1. SMALL INTESTINE

2. Small Intestine Majority of digestion and absorption
Figure 24.18
Small Intestine
Majority of digestion and absorption
Extends from pyloric sphincter  ileocecal sphincter
Divided into 3 regions
Same 4 layers as most of GI

3. Figure 24.18b

4. Figure 24.19b Histology of the small intestine

5. Mucosa
Figure 24.19
S cells
CCK cells
K cells

6. Figure a

7. Figure 24.20

8. Figure 24.20d Brush border of Absorptive cells
Brush border enzymes work inside epithelial cells (surface of microvilli)
Some absorptive cells slough off to act in the lumen

9. Submucosa Duodenum Ileum Duodenal glands (Brunner’s)
Figure 24.20c
Duodenum
Duodenal glands (Brunner’s)
Alkaline mucous
Ileum
Lymphatic nodules (Peyer’s patches)

10. Mechanical Digestion
Segmentation and Peristalsis (MMC)

11. Chemical Digestion
Read through your notes. Refer to your textbook if needed.
Pay attention to enzymes and where they act and what they break down.
Take note of when they are activated / inactivated.
Focus on tables 24.4 and 24.5

12. TABLE 24.4

14. Absorption End products of digestion moves into the blood or lymph.
Occurs by diffusion, facilitated diffusion, osmosis and various forms of active transport.
MICELLES
CHYLOMICRON

17. Water Absorption via osmosis Fig 24
Water Absorption via osmosis Fig Based on electrolyte and nutrient [ ]

18. LARGE INTESTINE

19. Large Intestine (colon)
Terminal portion of GI tract.
Completion of absorption, production of vitamins and formation and expulsion of feces.
Extends from the ileocecal sphincter to the anus.
Cecum, colon, rectum, and anal canal.
The colon is divided into the ascending, transverse, descending, and sigmoid portions.

20. Figure 24.23a

21. Eiploic appendages or omental appendices

22. Rectum and Anus Rectum Anal canal
Figure 24.23b
Rectum
Anal canal
Anal columns  mucous membrane  longitudinal folds
Anus
Internal anal sphincter  smooth muscle
External anal sphincter  skeletal muscle

23. Figure 24.24a

24. Figure 24.24b

25. Figure 24.24c and d

26. Histology of the L.I Summary
Mucosa
Simple columnar epithelium
Absorptive and goblet cells in crypts
Submucosa
Areolar connective tissue
Muscularis
Internal smooth muscle
External longitudinal muscle
Teniae coli
Haustra
Serosa
Visceral peritoneum
Omental appendices

28. Mechanical Digestion
Chemical Digestion
Gastroileal reflex
Haustral churning
Peristalsis
Mass peristalsis
Bacterial fermentation
Absorption
Feces Formation
Water
Electrolytes
Some vitamins
Inorganic salts
Sloughed-off epithelial cells
Bacteria
Indigestible and unabsorbed food

29. Defecation Reflex

32. PHASES OF DIGESTION

33. Three Phases of Digestion
Cephalic Phase
Gastric Phase
Intestinal Phase

34. Cephalic Phase
Cerebral cortex, hypothalamus, and brainstem activated by sight, smell, thought, and taste of food.
Brainstem activates parasympathetic nuclei:
CN VII – salivation
CN IX – salivation
CN X – gastric juice
Prepares mouth and stomach for food that is about to be eaten

35. Gastric Phase Begins when food reaches the stomach
Promotes gastric secretion and motility
Regulated by neural and hormonal activities

36. Gastric Phase – Neural Regulation
Food entering stomach increases gastric juice pH and distends stomach walls.
Chemoreceptors and stretch receptors in stomach
Detect pH increase
Detect distention
Send nerve impulses to submucosal plexus.
Submucosal plexus stimulates:
Parietal cells to secrete HCl
Muscularis to contract more vigorously
Causes mixing and initiates gastric emptying.

37. Figure 24.25 Neural Feedback Loop
Food entering stomach
Disrupts homeostasis
by increasing
CONTROLLED CONDITION
pH of gastric juice
Distention (stretching) of stomach walls
RECEPTORS
Chemoreceptors and stretch receptors in stomach detect pH increase and distension
Input
Nerve impulses
CONTROL CENTER
Return to homeostasis when response brings pH of gastric juice and distention of stomach walls back to normal (pre-eating status)
Submucosal plexus
Output
Nerve impulses (parasympathetic)
EFFECTORS
Smooth muscle in stomach wall
Parietal cells
HCI
Parietal cells secrete HCI
Smooth muscle contracts more vigorously
RESPONSE
Increase in acidity of stomach chyme; mixing of stomach contents; emptying of stomach

38. Gastric Phase – Hormonal Regulation
Food entering stomach increases gastric juice pH and distends stomach walls.
ANS is triggered to release acetylcholine.
ACh stimulates G cells in pyloric antrum and secrete gastrin hormone into blood.

39. Gastrin’s Actions Major Effects Promotes gastric juice secretion
Increases gastric motility
Promotes gastric mucosal growth
Minor Effects
Constricts lower esophageal sphincter
Relaxes pyloric sphincter

40. Intestinal Phase Begins when food enters the small intestine.
Inhibits gastric secretion and motility.
Promotes intestinal and pancreatic juice secretion, bile ejection, and intestinal motility.
Regulated by neural and hormonal activities.

41. Intestinal Phase – Neural Regulation
Gastric emptying of chyme into small intestine distends duodenal walls.
Stretch receptors detect distention  nerve impulses to brainstem.
Brainstem ↓ parasympathetic and ↑ sympathetic nerves to stomach and pyloric sphincter.
Gastric motility and emptying is inhibited.

42. Intestinal Phase – Hormonal Regulation
Chyme containing digested proteins and fatty acids stimulates intestinal glands to secrete cholecystokinin into blood.
Acidic chyme stimulates intestinal glands to secrete secretin into blood.

43. Secretin’s Actions
Major Effects
Stimulates secretion of pancreatic juice and bile rich in HCO3-
Minor Effects
Inhibits gastric juice secretion
Promotes normal pancreatic growth and maintenance
Enhances CCK’s effects

44. CCK’s Actions Stimulates secretion of enzyme-rich pancreatic juice
Major Effects
Stimulates secretion of enzyme-rich pancreatic juice
Causes ejection of bile from gallbladder
Opens sphincter of hepatopancreatic ampulla
Minor Effects
Inhibits gastric emptying
Promotes normal pancreatic growth and maintenance
Enhances secretin’s effects

45. Table 24.8 Major Hormones that Control Digestion
There are at least 10 other hormones involved in the GI tract

46. Development and Aging of the Digestive System
Read the last page in your notes
Read page 932 in your textbook
With a friend, add any important information to your notes on these two topics.