MCAT Biology Problem Drill 20: The Digestive System

Transcription

1 MCAT Biology Problem Drill 20: The Digestive System Question No. 1 of 10 Question 1. During the oral phase of swallowing,. Question #01 A. Initially, the food bolus is moved to the back of the tongue and then swallowing proceeds under voluntary control. B. The anterior of the tongue lifts to the hard palate and forces the bolus to the Pharynx, then the posterior portion of the tongue is lifted which closes the nasopharynx. C. The anterior of the tongue lifts to the hard palate and forces the bolus to the Pharynx, then the posterior portion of the tongue is lifted which opens the nasopharynx. D. The food bolus is propelled into the pharynx by contractions of the three muscle layers in the stomach. Initially, the food bolus is moved to the back of the tongue under voluntary control, then swallowing proceeds under involuntary control. B. Correct! The anterior of the tongue lifts to the hard palate and forces the bolus to the Pharynx, then the posterior portion of the tongue is lifted which closes the nasopharynx. The anterior of the tongue lifts to the hard palate and forces the bolus to the Pharynx, then the posterior portion of the tongue is lifted which closes the nasopharynx. The food bolus is propelled into the pharynx by an anterior to posterior movement of the tongue. Swallowing is a complex event, which is coordinated by the swallowing center in the lower portion of the brainstem. During this process, food passes from the mouth to the pharynx and into the esophagus, this occurs in three phases (a) oral phase (b) pharyngeal phase and (c) esophageal phase. Oral Phase: Initially, the food bolus is moved to the back of the tongue. This triggers swallowing, by stimulating touch receptors in the pharynx. Then, the anterior of the tongue lifts to the hard palate and forces the bolus to the Pharynx. Then the posterior portion of the tongue is lifted which closes the nasopharynx and prevents food from entering the nasal passages. The food bolus is propelled into the pharynx by an anterior to posterior movement of the tongue.

2 Question No. 2 of 10 Question 2. Which of the following statements about the pharyngeal phase of swallowing is correct? Question #02 A. During the pharyngeal phase the larynx is pulled forward and upward under the tongue by muscular contraction. B. During the pharyngeal phase the larynx is pushed outward away from the tongue by muscular contraction. C. As the larynx is lowered the epiglottis moves forward and up to open the glottis and the airways. D. The upper esophageal sphincter closes and the bolus of food then moves into the esophagus. A. Correct! During the pharyngeal phase the larynx is pulled forward and upward under the tongue by muscular contraction. During the pharyngeal phase the larynx is pulled forward and upward under the tongue by muscular contraction. As the larynx rises the epiglottis moves backwards and downwards to seal off the glottis and the airways. The upper esophageal sphincter opens and the bolus of food then moves into the esophagus. Pharyngeal Phase: During the pharyngeal phase the larynx is pulled forward and upward under the tongue by muscular contraction. As the larynx rises the epiglottis moves backwards and downwards to seal off the glottis (the entrance to the respiratory system). The upper esophageal sphincter opens and the bolus of food then moves into the esophagus.

3 Question No. 3 of 10 Question 3. During the esophageal phase of swallowing,. Question #03 A. The food bolus is pushed through the esophagus by voluntary muscle contractions called peristalsis. B. The food bolus is pushed through the esophagus by involuntary muscle contractions called peristalsis. C. The muscle fibers just below the bolus contract; this constricts the esophageal wall and pushes the bolus downward. D. The lower esophageal sphincter closes, and this also facilitates the bolus moving into the stomach. During the esophageal phase the food bolus is pushed through the esophagus by involuntary muscle contractions called peristalsis. B. Correct! During the esophageal phase the food bolus is pushed through the esophagus by involuntary muscle contractions called peristalsis. The muscle fibers just above the bolus contract; this constricts the esophageal wall and pushes the bolus downward. The lower esophageal sphincter relaxes and opens, and this also facilitates the bolus moving into the stomach. Esophageal Phase: During the esophageal phase the food bolus is pushed through the esophagus by involuntary muscle contractions called peristalsis. The muscle fibers just above the bolus contract; this constricts the esophageal wall and pushes the bolus downward. These contractions proceed in a wave pushing the bolus toward the stomach. The lower esophageal sphincter relaxes, and this also facilitates the bolus moving into the stomach.

