1. Digestive system

2. The Digestive System

3. Organs of the Digestive System
Two main groups
Alimentary canal – continuous coiled hollow tube, extends from the oral entrance up to the anal exit.
Accessory digestive organs, enclosed or connected to the alimentary canal.

4. Digestive Mucosa
The Digestive Epithelium
Mucosal epithelium is simple or stratified
Depending on location, function, and stresses:
oral cavity, pharynx, and esophagus are subjected to mechanical stress. They are lined by stratified squamous epithelium
stomach, small intestine, and most of large intestine are
sites for digestion and absorption. They are lined by
simple columnar epithelium with mucous (goblet) cells.

5. Alimentary Canal
It consists of the long, continuous tube that extends from the oral cavity to the anus.
Along this tube, the breakdown of food or digestion occurs, absorption of nutrients and elimination of waste products also takes place.
The final product of this process, a material called feces is discarded through the anal aperture.

6. Organs of the Alimentary Canal
Mouth
Pharynx
Esophagus
Stomach
Small intestine (duodenum, jejunum, ileum)
Large intestine (cecum, ascending colon, transverse colon, descending colon, sigmoid colon, rectum)
Anus

7. Accessory Digestive Organs
Salivary glands (Parotids, Sublingual and Submandibular)
Tongue
Teeth
Liver and Gallbladder
Pancreas

8. Mouth (Oral Cavity) Anatomy
Lips (labia) – protect the anterior opening
Cheeks – form the lateral walls
Hard palate – forms the anterior roof
Soft palate – forms the posterior roof
Uvula – fleshy projection of the soft palate
Figure 14.2a

9. Oral Cavity
11/15/2018
ALFONSO A. PINO. MD.

10. Actions of the Mouth Mastication (chewing) of food
Mixing masticated food with saliva
Initiation of swallowing by the tongue
Allowing for the sense of taste

11. Salivary Glands

12. Salivary Secretions Salivary Glands
Produce 1.0–1.5 liters of saliva each day
70% by submandibular glands
25% by parotids
5% by sublingual glands

13. Nasopharynx – not part of the digestive system
Pharynx Anatomy
Nasopharynx – not part of the digestive system
Oropharynx – posterior to oral cavity
Laryngopharynx – below the oropharynx and connected to the esophagus
Figure 14.2a

14. Pharynx Function Serves as a passageway for air and food
Food is propelled to the esophagus by two muscle layers
Longitudinal inner layer
Circular outer layer
Food movement is by alternating contractions of the muscle layers (peristalsis)

15. Esophagus
Runs from pharynx to stomach through the diaphragm; it is around 10 inches (25 cm) long
Conducts food by peristalsis (slow rhythmic squeezing)
Passageway for food only
It connects to the stomach at the cardial region, a lower esophageal sphincter prevents the reflux of gastric acid content into the esophagus

16. The Esophagus

17. Stomach Anatomy

18. The Stomach

19. Gastric Mucosa, its secretions
Simple columnar epithelium lines the interior of the stomach
Mucous Cells: secrete a thick mucus to protect the gastric mucosa
Parietal cells: Secrete Hydrochloric acid a potent antiseptic and the initiator of the breakdown of proteins. Also secrete Intrinsic factor for the absortion of Complex B vitamines
Chief cells: Secrete a non active enzyme, Pepsinogen, once activated to Pepsin in the gastric acid medium, is one of the several digestors of proteins

20. Gastric Mucosa

21. Stomach: Functions Acts as a storage tank for food
Site of food breakdown, mainly by mechanical digestion
Chemical breakdown of protein begins
Delivers chyme (processed food) to the small intestine

22. Small Intestine The body’s major digestive organ
Site of nutrients absorption into the blood
Muscular tube extending form the pyloric sphincter to the ileo-cecal valve
Suspended from the posterior abdominal wall by the mesentery

