1. List and define briefly the major processes occurring during digestive system activity.
2. Describe the tissue composition and the general function of each of the four layers of the alimentary tube.
3. Describe the anatomy and basic function of each organ and accessory organ of the alimentary canal.
4. Describe the composition and functions of saliva, and explain how salivation is regulated.
5. Describe the mechanisms of chewing and swallowing.
6. Identify structural modifications of the wall of the stomach and small intestine that enhance the digestive process in these regions.
7. Describe the composition of gastric juice, name the cell types responsible for secreting its various components, and indicate the importance of each component in stomach activity.
8. Explain how gastric secretion and motility in the stomach are regulated.
9. Describe the function of local hormones produced by the small intestine.
10. State the roles of bile and of pancreatic juice in digestion.
11. Describe how entry of pancreatic juice and bile into the small intestine is regulated.
12. List the major functions of the large intestine, and describe the regulation of defecation.
13. List the enzymes involved in chemical digestion; name the foodstuffs on which they act and then end products of protein, fat, carbohydrate, and nucleic acid digestion.
14. Describe the process of absorption of digested foodstuff that occurs in the small intestine.
See figure 22.2
1.
Ingestion: taking food into digestive tract
2.
Propulsion: moving food through – swallowing and peristalsis
3.
Mechanical digestion: chewing, churning, segmentation See figure 22.3
4.
Chemical digestion
5.
Absorption
6.
Defecation
See figure 22.6
1.
Mucosa or mucous membrane: secretion, absorption, protection, made of simple columnar epithelium
2.
Submucosa: dense connective tissue w/ blood and lymphatic vessels, lymph nodules, and nerves
3.
Muscularis: inner circular layer and outer longitudinal layer of smooth muscle
4.
Serosa: visceral peritoneum of areolar CT covered w/ simple squamous epithelium
See figure 22.14
Serosa: outer layer
Muscularis layer has 3 layers of smooth muscle: circular, longitudinal, and oblique to churn stomach for mechanical digestion
Submucosa
Mucosa: made of simple columnar epithelium of goblet cells which secrete alkaline mucus. It is dotted with gastric pits which lead to gastric glands that produce gastric juice (mucus, gastrin)
See figure 22.15

See figure 22. 15
 Mucous neck cells produce acidic mucus
 Parietal cells make HCl (pH 1.5-3.5)and intrinsic factor for absorption of vitamin B12 in sm. intestine
 Chief cells make pepsinogen (positive feedback)
 Enteroendocrine cells make gastrin, and other hormones
: made of bicarbonate rich mucus, tight junctions of epithelial cells, cell membranes of glandular cells impermeable to HCl, surface epithelium renewed every 3-6 days.
: gastritis occurs when mucosal barrier is breached. Gastric ulcers occur due to hypersecretion of HCl, hyposecretion of mucus, and presence of Helicobacter pylori.
: A bolus enters the stomach and leaves as acid chyme. Protein digestion w/ pepsin occurs in stomach. In children, the stomach also secretes rennin for milk protein digestion.
Aspirin and alcohol can pass through stomach mucosa into blood.
See figure 22.16
: vagus and enteric nerves. Parasympathetic (through vagus) increases secretion, sympathetic decreases secretion.
: gastrin stimulates HCl and enzymes; small intestine hormones are gastrin antagonists
See table 22.1
: (conditioned reflex) before food enters. Aroma, taste, sight, or thought of food.
Signals go to hypothalamus, stimulates vagal nuclei that in turn signal stomach glands)
: once food reaches stomach. Stimuli are distention, peptides, low acidity of stomach.
Peptides, caffeine and increasing pH activate gastrin secretion. Then more HCl is released.
: both excitatory and inhibitory. Excitatory: food goes into duodenum and gastrin is released that stimulates gastric glands. Inhibitory: occurs as intestine distends and substances in chime trigger enterogastric reflex
: inhibits vagal nuclei, activates sympathetic fibers to tighten pyloric sphincter.
Gastric secretion decreases, hormones (secretin, CCK, VIP, GIP) all inhibit gastric secretion.
: adapted for nutrient absorption See figure 22.21,
22.22
 Plicae circularis, villi, macrovilli, all increase surface area

