GI Physiology Quiz Questions

The contraction of the circular layer of a structure, such as a blood vessel or a tube, would indeed cause the lumen (the central opening) to become narrower. This is because the circular layer, when it contracts, reduces the diameter of the structure, thus making the lumen smaller.

Peristalsis is the most common type of motility associated with the esophagus. It is a coordinated contraction and relaxation of the muscles that helps propel food from the mouth to the stomach. This rhythmic movement allows for efficient swallowing and prevents food from regurgitating back into the mouth. Peristalsis is essential for the proper functioning of the digestive system and ensures that food is transported smoothly through the esophagus.

The myenteric plexus, also known as Auerbach's plexus, controls gut motility. It is a network of nerve fibers located between the longitudinal and circular muscle layers of the gastrointestinal tract. The myenteric plexus regulates the contractions and movements of the gut, coordinating the peristaltic waves that propel food through the digestive system. It plays a crucial role in regulating the speed and coordination of gut motility, ensuring efficient digestion and absorption of nutrients.

The submucosal plexus, also known as Messiner's plexus, controls gut secretions. This plexus is located in the submucosal layer of the gastrointestinal tract and is responsible for regulating the secretion of enzymes, mucus, and fluid into the gut lumen. It receives signals from the central nervous system and coordinates the release of these secretions to aid in digestion and absorption of nutrients. The myenteric plexus, or Auerbach's plexus, on the other hand, primarily controls gut motility and the contraction of smooth muscles in the gastrointestinal tract.

The intrinsic stimulation of the large intestine through the release of Ach and substance P causes the stimulation of colonic movement. Ach and substance P are neurotransmitters that play a role in the regulation of smooth muscle contraction in the intestines. When released, they promote the contraction of the colonic muscles, leading to an increase in colonic movement. This stimulation helps propel the contents of the large intestine forward, aiding in the process of digestion and elimination.

Contraction of the longitudinal layer causes the length of the GI tract to become shorter.

The circular layer of GI smooth muscle exhibits stronger constrictions because it has more gap junctions. Gap junctions are specialized protein channels that allow for direct communication and coordination between adjacent cells. In the circular layer, the presence of more gap junctions enables a stronger and more coordinated contraction of the smooth muscle, leading to a more effective constriction of the gastrointestinal tract.

Segmentation is the correct answer because it refers to the type of motility that occurs in the small intestine to facilitate mixing. Segmentation involves the contraction and relaxation of different segments of the intestine, which helps to mix the food and digestive juices together. This process is bidirectional, as it moves the contents of the intestine back and forth, allowing for thorough mixing and absorption of nutrients.

The correct answer is inhibition of colonic movement. Intrinsic stimulation of the large intestine through the release of VIP (vasoactive intestinal peptide) and NO (nitric oxide) leads to the inhibition of colonic movement. VIP and NO act as inhibitory neurotransmitters, causing relaxation of the smooth muscles in the colon and reducing peristalsis, which results in a decrease in colonic movement. This helps in the absorption of water and electrolytes from the fecal matter, allowing for the formation of solid stool.

Elevated free fatty acids in the gut are most likely to stimulate the secretion of cholecystokinin (CCK) from the duodenal mucosa. CCK is a hormone released in response to the presence of fat in the small intestine. It stimulates the release of bile from the gallbladder and pancreatic enzymes, which aid in the digestion and absorption of fats. Therefore, when there are elevated levels of free fatty acids in the gut, it signals the need for increased secretion of CCK to facilitate fat digestion and absorption.

The primary pre-ganglionic neurotransmitter in the sympathetic nervous system is Ach (acetylcholine). Acetylcholine is released by the preganglionic neurons and binds to nicotinic receptors on the postganglionic neurons. This neurotransmitter is responsible for transmitting signals from the central nervous system to the ganglia in the sympathetic nervous system.

