1. The Digestive System

2. Organ groups of digestion
Alimentary organs
Mouth
Pharynx
Esophagus
Stomach
Small and large intestine
Accessory digestive organs
Teeth and tongue
Liver
Pancreas
Salivary glands
gallbladder

3. The processes of digestion
Ingestion
Secretion
Mixing and propulsion
Mechanical and chemical digestion
Absorption
Defecation

4. Peristalsis and segmentation

5. Layers of the GI tract Mucosa Submucosa Muscularis Serosa
Layer of epithelium
Lamina propria (connective tissue)
Thin layer of smooth muscle (muscularis mucosae)
Submucosa
Muscularis
Serosa

6. ANS input
Vagus nerve supplies parasympathetic input to most parts of the GI tract.
Preganglionic parasympathetic neurons synapse on postsynaptic neurons in the submucosal and myenteric plexuses.
Parasympathetic stimulation increases motility and GI secretion.
Sympathetic postsynaptic neurons in the plexuses decrease GI section and decrease motility by inhibiting neurons of ENS

9. Mouth Buccal cavity Oral mucosa Vestibule Gingivae Hardpalate
Soft palate
Uvula

10. Salivary glands Cleanse mouth Dissolve food chemicals Moisten food
Enzymes break down carbs
Fluid is excreted into the mouth by several different salivary glands, but the majority comes from three
Parotid – at the base of the ear – secretes through the parotid duct
Sublingual – below the tongue – secretes through the sublingual duct
Submandibular – below the jaw – secretes into the submandibular duct
Saliva – mixture of different fluids secreted by these glands—average output is liters a day.
99.5% is water
Mucus – responsible for the lubricating action of the saliva
Buffers – keep the pH of your mouth around 7 to prevent the buildup of acids produced by bacteria
Salivary amylase – enzyme that breaks down carbohydrates as they enter the mouth
Lingual lipase – produced by glands on the tongue – begins the digestion of lipids, enzyme is activated in the stomach.
Lysozyme – enzyme that attacks bacteria and inhibits their growth
Immunoglobulins – IgA antibodies to attack bacteria – keeps them from attaching to the epithelium so they cannot penetrate
Defensins—granules that contain a brew of antibacterial proteins

11. Teeth Crown, neck and root Peridontal ligament Enamel Dentin
Root canal
Periodontal ligament – teeth are embedded in sockets in the jaw bones
Sockets are lined with this membrane of dense fibrous connective tissue (gomphosis)
Anchors the teeth and absorbs shock while chewing
Crown, neck, and root – crown is the exposed part of the tooth, neck is the point where the crown and root join, and the root is the part that is embedded in the jaw
Enamel – outermost part of the tooth – hardest biologically manufactured molecule
Dentin – similar to bone – does not contain cells – projections from dentin extend into the cavity below
Pulp cavity – interior chamber that receives nerves and blood vessels
Root canal – tunnel located at the base of the tooth that allows vessels and nerves to enter the tooth
Apical foramen – opening at the base of the tooth that allows them in

12. Tooth varieties
Incisors
Cuspids
Bicuspids
Molars
Mastication
Bolus

13. Tongue
Bolus moves from the mouth into the different parts of the pharynx – various muscles are involved in adjusting the position of the pharynx to facilitate swallowing.

14. Swallowing Deglutition 3 phases Peristalsis Buccal Pharyngeal
Esophogeal
Peristalsis
Secondary peristaltic waves

15. Deglutition

16. Stomach
Fundus
Body
Pylorus
Pyloric sphincter
Rugae

17. Stomach histology

18. Gastric Glands Mucous cells G cells Parietal cells Chief cells
Surface & neck
G cells
Parietal cells
Chief cells
Enteroendocrine cells

19. Stomach and chemical digestion
Cephalic (Reflex) phase
Triggered by sensory signals surrounding food.
Activates vagal nerve and ANS to enhance secretions
Hydrochloric Acid Production in Parietal Cells

20. Stomach and chemical digestion
Gastric Phase
Activation of local myeteric reflexes and vagovagal reflexes
Gastrin
Release of HCl from parietal cells

