1. The digestive system
Chapter 14

2. Overview The main functions of the digestive system are…
To take in food (ingestion).
To physically and chemically break down food into nutrient molecules (digestion).
To absorb nutrient molecules into the bloodstream (absorption).
To rid the body of indigestible material (defecation).

3. Learning Target #1 2 divisions of the digestive system:
Alimentary canal
Continuous coiled tube from one end of the body to the other
Carries out all digestive functions
Accessory organs
Assist in the process of chemical and mechanical breakdown of foodstuffs

4. Organs of the alimentary canal:
Mouth
Pharynx
Esophagus
Stomach
Small intestine
Large intestine
Accessory organs:
Salivary glands
Teeth
Pancreas
Liver and gallbladder

5. Salivary Glands
Mouth
Pharynx
Esophagus
Stomach
Liver
Pancreas
Gall Bladder
Large Intestine
Small Intestine
= alimentary canal
= accessory organs

6. Learning Target #2  Mouth
Functions
Anatomy
Chewing of food (mastication)
Mixing of masticated food with saliva
Initiation of swallowing by the tongue
Sense of taste
Lips (labia)
Cheeks
Hard and soft palates
Uvula
Vestibule
Oral cavity
Tongue
Lingual frenulum

7. Mouth Anatomy Hard Palate Oral cavity Soft Palate Uvula Tongue
The space between the lips/cheeks and the teeth/gums is called the vestibule.
The area contained by the teeth is called the oral cavity.
The hard and soft palates form the roof of the mouth.
The lingual frenulum secures the tongue to the floor of the mouth and limits its movement.
Tongue
Lingual Frenulum
Vestibule
Hard Palate
Soft Palate
Uvula

8. Learning Target #2  Salivary Glands
Function
Anatomy
Production of saliva
Mucus moistens and helps bind food together to form a bolus
Serous fluid contains salivary amylase, an enzyme that begins the digestion of carbohydrates
Contains lysozymes and antibodies that inhibit bacterial growth
Dissolves food chemicals so they can be tasted
3 pairs of glands:
Parotid
Submandibular
Sublingual

9. Learning Target #2  Teeth
Function
Anatomy
Physical breakdown of food by chewing (mastication)
Classification:
Structure:
Incisors
Crown
Canines
Root
Premolars
Gingiva
Molars
Enamel
Neck
Cementum
Periodontal ligament
Dentin
Pulp cavity
Pulp
Root canal

10. Tooth Anatomy Enamel Dentin Crown Pulp cavity Gingiva Neck
Enamel is the hardest substance in the body and makes up the outer covering of the tooth. It is composed mainly of calcium salts
Dentin is the bone-like material that forms the bulk of the tooth.
Cementum is a substance that connects the tooth to the periodontal ligament, which holds the tooth in place within the gingiva.
The pulp is a combination of blood vessels and nerve fibers. It provides nutrients to the tooth and allows for sensation.
Crown
Pulp cavity
Gingiva
Neck
Periodontal ligament
Bone
Root
Cementum
Root canal

11. Classification of Teeth
Deciduous teeth (also called baby or milk teeth) begin to emerge around 6 months of age and finish forming around age 2.
Full set = 20 teeth
Children generally lose their deciduous teeth between ages 6-12, after which the permanent teeth emerge.
Full set = 32 teeth*
*includes wisdom teeth

12. Learning Target #2  Pharynx
Function
Anatomy
Movement of the food bolus from the mouth to the esophagus.
Common passageway for food, fluids, and air
3 subdivisions:
Nasopharynx
Oropharynx
Laryngopharynx
Walls of the pharynx contain 2 layers of skeletal muscle that move food via peristalsis

13. Learning Target #3  Esophagus
Function
Anatomy
Passageway that carries food from the pharynx to the stomach (via peristalsis)
Pharynx branches into esophagus and trachea
Esophagus (and rest of the alimentary canal) are made of 4 tissue layers:
Mucosa
Submucosa
Muscularis externa
Serosa

14. Learning Target #3  Esophagus
Tissue Layers of the Esophagus (and the rest of the alimentary canal):
Mucosa
Inner, moist layer responsible for most secretion and absorption
Made mostly of epithelial tissue (stratified squamous in esophagus, simple columnar in rest of canal)
Also includes a small amount of connective tissue (called the lamina propria) and smooth muscle
Submucosa
Found beneath the mucosa
Made of dense irregular connective tissue and contains blood vessels, nerve endings, lymph nodules, and lymphatic vessels.

