1. Digestive System Gastrointestinal Tract 1. Mouth Accessory Structures
2. Pharynx
3. Esophagus
4. Stomach
5. Small Intestine
6. Large Intestine
Accessory Structures
1. Teeth
2. Tongue
3. Salivary Glands
4. Liver
5. Gallbladder
6. Pancreas

2. The Processes of Digestion
1. Ingestion
taking food into the mouth
2. Secretion
GI tract and accessory cells secrete water, acid, buffers, and enzymes into lumen
3. Mixing and Propulsion
alternating contraction and relaxation of smooth muscles in the walls of the GI tract
4. Digestion
Breaking down of larger food particles into smaller molecules
Mechanical Digestion
Chemical Digestion
5. Absorption
small molecules pass from the lumen into the blood and lymph
6. Defecation
elimination of indigestible substances and bacteria from the GI tract

3. Mouth (Oral Cavity) Mechanical Digestion mastication (chewing)
tongue manipulates food
teeth grind food saliva mixes so that food is
reduced to a soft flexible
mass called a bolus
that is easily swallowed

4. Salivary Glands Chemical Digestion salivary amylase
initiates the breakdown of
starch ingested disaccharides
and starches must be broken
down into monosaccharides
lingual lipase
initiates digestion of
triglycerides into fatty acids
and monoglycerides

5. Esophagus and Swallowing

6. Stomach Functions: connects the esophagus to the duodenum
(first part of the small intestine)
Functions:
1. serves as a mixing area for saliva,
food and gastric juice
2. serves as a reservoir for holding food
before release into the SI
3. secretes gastric juice (HCL, pepsin,
intrinsic factor, gastric lipase)
HCL kills bacteria, denatures protein
pepsin begins digestion of proteins
intrinsic factor aids absorption of
vitamin B12
gastric lipase aids digestion of
triglycerides
4. secretes gastrin (digestive hormone)
into the blood

7. Physiology of Digestion and Absorption in the Stomach
Mechanical Digestion
after food enters the stomach, gentle
mixing waves pass over the stomach
every seconds
it macerates the food and mixes it
with gastric juice, forming chyme
the chyme moves back and forth
and keeps mixing until it is sent
through the pyloric sphincter into
the duodenum
Chemical Digestion
lingual lipase and salivary amylase
continue to break down fats and
carbohydrates respectively
pepsin and HCL break down proteins
gastric lipase splits triglycerides into
fatty acids and monoglycerides
Peristalsis

8. Segmentation

9. Regulation of Gastric Secretion and Motility
Cephalic Phase:
Sight, smell, taste, and thought initiate reflex
Cortex and hypothalamus send impulses to medulla
Parasympathetic (Vagus nerve) impulses from medulla promote:
Peristalsis in stomach
Gastric glands to secrete:
Pepsinogen
HCL
Mucus
gastrin
Gastric Phase:
Stretch receptors detect distention of stomach
Chemoreceptors detect increased pH of gastric juice
Stimulates stomach churning and secreting
ACH from parasympathetic activity stimulates gastrin secretion
Stimulates gastric juice secretion
Stimulates stomach motility
Intestinal Phase
Stretch receptors detect distention of duodenum
Chemoreceptors detect fatty acids and glucose in duodenum
Impulses from small intestine inhibit stomach secretions and motility
Stimulates release of:
Gastric inhibitory peptide (GIP)
Inhibits gastric secretions and gastric motility in stomach
Secretin
Decreases gastric secretions
Cholecystokinin (CCK)
Inhibits stomach emptying

10. Stomach Cell Layers

11. Stomach Cells

12. Small Intestines Functions:
source of the major events of digestion and absorption
its long length (over 10 feet) is to increase the surface area
it has many circular folds, villi and microvilli
Functions:
1. mixes chyme with digestive
juices and brings food in
contact with surface
mucosa for absorption
2. completes digestion of
carbohydrates, proteins,
& lipids
begins & completes
digestion of nucleic acids
3. is responsible for the
absorption of about 90%
of all nutrients

13. Small Intestines Physiology
Digestion
chyme remains in SI for 3-4 hours
Mechanical Digestion
mixes chyme with digestive
enzymes
undergoes peristalsis
Chemical Digestion
pancreatic juice assists in
digestion
Absorption
food products pass through
mucosa absorptive cells
passage of these molecules from
the GI tract to the blood or lymph
is called absorption

14. Small Intestine Cell Layers

15. Small Intestine Cells

16. Liver and Gall Bladder

17. Brush Border Enzymes Carbohydrate digesting: Protein digesting:
Alpha-dextrinase
Maltase
Sucrase
Lactase
Protein digesting:
Aminopeptidase
Dipeptidase
Nucleic Acid digesting
Nucleosidase
Phosphatase

18. Glucose Absorption Carbohydrates are broken down into
monosaccharides like
glucose
Glucose passes through
SI Absorptive cells via
facilitative diffusion,
actually with the help
of a Na+ co-transporter
Glucose then passively
diffuses into the blood

19. Protein Absorption Proteins are broken down into amino acids
Amino acids and the slightly
larger di-peptides passively
diffuse across the membranes
of the SI Absorptive cells
Amino acids then passively
diffuse into the blood

20. Pancreatic Juice Enzymes
Carbohydrate digesting:
Pancreatic amylase
Protein digesting:
Trypsin
Chymotrypsin
Carboxypeptidase
Elastace
Lipid digesting
Pancreatic lipase
Nucleic Acid digesting
Ribonuclease
Deoxyribonuclease

21. Fat Absorption Large fat droplets are emulsified
into monoglycerides and fatty
acids by bile salts from the liver
and are packaged into micelles
Micelles merge with SI Absorptive
cells and via a type of endocytosis
deposit the fat fragments in the cells
The fat fragments are then
reassembled into triglycerides in the
cell and packaged in chylomicrons
Chylomicrons then exit the cell and
enter the lymph on their way to the
liver for final digestion and storage

22. Large Intestine (Colon)
Functions:
1. completion of absorption
2. manufactures vitamins
(some B’s & K)
3. formation of the feces
4. expulsion of the feces
Structures:
cecum
ascending colon
transverse colon
descending colon
sigmoid colon
rectum
anal canal
anus
anal sphincters

23. Rectum and Anus
Internal Anal Sphincter
External Anal Sphincter

24. Larger Intestine Cell Layers

25. Large Intestine Cells