1. The Digestive System I
Anatomy

2. The digestive system
The organs of the digestive system can be separated into 2 main groups:
Alimentary canal: digests food and absorbs the digested fragments through its lining into the blood
The accessary digestive organs: assist the process of digestive breakdown in various ways

3. Organs of the Alimentary Canal
It is also called the gastrointestinal (GI) tract
It is a continuous, coiled, hollow, muscular tube that pass through the ventral body cavity and is open at both ends
Its organs are:
The mouth
Pharynx
Esophagus
Stomach
Small intestine
Large intestine

4. Organs of the Alimentary Canal
In a cadaver, the alimentary canal is approximately 9 meters long, but in a living person, it is considerably shorter because of its relatively constant muscle tone
Food material within this tube is technically outside the body, because it has contact only with cells lining the tract and is open to the external environment at both ends

5. Mouth Mouth: oral cavity, a mucous membrane-lined cavity
Lips: Labia, protect the mouth’s anterior opening
Cheeks: Form the mouth’s lateral wall
Hard palate: Forms the mouth’s anterior roof
Soft palate: Forms the mouth’s posterior roof
Uvula: A fleshy fingerlike projection of the soft palate, which extends downward from its posterior edge

6. Mouth
Vestibule: The space between the lips and cheeks externally and the teeth and gums internally

7. Tongue The muscular tongue occupies the floor of the mouth
The tongue has several bony attachments:
2 hyoid bones
The styloid process of the skull
The frenulum, a fold of mucous membrane, secures the tongue to the floor of the mouth and limits its posterior movements
The Papillae on the tongue containing taste buds, or taste receptors

8. Pharynx
From the mouth, food passes posteriorly into the oropharynx and laryngopharynx: Both of Which are common passageways for food, fluids and air
Oropharynx: posterior to the oral cavity
Laryngopharynx: continuous with the esophagus below

9. Pharynx The walls of the pharynx contain two skeletal muscle layers:
The cells of the inner layer run longitudinally
The cells of the outer layer run around the wall in a circular fashion
Alternating contractions of these two muscle layers propel food through the pharynx into the esophagus

10. Esophagus
The esophagus, or gullet, runs from the pharynx through the diaphragm to the stomach
The mechanism that esophagus propel food down is called peristalsis

11. Walls of the alimentary canal organs
The walls of the esophagus to the large intestine are made up of the same four basic tissue layers or tunics:
The mucosa: The inner most layer, a moist membrane that lines the cavity or lumen of the organ

12. Walls of the alimentary canal organs
2. The submucosa: Is found just beneath the mucosa. It is a soft connective tissue layer containing blood vessels, nerve endings, lymph nodes and lymphatic vessels

13. Walls of the alimentary canal organs
3. The muscularis externa: A muscle layer typically made up of an inner circular layer and an outer longitudinal layer of smooth muscle cells

14. Walls of the alimentary canal organs
4. The serosa: the outermost layer of the wall. It consists of a single layer of flat serous fluid-producing cells, the visceral peritoneum

15. Nerve Plexus
The alimentary canal wall contains 2 important nerve plexus (a branching network of axons outside of the central nervous system): Submucosal nerve plexus and the mysenteric nerve plexus
They help regulate the mobility and secretory activity of GI tract organs

16. Stomach
The C shaped stomach is on the left side of the abdominal cavity
The stomach has 2 sphincters:
Esophageal sphincter (Superior)
Pyloric sphincter (Inferior)

17. Stomach The fundus is the expanded part of the stomach
The body is the mid-portion
The funnel shaped pylorus is the terminal part

18. Stomach
The stomach is approximately 25 cm long, but its diameter depends on how much food it contains:
When its full, it holds about 4 liters of food
When its empty, it collapses inward on itself and its mucosa is thrown into large folds called rugae (roo’ge)

19. Stomach
The lateral convex surface of the stomach is called the greater curvature
The medial surface is the lesser curvature

20. Stomach
The lesser omentum is a double layer of peritoneum extends from the liver to the lesser curvature
The greater omentum drapes downward and covers the abdominal organs like a lacy apron
The infection of peritoneum is called peritonitis : the peritoneal membranes tend to stick together around the infection site

21. Stomach
The stomach acts as a temporary “storage tank” for food as well as a site for food breakdown:
1. Physical break down:
Besides the usual longitudinal and circular layers, its wall contains a third obliquely arranged layer of muscle in the muscularis externa
This muscle allows the stomach to churn, mix and physically breaking the food down

22. Stomach 2. Chemical breakdown:
The mucosa of the stomach is dotted with millions of deep gastric pits, which lead into gastric glands that secrete the solution called gastric juice
The chief cells produce protein-digesting enzymes, mostly pepsinogens
The parietal cells produce corrosive hydrochloric acid
The mucous neck cells produce a sticky alkaline mucus, which clings to the stomach mucosa and protects the stomach wall itself from being damaged

23. Stomach
Most digestive activity occurs in the pyloric region of the stomach
After food has been processed in the stomach, it resembles heavy cream and is called chyme
The chyme enters the small intestine through the pyloric sphincter

24. Small Intestine It is the body’s major digestive organ
It is the longest section of the alimentary tube (avg. 2m)
The small intestine is a convoluted tube extending from the pyloric sphincter to the ileocecal valve

25. Small intestine duodenum: beginning Jejunum: middle Ileum: terminal
The small intestine has 3 subdivisions:
duodenum: beginning
Jejunum: middle
Ileum: terminal

26. Small intestine
The small intestine is able to process only a small amount of food at one time
The pyloric sphincter controls food movement into the small intestine from the stomach

27. Small intestine
Enzymes produced by the intestinal cells and by the pancreas (more important) are ducted into the duodenum through the pancreatic duct
Bile (produced by the liver, stored in the gallbladder) also enters the duodenum through the bile duct
The pancreatic and bile duct join at the duodenum, to form the flask-like hepatopancratic ampulla

28. Small intestine
The wall of the small intestine has 3 structures that increase the absorptive surface:
Microvilli: tiny projections of the plasma membrane of the mucosa cell, sometimes it is referred to as the brush border
Villi: fingerlike projection of the mucosa
Circular folds: deep folds of both mucosa and submucosa layers

29. Villi and microvilli

30. Villi
Within each villus is a rich capillary bed and a modified lymphatic capillary called a lacteal
The digested food are absorbed through the mucosa cells into both the capillary and the lacteal

31. Circular folds
Unlike the rugae folds of the stomach, the circular folds do not disappear when food fills the small intestine
The number of folds decrease toward the end of the small intestine
Payer’s patch (lymphatic tissue) increase toward the end of the small intestine

32. Large Intestine The large intestine is about 1.5 m long
Its major functions are to dry out the indigestible food residue by absorbing water and eliminate these residues from the body as feces

33. Large intestine
It frames the small intestine on three sides and has the following subdivisions:
Cecum
Appendix
Colon
Rectum
Anal canal

34. Colon The colon is divided into several distinct regions:
The ascending colon
The transverse colon
The descending colon
Sigmoid colon

35. Anal Canal
The anal canal has an external voluntary sphincter formed by skeletal muscle and internal involuntary sphincter formed by smooth muscle

36. Large intestine
Because most nutrient absorption has occurred before the large intestine, no villi are seen in the large intestine
There are tremendous numbers of goblet cells in its mucosa that produce mucus
The pocket like sacs on the large intestine are called haustra