The muscularis mucosa is a sublayer of the mucosa that is primarily composed of intestinal smooth muscle. This layer is responsible for the movement and contraction of the mucosa, which helps with the absorption and digestion of nutrients in the intestines. The presence of smooth muscle in the muscularis mucosa allows for coordinated contractions that aid in the movement of food through the digestive tract. Therefore, the correct answer is intestinal smooth muscle.

The submucosa is the correct answer because it is the layer of the gastrointestinal (GI) system that contains glands. The submucosa is located beneath the mucosa and is made up of connective tissue. It contains various glands, including the submucosal glands, which secrete mucus and other substances that aid in digestion and protect the GI tract. The other layers of the GI system, including the mucosa, muscularis externa, and serosa, do not typically contain glands.

Segmentation is the most common type of motility associated with the small intestine. Segmentation refers to the contraction and relaxation of the circular muscles in the intestinal wall, which helps to mix and break down food, as well as facilitate absorption of nutrients. This type of motility creates small segments or compartments within the intestine, allowing for efficient digestion and absorption of nutrients.

The lamina propria and submucosa are both layers of the mucosa. The mucosa is the innermost layer of the gastrointestinal tract that lines the lumen. The lamina propria and submucosa are composed primarily of loose connective tissue. Loose connective tissue is a type of connective tissue that contains a network of collagen and elastic fibers, as well as various cells, such as fibroblasts and immune cells. It provides support, flexibility, and allows for the movement of substances through the mucosa.

Extrinsic stimulation of the large intestine through the vagus nerve causes haustrations. Haustrations refer to the formation of pouches or sacs in the colon, which aid in the mixing and propulsion of fecal matter. The vagus nerve, part of the parasympathetic nervous system, plays a role in regulating gastrointestinal motility. Stimulation of the vagus nerve leads to increased activity in the colon, resulting in the formation of haustra. This helps to facilitate the movement of feces through the large intestine.

Extrinsic stimulation of the large intestine through the vagus nerve causes haustrations. Haustrations refer to the contractions and relaxations of the muscles in the colon that create the characteristic pouch-like structures called haustra. This stimulation leads to the segmentation of the colon, allowing for the mixing and absorption of water and electrolytes. These haustral contractions also help in the movement of feces through the colon, promoting efficient digestion and elimination.

Peristalsis is the type of motility that occurs in the small intestine to move chyme caudally. Peristalsis is a coordinated contraction and relaxation of the smooth muscles in the intestinal wall, which propels the chyme in a wave-like motion through the digestive tract. This movement helps to mix and churn the chyme, aiding in digestion and absorption of nutrients.

The primary post-ganglionic neurotransmitter in the sympathetic (SNS) nervous system is NE (norepinephrine). This neurotransmitter is released by post-ganglionic neurons and binds to adrenergic receptors in target organs, activating the fight-or-flight response. NE plays a crucial role in regulating various physiological processes, including heart rate, blood pressure, and pupil dilation.

Extrinsic stimulation of the large intestine through the mesenteric and hypogastric nerves, which are part of the sympathetic nervous system (SNS), leads to the inhibition of colonic movement. This means that the SNS activation reduces the contractions and movements of the colon, resulting in a decrease in colonic motility.

Plexuses of the enteric nervous system are found in the submucosal (Meissner's plexus) and myenteric (Auerbach's plexus) layers of the gastrointestinal tract. These plexuses play a crucial role in regulating various gastrointestinal functions, including motility, secretion, and blood flow.

The presence of a low pH (high acidity) in the gut, primarily caused by the entry of gastric acid from the stomach, serves as a stimulus for the secretion of secretin from the duodenal mucosa. Secretin, in response to this acidic environment, triggers the pancreas to release bicarbonate-rich pancreatic juices, aiding in neutralizing the acidity and creating an optimal pH for digestive processes in the small intestine.

The vagus nerve provides parasympathetic innervation to the cecum, ascending colon, and transverse colon. The parasympathetic nervous system is responsible for rest and digest functions, and the vagus nerve plays a key role in regulating these processes in the gastrointestinal tract. It stimulates smooth muscle contractions and increases blood flow to promote digestion and absorption of nutrients in these parts of the colon.