15. Learning Target #3  Esophagus
Muscularis externa
Found beneath the submucosa
Made of 2 layers of smooth muscle (inner circular layer and outer longitudinal layer)
Serosa
Outermost layer
Made of a single layer of cells, called the visceral peritoneum, that produces serous fluid
Is continuous with the parietal peritoneum that lines the abdominopelvic cavity via the mesentery

16. Nerve Supply Serosa Muscularis externa Lumen Submucosa Mucosa
Nerve plexuses (located primarily in the submucosa) are associated with movement of food through the alimentary canal and secretion of substances from the digestive organs.
Can you see the…
Lamina propria?
Layers of circular and longitudinal muscle?
Glands that produce serous fluid?
Mesentery?
Lumen
Submucosa
Mucosa

17. Learning Target #4  Stomach
Function
Anatomy
Acts as a storage tank for food
Mechanical breakdown of food
Chemical breakdown of protein begins
Delivers chyme (processed food) to the small intestine
Located on the left side of the abdominal cavity
4 regions of the stomach:
Cardiac region
Fundus
Body
Pylorus
Contains many internal folds of the mucosa called rugae

18. Cardioesophageal sphincter
Cardiac region
Stomach Anatomy
Fundus
Food enters the stomach from the esophagus through the cardioesophageal sphincter.
The pyloric sphincter controls the passage of food from the stomach into the small intestine.
The convex lateral surface is called the greater curvature, while the concave, medial surface is called the lesser curvature.
Contains 3 layers of muscle – longitudinal (outermost), circular, and oblique (innermost).
Cardioesophageal sphincter
Body
Pyloric sphincter LC GC
Pylorus
Rugae

19. Connective Tissue Lesser omentum Greater omentum
The stomach is connected to the surrounding organs and body cavity via the omentum
Lesser omentum – connects lesser curvature to liver
Greater omentum – drapes downward and covers the abdominal organs
The omentum contains mainly fat, which helps to insulate, cushion, and protect the abdominal organs.
Greater omentum

20. Learning Target #4  Stomach
The simple columnar epithelium of the stomach contains millions of gastric pits with specialized cells that produce gastric juice:
Mucous neck cells: produce a sticky, alkaline mucus that protects the stomach
Chief cells: produce pepsin (protein-digesting enzyme)
Parietal cells: produce hydrochloric acid
Endocrine cells: produce gastrin (hormone that regulates stomach activities)

21. Learning Target #5  Small Intestine
Function
Anatomy
The body’s major digestive organ.
Site of nutrient absorption into the blood.
Muscular tube extending from the pyloric sphincter (of the stomach) to the ileocecal valve (of the large intestine).
Attached to the posterior body wall by connective tissue called the mesentery.

22. Learning Target #5  Small Intestine
The small intestine has 3 subdivisions:
Duodenum
First section (~ 10 inches long)
Connects to the pyloric sphincter of the stomach
Curves around the pancreas
Jejunum
Middle section (~ 8 feet long)
Ileum
Last section (~ 12 feet long)
Connects to ileocecal valve of the large intestine

23. The Small Intestine Duodenum Jejunum Ileum Large Intestine Rectum
Chyme enters the small intestine from the stomach gradually.
Chyme is mixed with enzymes from the pancreas, which enter the SI through the pancreatic ducts.
Bile enters the SI through the bile duct, coming from the liver.
The pancreatic and bile ducts connect to the duodenum of the small intestine.
Duodenum
Jejunum
Ileum
Large Intestine
Rectum

24. Learning Target #5  Small Intestine
The small intestine maximizes its surface area for absorption through…
Microvilli
Small projections of the plasma membrane of each individual epithelial cell
Give the cell a “fuzzy” appearance known as the “brush border”
Villi
Finger-like structures formed by the mucosa (inner-most layer)
Each villus contains a capillary and lymphatic bed called a lacteal, which is where absorption of nutrients into the blood stream actually occurs
Plicae Circulares
Deep folds of the mucosa and submucosa to further increase surface area

