)(emulsification of fat)

3. Gallbladder: Stores bile3. Gallbladder: Stores bile4. Bile: Only bile salts and phospolipids aid in 4. Bile: Only bile salts and phospolipids aid in digestion (emulsify fat) other components that do digestion (emulsify fat) other components that do not contribute to digestion will not be discussednot contribute to digestion will not be discussed

5. Regulation of bile release: CCK from small 5. Regulation of bile release: CCK from small intestine is released into blood in response to fatty intestine is released into blood in response to fatty chyme entering small intestine. CCK stimulates chyme entering small intestine. CCK stimulates secretion of pancreatic juice & relaxes hepato-secretion of pancreatic juice & relaxes hepato-pancreatic sphincter (controls entry of pancreatic pancreatic sphincter (controls entry of pancreatic juice and bile entering duodenum)juice and bile entering duodenum)

Pancreas Pancreas 1. Accessory digestive organ1. Accessory digestive organ2. Produces digestive enzymes: Exocrine product 2. Produces digestive enzymes: Exocrine product (pancreatic juice)(pancreatic juice)3. Acini: Secretory cells surrounding ducts3. Acini: Secretory cells surrounding ducts4. Composition of pancreatic juice: Proteases, 4. Composition of pancreatic juice: Proteases, amylase, lipases & nucleasesamylase, lipases & nucleases

Regulation of pancreatic secretion: Local Regulation of pancreatic secretion: Local hormones (CCK & secretin) & parasympathetic hormones (CCK & secretin) & parasympathetic nervous systemnervous system

Large IntestineLarge Intestine

Gross anatomy Gross anatomy 1. Ileocecal valve to the anus1. Ileocecal valve to the anus2. Absorbs water from indigestible food residues2. Absorbs water from indigestible food residues3. Unique features: 3. Unique features: TeniaeTeniae coli (3 bands of longi- coli (3 bands of longi-tudinal smooth muscle), tudinal smooth muscle), haustrahaustra (pocketlike sacs) (pocketlike sacs) & & epiploic appendagesepiploic appendages (fat-filled pouches) (fat-filled pouches)

4. Subdivisions: 4. Subdivisions: CecumCecum (1 (1stst segment: saclike), segment: saclike), appendixappendix (lymphatic dead end), (lymphatic dead end), coloncolon (several (several regions: regions: ascendingascending, , transversetransverse, , descendingdescending & & sigmoidsigmoid), ), rectumrectum (contains rectal valves: internal (contains rectal valves: internal transverse folds) & transverse folds) & anal canalanal canal (two sphincters: (two sphincters: internal involuntary and external voluntary)internal involuntary and external voluntary)

5. Digestive processes: No breakdown, just water 5. Digestive processes: No breakdown, just water and vitamin absorption & major function is the and vitamin absorption & major function is the peristaltic movement of fecal materialperistaltic movement of fecal material6.Defecation: rectal walls stretch(defecation reflex)6.Defecation: rectal walls stretch(defecation reflex)which is spinal-parasympathetic reflex (causes which is spinal-parasympathetic reflex (causes colon colon && rectum to contract rectum to contract && anal sphincters relax) anal sphincters relax)

Chemical DigestionChemical Digestion

Background Background 1. Hydrolysis1. Hydrolysisa. Catabolic processa. Catabolic processb. Large molecules into monomersb. Large molecules into monomersc. Enzymes into lumen of alimentary canalc. Enzymes into lumen of alimentary canal i. Intrinsic and accessory glandsi. Intrinsic and accessory glands

Carbohydrates (starch) Carbohydrates (starch) 1. Carbohydrates are broken down into 1. Carbohydrates are broken down into glucose, fructose and galactoseglucose, fructose and galactose2. Process2. Processa. Salivary amylasea. Salivary amylaseb. Pancreatic amylaseb. Pancreatic amylase

ProteinsProteins1. Begins in stomach1. Begins in stomacha. Pepsinogen to pepsina. Pepsinogen to pepsin2. Continues in small intestine2. Continues in small intestinea. Trypsin and chymotrypsina. Trypsin and chymotrypsin i. Pancreatic enzymesi. Pancreatic enzymesb. Carboxypepsidaseb. Carboxypepsidase i. Pancreatic enzymesi. Pancreatic enzymes

Lipids Lipids 1. Digestion occurs solely in small intestine1. Digestion occurs solely in small intestinea. Lipases from pancreasa. Lipases from pancreas2. Bile emulsifies fats so they are soluble2. Bile emulsifies fats so they are solublea. Only increases area that enzymes can contacta. Only increases area that enzymes can contact

Nucleic acids Nucleic acids 1. Pancreatic nucleosides1. Pancreatic nucleosides

AbsorptionAbsorption

Active transport through the intestinal villiActive transport through the intestinal villi1. Lipids can pass through cell membranes1. Lipids can pass through cell membranesa. Active transpost is not requiresa. Active transpost is not requires2. Carbohydrates2. Carbohydratesa. Protein carriersa. Protein carriers i. Metabolic energy is requiredi. Metabolic energy is required