4 Question No. 4 of 10 Question 4. Which of the following statements about the stomach is correct? Question #04 A. The fundus is a storage are of the stomach, food can remain in this region for up to an hour prior to mixing with gastric juices. Food mixes with gastric juices in the pyloric region. B. The pyloric region is a storage are of the stomach, food can remain in this region for up to an hour prior to mixing with gastric juices. Food mixes with gastric juices in the fundal region. C. CCK is an enzyme made by chief cells in the stomach; it is released into the stomach as a precursor called pepsinogen. D. Maltase begins the digestion of proteins in the stomach and it contributes to the digestion of food. A. Correct! The fundus is a storage are of the stomach, food can remain in this region for up to an hour prior to mixing with gastric juices. Food mixes with gastric juices in the pyloric region. The fundus is a storage are of the stomach, food can remain in this region for up to an hour prior to mixing with gastric juices. Food mixes with gastric juices in the pyloric region. Pepsin is an enzyme made by chief cells in the stomach; it is released into the stomach as a precursor called pepsinogen. Pepsin begins the digestion of proteins in the stomach and it contributes to the digestion of food. The fundus is a storage are of the stomach, food can remain in this region for up to an hour prior to mixing with gastric juices. Food mixes with gastric juices in the pyloric region. The pyloric region of the stomach can be completely shut off from the rest of the stomach during digestion, by peristaltic waves. This facilitates the mixing of food with the gastric juices to produce chyme. Chyme passes into the small intestine to continue the digestive process. The stomach is lined with rugae, these folds of mucosa allow the stomach to expand when filled. Pepsin is an enzyme made by chief cells in the stomach; it is released into the stomach as a precursor called pepsinogen. Pepsin is converted to pepsin when it comes into contact with the hydrochloric acid secreted by the parietal cells. Pepsin begins the digestion of proteins in the stomach and it contributes to the digestion of food.

5 Question No. 5 of 10 Question 5. Which of the following statements about the liver is correct? Question #05 A. The hepatic artery distributes blood to the liver, gallbladder and pancreas and the portal vein brings venous blood from the spleen, pancreas and small intestines for processing by the liver. B. The portal vein distributes blood to the liver, gallbladder and pancreas and the hepatic artery brings venous blood from the spleen, pancreas and small intestines for processing by the liver. C. The liver stores protein in the form of glycogen (glycogenesis). D. The liver is not involved in protein metabolism. A. Correct! The hepatic artery distributes blood to the liver, gallbladder and pancreas and the portal vein brings venous blood from the spleen, pancreas and small intestines for processing by the liver. The hepatic artery distributes blood to the liver, gallbladder and pancreas and the portal vein brings venous blood from the spleen, pancreas and small intestines for processing by the liver. The liver stores glucose in the form of glycogen (glycogenesis). The liver is responsible for the majority of protein metabolism. The liver is supplied by two main blood vessels on its right lobe: (a) hepatic artery- which distributes blood to the liver, gallbladder and pancreas and (b) portal vein- brings venous blood from the spleen, pancreas and small intestines for processing by the liver. The liver is involved in many aspects of nutrient metabolism, and the regulation of the products of digestion in the blood: (A) Carbohydrate metabolism: the liver stores glucose in the form of glycogen (glycogenesis). The liver breaks down glycogen when blood levels are low, and delivers glucose into the circulation (glycogenolysis). The liver can produce glucose from amino acids and lactate (gluconeogenesis). (B) Protein and lipid metabolism: the liver is responsible for the majority of protein metabolism; it also synthesizes cholesterol and produces triglycerides. The liver also breakdown hormones such as insulin. (C) Vitamin storage: the liver stores various vitamins and minerals such as vitamin B12, iron and copper.

6 Question No. 6 of 10 Question 6.The gallbladder? Question #06 A. Secretes bile which is an alkaline fluid produced by hepatocytes in the gallbladder. B. Ejects bile in response to the hormone Pepsidase. C. Ejects bile in response to the hormone cholecystokinin (CCK). D. Ejects bile into the small intestine, via the portal vein. Secretes bile which is an alkaline fluid produced by hepatocytes in the liver. Ejects bile in response to the hormone cholecystokinin (CCK). C. Correct! Ejects bile in response to the hormone cholecystokinin (CCK). Ejects bile into the small intestine, via the common bile duct. Bile is an alkaline fluid produced by hepatocytes in the liver, and helps to emulsify fats during digestion and absorption in the small intestine. Bile contains taurocholic and deoxycholic salts, these salts combine with fat globules and break them down into small droplets fro absorption in the small intestine. Bile also serves to excrete bilirubin, which is a product of processing old or damaged red blood cells. The gallbladder is a pear-shaped organ underneath the liver, that stores and concentrates bile until its needed for digestion. Bile is ejected from the gallbladder in response to the hormone cholecystokinin (CCK). When chyme enters the small intestine, which contains high concentrations of fat, stimulates the intestinal mucosa to secrete CCK. This hormone causes the gallbladder to contract and eject bile into the small intestine, via the common bile duct.

7 Question No. 7 of 10 Question 7. Which of the following statements about the small intestine is correct? Question #07 A. The small intestine is 8-22 ft in length in an adult, it is divided into three main segments: duodenum, hepatic flexure and the ileum. B. The small intestine is 8-22 ft in length in an adult, it is divided into three main segments: duodenum, jejunum and the ileum. C. The duodenum is the last portion of the small intestine; it is attached to the stomach. It is mainly involved with the break down of food particles.d. The jejunum is the final section of the small intestine and its primary role is the absorption of primarily vitamin B12 and bile salts. The small intestine is 8-22 ft in length in an adult, it is divided into three main segments: duodenum, jejunum and the ileum. B. Correct! The small intestine is 8-22 ft in length in an adult, it is divided into three main segments: duodenum, jejunum and the ileum. The duodenum is the first portion of the small intestine; it is attached to the stomach. It is mainly involved with the break down of food particles. The ileum is the last portion of the small intestine; it is attached to the stomach. It is mainly involved with the break down of food particles. The small intestine is 8-22 ft in length in an adult, it is divided into three main segments: duodenum, jejunum and the ileum. The small intestine is the site were most of the nutrients from digested food takes place. The intestine is lined with villi, which are finger-like structures that increase the absorption surface of the intestines greatly. The duodenum is the first portion of the small intestine; it is attached to the stomach. It is mainly involved with the break down of food particles. The jejunum is primarily involved with the absorption of nutrient food particles from the digestion process. The ileum is the final section of the small intestine and its primary role is the absorption of primarily vitamin B12 and bile salts.

