Question

JM is a 55-year-old male who tells you that he has suffered from indigestion for quite a while. He decides it is time to try and understand the roll of digestion, particularly in the stomach and small bowel. Discussion Questions:

1. Describe the process of digestion in relation to food entering the stomach and progressing into the duodenum.

2. Explain process of absorption in the small intestine.

3. Discuss where each hormone is secreted and its action: Gastrin: Secretin: Cholecystokinin:

Answer 1

1. PROCESS OF DIGESTION :

After the process of mastication the bolus is made which help the bolus in deglutition process, the bolus then travels down the oesophagus and reaches the stomach, the stomach is a J shaped dilated portion of the alimentary tract situated in the epigastric, umbilical and left hypochondriac regions of the abdominal cavity. The stomach is divided into three regions : the fundus, the body and the pylorus. At the distal end of the pylorus is the pyloric sphincter, guarding the opening between stomach and the duodenum. When the stomach is inactive the pyloric sphincter is relaxed and open, and when the stomach contains food the sphincter is closed, in stomach the mechanical breakdown of the food will take place, gastric juice is addedd making the bolus liquified which is known as chyme, the chyme then enters the duodenum where it combines with the bile and gastric juices and then travels down the small intestine.

2. PROCESS OF ABSORPTION IN SMALL INTESTINE :

The small intestine is continuous with the stomach at the pyloric sphincter. The small intestine is a little over 5 metres long and leads into the large intestine at the ileocaecal valve. In the small intestine the chemical digestion of food is completed and absorption of most nutrients takes place. When acid chyme passess into the small intestine it is mixed with pancreatic juice, bile, and intestinal juice,and is in contact with the enterocytes of the villi. In the small intestine digestion of all the nutrients such as carbohydrates are broken down to monosaccharides, proteins are broken down to amino acids, fats are broken down to fatty acids and glycerol, it also provides protection against infection by microbes that have survived the antimicrobial action of the hydrochloric acid in stomach, by the solitary lymph follicles and aggregated lymph follicles, it also secreted hormones such as cholecystokinin and secretin.

3. GASTRIN :

When stimulated by the presence of food the enteroendocrine cells in the pylorus and duodenum secrete gastrin, a hormone which passes directly into the circulating blood. Gastrin, circulating in the blood which supplies the stomach, stimulates the gastric glands to produce more gastric juice. In this way secretion of digestive juice is continued after completion of a meal and end of the cephalic phase. Gastrin secretion is suppressed when the pH in the pylorus falls to about 1.5. This process takes place in Gastric phase.

SECRETIN AND CHOLESYSTOKININ :

When the partially digested food contents of the stomach reach the small intestine, two hormones, secretin and cholesystokinin, are synthesized by the endocrine cells in the intestinal mucosa. They slow down the secretion of gastric juice and reduce gastric motility. By slowing the emptying rate of the stomach, the chyme in the duodenum becomes more thoroughly mixed with bile and pancreatic juice. This phase of gastric secretion is most marked following a meal with a high fat content. It occurs in an intestinal phase.