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 Cuspids Bicuspids and Molars 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 Mucous 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 Submandibular glands
Largest
Mostly serous secretions
Submandibular glands
Sublingual glands
Smallest
Mostly mucous secretions

18. Regions of the Pharynx Nasopharynx Oropharynx Laryngopharynx
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 Gastric juice
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. 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
Intestinal Villi

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 Hemorrhoids
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 75% water
Electrolytes
Mucus
Bacteria
75% water
Color from bile pigments altered by bacterial action
Odor from compounds produced by bacteria