23. Subdivisions of the Small Intestine
Duodenum
Attached to the stomach
Curves around the head of the pancreas
Jejunum
Attaches anteriorly to the duodenum
Ileum
Extends from jejunum to large intestine

24. Small Intestine

25. Small Intestine: Duodenum
The C shaped duodenum is just around 10 inches (25 cm.) long.
It forms a “ picture frame” around the head of the pancreas
It receives chyme from the stomach and is the site where most of the digestive process takes place
The pancreatic duct and the bile duct open into the duodenum bringing their digestive secretions into its lumen
Trypsinogen, a proenzyme secreted by the pancreas activates in the duodenum to Trypsin, the final digestor of proteins

26. Small Intestine: Jejunum & Ileum
Jejunum: About 8 feet (2.5 m) long. The bulk of absorption of nutrients occurs in this segment of the small intestine. The presence of villi and microvilli in the jejunal mucosa increases greatly its surface of absorption
Ileum: The longest segment of the small intestine, around feet (3.5 m) long. Reabsorption of water and electrolytes occurs in the ileum. It ends opening into the proximal end of the colon, the Cecum. An sphincter (ileo-cecal valve) controls the flow of material from the ileum into the cecum

27. Villi of Small intestine
Fingerlike projections
Lined by simple columnar epithelium carpeted by microvilli
Each villus contains:
Absorptive cells
Blood capillaries
Lacteals (specialized lymphatic capillaries)

28. Pancreas
A “fishlike” organ located in transverse orientation in the abdomen
Its excretory duct, (Wirsung’s duct) runs along the full length of the organ and opens into the Duodenum, after merging with the Common Bile duct (Ductus Choledocus)
An Accessory pancreatic duct (Santorini’s duct) often opens into the duodenum, usually at a proximal location from the main pancreatic duct.
The exocrine cells of the pancreas (acinar and epithelial cells) secrete sodium bicarbonate and the main lipid digestive enzyme, Lipase

29. The Pancreas

30. Liver
Located in the right upper abdominal quadrant, it is the most voluminous viscera in the body
Consists of four lobes: Right lobe, left lobe, quadrate lobe and caudate lobe
Right and left lobes are separated by the Falciform ligament.
Each lobe is organized in around lobules, each one is a secretory unit formed of thousands of hepatocytes, the productors of Bile, a catabolite of hemoglobin, whose action is the breakdown of the large lipid particles in the chyme, a process called fat emulsification.

31. Liver: Anterior & Inferior Views

32. Gallbladder
A small, muscular sac, located inferior to the right hepatic lobe, its function is to store and concentrate the bile between meals, and pouring it into the duodenum for the breakdown of lipids.
Contractions of the gallbladder wall occur under the stimulus of a hormone released by the duodenal mucosa (Cholecystokinin). This hormone also stimulates pancreatic secretion and relaxes the hepato-pancreatic sphincter

33. Bile Tree A I B D H C G E F Right & Left hepatic ducts
Common hepatic duct
Cystic duct
Common bile duct (Ductus Choledocus)
Main Pancreatic Duct (Wirsung’s duct)
Duodenal Papilla (Papilla of Vater)
Duodenum
Accesssory pancreatic duct (Duct of Santorini)
Gallbladder I B D C H G E F

34. Structures of the Large Intestine
Around 4.9 feet (1.5 m) long, and 3 inches (7.5 cm) in diameter
Colon
-Cecum
-Ascending
-Transverse
-Descending
-“S-shaped” sigmoid
Rectum
Anus – external body opening, guarded by two sphincters; the internal anal sphincter formed of smooth muscle and thus involuntary, and the external anal sphincter, a ring of skeletal muscle and hence under voluntary control

35. The Large Intestine

36. Functions of the Large Intestine
Reabsorption of water, small amounts of bile salts and some vitamins (like Vitamin K, synthesized by colonic bacteria)
Eliminates indigestible food from the body as feces
Does not participate in digestion of food
Goblet cells produce mucus to act as a lubricant