1. Digestive System
Anatomy & Physiology

2. Function & Organization
The breakdown of food into small
enough particles to be absorbed
Organization
Alimentary Canal aka GI tract
Accessory Organs

3. Digestive Processes Ingestion: bringing food into the system
Mechanical Digestion: the mechanical breakdown of food (chewing, mixing, churning)
Propulsion: movement of food through system

4. Digestive Processes
Chemical Digestion: breakdown of large food molecules by enzymes
Absorption: transport of digested food materials to the blood or lymph
Defecation: elimination of indigestible material from the body

5. Peritoneum
The largest serous membrane of the body lining all organs of the abdominal cavity and the cavity wall
Parietal peritoneum: lines walls
Visceral peritoneum: lines organs
Peritoneal cavity: potential space between membranes; produces serous fluid

6. Extensions of the Peritoneum
Falciform ligament: connects liver to anterior abdominal wall and diaphragm
Lesser omentum: attaches to medial stomach, attaching it to anterior wall

7. Extensions of the Peritoneum
Greater Omentum: extends off stomach; contains lymph nodes and holds fatty deposits
Mesentary: suspends coils of small intestine and attaches it to posterior abdominal wall

8. Wall Structure of Alimentary Canal
4 layers
Mucosa/mucus membrane
Submucosa
Muscularis
Serosa

9. Wall Structure of Alimentary Canal
1. Mucosa: lines lumen of alimentary canal
Protects from microorganisms
Absorbs digested food materials
Secretes mucous & digestive enzymes

10. Wall Structure of Alimentary Canal
2. Submucosa
-Rich in blood vessels, lymphatic vessels and nerve endings
-Provides nourishment for tissues and carries away absorbed materials

11. Wall Structure of Alimentary Canal
Muscularis
- smooth muscular layer (has 2 parts)
inner layer runs longitudinally
outer layer (constrictor layer) runs circularly
induces a propelling action called peristalsis

12. Wall Structure of Alimentary Canal
4. Serosa
- visceral peritoneum
-outermost covering of alimentary canal

13. Alimentary Canal: Mouth
Function: receives food and starts digestion and prepares it for swallowing
- Teeth: performs mastication (chewing)
- Uvula: fingerlike extension from archway; works with soft palate to close opening to nasal cavity upon swallowing

14. Mouth continued
Salivary Glands: accessory organs around mouth; secretes saliva
saliva: 99.5% water, 0.5% solutes
Lysozome: destroys bacteria
Salivary amylase: begins chemical digestion of carbohydrates
Mucus: lubricates and binds food particles to form a bolus

15. Alimentary Canal: Pharynx
Function: transports food from oral cavity to esophagus
-uvula and epiglottis assist pharynx in transporting bolus to the esophagus ONLY

16. Alimentary Canal: Esophagus
Function: 10 inch muscular tube that transports bolus to stomach from pharynx
- Peristalsis: alternate waves of muscle contraction & relaxation; moves bolus along alimentary canal

17. Esophagus continued
- Mucosa: made of stratified squamos epithelium to resist abrasion
- Cardio-esophageal sphincter: found at distal end; acts as a valve to prevent stomach contents from entering esophagus

18. Alimentary Canal: Stomach
Function: c-shaped organ acting as a temporary storage site for food; performs mechanical and chemical digestion
-Rugae: deep folds formed by inner lining of stomach when empty
-Full stomach: can hold up to 1 gallon of food
- Pyloric sphincter: valve that controls
movement of food from stomach into small intestine

19. Stomach Wall 4 basic layers: mucosa, submucosa, muscularis and serosa
Mucosa & muscularis is functionally and structurally different
Mucosa: gastric pits work to produce and secrete gastric juices
HCL, digestive enzymes and mucus

20. Stomach Wall Muscularis
Stomach has an additional layer of muscle fibers
Allows stomach to churn and mix stomach contents

21. Stomach Functions
Mechanical Digestion: churning and mixing of stomach contents to aid digestion
Chemical Digestion: pepsin: breaks down proteins (works only in acidic environments)

22. Stomach Functions
Absorption: limited absorptive abilities (water, salts, glucose, alcohol, aspirin and some lipid-soluble drugs)
Propulsion: propels food into small intestine in the form of CHYME (mixture of food particles & gastric juice)
Chyme presses against pyloric sphincter causing it to relax and allowing chyme to pass

23. Alimentary Canal: Small Intestine
Completes mechanical and chemical digestion & is the main site of nutrient absorption
Propels food through with peristaltic waves
20 feet long, highly coiled
Takes ~ 3-10 hours to move chyme through
Suspended to posterior abdominal wall via mesentary

24. Small Intestine continued
3 Segments:
Duodenum: receives chyme from stomach & digestive enzymes from accessory organs; about 10 inches long
Jejunum: site of absorption; about 8 feet long

25. Small Intestine continued
Ileum: about 12 feet long; the end of digestion and absorption of nutrients
Ileocecal valve: the junction at which the small & large intestine join; sphincter muscle controlling the flow of material between organs

26. Wall of Small Intestine
Highly convoluted mucosa for better absorption through increased surface area
Intestinal villi: tiny projections of mucosa
Microvilli: even smaller projections on the intestinal villi

27. Wall of Small Intestine
Within each villi is:
Blood capillaries
Lacteals (lymphatic vessels)
- Act to carry absorbed nutrients away

28. Alimentary Canal: Large Intestine
Final segment of alimentary canal
~5 feet long but larger in diameter than small intestine
Function: to dry out indigestible material by absorbing water; eliminate unwanted materials

29. Large Intestine continued
5 main segments of large intestine
Cecum: sac-like pouch receiving material from ileum
Vermiform appendix: worm-like extension holding lymphatic tissue
Colon: ascending, transverse, descending, sigmoid
Rectum
Anus

30. Large Intestine continued
Anus: has 2 sphincters
Internal: involuntary; told to relax when fecal matter stimulates the defecation reflex in the rectum
External: voluntary; if relaxed, elimination occurs

31. Fecal Formation
Fecal matter: 75% water, 25% indigestible material, mucus and bacteria
Color: produced by bile
Gas: produced by the metabolism of bacteria or from swallowing air
Movement of matter is very slow ~ hours

32. Carbohydrate Digestion
Carbohydrate: nutrient; main source of energy in the body
Glucose: a simple sugar; the end product of carbohydrate digestion
Takes place in the mouth & small intestine

33. Protein Digestion
Protein: basic nutrient; used in anabolism (tissue building)
Amino Acid: the building blocks of proteins; the end product of protein digestion
Takes place in the stomach & small intestine

34. Fat Digestion Fat: basic food type; used for energy
Fatty acids and glycerol: end products of fat digestion
Takes place in the small intestine
Enzymes:
Bile in duodenum: fat droplets into smaller fat droplets

35. Time to Digest
Carbohydrate-rich meal: moves through the stomach rapidly
Fat-rich meals: may take up to 6 hours to pass through the stomach

36. Digestion Mishaps
Heartburn: the damage to esophageal mucosa due to presence of stomach acids because of a weak cardio-esophageal sphincter
Gastric ulcer: when the mucus layer of the stomach is not strong enough to withstand gastric acids; burns a hole in stomach wall

37. Digestion Mishaps
Diarrhea: the decreased absorption of water and electrolytes in the small & large intestine leading to watery stool
Constipation: the increased absorption of water and electrolytes in the large intestine; leads to hard, impacted stool