Chapter 25

The Digestive System

Kevin Yocum

Fall 2013

Objectives for 25.1

• List the structures and major functions of the digestive system.

• Distinguish between chemical and mechanical digestion.

• Discuss substrates and digestion.

• List regions and accessory organs.

Digestive Function

• Ingestion

• Digestion

• Absorption

• Compaction

• Defecation

Chemical Vs. Mechanical

• Mechanical– Physical breakdown of food– Mouth, stomach, small intestines

• Chemical– Hydrolysis reactions– Breakdown of macromolecules– Mouth, stomach, small intestines

Digestive Anatomy

• Tract– Mouth to anus

• Accessory organs– Teeth, tongue, salivary glands– Liver, gall bladder, pancreas

• Figure 25.1

Fig. 25.1

Notes: From Saladin 6th Ed.

Digestive Tract Layers

• Mucosa

• Submucosa

• Muscularis

• Serosa

• Figure 25.2

Fig. 25.2

Notes: From Saladin 6th Ed.

Peritoneum

• Parietal peritoneum

• Visceral peritoneum

• Mesentery

• Omentum– Greater– Lesser

• Figure 25.3

Fig. 25.3

Notes: From Saladin 6th Ed.

Checkpoint Questions

• The inner lining of the digestive tract is called the ______.

• The salivary glands are ________ digestive organs.

• A large, fatty “apron” that covers the small intestines is called the _____

_______.

Checkpoint Answers

• The inner lining of the digestive tract is called the mucosa.

• The salivary glands are accessory digestive organs.

• A large, fatty “apron” that covers the small intestines is called the greater omentum.

Objectives for 25.2

• Describe the anatomy of the mouth through the esophagus.

• Describe the composition and functions of saliva.

• Explain the neural control of salivation and swallowing.

The Mouth

• Oral (Buccal) cavity- Fig. 25.4

• Cheeks and lips

• Tongue– Papillae and tonsils

• Palate– Hard and soft– Uvula

Fig. 25.4

Notes: From Saladin 6th Ed.

The Teeth

Notes: From Saladin 6th Ed.

Salivation

• Mastication

• Saliva– Amylase and lipase– Lysozomes– IgA

• Salivary glands- Fig. 25.9-10– Parotid, submandibular, and sublingual

• Salivary nuclei

Fig. 25.9

Notes: From Saladin 6th Ed.

Fig. 25.10

Notes: From Saladin 6th Ed.

Salivary Nuclei

• Pons and medulla

• Autonomic fibers– Parasympathetic response

– Sympathetic response

The Esophagus

• Cardiac orifice

• Lower esophageal sphincter (LES)– “Heartburn”

• Esophageal glands

Swallowing

• Deglutition- Fig 25.11

• Buccal phase– Voluntary control

– Bolus

• Pharyngoesophageal phase– Involuntary

– Peristalsis

Fig. 25.11

Notes: From Saladin 6th Ed.

Checkpoint Questions

• The teeth are collectively called the _______.

• Salivary _______ begins starch digestion in the mouth.

• Swallowing is also known as ________.

Checkpoint Answers

• The teeth are collectively called the dentition.

• Salivary amylase begins starch digestion in the mouth.

• Swallowing is also known as deglutition.

Objectives for 25.3

• Describe the anatomy of the stomach.

• State the functions of the epithelial cells of the gastric mucosa.

• Describe the gastric secretions.

• Explain hydrochloric acid & pepsin.

• Describe the phases of gastric function.

The Stomach

• Cardiac region

• Fundic region

• Body

• Pyloric region

• Rugae

Notes: From Saladin 6th Ed.

Microanatomy

• Mucous cells

• Stem cells

• Parietal cells

• Chief cells

• Enteroendocrine cells

Notes: From Saladin 6th Ed.

Hydrochloric Acid (HCl)

• Activates pepsin and lingual lipase

• Breaks up CT and plant cell walls

• Converts ferric ions to ferrous ions

• Destroys ingested pathogens

• Figure 25.14

Figure 25.14

Notes: From Saladin 6th Ed.

Other Gastric Secretions

• Pepsin- Figure 25.15

– Proteins

• Gastric lipase

• Intrinsic factor– Vitamin B12

• Gut-brain peptides

Fig. 25.15

Notes: From Saladin 6th Ed.

Gastric Secretions

Notes: From Saladin 6th Ed.

Regulation of Gastric Function

• Cephalic phase

• Gastric phase

• Intestinal phase

• Figures 25.17-18

Fig. 25.17

Notes: From Saladin 6th Ed.

Fig. 25.18

Notes: From Saladin 6th Ed.

Checkpoint Questions

• The inferior-most region of the stomach is the _____.

• Protein digestion is aided by the presence of the enzyme _____.

• During the ______ phase, the vagus nerve stimulates gastric secretion before food is swallowed.

Checkpoint Answers

• The inferior-most region of the stomach is the pyloric.

• Protein digestion is aided by the presence of the enzyme pepsin.

• During the cephalic phase, the vagus nerve stimulates gastric secretion before food is swallowed.

References

Saladin, Kenneth (2012). Anatomy and Physiology, The Unity of Form and Function, Sixth Ed. New York, NY: McGraw-Hill.