1. DIGESTIVE SYSTEM

2. GENERAL 1st System to Develop “Tube” Within a Tube
Contents Remain External Until Absorbed Through Walls
Humans are (Anatomical) Omnivores
Consists of Alimentary Canal/Digestive Tract and Accessory Organs

3. DIGESTIVE SYSTEM FUNCTIONS
Ingestion – Food Enters Through Mouth
Digestion – Breaking Large Molecules into Smaller, Absorbable Molecules
Mechanical (Physical)
Chemical (Enzymatic)
Absorption – Passage of Molecules Through GI Tract Wall into Blood or Lymph
Egestion – Elimination of Non-digestible Substances Through Anal End

4. DIGESTIVE SYSTEM ORGANIZATION
Alimentary Canal (Gastrointestinal or Digestive Tract)
Mouth, Pharynx, Esophagus, Stomach, Small Intestine, Large Intestine
Lumen is part of External Environment
Accessory Organs
Salivary Glands
Liver
Gall Bladder
Pancreas

6. ALIMENTARY CANAL HISTOLOGY
Mucosa
Innermost, Surrounds Lumen
Mucous Membrane
Secretes, Absorbs, Protects
Submucosa
Below Mucosa
C.T., Blood Vessels, Lymphatics, Nervous Tissue

7. ALIMENTARY CANAL HISTOLOGY continued
Muscularis (Externa)
Smooth Muscle
Inner, Circular,  Diameter of Lumen
Outer, Longitudinal,  Diameter of Lumen
Propels Substances
Serosa (Visceral Peritoneum)
Outermost
Serous Membrane, Lubricates
Adventitia outside of Ventral Body Cavity

9. MOVEMENT OF FOOD
Peristalsis - Wave-like Contraction of Circular & Longitudinal Smooth Muscle for Propulsion
ANS
Stimulated by Parasympathetic
Inhibited by Sympathetic

11. ALIMENTARY CANAL ORGANIZATION
MOUTH
Oral (Buccal) Cavity Functions in Ingestion
Digestion:
Mechanical (Teeth, Tongue)
Chemical (Saliva Begins Carbohydrate Digestion)
Cheeks
Hard Palate (Bony)

13. MOUTH continued Soft Palate (Muscular)
Blocks Nasopharynx During Swallowing
Uvula - Dangling end
Tongue
Frenulum Anchors to Floor of Mouth
Skeletal Muscle Tissue covered with Mucosa
Papillae with Taste Buds
Lingual Tonsil & Sublingual Gland

14. MOUTH continued Teeth Vestibule – Space between Teeth & Lips
Two Sets: Deciduous (20) & Permanent (32)
Four Types:
Incisors – Biting
Canines – Tearing & Grasping
Bicuspids & Molars - Grinding

16. ALIMENTARY CANAL ORGANIZATION continued
PHARYNX
Connects Oral Cavity, Nasal Cavity, Larynx & Esophagus
Passageway for Food, Water, Air
Muscular Walls (Swallowing)
3 Regions: Nasopharynx, Oropharynx, Laryngopharynx

17. ALIMENTARY CANAL ORGANIZATION continued
ESOPHAGUS
Collapsible, 10” Tube
Connects Pharynx & Stomach
Lies Posterior to Trachea
Lower Esophageal Sphincter Prevents Stomach Contents from Entering Esophagus
Passes Through Neck  Thoracic Cavity  Esophageal Hiatus  Abdominal Cavity

19. ALIMENTARY CANAL ORGANIZATION continued
STOMACH
J-Shaped Organ, Inferior to Diaphragm
Functions:
Storage
Digestion (Mechanical & Chemical)
Protein Digestion Begins here
Absorption of Water, Alcohol, Drugs

20. STOMACH continued Enters as Bolus – Mixture of Food & Saliva
Leaves as Chyme – Milky Mixture of Partially Digested Food & Gastric Juices

21. STOMACH continued 4 Regions: Cardia – Connects with Esophagus
Body – Principal, Main Part
Fundus – Superior, Bulge, Food Storage
Pylorus – Terminal Part, Pyloric Sphincter
2 Curves:
Greater Curvature
Lesser Curvature

