Question

Digestive System

• Roles of the digestive tract lining
• Sympathetic vs. parasympathetic stimulation digestive tract
• Myenteric plexus
• Pre/Enzyme- where secreted from and function (gastrin, somatostatin, pepsinogen, mucus, lipase, secretin, insulin, CCK, GIP)… what/where does it stimulate or inhibit
• What is deglutition?
• Gastric regulation- cephalic vs. gastric vs. intestinal
• Where does blood go after leaving the intestine?
• What does the colon do?
• Process of defecation

Answer 1

• Roles of the digestive tract lining

The digestive tract lining is a mucous membrane that covers the inside of the digestive tract from mouth to anus. Depending on the section of the digestive tract, it protects the digestive tract wall, secretes substances, and absorbs the end products of digestion. It is composed of three layers: the internal epithelium , the lamina propria outside the eipithelium, and the external muscularis mucosae (smooth muscle responsible for generating local movements). For example, the serosa is a serous membrane that covers the muscularis externa of the digestive tract in the peritoneal cavity; the visceral peritoneum is the serous membrane that lines the stomach, large intestine, and small intestine.

• Sympathetic vs. parasympathetic stimulation digestive tract

The Sympathetic nervous system (SNS) directs blood away from your digestive tract, which slows down digestion. The body may react to this with constipation, diarrhea, or bloating. The reason is so that your body can reserve energy needed by vital organs like the heart and lungs. In this state, your body can concentrate on taking action that will alleviate the danger. Conversely, the parasympathetic nervous system (PNS) is responsible for the digestion response when the body is relaxed, resting, or feeding. The PNS decreases respiration and heart rate and increases digestion through increasing the blood flow directly to your digestive tract. As opposed to the SNS response, your salivary gland is stimulated; increasing the saliva that contains enzymes which aid in the initial chemical process of digestion.

• Myenteric plexus. This plexus is composed of cell bodies of both the sympathetic and parasympathetic systems and innerves the layers of the muscular layer of the gut. It controls the gastrointestinal tract motility. The myenteric plexus receives its messages from the vagus nerve and responds by transmitting the message to muscle cells, which are thereby activated to contract. The muscles of the stomach and intestines play an active role in digestion, as waves of muscle contractions (peristaltic waves) push food through the parts of the digestive tract. It is thought that the myenteric plexus stimulates the muscles to contract in peristaltic waves and that it helps keep muscle tone throughout the intestine walls, promotes secretions of intestinal juices, and allows muscular constrictions (sphincters) to open, thus permitting food to pass from one part of the digestive system to another.
• Pre/Enzyme- where secreted from and function (gastrin, somatostatin, pepsinogen, mucus, lipase, secretin, insulin, CCK, GIP) what/where does it stimulate or inhibit
• Gastrin: it is a peptide hormone secreted by the stomach responsible for enhancing gastric mucosal growth, gastric motility, and secretion of hydrochloric acid.
• Somatostatin: it is a peptide hormone also known as growth hormone-inhibiting hormone because inhibits the secretion of several other hormones, including growth hormone, thyroid stimulating hormone. It is produced in the pancreas and inhibits the secretion of other pancreatic hormones such as insulin and glucagon.
• Pepsinogen: it is an edopeptidase, an enzyme secreted by the gastric cells, which breaks downs proteins into smaller pepetids.
• Mucus: the gastric mucus is secreted by the epithelial cells of the stomach. It protects the stomach of being digested by its own enzymes and provides a lubrication for food masses in order to facilitate movement.
• lipase: this enzyme is produced by the pancreas and catalyzes the hydrolysis of triglycerides (triacylglycerols). It could be found in the blood, gastric juices, pancreatic secretions, intestinal juices, and adipose tissues.
• Secretin: is secreted by the small intestine (the duodenum) and regulates gastric acid secretion and PH levels in the duodenum.
• Insulin: this hormone is secreted by the pancreas in order to control glucose levels in our body.
• CCK: this hormone (cholecystokinin) is secreted by the upper small intestine and stimulates the gallbladder to contract and release stored bile into the intestine.
• GIP: gastric inhibitory polipeptid: one of its roles is as inhibitor of gastric acid secretion, but its main role is to stimulate insulin secretion.

• What is deglutition? Is the process through which a bolus of food or liquid is transported from the mouth to the stomach.
• Gastric regulation- cephalic vs. gastric vs. Intestinal:

In the cephalic phase the stomach responds to sight, smell, or taste. In consequence, this sensory imput activate the gastric through the nervous system.

The gastric phase occurs when the ingested food stimulates gastric activity trough stretching the stomach and gastric contents.

In the intestinal phase, the duodenum responds to arriving of the semi-fluid mass of partly digested food that is expelled by the stomach, and moderates gastric activity.

• Where does blood go after leaving the intestine? After leaving the intestine, part of blood goes to the liver (liver cleans the blood), while other part goes to kidneys.
• What does the colon do? The colon is the final part of the digestive system (large intestine) that reabsorbs fluids and salts, and lubricates and stores waste products.
• Process of defecation: is the act of eliminating solid or semisolid feces from the digestive tract through the muscular contractions.