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The Digestive System. Digestion Digestion = the mechanical and chemical breakdown of foods into nutrients that cell membranes can absorb 2 Components.

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Presentation on theme: "The Digestive System. Digestion Digestion = the mechanical and chemical breakdown of foods into nutrients that cell membranes can absorb 2 Components."— Presentation transcript:

1 The Digestive System

2 Digestion Digestion = the mechanical and chemical breakdown of foods into nutrients that cell membranes can absorb 2 Components of the digestive system: –Alimentary canal – mouth, pharynx, esophagus, stomach, small intestine, large intestine, anal canal –Accessory organs – secrete products into the canal; salivary glands, liver, pancreas, gallbladder

3 Components of the Digestive System

4 Alimentary Canal Around 9 meters long Muscular tube that passes through the ventral cavity Lumen

5 Alimentary Wall Structure Mucosa Submucosa Muscular layer –Circular fibers –Longitudinal fibers –Oblique fibers Serosa

6 Movements of the Alimentary Canal Mixing movements Propelling movements

7 Mouth Structure Surrounded by lips, cheeks, tongue, and palate Oral cavity Vestibule Cheeks Lips

8 Tongue Frenulum Papillae Hyoid bone Lingual tonsils

9 Palate Hard palate Soft palate Uvula Palatine tonsils Pharyngeal tonsils (adenoids)


11 Primary and Secondary Teeth Primary teeth –Deciduous teeth –Erupt between 6 months and 2-4 years –20 teeth Secondary teeth –Appear around 6 years –32 teeth

12 Tooth Types Incisors –Chisel-shaped –Bite off large pieces of food Cuspids –Cone-shaped –Grasp and tear food Bicuspids and Molars –Flattened surfaces –Grind food


14 General Tooth Structure Crown Root Neck Enamel Dentin Pulp Root canals Cementum Periodontal ligament

15 Salivary Glands Secrete saliva: –Moistens food particles –Helps bind food particles –Begins chemical digestion of carbohydrates –Dissolves food for tasting –Helps cleanse mouth and teeth

16 Salivary Cells Serous cells –Produce watery fluid that contains amylase –Amylase splits starch and glycogen into disaccharides Mucous cells –Secrete mucus to bind food particles and lubricate during swallowing

17 Major Salivary Glands Parotid glands –Largest –Mostly serous secretions Submandibular glands –Mostly serous secretions Sublingual glands –Smallest –Mostly mucous secretions

18 Regions of the Pharynx Nasopharynx –Open to nasal cavity –Passage for air during breathing Oropharynx –Behind soft palate –Passage for air and food Laryngopharynx –Passage for food to the esophagus

19 Swallowing Reflex Food is chewed and mixed with saliva to form a mass called a bolus. Bolus is forced into the pharynx. Swallowing reflex is stimulated by sensory receptors around the pharyngeal opening.


21 Swallowing Reflex Soft palate rises to prevent food from entering the nasal cavity. Hyoid bone and larynx are elevated, and the epiglottis of the larynx closes off the top of the trachea. Breathing is briefly inhibited.


23 Swallowing Reflex Tongue presses against the soft palate, sealing the oral cavity off from the pharynx. Longitudinal muscles in the pharyngeal wall contract, moving the pharynx up toward the bolus. Muscles in the lower pharynx relax, and the esophagus opens. Peristalsis moves the bolus through the esophagus.


25 Esophagus Straight, collapsible tube Approximately 25 cm long Passageway from pharynx to stomach Cardiac sphincter Mucous glands for lubrication

26 Movement through Esophagus - Peristalsis

27 Stomach J-shaped, pouchlike organ Hangs under the diaphragm 1 liter capacity Rugae

28 Stomach Functions Receives food from the esophagus Mixes food with gastric juices Initiates protein digestion Performs limited absorption of water, salts, alcohol, and lipid-soluble drugs Moves food into the small intestine

29 Stomach Regions Cardiac Fundic Body Pyloric

30 Gastric Secretions Gastric pits Gastric glands –Goblet cells –Chief cells – pepsinogen –Parietal cells – HCl and intrinsic factor Gastric juice Regulated by ACh, gastrin, and cholecystokinin