23. STOMACH continued Wall Modifications:
Rugae –Expandable Folds, Accommodate More Food
Oblique Muscle in Muscularis
Gastric Glands in Mucosa
Mucus Cells (Protective Coating)
Parietal Cells (HCl, pH = 2)
Chief Cells (Pepsinogen + HCl  Pepsin (Proteolytic)

25. ALIMENTARY CANAL ORGANIZATION continued
SMALL INTESTINE
Site of Most Chemical Digestion
Site of 90% of Absorption
Monosaccharides  Blood
Amino Acids  Blood
Fatty Acids & Glycerol  Lymph

26. SMALL INTESTINE continued
3 Subdivisions:
Duodenum
First 10-12”
Ampulla of Vater Receives Secretions from Liver & Pancreas
Bile through Common Bile Duct
Pancreatic Juice through Pancreatic Duct
Jejunum –Middle Length
Ileum – Last, Joins with Large Intestine at Ileocecal Valve

28. SMALL INTESTINE continued
Wall Modifications:
All Increase Surface Area for Maximum Absorption
Plicae Circulares – Transverse Folds of Mucosa & Submucosa
Villi – Finger-like Projections of Mucosa, contain Capillaries & Lacteal
Microvilli – Microscopic Folds of Cell Membrane

30. ALIMENTARY CANAL ORGANIZATION continued
LARGE INTESTINE
Functions:
Secretes Mucus
Absorbs Water, Ions, Vitamins (From Bacterial Metabolism)
Forms & Compacts Feces (Undigested Food, Bacteria, Water)

31. LARGE INTESTINE continued
3 Divisions:
Cecum
Blind Pouch
Appendix Attached
Colon - Divided into Ascending, Transverse, Descending, Sigmoid
Rectum – Anal Canal
Internal Anal Sphincter (Smooth)
External Anal Sphincter (Skeletal)

32. Radiograph of large intestine following barium enema.

33. LARGE INTESTINE continued
Wall Modifications:
Taenia Coli – 3 Bands of Longitudinal Muscle from Muscularis of Colon
Haustra – Pouches in Wall of Colon
No Villi

34. ALIMENTARY CANAL MOVEMENTS
Peristalsis - Wave-like Contraction of Circular & Longitudinal Smooth Muscle for Propulsion
Segmentation – Mixes & Pushes Chyme Against Wall of Small Intestine
Haustral Churning – Pouch-to-Pouch Movement in Large Intestine
Reverse Peristalsis

36. Image is radiograph following barium enema

37. ACCESSORY ORGANS SALIVARY GLANDS Exocrine Glands
Ducts Carry Secretions (Saliva) into Mouth
Saliva: Amylase, Mucous, Water, Antibodies, Lysozyme
3 Pairs:
Parotid (Most Salivary Amylase)
Submandibular
Sublingual

39. ACCESSORY ORGANS continued
LIVER
Largest Gland in Body (Exocrine)
Produces & Secretes Bile (Fat Emulsifier)
Nutrient Storage & Conversion
Synthesizes Blood Proteins
Detoxification

42. ACCESSORY ORGANS continued
GALL BLADDER
Muscular Sac
Stores & Concentrates Bile
Receives Bile from Liver via Common Hepatic Duct  Cystic Duct
Releases into Duodenum via Cystic Duct  Common Bile Duct  Ampulla of Vater (Sphincter of Oddi)

44. ACCESSORY ORGANS continued
Bile Release:
Chyme Enters Duodenum
Cholecystokinin (CCK) & Secretin Secreted by Duodenum, Enters Blood
Secretin stimulates liver to produce bile
CCK Stimulates Contractions in Gall Bladder & Relaxation of Sphincter

45. Parasympathetic stimulation via Vagus Nerve also stimulated gallbladder to contract

46. ACCESSORY ORGANS continued
PANCREAS
Exocrine (& Endocrine) Gland
Secretes Pancreatic Juice (Digestive Enzymes & Buffers)
Leaves Pancreas Through Pancreatic Duct(s), Enters Duodenum Through Ampulla of Vater
Raises pH of Duodenum (pH 8, “Natural Antacid”) via bicarbonate ions
Secretin stimulates release by Pancreas of watery solution with high HCO3-
CCK stimulates release by Pancreas of enzymatic solution