1. Chapter
The Digestive System

2. The Gall bladder Hollow, pear-shaped organ
Stores, modifies and concentrates bile
Contraction of the gall bladder and release of bile is controlled by CCK and vagal stimulation
Empties into the Cystic duct
Gall stones

3. The Gallbladder

4. Bile Made of water, billirubin, ions, cholesterol, other lipids
Acts as an emulsifier to aid lipid digestion
90% is reabsorbed in the ileum - enterohepatic circulation of bile

5. Functions of the large intestine
Reabsorb water and compact material into feces
1500 mL chyme enter the cecum, 90% of volume reabsorbed yielding mL of feces
Absorb vitamins produced by bacteria
Store fecal matter prior to defecation

6. General anatomy of the large intestine
Lies inferior to the stomach
Frames the small intestine
Parts of the large intestine
Cecum
Colon
Ascending
Transverse
Descending
Sigmoid
Rectum
Anal canal

7. The Large Intestine

8. Cecum and Rectum Cecum opening protected by ileocecal valve
veriform appendix
Rectum
Last portion of the digestive tract
Terminates at the anal canal
Internal anal sphincter - involuntary smooth muscle
External anal sphincter - voluntary muscle
Hemorrhoids -inflamed veins

9. Rectum

10. Histology of the large intestine
Columnar cells except the rectum and anal canal (stratified squamous)
Muscularis externa
circular muscle
only 3 bands longitudinal smooth muscle - taeniae coli
Absence of villi
Presence of goblet cells
Deep intestinal glands

11. Physiology of the large intestine
Absorption in the large intestine includes:
Water
Vitamins – K, biotin, and B5
Organic wastes – urobilinogens and sterobilinogens
Bile salts
Some ammonia and other toxins
Mass movements of material through colon and rectum
Defecation reflex triggered by distention of rectal walls

12. Movement in Large Intestine
Mass movements
Common after meals
Integrated by the enteric plexus
Local reflexes
instigated by the presence of food in the stomach and duodenum
Gastrocolic reflex: initiated by stomach
Duodenocolic reflex: initiated by duodenum

13. Long reflexes of defecation

14. Coordination secretion and absorption
Neural and hormonal mechanisms coordinate glands
GI activity stimulated by parasympathetic innervation
Inhibited by sympathetic innervation
Enterogastric, gastroenteric and gastroileal reflexes coordinate stomach and intestines
Several hormones alter motility and secretion

15. Summary Hormone Table
GIP duodenum fats, carbohydrates stim pancreas insulin secretion, inhibits stomach, stim adipose glucose and FA uptake & lipogenesis
Marieb Table

16. Summary Hormone Table (continued)
Marieb Table

17. Activities of Major Digestive Tract Hormones
From Martini Figure 24.22

18. Digestion, Absorption, Transport
Disassembles organic food into smaller fragments
Mechanical: breaks large food particles to small
Chemical: breaking of covalent bonds by digestive enzymes
Hydrolyzes carbohydrates, proteins, lipids and nucleic acids for absorption
Absorption and transport
Molecules are moved out of digestive tract and into circulation for distribution throughout body

19. Carbohydrate digestion and absorption
Begins in the mouth (salivary amylase) completed in small intestine
Salivary and pancreatic amylase
Convert starches to disaccharides, trisaccharides, monosaccharides
Brush border enzymes
Make monosaccharides from disaccharides
maltase (glucose / glucose)
sucrase (glucose / fructose)
lactase (glucose / galactose)
Absorption of monosaccharides occurs across the intestinal epithelia by facilitaed diffusion or Na+ linked co-transporters

20. Lipid digestion and absorption
Begins in stomach (minor) completed in small intestine
Lipid digestion utilizes lingual and pancreatic lipases converts triglycerides to monoglycerides
Bile salts improve chemical digestion by emulsifying lipid drops
Lipid-bile salt complexes called micelles are formed
Micelles diffuse into intestinal epithelia which re-synthesis triglycerides and then release lipids into the circulation as chylomicrons - mixtures of phopholipids and proteins
carried by lymphatic system

21. Lipid Absorption also (see Saladin fig 25.30)
from Seeley, Stephens and Tate

22. Protein digestion and absorption
(See Saladin Fig 25.29)
In the stomach, the low pH destroys tertiary and quaternary structure allows pepsin to digest specific peptide bonds
In the small intestine, pancreatic enzymes and intestinal brush border peptidases work at pH 7-8
Trypsin - breaks bonds next to arginine or lysine
Chymotrypsin- breaks bonds next to phenylalanine or tyrosine
Liberated amino acids, and some dipeptides are absorbed through by several different carrier proteins via by facilitaed diffusion or Na+ linked co-transporters

23. Absorption of other molecules
Water
Nearly all that is ingested is reabsorbed via osmosis
Ions
Absorbed via diffusion, cotransport, and active transport
Vitamins
Water soluble vitamins (C and B vitamins) are absorbed by diffusion
Vitamin B12 requires intrinsic factor
Fat soluble vitamins (A,D, E, K) are absorbed as part of micelles

24. Water Intake, Secretion and Absorption
Diarrhea
Constipation
from Seeley, Stephens and Tate

25. Great Summary slide (a)
Marieb Figure 23.33a

26. Great Summary slide (b)
Marieb Figure 23.33b