 Villi contain capillary bed and lacteal for absorption. They have a brush border of microvilli w/brush border enzymes for final stages of digestion
 Made of absorptive cells, goblet cells, lymphocytes, enteroendocrine cells
See figure 22.24
 Hepatocytes filter and process nutrient rich blood. Leaky capillaries (sinusoid) to allow blood through. Macrophages (Kupffer cells) in liver help protect.
 Hepatocytes produce bile, process nutrients (glucose), store fat soluble vitamins (ADE) and detoxify blood.
:
 yellow green, alkaline w/ bile salts, pigments (bilirubin from RBC’s) cholesterol, phospholipids, electrolytes.
 Bile salts emulsify fats and also facilitate fat and cholesterol absorption. Bile salts are recycled in the large intestine and the rest is eliminated in feces (give them their color). Fatty chyme stimulates the release of bile and increases bile output.
See figure 22.25
 Stored in gall bladder when not needed for digestion.
 Gall bladder and sphincter of Oddi are stimulated when CCK (cholecystikinin) is released during the intestinal phase.
 Bile is released when acidic, fatty chime enters duodenum. CCK also stimulates secretion of pancreatic juice.
See figure 22.26
 Produces pancreatic juice of water, enzymes, electrolytes. Clusters of acinar cells produce enzymes. Epithelial cells release HCO
3
that neutralizes acid chime and provides optimal environment for intestinal and pancreatic enzymes.
See figure 22.28
 Secretin released from enteroendocrine cells of duodenum stimulates release of bicarbonate-rich pancreatic juice to neutralize HCl.
 CCK is released in response to entry of fats and protein into duodenum. Stimulates release of enzyme-rich pancreatic juice.
See figure 22.29, 22.31
 Responsible for the recovery of water and electrolytes from remaining materials. 90% of water has already been absorbed, but considerable water and electrolytes remain (Na and Cl) and must be recovered.
 Forms and stores feces. The remaining material is dehydrated, mixed with bacteria and mucus and formed into feces.
 Microbes in the large intestine produce enzymes capable of digesting many molecules that are indigestible to us, mainly cellulose. As they digest carbohydrates, intestinal gas develops. Vitamin
K is synthesized by colonic bacteria
: food broken down into monomers by hydrolysis See figure 22.23
: monosaccharides (glucose, fructose, galactose) produces by salivary amylase
(mouth), pancreatic amylase (pancreas into duodenum), and intestinal brush border enzymes
(duodenum).

: polypeptides are produed from protein by pepsin in stomach (in presence of acidic pH). Trypsin, chymotrypsin, and carboxypeptidase from pancreas (activated in duodenum at alkaline or neutral pH) produce small peptides. Brush border peptidases finish digestion into amino acids.
: small intestine is the sole site for digestion. Bile from liver emulsifies while lipases from pancreas break it up into glycerol and fatty acids. See figure 22.35
: pancreatic nucleases and brush border enzymes digest to nucleotide components.
: 10 L enter but 1 L or less reaches the large intestine. All food, 80% of electrolytes, and most water is absorbed in the small intestine. Most absorption is completed by the time it gets to the ileum. Bile salts are absorbed by the ileum. Most nutrients are absorbed through mucosa by cotransport and active transport. Bile salts and lecithin w/ lipid byproducts form micelles for absorption into the lacteals.
: sodium is absorbed with glucose and amino acids. Chloride ions are absorbed by active transport and exchanged with bicarbonate ions. Potassium is absorbed as water is absorbed. Anything interfering with water absorption will affect potassium absorption. Also, as diarrhea occurs, it pulls potassium into lumen of intestine. Calcium absorption is regulated by the active form of vitamin D.
Vitamins A,D,E, and K need to be dissolved in fat-containing food for absorption. Vitamins B and C are water soluble, except Vit B12 needs intrinsic factor that is made by the stomach.