1. Gastrointestinal System
Digestion
Anatomy of digestive system (review!)
4 major processes of digestive system:
Motility
Secretion
Digestion
Absorption
Gastrointestinal System

2. Fig. 14.1

3. Peritoneum and Peritoneal Cavity
Peritoneum - serous membrane of abdominal cavity
Visceral peritoneum on external surface of most digestive organs
Parietal peritoneum lines body wall
Peritoneal cavity
Between two peritoneums
Fluid lubricates mobile organs
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4. Phases of Digestion/Absorption
Cephalic
Gastric
Intestinal
Defecation

6. Cephalic Gastric Intestinal Defecation Anticipation
Begins with sensory input that is sent to the cerebral cortex and then to the hypothalamus to stimulate the PNS
Salivation, relaxation of the GE sphincter, relaxation of stomach muscles, increase gastric motility
Mastication
Mechanical digestion
Teeth, tongue
Deglutition
Bolus formation for swallowing
Peristalsis in esophagus

10. Salivary Glands Parotid Glands
Secretes Mucous
Allows for smooth swallowing of bolus
Mumps
Sublingual and Submandibular glands secrete Amylase
Breaks down complex carbohydrates into simple carbohydrates

11. Deglutition

14. Cephalic Gastric Intestinal Defecation Storage
Relaxation or contraction as needed.
Digestion
HCl - Hydrochloric Acid (Parietal cells)
Pepsin (Chief cells)
Mechanical
Immune Protection
Ingested pathogens
Respiratory mucus

16. Gastroesphogeal Reflux Disease Lower esophageal sphincter dysfunction
Reflux Esophagitis = Heartburn = GERD
Gastroesphogeal Reflux Disease
Lower esophageal sphincter dysfunction
Why reflux against gravity?

17. GERD, cont’d Intrapleural pressure  during inspiration
 Wall of esophagus expands
Subatmospheric pressure in esophageal lumen sucks acidic stomach contents into esophagus
May also occur during pregnancy or obesity

18. Mechanical Digestion
Rugae are used along with the Gastric Muscles for mechanical digestion

20. Chemical Digestion Gastric Pits Chief Cells
Invaginations of the stomach wall
Lined with several different types of cells
Chief Cells
At the bottom of the pits
Secretes pepsinogen
Inactive form of the enzyme pepsin
Pepsinogen is converted into pepsin upon mixing with HCl
Pepsin breaks down proteins into amino acids

21. Chemical Digestion Cont.
Parietal Cells
Above Chief Cells
Secret H+ and Cl- into the Gastric Pits
Used for Digestion of foodstuff
Gastric Glands or G cells
Secretes the hormone Gastrin
Gastrin secretion increases when the contents of the stomach is basic
Gastrin secretion decreases when the contents of the stomach is acidic
Gastrin’s functions are
To increase HCl secretion from the Parietal Cells
To increase Gastric Motility

22. Mucous Cells Secrete Mucous to coat the lumen of the stomach
Prevents ulceration
H. Pylori also responsible for ulcers

25. Intestinal – Chyme (ingesta) enters small intestine Defecation
Cephalic
Gastric
Intestinal – Chyme (ingesta) enters small intestine
Defecation
Neutralization of HCl
NaHCO3 from pancreas
Running Problem: Peptic Ulcer and antacids, including H2 antagonists and proton pump inhibitors
Pancreatic enzymes
Digest protein, CHO
Bile acids
Emulsification of Fat
Absorption of H2O

27. Mechanical Digestion Peristalsis and Segmentation
Occurs in the small intestine
Food is basically shaken back and forth in small segments along the length of the small intestine

28. Chemical Digestion Release of Digestive Enzymes Release of Bile
Pancreas releases digestive enzymes into the duodenum
Release of Bile
Emulsification of Fat
Storage and Release by Gall Bladder
Production of Bile by Liver
Bile contains:
Cholesterol
Bile Salts
Lecithin
Billirubin

30. Table 14.2

36. Bacterial fermentation of CHO and proteins
Cephalic
Gastric
Intestinal
Defecation
Bacterial fermentation of CHO and proteins
Lactate, some vitamins are digested and/or absorbed
More H2O absorption
Osmotic diarrhea vs. secretory diarrhea
Osmotic-solutes prevent H2O reabsorption
Lactose intolerance
Secretory- bacterial toxins ("flush out' pathogens)
Defecation Reflex

38. Colon Three Major Functions of the Large Intestine Absorption of H2O
Storage of Feces
Usually 24 hours
Production of Vitamin K
From E. Coli
Used in the Blood Clotting Process

43. Motility Forward movement of food Mechanical mixing
Secretion
Digestion
Absorption
Motility
2 purposes:
Forward movement of food
Mechanical mixing
GI smooth muscles contract spontaneously
Pacemaker cells, (Interstitial Cells of Cajal), connected by gap junctions, generate slow wave potentials
AP’s spread throughout longitudinal muscles (gap junctions)  wave of contraction
Like cardiac muscle, Ca2+ can regulate contraction strength

44. Different Patterns of Contraction
Tonic Contractions
Sustained contraction, usually in the stomach
Phasic Contractions
Peristaltic contractions
progressive waves moving along segments of longitudinal layer  forward propulsion
circular layer contracts proximal to bolus
Especially esophagus
Segmental contractions
alternate contraction & relaxation lead to mixing
A side effect of narcotics

45. Secretion
Motility
Secretion
Digestion
Absorption
9 L of fluid pass through the GIT (only 2 L from food & drink)  Secretion and Reabsorption important
Ions and water; similar to renal mechanisms
Saliva
Hydrochloric Acid (Parietal Cells)
Bicarbonate (enzyme necessary ?)
Enzymes (zymogens)
Mucus (Goblet cells)
Bile (bile salts – function?)
Net Fluid Balance in GI system

46. Digestion Overview Bile emulsifies fats
Motility
Secretion
Digestion
Absorption
Digestion Overview
Mechanical breakdown and mixing aid enzymatic breakdown
Chewing
Tonic contractions, esp. stomach
Enzymatic breakdown converts macromolecules into absorbable units
Bile emulsifies fats
Optimal pH of enzymes indicates location of activity

47. Absorption Overview Most nutrient absorption takes place in ?
Motility
Secretion
Digestion
Absorption
Absorption Overview
Most nutrient absorption takes place in ?
Fats absorbed into lacteals
Everything else absorbed into portal vein
Alcohol & aspirin across gastric epithelium
Additional: H2O, ions & some vitamins absorbed in ________________
Mechanisms analogous to renal absorption