31 Mixing and Emptying Actions of the Stomach

32 Pancreas Secretes pancreatic juice from acinar cells Mixed gland Pancreatic duct Hepatopancreatic sphincter

33 Pancreatic Secretions Pancreatic juice contains several enzymes: –Pancreatic amylase –Pancreatic lipase –Nucleases –Trypsin, chymotrypsin, and carboxypeptidase –Bicarbonate ions Release regulated by secretin

34 Liver Located in upper right quadrant below the diaphragm Color from rich supply of blood vessels Divided into left and right lobes by fibrous capsule Each lobe separated into hepatic lobules functional units of liver

35 Hepatic Lobule Structure Consists of many hepatic cells radiating out from a central vein Hepatic sinusoids Portal vein Central veins Kupffer cells Bile canals Common hepatic duct


37 Liver Functions Cells respond to insulin and glucagon to maintain normal glucose levels Carbohydrate, lipid, and protein metabolism –Glucose Glycogen –Noncarbs Glucose –Makes cholesterol and fats –Amino acids Urea –Makes plasma proteins Storage of glycogen, iron, vitamins A, D, and B12 Blood filtering Detoxification Secretion of bile

38 Bile Yellowish-green liquid that contains: –Bile salts – for emulsification and absorption of fatty acids, cholesterol, vitamins A, D, E, and K –Bile pigments – bilirubin and biliverdin –Cholesterol –Electrolytes

39 Gallbladder Pear-shaped sac on the inferior liver surface Connects to the cystic duct which feeds into the common hepatic duct Stores bile between meals Reabsorbs water to concentrate bile Releases bile into the small intestine Common bile duct Stimulated by cholecystokinin

40 Gallbladder and Liver Problems Jaundice Hepatitis Gallstones

41 Small Intestine Extends from pyloric sphincter to the large intestine Receives secretions from the pancreas and liver Completes digestion of nutrients in chyme and absorbs products of digestion Mixing movements and peristalsis – chyme moves through in 3-10 hours Transports digestive residue to the large intestine

42 Regions of the Small Intestine Duodenum –25 cm long –Most fixed portion of the small intestine Jejunum Ileum –Jejunum and ileum are not distinctly separate –Both are mobile

43 Mesentery Double-layered fold of peritoneal membrane Suspends the jejunum and ileum from the posterior abdominal wall Supports the blood vessels, nerves, and lymphatic vessels that supply the intestinal wall

44 Greater Omentum Filmy, double-layered fold of the peritoneal membrane Drapes like an apron from the stomach over the transverse colon and the folds of the small intestine May adhere to infected areas of the alimentary canal to wall it off

45 Intestinal Villi Tiny projections on the inner wall off the small intestine Densest in the duodenum Increase surface area for absorption Lacteals – absorb fatty acids and glycerol Goblet cells Intestinal glands Microvilli –Secrete peptidases, sucrase, maltase, lactase, intestinal lipase Capillaries absorb simple sugars, amino acids, electrolytes, and water



48 Large Intestine Ileocecal valve 1.5 meters long Extends up right side, crosses obliquely to the left side, and descends into the pelvis Opens to the outside of the body as the anus

49 Regions of Large Intestine Cecum –Vermiform appendix Colon –Ascending colon –Transverse colon –Descending colon –Sigmoid colon Rectum Anal canal

50 Anal Canal Structure Anal columns Anus –Internal anal sphincter –External anal sphincter Hemorrhoids

51 Large Intestine Anatomy Lack villi Teniae coli Many goblet cells –Protect intestinal wall –Bind particles of fecal matter –Help control pH

52 Large Intestine Functions Proximal end functions primarily in water and electrolyte absorption Distal end functions primarily to store feces Little to no digestive function More sluggish movements – peristaltic waves 2-3 times per day (mass movements)

53 Defecation Reflex Can be initiated by person (deep breath and abdominal contraction) Forces feces into rectum Reflex involves relaxation of the internal anal sphincter and peristaltic waves through the descending colon Can be prevented by contraction of the external anal sphincter

54 Feces Made of materials not digested or absorbed –Water –Electrolytes –Mucus –Bacteria 75% water Color from bile pigments altered by bacterial action Odor from compounds produced by bacteria

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