Module 7 - GI Tract Disorders Flashcards
What is saliva made up of
Saliva is a hypotonic solution of water and solutes with the enzyme amylase that can break down starches. May also contain mucus, lysozyme to break down bacteria, IgA to inhibit bacterial growth, and electrolytes.
Describe the two types of digestion that takes place in the stomach:
Chemical digestion - pepsinogen is a proenzyme, or inactive enzyme. The stomach acid is going to activate pepsinogen into its active form pepsin, which can digest proteins into smaller peptides or amino acids.
Mechanical digestion via muscular contractions - 3 layers of smooth muscle. Mechanical digestion breaks food down into smaller pieces and gives the food a greater surface area. The enzymes can then work on chemical digestion.
What are the three main cells in the stomach necessary for digestion?
The parietal cells (HCl and intrinsic factor), chief cells (pepsinogen), and G cells (Gastrin)
What functions does the liver have?
It produces bile; metabolizes hormones and drugs; synthesizes proteins, glucose, and clotting factors; stores vitamins and minerals and converts them to be usable by the body; changes ammonia ot urea; and converts fatty acids to ketones. The liver can store large amounts of glucose as glycogen; synthesize glucose from amino acids, glycerol, and lactic acid during times of fasting or increased demand; convert excess carbohydrates to triglycerides for storage in adipose tissue; major site for protein synthesis and degradation.
What is the structure and function of the 4 layers of the GI wall?
The mucosal layer - it is made up of epithelium, connective tissue, and smooth muscle cells. It produces mucus that lubricates and protects the inner surface of the alimentary canal. It secretes digestive enzymes and substances that break down food. It absorbs the breakdown products of digestion. It maintains a barrier to prevent the entry of noxious substances and pathogenic organism.
The submucosal layer - contains dense connective tissue and some adipose tissue. Has blood vessels, nerves, and structures that secrete digestive enzymes.
The muscularis externa - consists of an inner layer of ciruclarly arranged muscle cells and an outer layer of longitudinally arranged smooth muscle layers. THese layers alternately contract to help move the contents through the GI tract via peristalsis.
The serosal layer - the outermost layer of organs and also called the visceral peritoneum. The peritoneum is the largest serous membrane in the body. It is comprised of two continuous layers, the visceral and parietal peritoneum. The parietal peritoneum lines the wall of the abdominopelvic cavity. Between the two layers is the peritoneal cavity, a potential space containing fluid secreted by the serous membranes. This serous fluid keeps a moist surface to prevent friction between the moving abdominal organs.
What does the pancreas produce?
Pancreatic juice with enzymes (proteases - protein, lipases - lipids, amylase - starch) and alkaline buffer to neutralize stomach acid so doesn’t harm the lining of the small intestine as chyme enters from stomach. Pancreas also secretes insulin and glucagon to regulate blood glucose levels. Insulin signals cells to take in glucose after we eat and that drops our blood glucose levels. Secretes glucagon to increase glucose levels between meals.
What is the role of the stomach in digestion
Holds food in storage during the early stages of digestion and carbohydrate and protein digestion occur.
What is the role of the small intestine in digestion
Duodenum, jejunum, and ileum.
Majority of digestion and absorption take place. Bile and pancreatic juices enter the intestine through the common bile duct and main pancreatic duct. Fat is broken into smaller pieces so enzymes can act on the surface molecules (emulsification).
The small intestine has a lot of surface area (villi, circular folds) which allows absorption of nutrients.
What is the role of the large intestine in digestion
Cecum, ascending/transverse/descending/sigmoid colon, rectum, anal canal.
Absorbs mainly water and a storage for waste until defecation.
The microflora help produce vitamins B & K
What is the mesentery?
The mesentery is the double layer of peritoneum that encloses some or all of the abdominal viscera and attaches it to the abdominal wall. There are also blood vessels, nerves, and lymphatic vessels that supply the intestinal wall. It also holds the organs in place and stores fat.
What is the omentum?
The omentum is a double layered extension or fold of peritoneum that passes from the stomach to adjacent organs in the abdominal cavity or wall. The greater omentum contains fat and has a lot of mobility to follow the movements of the intestines.
What’s the difference between rhythmic and tonic movements?
Rhythmic movements are intermittent contractions that help to mix and move food along - esophagus, antrum of the stomach, and small intestine.
Tonic movements have a constant level of contraction or tone without regular periods of relaxation - lower esophagus, upper region of stomach, ileocecal valave, and internal anal sphincter.
What is the enteric nervous system?
The myenteric and submucosal plexuses both make up the enteric nervous system. These two plexuses are networks of nerve fibers and ganglion cell bodies. Interneurons connect afferent sensory fibers, efferent motor neurons, and secretory cells to form reflex circuits.
What are the myenteric and submucosal plexuses.
The myenteric plexus is a chain of neurons that are involved in GI motility situated between the muscular layers of the GI tract.
The submucosal plexus plays a role in controlling secretions, absorption, and contraction of each segment of the intestinal tract. It is situated between the mucosal and muscular layers of the intestinal wall.
Explain how the stomach churns food.
The stomach churns and mixes food in a peristaltic fashion of 3-5 contractions per minute, each lasting 2-20 seconds. Contraction of the antrum pushes food toward the closed pyloric sphincter. Larger particles are returned to the body of the stomach for further churning. The other contents are emptied into the duodenum between contractions.
Describe the two patterns of contractions in the small intestine.
Segmentation waves are slow contractions of the circular muscle layer. They occlude the lumen and push digestive contents back and forth, using small portions of the intestine at a time. Chyme gets mixed with digestive enzymes from the pancreas and all surface area is exposed to the intestinal surface for absorption. Segmentation activity is higher after a meal.
Peristaltic contractions are rhythmic movements designed to propel the chyme along toward the large intestine, one direction. When they reach the ileoccecal junction, the stretching of the ileum elicits a reflex which relaxes the sphincter, allowing fluid to move into the cecum.
What are the two types of movements in the colon?
Haustral churning is in the compartments of the colon called haustra and these movements fill and expel contents from the haustral, to ensure the entire surface area of the fecal mass is exposed to intestinal surface.
Propulsive mass movements contract a larger segment of the colon to move a collective amount of fecal matter. This is what triggers a need for a bowel movement.
Explain how the GI tract is involved in both endocrine and paracrine regulation
Alhough the GI tract is the largest endocrine organ in the body, it is involved in both endocrine (distant) and paracrine (cell-to-cell) regulation. Endocrine regulation begins by releasing a hormone (or protein) into the blood stream. Once in the circulatory system, it travels until reaching the appropriate target cell, which then responds by releasing another hormone or chemical messenger. For example, once stomach acid (present in chime) enters the intestine, it stimulates the release of secretin. In contrast, paracrine regulation only occurs locally, for example a hormone reaches a target cell by crossing a neighboring cell membrane.