The condition most likely to stimulate the secretion of gastrin from the duodenal mucosa is high pH in the gut. Gastrin is a hormone that plays a role in stimulating the release of gastric acid in the stomach. When the pH in the stomach becomes relatively high (less acidic), it triggers the release of gastrin from the duodenal mucosa. Gastrin then acts to increase the secretion of gastric acid, helping to lower the pH and maintain the proper acidic environment for digestion.

The parasympathetic innervation of the descending colon, sigmoid colon, rectum, and anal canal is provided by the pelvic nerves. These nerves originate from the sacral spinal cord and travel through the pelvic plexus to reach the target organs. The parasympathetic fibers in the pelvic nerves help regulate various functions of the gastrointestinal tract, including smooth muscle contractions, glandular secretions, and blood flow. Therefore, the pelvic nerves are responsible for the parasympathetic control of the descending colon, sigmoid colon, rectum, and anal canal.

Haustrations refer to the rhythmic contractions and relaxations of the circular muscles in the colon, which help to create the characteristic pouches or haustra in the descending colon. This type of motility is the most common in the descending colon and is responsible for moving fecal matter through the colon for eventual elimination.

The sympathetic innervation of the cecum and ascending colon is provided by the superior mesenteric nerve.

Mechanoreceptors and chemoreceptors of the intrinsic nervous system of the enteric nervous system are found in the mucosa layer. The mucosa is the innermost layer of the gastrointestinal tract and is responsible for absorption and secretion. It contains various types of cells, including sensory cells that detect mechanical and chemical stimuli. These receptors play a crucial role in regulating gastrointestinal functions such as peristalsis and secretion of digestive enzymes.

The sympathetic innervation of the rectum and anal canal is provided by the inferior hypogastric nerve.

The small intestine is a crucial component of the digestive system, measuring approximately 20 feet in length. It is composed of three sections: the duodenum, jejunum, and ileum. The inner lining of the small intestine is folded into villi and microvilli, which significantly increase the surface area available for efficient absorption of nutrients into the bloodstream.

The sympathetic innervation of the descending colon and transverse colon is provided by the inferior mesenteric nerve.

Hypotonicity in the gut is most likely to stimulate the secretion of an unknown hormone from the duodenal mucosa that plays a role in decreased gastric emptying. When the gut is hypotonic, meaning that the concentration of solutes is lower than normal, it signals the body to slow down gastric emptying in order to allow more time for absorption of water and electrolytes. This hormone secretion helps regulate the movement of food through the digestive system and maintain proper fluid balance.

The intake and absorption of nutrients like glucose, elevated amino acids, and long-chain fatty acids orally stimulate the release of GIP. K-cells detect glucose through a variation of sodium-coupled glucose transporter-1 (SGLT-1), leading to the secretion of GIP.

The sympathetic innervation of the sigmoid colon is provided by the superior hypogastric nerve. The superior hypogastric nerve is a major nerve that arises from the aortic plexus and provides sympathetic fibers to the pelvic organs, including the sigmoid colon. It plays a role in regulating the smooth muscle tone and blood flow to the sigmoid colon.

The large intestine has a unique structure in its muscularis externa called the teniae coli. These are three bands of longitudinal muscle that run along the length of the large intestine. They are responsible for creating the characteristic pouches or haustra in the colon. These pouches allow for the expansion and contraction of the large intestine, aiding in the movement and processing of waste material.

The serosa is the outermost layer of the digestive tract and is composed of areolar connective tissue and squamous mesothelial cells. Areolar connective tissue provides support and elasticity to the serosa, while squamous mesothelial cells form a protective lining. These cells are flat and thin, allowing for easy movement and flexibility of the digestive organs. Together, areolar connective tissue and squamous mesothelial cells contribute to the structure and function of the serosa.