1. 5 – Deglutition & The Stomach
Chapter 24
5 – Deglutition & The Stomach

2. Deglutition
A bolus is a soft, rounded mass of food that is formed in the mouth when food is mixed with saliva.

3. Deglutition
Once the bolus is swallowed, it passes from the mouth into the pharynx.

4. Deglutition
The pharynx is a funnel-shaped tube that starts at the back of the mouth and runs down the neck where it opens into the esophagus posteriorly and the larynx anteriorly.

5. Deglutition
The esophagus is a hollow muscular tube that connects the pharynx to the stomach.

6. Deglutition
Deglutition (swallowing) is the movement of food from the mouth into the stomach.

7. Deglutition Deglutition occurs in three stages: The voluntary stage
The pharyngeal stage
The esophageal stage

8. Deglutition
The voluntary stage starts when the bolus is forced to the back of the oral cavity and into the pharynx by the movement of the tongue.

9. Deglutition
The pharyngeal stage begins when the bolus moves into the pharynx and the brain stem sends impulses to the epiglottis to close the opening of the larynx which prevents the bolus from entering the trachea.

10. Deglutition
The esophageal stage begins once the bolus enters the esophagus; during this phase peristalsis pushes the bolus into the stomach.

11. Deglutition
Peristalsis is a progression of successive muscular contractions that occurs in the muscularis of the GI tract.

12. The Stomach
The stomach is a J-shaped enlargement of the GI tract that connects the esophagus to the duodenum.

13. The Stomach The stomach has four main regions: The cardia The fundus
The body
The pylorus

14. The Stomach
The carida surrounds the superior opening of the stomach.

15. The Stomach
The fundus is the rounded portion superior to and to the left of the cardia.

16. The Stomach
The body is the large central portion of the stomach inferior to the fundus.

17. The Stomach
The pylorus is the region of the stomach that connects the duodenum; it communicates with the duodenum via a sphincter called the pyloric sphincter.

18. The Stomach
**The stomach wall is composed of the same four basic layers of the GI tract, with certain modifications.

19. The Stomach
**Recall – the four layers of the GI tract are: the mucosa, the submucosa, the muscularis, and the serosa.

20. The Stomach
**The mucosa of the stomach contains secretory cells called ‘gastric glands’ that empty their secretions into narrow channels called gastric pits.

21. The Stomach
Gastric glands are glands in the mucosa of the stomach; the four types of cells are chief cells, parietal cells, mucous neck cells and G cells.

22. The Stomach Chief cells secrete pepsinogen & gastric lipase
Pareital cells secrete hydrochloric acid (HCl)
Mucous neck cells secrete mucus
G cells secrete gastrin

23. The Stomach
**The digestion that occurs in the stomach is both mechanical and chemical.

24. The Stomach
Mechanical digestion in the stomach consists of peristaltic movements called ‘mixing waves’ that intensify as food reaches the pylorus.

25. The Stomach
Mixing waves macerate food, mix it with secretions of the gastric glands, and reduce it to chyme.

26. The Stomach
Chyme is the semifluid mixture of partly digested food and digestive secretions found in the stomach and small intestine during the digestion of a meal.

27. The Stomach
**As food reaches the pylorus, each mixing waves periodically forces about 3 mL of chyme into the duodenum through the pyloric sphincter.

28. The Stomach
Most of the chyme is forced back into the stomach where mixing continues; the next wave pushes the chyme forward again and forces a little more into the duodenum.

29. The Stomach
Chemical digestion in the stomach consists of the conversion of proteins into peptides by pepsin, and triglycerides into fatty acids and glycerol by the enzymes lingual lipase & gastric lipase.

30. The Stomach
**Pepsin, lingual lipase & gastric lipase are all activated in extremely acidic environments.

31. The Stomach
**Recall – the acid (HCl) is secreted by the stomach’s parietal cells; it creates a very acidic environment (pH 2) in the stomach.

32. The Stomach
**Recall – ‘pepsinogen’ is secreted by the stomach’s chief cells.

33. The Stomach
**Pepsinogen is converted into active ‘pepsin’ when it comes in contact with HCl.

34. The Stomach
The stomach wall is impermeable to most substances; however, some water, electrolytes, certain drugs (especially aspirin), and alcohol can be absorbed through the stomach lining.

35. The Stomach
From the stomach, chyme passes into the small intestine; chemical digestion in the small intestine is not autonomous, it depends on activities of accessory digestive organs.

36. Homework Finish handout: Study for mini-quiz
“Deglutition & The Stomach”
Study for mini-quiz