25. Learning Target #5  Small Intestine
Microvilli
Plicae circulares
In addition to the villi, microvilli, and plicae circulares, there are also small collections of lymphatic tissue, called Peyer’s patches, found in the submucosa of the small intestine.
Peyer’s patches prevent the bacteria found in food from entering the bloodstream.
Lacteal
(green)
Blood capillaries
Villi

26. Learning Target #6  Large Intestine
Functions
Anatomy
Absorb water from indigestible food residue
Eliminate indigestible food residue as feces
Larger in diameter but shorter in length than the small intestine
Extends from the ileocecal valve to the anus
5 subdivisions: cecum, appendix, colon, rectum, anal canal

27. Learning Target #6  Large Intestine
Subdivisions of the large intestine:
Cecum: sac-like first part of the large intestine
Appendix: hangs from the cecum, accumulation of lymphatic tissue
Colon: majority of the large intestine, divided into regions:
Ascending colon
Transverse colon
Descending colon
Sigmoid colon
Rectum: stores feces prior to defecation
Anus: contains two sphincters to control the release of feces during defecation

28. Learning Target #6  Large Intestine
Transverse colon
Haustra
Ascending colon
Descending colon
Cecum
Sigmoid colon
Appendix
Anus
Rectum

29. Learning Target #6  Large Intestine
Specializations of the large intestine:
Walls are formed into pocket-like sacs called haustra
Contains lots of mucus-producing goblet cells to lubricate the passageway for feces

30. Learning Target #7  Chemical Digestion
Chyme enters the small intestine from the stomach.
It mixes with substances from the intestinal cells, pancreas, and liver/gall bladder in the duodenum.

31. Learning Target #7  Pancreas
Function
Anatomy
Produces enzymes that break down all categories of foodstuffs
Produces hormones (insulin and glucagon) that regulate blood sugar levels
Extends across the abdomen, close to the duodenum of the small intestine

32. Learning Target #7  Liver and Gall Bladder
Function
Anatomy
The liver is the largest gland in the body
Secretes bile
Has many detoxification functions that are not directly related to digestion
The gall bladder stores bile until it is needed in the small intestine
Under the diaphragm, to the right of the stomach
Made of 4 lobes
Connected to the gall bladder by the hepatic duct

33. Hepatopancreatic ampulla
Learning Target #7
Liver
Hepatic duct(s)
Cystic Duct
The cystic duct (from the gall bladder) and the hepatic duct (from the liver) combine to form the bile duct.
The bile duct combines with the pancreatic duct to form the hepatopancreatic ampulla, which delivers bile and digestive enzymes into the duodenum of the small intestine.
Bile duct
Gall Bladder
Pancreas
Duodenum
Pancreatic duct
Hepatopancreatic ampulla

34. Learning Target #7  Digestive Actions
Swallowing (also called deglutition) – occurs when a food bolus is forced into the pharynx by the tongue
Vomiting – reverse peristalsis (of the stomach and esophagus) caused by local irritation of the stomach
Defecation – the presence of feces in the rectum, triggers stretch receptors causing the movement of feces into the anal canal

35. Learning Target #8  Peristalsis
Peristalsis is the major means of moving food through the alimentary canal.
Involves waves of contraction, followed by waves of relaxation
Accomplished by smooth muscles located in the muscularis externa

36. Learning Target #8  Hormones
Hormones trigger digestive activities:
Acting on the stomach:
Gastrin – triggered by food in the stomach; stimulates the release of gastric juices and movement of chyme into the small intestine
Acting on the small intestine:
Secretin – triggered by chyme in the duodenum; stimulates the output of pancreatic enzymes and bile
Secreted by the pancreas:
Insulin – hormone that causes the liver, muscle, and fat tissue to take up glucose from the blood when glucose levels are high
Glucagons – hormone that causes the liver, muscle, and fat tissue to release glucose into the blood when glucose levels are low

37. Learning Target #9  Digestive Enzymes
Major categories of foodstuffs:
Carbohydrates
Broken down by salivary amylase in the mouth, pancreatic amylase in the small intestine
Monomer = monosaccharides (Example = glucose)
Specific  lactase breaks down the milk sugar lactose
Lipids
Emulsified by bile from the liver and gall bladder
Broken down by lipase from the pancreas
Monomer = glycerol and fatty acids (Example = saturated fat)
Proteins
Broken down by pepsin in the stomach, and trypsin and aminopeptidase in the small intestine
Monomer = amino acids (Example = tryptophan)