8 Question No. 8 of 10 Question 8. Which of the following statements about the absorption of amino acids in the small intestine is correct? Question #08 A. Proteins are reduced to galactose and fructose. B. Amino acids are transported across the intestinal epithelial cells by a GLUT transporter. C. Amino acids are transported across the intestinal epithelial cells by four sodium dependent amino acid transporters. D. Amino acids are transported across the intestinal epithelial cells by four sodium independent amino acid transporters. Proteins are digested into amino acids for absorption. Amino acids are transported across the intestinal epithelial cells by four sodium dependent amino acid transporters. C. Correct! Amino acids are transported across the intestinal epithelial cells by four sodium dependent amino acid transporters. Amino acids are transported across the intestinal epithelial cells by four sodium dependent amino acid transporters. The small intestine is lined with villi, which increase the surface for absorption. On the surface of the villi there are brush border enzymes, which facilitate the final process in digestion, reducing proteins and carbohydrates to amino acids and sugars (the form absorbed by the intestine). Absorption in the intestine is the movement of food particles across the intestinal wall into the bloodstream. Carbohydrates are reduced to simple sugars and are absorbed as glucose, galactose and fructose. Proteins are digested into amino acids for absorption. Water and electrolyte ions (Na+, Ca2+, Cl-) move across the intestinal epithelial cells by passive diffusion and are absorbed into the bloodstream. Glucose and the other simple sugars are transported across the intestinal epithelial cells by a GLUT transporter. This is a sodium dependent transporter that binds sodium then glucose and transports them inside the cell. A similar transporter moves the glucose from inside the cell across the basolateral membrane into the capillary. Amino acids are transported across the intestinal epithelial cells by four sodium dependent amino acid transporters.

9 Question No. 9 of 10 Question 9. Which is true about the large intestine? Question #09 A. It is the last stage of digestion occurs in the large intestine through bacterial action, not enzymes. B. It is the last stage of digestion occurs in the large intestine through the action of intestinal enzymes. C. It is the primary location for the absorption of amino acids and glucose. D. After Chyme that has resided in the large intestine for 3-10 hours, additional water has been added it is now a semisolid known as feces. A. Correct! It is the last stage of digestion occurs in the large intestine through bacterial action, not enzymes. The last stage of digestion occurs in the large intestine through bacterial action, not enzymes. It is the primary location for the absorption of liquids, primarily water, and salt ions. After Chyme that has resided in the large intestine for 3-10 hours, the majority of the water has been removed and it is now a semisolid known as feces. The last stage of digestion occurs in the large intestine through bacterial action, not enzymes. Intestinal flora are bacteria that reside in the large intestine and ferment any remaining carbohydrates or break down any remaining protein into amino acids. These bacteria also from vitamin K and some B vitamins in the large intestine, which are then absorbed for use inside the body. The large intestine is the primary location for the absorption of liquids, primarily water, and salt ions. Water-soluble vitamins are also absorbed in the large intestine. There are mass movements that occur in the transverse and descending colon to move the waste towards the rectum for disposal.

10 Question No. 10 of 10 Question 10.Which of the following statements about the enteric nervous system is correct? Question #10 A. The digestive system is innervated and controlled entirely by the central nervous system. B. The submucosal plexus, lies between the circular and longitudinal muscle layers.c. The myenteric plexus, lies between the circular and longitudinal muscle layers. D. The myenteric plexus is responsible for regulating the glandular activities in the digestive organs hormone secretion. While the central nervous system inputs control on the enteric nervous system, the enteric nervous system can operate independently. The myenteric plexus, lies between the circular and longitudinal muscle layers. C. Correct! The myenteric plexus, lies between the circular and longitudinal muscle layers. The submucosal plexus is responsible for regulating the glandular activities in the digestive organs hormone secretion. The digestive system is innervated and controlled by the enteric nervous system. While the central nervous system inputs control on the enteric nervous system, the enteric nervous system can operate independently. The enteric nervous system is composed of two layers: (a) Myenteric plexus, which lies between the circular and longitudinal muscle layers, and (b) Submucosal plexus, which lies between the layer of circular muscle and the submucosa. The two layers of the enteric nervous system are interconnected and operate together. The primary role of the myenteric plexus is to transmit sensory signals and deliver motor impulses for muscular contraction. The submucosal plexus is responsible for regulating the glandular activities in the digestive organs hormone secretion.