The DIGESTIVE System

1. The DIGESTIVE System

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3. Digestion • The breaking down of food by both mechanical and chemical means • Mechanical Digestion - various movements of the alimentary canal that aid in chemical digestion • Grinding of teeth to soften food • Churning of food by smooth muscles to mix with digestive enzymes • Chemical Digestion - series of catabolic reactions that break down large molecules into smaller molecules

4. Absorption The passage of digested food from the alimentary canal into the cardiovascular and lymphatic systems for distribution to body cells

5. Defecation (Excretion) The elimination of indigestible substances from the alimentary canal

6. Ingestion Taking food into the body (EATING)

7. Movement (Propulsion) Passage of food along the alimentary canal

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9. Types of Digestion • Chemical digestion is the chemical breakdown of larger nutrient molecules to smaller ones which can be absorbed and used by the body. • Mechanical digestion is the physical breakdown of food into smaller pieces.

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11. Gastrointestinal Tract (Alimentary Canal) • A continuous tube running through the ventral body cavity extending from the mouth to the anus • Organs of the Alimentary Canal • mouth - pharynx - esophagus • stomach - S. intestine - L. intestine • Accessory Organs • teeth - tongue • salivary glands - liver • gallbladder - pancreas

12. Structures of the Digestive System

13. Mouth(Oral or Buccal Cavity) • Cheeks • Lips (Labia) • Vestibule • Hard Palate • Soft Palate • Uvula • Tongue • Papillae • Lingual Frenulum

14. Oral Cavity

15. Pharynx • Also called the throat. • Serves as a passageway for food and air. • Also helps in the formation of words.

16. Esophagus • Muscular tube located posterior to the trachea • About 10 inches long • Does not participate in digestive processes - simply a transport corridor • Food is pushed through the esophagus by peristaltic action • Forces food down into the stomach • Esophageal hiatus - opening in the diaphragm for the esophagus

17. Lining of the Esophagus

18. Stomach • J-shaped enlargement of the digestive tract located just below the diaphragm • Superior portion - continuation of the esophagus • Inferior portion empties into the duodenum • Position and size of the stomach varies from individual to individual

19. Histology of the Stomach • Composed of the same four tissue types as the other structures of the alimentary canal • When the stomach is empty the mucosa lie in large folds called rugae • mucosa contains millions of tiny openings called gastric pits that open into gastric glands • Secretes digestive enzymes and a fluid called gastric juice (2-3 liter per day)

20. Histology of the Stomach

21. Small Intestine • The next part of the alimentary canal. • Divided into three sections – the duodenum, jejunum, and ileum. • In the duodenum, chemical digestion is completed. • The majority of nutrients are absorbed in the jejunum and ileum.

22. Large Intestine • The last part of the alimentary canal. • Responsible for the absorption of water, compaction of feces, and the production of Vitamin K.

23. Accessory Organs • The accessory organs include the liver, gallbladder, pancreas, and salivary glands which will be discussed in more detail later on in this unit.

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25. Salivary Glands • Paired accessory structures that lie outside the oral cavity • Secrete their contents (saliva) into ducts that empty into the mouth • Parotid Glands - underneath the ears • Submandibular Glands - under the mandible • Sublingual Glands - under the tongue

26. Salivary Glands

27. Saliva • Fluid secreted by the salivary glands • 99.5% water • .5% solutes • chlorides - bicarbonates - sodium • potassium - phosphates - urea • uric acid - globulin -mucin • serum albumin • Salivary amylase - digestive enzyme • begins carbohydrate digestion in the mouth • Lysozyme - destroys bacteria in the mouth

28. Digestion in the Mouth • Mechanical Digestion • Chewing (Mastication) • Tongue manipulates the food • Teeth grind up the food and mix it with saliva • The result of mechanical digestion is a soft flexible mass of food called a bolus • Chemical Digestion • Salivary amylase initiates the breakdown of carbohydrates • Only chemical digestion in the mouth

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30. Teeth • Accessory structures of the digestive system • Deciduous teeth (baby teeth) - 20 • Permanent teeth - 32 • Incisors (8) - 4 on top, 4 on bottom • chisel shaped - front of mouth • Canines (4) - 2 on top, 2 on bottom • sharp pointed tearing teeth • Premolars (8) - 4 on top, 4 on bottom • Molars (12) - 6 on top, 6 on bottom • broad, flat, crushing teeth

31. Teeth

32. Portions of the Tooth • Crown - exposed portion of the tooth above the gum line • Neck - constricted junction line in the tooth between the crown and the root • Root - one to three projections of the tooth that are embedded in the sockets of the alveolar processes of the mandible and maxillae

33. Tooth Structures

34. Composition of Teeth • Enamel - outermost portion of the tooth, protects the tooth from wear and tear • the hardest substance in the body • Dentin - calcified connective tissue that gives the tooth its basic shape and rigidity • Pulp Cavity - large cavity enclosed by the dentin that is filled with pulp • Cementum - a bone-like substance that covers the dentin of the root

35. Periodontal Ligament • An area of dense fibrous connective tissue attached to the socket walls and the cemental surface of the roots of the teeth • Anchors teeth in position • Serves as a shock absorber when chewing

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37. Swallowing (Deglutition) • Moving food from the mouth to the stomach • Voluntary Stage - bolus is moved through the mouth into the oropharynx • Pharyngeal Stage - involuntary passage of the bolus through the pharynx and into the esophagus • Esophageal Stage - involuntary passage of the bolus through the esophagus and into the stomach

38. Swallowing

39. Deglutition

40. Digestive Processes • Mastication – chewing • Maceration – muscular waves in the stomach which mix food with gastric juice to form a liquid paste called chyme. • Segmentation – Short, small mixing movements of the alimentary canal.

41. Digestive Processes • Peristalsis – wave-like smooth muscle contractions which help to propel food and wastes along the alimentary canal. • Haustral Churning – movement of wastes along the large intestine by the contraction of the pouches or the haustra.

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43. Features of the Stomach • Cardiac Region – where the stomach is connected to the esophagus. • Fundus – the rounded, superior area of the stomach that acts as a temporary storage for food. • Body – the large, central portion of the stomach below the fundus.

44. Features of the Stomach • Pylorus – the narrow, inferior region of the stomach. • Rugae – the folds in the stomach that allow for stretching of the stomach with the intake of food. • Pyloric Sphincter – the one-way valve located between the stomach and the duodenum.

45. Structures of the Stomach

46. Stomach Structures

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48. Secretory Cells of the Gastric Glands • Chief Cells • Digestive enzymes • Pepsinogen activated by HCl and converted to • Pepsin • Parietal Cells • HCl • Intrinsic Factor (absorption of Vitamin B12) • Goblet Cells • Secrete mucus to protect the stomach mucosa from the acidic environment

49. Gastric Gland

50. GastricGland