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. Alimentary Canal Around 9 meters (30 feet) long
Muscular tube that passes through the ventral cavity

4. Alimentary Wall Structure
Mucosa-innermost layer
Submucosa- 2nd layer
Muscular layer-3rd
Circular fibers
Longitudinal fibers
Oblique fibers
Serosa-Outside layer

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

6. Tongue Frenulum Secures tongue to floor of mouth Papillae Hyoid bone
Lingual tonsils

7. Palate Hard palate Soft palate Uvula Palatine tonsils
Pharyngeal tonsils (adenoids)
Tonsils are lymphatic tissue used to protect you from infection

9. 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
All teeth have a coating of enamel (hardest substance in human body)

10. Salivary Glands Secrete saliva: Moistens food particles
Helps bind food particles
Amylase (enzyme) begins chemical digestion of carbohydrates (used first for energy)
Dissolves food for tasting
Helps cleanse mouth and teeth
Mucus softens food & lubricates G.I tract

11. 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

12. Swallowing Reflex= deglutition
Food is chewed (mastication)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.
Soft palate rises and seals the nasal cavity off with the uvula to stop 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.

13. 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.

14. Swallowing Reflex

15. Esophagus Straight, collapsible tube Approximately 25 cm long
Passageway from pharynx to stomach
Cardiac or esophageal sphincter (entry to stomach)
Mucous glands for lubrication
Disorders:
Acid Reflux
Ulcers
Heart Burn

16. Stomach 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
Bolus now turns into chyme (creamy paste)
Food enters through esophageal sphincter and exits via pyloric sphincter
Exploratory Surgery
Stomach
Disorders:
Ulcers
Tortion

17. Gastric Secretions Gastric pits Gastric glands Gastric juice HCl
Goblet cells
Chief cells – pepsinogen
Parietal cells – HCl
Gastric juice
HCl
Pepsin-digest protein
Regulated by ACh, gastrin, and cholecystokinin
Mucosal layer of stomach prevents stomach acid from eating through itself and releasing acid into the abdomen
Lower pH (Acids)
Gastric Secretions

18. Pancreas Secretes pancreatic juice from acinar cells Mixed gland
Pancreatic duct
Hepatopancreatic sphincter
Helps digest carbohydrates, proteins, fats & nucleic acids

19. Pancreatic Secretions
Pancreatic juice contains several digestive enzymes:
Pancreatic amylase
Pancreatic lipase
Nuclease
Trypsin, chymotrypsin, and carboxypeptidase
Bicarbonate ions

20. What does the Pancreas do?

21. Liver Carbohydrate, lipid, and protein metabolism
Storage of glycogen, iron, vitamins A, D, and B12
Blood filtering
Detoxification
Secretion of bile (emulsifies/breaks down fats)

22. How does the Liver work?

23. 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

24. 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 nutrients of digestion
Mixing movements and peristalsis – chyme moves through in 3-10 hours
Transports digestive residue to the large intestine

25. Regions of the Small Intestine
Duodenum
Portion closest to stomach
25 cm long
Most fixed portion of the small intestine
Jejunum-middle portion
Ileum
Final portion of small intestines prior to large intestines

26. Tiny projections on the inner wall off the small intestine
Densest in the duodenum
Increase surface area for absorption
Microvilli
Secrete peptidases, sucrase, maltase, lactase, intestinal lipase
Capillaries absorb simple sugars, amino acids, electrolytes (coenzymes that help control metabolism), and water
Intestinal Villi

28. Large Intestine Ileocecal valve 1.5 meters long
Proximal end functions primarily in water and electrolyte absorption
Distal end functions primarily to store feces
Little to no digestive function

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

30. To Gas or not to Gas?

31. Anal Canal Structure Anal columns Anus Hemorrhoids
Internal anal sphincter
External anal sphincter
Hemorrhoids

32. 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

33. 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