21. Stomach and chemical digestion
Intestinal Phase
Excitatory component
Inhibitory component

22. Gastric Secretion: 3 Phases

23. Stomach and mechanical digestion
Stomach filling
Contractile activity
Peristalsis
Gastric emptying

24. Small intestine and associated organs

25. Small intestine histology

26. Small intestine histology

27. Liver Digestive function is to produce bile.
Metabolic function is to process venous blood from digestive tract
Functional unit is a lobule

28. Liver

29. Liver Functions Carbohydrate metabolism Lipid metabolism
Protein metabolism
Processing of drugs and hormones
Excretion of bilirubin
Synthesis of bile salts
Storage
Phagocytosis
Activation of vitamin D

30. Cholesterol

31. Accessory organs

32. Bile
Alkaline solution that includes bile salts, phospholipids and electrolytes.
Bile salts derived from cholesterol
Bile salts emulsify fats and solubilize cholesterol, increasing absorption.
Bile is recycled
Fatty chyme and bile returning to liver stimulates more production of bile.

33. Gallbladder The gallbladder stores and concentrates bile.
Bile release into duodenum
Fatty chyme stimulates release of CKK and secretin.
CKK enters bloodstream
Bile salts and secretin in the blood stimulate liver to rapidly produce bile.
Vagal stimulation leads to weak contractions.
CKK causes gallbladder to contract and the hepatopancreatic sphincter to relax; bile enters duodenum
Stores that which is not immediately needed and concentrates bile 10X

34. Pancreatic juice Insulin & Glucose Regulation
1200 to 1500 mL produced daily
Composed of water, salts, sodium bicarbonate and enzymes (pH )
Pancreatic juices buffer acidic gastric juices in chyme, stops the action of pepsin, and creates the proper pH for intestinal digestive enzymes.
Enzymes
Pancreatic amylase—starches
Trypsin—proteins, secreted as trypsinogen, pancrease also makes trypsin inhibitor; trypsinogen is cleaved by enterokinase to make trypsin. Trypsin acts on the other protein enzyme precursors
Chymotrypsin—proteins
Carboxypeptidase—proteins
Elastase—proteins
Pancreatic lipase—lipids
Ribonuclease—RNA
Deoxyribonuclease—DNA

35. 1200 to 1500 mL produced daily
Composed of water, salts, sodium bicarbonate and enzymes (pH )
Pancreatic juices buffer acidic gastric juices in chyme, stops the action of pepsin, and creates the proper pH for intestinal digestive enzymes.
Enzymes
Pancreatic amylase—starches
Trypsin—proteins, secreted as trypsinogen, pancrease also makes trypsin inhibitor; trypsinogen is cleaved by enterokinase to make trypsin. Trypsin acts on the other protein enzyme precursors
Chymotrypsin—proteins
Carboxypeptidase—proteins
Elastase—proteins
Pancreatic lipase—lipids
Ribonuclease—RNA
Deoxyribonuclease—DNA

37. Digestion in Small intestine: chemical
Digestion of carbohydrates
Pancreatic amylase
Brush-border enzymes
Digestion of proteins
Enzymes from pancreatic juice
Brush-border peptidases releases single AAs
Digestion of lipids
Digestion & Absorption of Fats
Digestion of nucleic acids

41. Digestion in Small intestine: mechanical
Segmentation leads to chyme being moved backwards and forwards.
Parasympathetic input increases intensity of contractions; sympathetic input decreases intensity.
Peristalsis occurs after nutrients are absorbed; regulated by motilin.
Migrating motility complex
Movement through ileocecal sphincter is enhanced by gastrin.
Once meal has passed through sphincter back pressure keeps the valve closed

44. Water
Water moves in both directions and follows flow of electrolyhtes

45. Large intestine (5 ft)
Mechanical digestion—haustral churning, peristalsis, mass peristalsis
Chemical digestion
Absorption
Feces formation
Reflexes in the Colon

46. Ulcerative Colitis

47. Defecation reflex Mass peristaltic movements
Voluntary contractions of diaphragm and abdominals
Parasympathetic input
Voluntary input

48. Resources Human Digestion Heart Burn Video Peristalsis Animation
Digestive System