Presentation on theme: "5 – Deglutition & The Stomach"— Presentation transcript:
1 5 – Deglutition & The Stomach Chapter 245 – Deglutition & The Stomach
2 DeglutitionA bolus is a soft, rounded mass of food that is formed in the mouth when food is mixed with saliva.
3 DeglutitionOnce the bolus is swallowed, it passes from the mouth into the pharynx.
4 DeglutitionThe 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 DeglutitionThe esophagus is a hollow muscular tube that connects the pharynx to the stomach.
6 DeglutitionDeglutition (swallowing) is the movement of food from the mouth into the stomach.
7 Deglutition Deglutition occurs in three stages: The voluntary stage The pharyngeal stageThe esophageal stage
8 DeglutitionThe 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 DeglutitionThe 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 DeglutitionThe esophageal stage begins once the bolus enters the esophagus; during this phase peristalsis pushes the bolus into the stomach.
11 DeglutitionPeristalsis is a progression of successive muscular contractions that occurs in the muscularis of the GI tract.
12 The StomachThe 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 bodyThe pylorus
14 The StomachThe carida surrounds the superior opening of the stomach.
15 The StomachThe fundus is the rounded portion superior to and to the left of the cardia.
16 The StomachThe body is the large central portion of the stomach inferior to the fundus.
17 The StomachThe 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 StomachGastric 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.
23 The Stomach**The digestion that occurs in the stomach is both mechanical and chemical.
24 The StomachMechanical digestion in the stomach consists of peristaltic movements called ‘mixing waves’ that intensify as food reaches the pylorus.
25 The StomachMixing waves macerate food, mix it with secretions of the gastric glands, and reduce it to chyme.
26 The StomachChyme 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 StomachMost 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 StomachChemical 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 StomachThe 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 StomachFrom 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