1. Chapter 14 – Part 2 The Digestive System

2. Stomach Anatomy Located on the left side of the abdominal cavity
C-shaped
Nearly hidden by the liver and diaphragm

3. Stomach Anatomy Regions of the stomach Cardiac region – near the heart
Fundus – expanded part lateral to the cardiac region
Body - midportion
Pylorus – funnel-shaped terminal end

4. Stomach Anatomy
Food enters the stomach at the cardioesophageal sphincter
Food empties into the small intestine at the pyloric sphincter

5. Stomach Anatomy The stomach is about 10 inches long
Its diameter depends on how much food it contains
When it is full it can hold about 1 gallon of food
When it is empty it collapses inward on itself

6. Stomach Anatomy
Rugae – internal folds of the mucosa (seen especially when the stomach is empty)
External regions
Lesser curvature – the convex lateral surface of the stomach (smaller curve)
Greater curvature – the concave medial surface of the stomach (larger curve)

7. Stomach Anatomy
There are two layers of peritoneum that are attached to the stomach:
Lesser omentum – attaches the liver to the lesser curvature
Greater omentum – attaches the greater curvature to the posterior body wall
Drapes downward and covers the abdominal organs like a lacy apron
Contains fat which helps to insulate, cushion, and protect abdominal organs

8. Greater and Lesser Omentum

9. Peritonitis Peritonitis – occurs when the peritoneum is infected
The peritoneal membranes tend to stick together around the infection site
Helps to seal off and localize many intraperitoneal infections
Provides time for macrophages to mount an attack

10. Stomach Anatomy

11. Stomach Functions Acts as a storage tank for food
Site of food breakdown
Chemical breakdown of protein begins
After food has been processed in the stomach, it delivers chyme (processed food) to the small intestine

12. Structure of the Stomach Mucosae
Besides the usual longitudinal and circular muscle layers, the stomach contains a third obliquely arranged layer in the muscularis externa.
Does more than just move food along the tract
Allows it to churn, mix and pummel the food, physically breaking it down to smaller fragments

13. Stomach Anatomy

14. Specialized Mucosa of the Stomach
The mucosae of the stomach is a simple columnar epithelium that produces large amounts of mucus.
It dotted with deep gastric pits (formed by folded mucosa)
Glands and specialized cells are in the gastric gland region

15. Specialized Mucosa of the Stomach
Mucous neck cells – produce a sticky alkaline mucus
Clings to the stomach mucosa and protects the stomach wall itself from being damaged by the acid and digested by the enzymes
Gastric glands – secrete gastric juice

16. Specialized Mucosa of the Stomach
Chief cells – produce protein-digesting enzymes (pepsinogens)
Parietal cells – produce hydrochloric acid, which makes the stomach acidic and activates the enzymes
Endocrine cells – produce gastrin (important for digestion)

17. Structure of the Stomach Mucosa

18. Small Intestine The body’s major digestive organ
Site of nutrient absorption into the blood
Muscular tube extending from the pyloric sphincter to the ileocecal valve
Longest section of the alimentary canal (6-13 feet in a living person)
Is encircled and framed by the large intestine

19. Small Intestine: Three Subdivisions
Duodenum
Attached to the stomach
Curves around the head of the pancreas
About 10 inches long
Jejunum
Extends from the duodenum to the ileum
About 8 feet long
Ileum
Terminal part of the small intestines
About 12 feet long

20. Chemical Digestion in the Small Intestine
The small intestine is able to process only a small amount of food at one time
The pyloric sphincter (literally, “gatekeeper”):
Controls food movement into the small intestine from the stomach
Prevents the small intestine from being overwhelmed

21. Chemical Digestion in the Small Intestine
Enzymes complete the chemical breakdown of food in the small intestine
Source of enzymes that are mixed with chyme
Produced by the intestinal cells
Produced by the pancreas and ducted into the duodenum of the small intestine via the pancreatic duct

22. Chemical Digestion in the Small Intestine
Bile enters the duodenum from the gall bladder via the bile duct
Bile is formed by the liver
Bile helps to break down fats

23. Chemical Digestion in the Small Intestine
Figure 14.6

24. Main Function of the Small Intestine
Nearly all food absorption occurs in the small intestine
Its wall has three structures that increase the absorptive surface tremondously
Microvilli
Villi
Circular Folds
Well suited for absorption
These structural modifications decrease in number toward the end of the small intestine

25. Villi of the Small Intestine
Villi - Fingerlike structures of the mucosa
Give the small intestine more surface area
Gives it a velvety appearance

26. Microvilli of the Small Intestine
Microvilli - small projections of the plasma membrane
Gives the cell surface a fuzzy appearance
Sometimes referred to as brush border
Found on absorptive cells

27. Microvilli and Villi of the Small Intestine

28. Structures Involved in Absorption of Nutrients
Digested foodstuffs are absorbed through the villus of mucosa cells via:
Rich capillary bed
A modified (specialized) lymphatic capillary called a lacteal

29. Folds of the Small Intestine
Circular folds, called plicae circulares, are deep folds of both the mucosa and submucosa layers
Do not disappear when filled with food (unlike the rugae)

30. Folds of the Small Intestine
The submucosa has Peyer’s patches (collections of lymphatic tissue)
More are found towards the end of the small intestine
The undigested food residue in the intestine contains huge numbers of bacteria, which must be prevented from entering the bloodstream