1. Overview and Histology
Digestive System
Overview and Histology

2. Please take out a (scrap) piece of paper and number from 1-24

4. Digestive System – Crash Course

6. Two groups of organs Alimentary canal (gastrointestinal or GI tract)
Digests and absorbs food
Mouth, pharynx, esophagus, stomach, small intestine, and large intestine
Accessory digestive organs
Teeth, tongue, gallbladder
Digestive glands:
Salivary glands
Liver
pancreas

8. Parotid gland Mouth (oral cavity) Sublingual gland Salivary glands
Tongue
Submandibular
gland
Pharynx
Esophagus
Stomach
Pancreas
(Spleen)
Liver
Gallbladder
Transverse colon
Duodenum
Descending colon
Small
intestine
Jejunum
Ascending colon
Ileum
Cecum
Large
intestine
Sigmoid colon
Rectum
Vermiform appendix
Anus
Anal canal
Figure 23.1

9. Digestive Processes Ingestion – taking food into the digestive tract
Propulsion – movement of food through the alimentary canal
Includes swallowing (initiated voluntarily) and peristalsis (peri-around, stalsis-constriction)
Mechanical digestion
Chemical digestion
Absorption – passage of digested end products, vitamins, minerals and water from lumen through mucosal cells (mostly in small intestine)
Defecation-elimination of indigestible substances (feces)

10. Two types of Digestion:
1. Chemical Digestion
2. Mechanical (Physical) Digestion

11. Mechanical Digestion Physically prepares food for chemical digestion
Food is crushed, broken or cut into smaller pieces through chewing, mixing of food by the tongue, churning of food in the stomach and segmentation
INCREASES the surface area of the food in order to aid in chemical digestion

12. (a) Peristalsis: Adjacent segments of
From
mouth
(a) Peristalsis: Adjacent segments of
alimentary tract organs alternately contract
and relax, which moves food along the tract
distally.
(b) Segmentation: Nonadjacent segments
of alimentary tract organs alternately
contract and relax, moving the food
forward then backward. Food mixing and
slow food propulsion occurs.
Figure 23.3

13. Chemical Digestion
Food molecules are broken down into their building blocks by ENZYMES secreted into the lumen
Example: Saliva -breaks down starch into disaccharides (contains the enzyme amylase)
Stomach acid (HCL or Hydrochloric Acid) - breaks down gastric protease which digests proteins
BILE -produced by the liver and stored in the gall bladder breaks down fats
Begins in mouth and is complete by small intestine

14. MECHANISM FOR CHEMICAL DIGESTION
Hydrolysis - the splitting of large, insoluble molecules into small, soluble molecules with the addition of water

15. Which type of digestion is the following?
Chewing a saltine? -
2. Saliva breaking the saltine down into molecules of glucose? -
3. Your tongue breaking pieces of a hamburger apart?
4. Pepsin (an enzyme) in your stomach breaking the hamburger into amino acids?
Mechanical
Chemical
Mechanical
Chemical

16. Ingestion Food Mechanical digestion Pharynx • Chewing (mouth)
Esophagus
• Churning (stomach)
Propulsion
• Segmentation
(small intestine)
• Swallowing
(oropharynx)
Chemical
digestion
• Peristalsis
(esophagus,
stomach,
small intestine,
large intestine)
Stomach
Absorption
Lymph
vessel
Small
intestine
Blood
vessel
Large
intestine
Mainly H2O
Feces
Defecation
Anus
Figure 23.2

17. Human digestive system
After chewing and swallowing, it takes 5 to 10 seconds for food to pass down the esophagus to the stomach, where it spends 2 to 6 hours being partially digested.
Final digestion and nutrient absorption occur in the small intestine over a period of 5 to 6 hours.
In 12 to 24 hours, any undigested material passes through the large intestine, and feces are expelled through the anus.

18. Histology of the Alimentary Canal
Four basic layers (tunics)
Mucosa
Submucosa
Muscularis externa
Serosa

19. Intrinsic nerve plexuses • Myenteric nerve plexus
• Submucosal nerve plexus
Glands in submucosa
Mucosa
• Epithelium
• Lamina propria
• Muscularis
mucosae
Submucosa
Muscularis
externa
• Longitudinal
muscle
• Circular muscle
Serosa
Nerve
• Epithelium
Artery
• Connective
tissue
Vein
Gland in mucosa
Lumen
Lymphatic
vessel
Duct of gland outside
alimentary canal
Mucosa-associated
lymphoid tissue
Mesentery
Figure 23.6

20. Mucosa Inner tunic that lines the lumen Functions Three sublayers:
Secretes digestive enzymes and hormones
Absorbs end products of digestion
Protects tissue through production of mucous
Three sublayers:
Mucous Epithelium
Lamina propria (lamino=thin plate, propria=one’s own / special)
Muscularis mucosae

21. Submucosa Tunic underneath the tunica mucosa
Holds blood, lymphatic, and nervous tissues that serve to nourish, protect, and communicate

22. Muscularis Externa
Two layers of circular and longitudinal smooth muscles that contract and relax around the tube
Responsible for segmentation and peristalsis
In some regions, forms sphincters (circular muscle that acts as a valve -> preventing backflow)

23. Serosa
tunic within the peritoneal cavity that emits a slippery fluid to counteract friction
The serosa and visceral peritoneum are synonymous.
Replaced by the fibrous adventitia in the esophagus
Retroperitoneal organs have both an adventitia and serosa

24. Peritoneum and Peritoneal Cavity
Peritoneum: serous membrane of the abdominal cavity
Visceral peritoneum on external surface of most digestive organs
Parietal peritoneum lines the body wall
Peritoneal cavity
Between the two peritoneums
Fluid lubricates mobile organs

25. (a) Schematic cross sections of abdominal cavity
Abdominopelvic
cavity
Vertebra
Dorsal
mesentery
Parietal
peritoneum
Ventral
mesentery
Visceral
peritoneum
Peritoneal
cavity
Alimentary
canal organ
Liver
(a) Schematic cross sections of abdominal cavity
illustrate the peritoneums and mesenteries.
Figure 23.5a

26. Mesentery A double layer of peritoneum
Routes for blood vessels, lymphatics, and nerves
Holds organs in place and stores fat