A. mouth
B. esophagus
C. stomach
D. small intestine
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a) mouth
- Correct: The chemical digestion of starch begins in the mouth. Salivary amylase, an enzyme secreted by the salivary glands, initiates the breakdown of starch molecules into maltose and other smaller carbohydrate molecules. This process begins as soon as food enters the mouth and continues as it is mixed with saliva during chewing and swallowing.
b) esophagus
- Incorrect: The esophagus is not directly involved in the chemical digestion of starch. It serves primarily as a conduit for the passage of food from the mouth to the stomach via peristaltic contractions.
c) stomach
- Incorrect: While some minor digestion may occur in the stomach due to the presence of salivary amylase from swallowed saliva, the stomach is not the primary site of starch digestion. Its acidic environment inhibits the activity of salivary amylase, so significant starch digestion does not occur there.
d) small intestine
- Incorrect: Starch digestion continues in the small intestine, primarily in the duodenum, but it does not begin there. Enzymes such as pancreatic amylase and brush border enzymes further break down starch into simpler sugars in the small intestine.
Therefore, the Correct Answer is A.
Where does the majority of chemical digestion in the stomach occur?
A. fundus and body
B. cardia and fundus
C. body and pylorus
D. body
The Correct Answer is A.a) fundus and body
- Correct: The majority of chemical digestion in the stomach occurs in the fundus and body regions. These regions contain gastric glands that secrete hydrochloric acid (HCl), pepsinogen, and mucus. Hydrochloric acid creates an acidic environment necessary for the activation of pepsinogen to pepsin, which is responsible for the digestion of proteins. Additionally, the stomach churns and mixes food with gastric juices in the fundus and body, facilitating the breakdown of food particles and the mixing of digestive enzymes with the food bolus.
b) cardia and fundus
- Incorrect: While the fundus region is involved in chemical digestion due to the presence of gastric glands, the cardia region primarily serves as the entry point of the esophagus into the stomach and does not significantly contribute to chemical digestion.
c) body and pylorus
- Incorrect: While the body region of the stomach is involved in chemical digestion, the pylorus region is primarily responsible for regulating the passage of partially digested food (chyme) into the small intestine through the pyloric sphincter. The pylorus region does not contribute significantly to chemical digestion.
d) body
- Incorrect: While the body region of the stomach is involved in chemical digestion, the majority of chemical digestion occurs in both the fundus and body regions. The body region alone does not represent the entirety of where chemical digestion occurs in the stomach.
Which phase of deglutition involves contraction of the longitudinal muscle layer of the muscularis?
A. voluntary phase
B. buccal phase
C. pharyngeal phase
D. esophageal phase
The Correct Answer is A.a) voluntary phase
- Correct: The voluntary phase of deglutition (swallowing) involves the initial voluntary movement of food from the mouth into the pharynx. During this phase, the tongue pushes the food bolus backward toward the oropharynx. Contraction of the longitudinal muscle layer of the muscularis propels the food bolus into the pharynx, which is part of the voluntary control of swallowing.
b) buccal phase
- Incorrect: The buccal phase of deglutition involves the initial formation of the food bolus and its movement toward the oropharynx by the coordinated action of the tongue and muscles of the cheeks. It does not involve contraction of the longitudinal muscle layer of the muscularis.
c) pharyngeal phase
- Incorrect: The pharyngeal phase of deglutition is involuntary and occurs when the food bolus reaches the pharynx. It involves the sequential contraction of muscles in the pharyngeal wall to propel the food bolus downward toward the esophagus. The contraction of the longitudinal muscle layer of the muscularis is not a significant component of the pharyngeal phase.
d) esophageal phase
- Incorrect: The esophageal phase of deglutition involves the passage of the food bolus through the esophagus and into the stomach. Peristaltic waves of contraction and relaxation of the muscularis propels the food bolus along the length of the esophagus. The contraction of the longitudinal muscle layer of the muscularis primarily occurs during the voluntary phase of deglutition, not the esophageal phase.
Which of these statements about the pharynx is true?
A. It extends from the nasal and oral cavities superiorly to the esophagus anteriorly.
B. The oropharynx is continuous superiorly with the nasopharynx.
C. The nasopharynx is involved in digestion.
D. The laryngopharynx is composed partially of cartilage.
The Correct Answer is D.d) The laryngopharynx is composed partially of cartilage.
- True: The statement that the laryngopharynx is composed partially of cartilage is true. The pharynx, commonly known as the throat, is a muscular tube that extends from the base of the skull to the level of the sixth cervical vertebra. It serves as a passageway for both air and food. The pharynx is divided into three regions: the nasopharynx, oropharynx, and laryngopharynx.
a) It extends from the nasal and oral cavities superiorly to the esophagus anteriorly.
- False: The pharynx extends from the nasal and oral cavities superiorly to the esophagus and larynx inferiorly, not anteriorly.
b) The oropharynx is continuous superiorly with the nasopharynx.
- False: The oropharynx is continuous inferiorly with the oral cavity, not superiorly with the nasopharynx. The nasopharynx is continuous superiorly with the nasal cavity.
c) The nasopharynx is involved in digestion.
- False: The nasopharynx is primarily involved in respiration and the passage of air. It contains the openings of the auditory tubes and tonsils but is not directly involved in digestion.
Chemical digestion of carbohydrates begins in the
A. esophagus
B. stomach
C. duodenum
D. oral cavity
The Correct Answer is D.D. oral cavity
- Correct: Chemical digestion of carbohydrates begins in the oral cavity. Salivary glands in the mouth secrete saliva, which contains an enzyme called amylase. Amylase breaks down complex carbohydrates (such as starch) into simpler sugars (such as maltose) through hydrolysis. This process initiates the digestion of carbohydrates before the food bolus reaches the stomach or small intestine.
A. esophagus
- Incorrect: The esophagus is primarily involved in the propulsion of food from the mouth to the stomach through peristaltic contractions. It does not play a significant role in the chemical digestion of carbohydrates.
B. stomach
- Incorrect: While the stomach plays a role in the digestion of proteins through the action of gastric juices containing pepsin and hydrochloric acid, it does not contribute significantly to the digestion of carbohydrates. In fact, the acidic environment of the stomach may temporarily inhibit the activity of salivary amylase.
C. duodenum
- Incorrect: The duodenum is the first part of the small intestine where the majority of chemical digestion occurs. While the duodenum receives pancreatic enzymes and bile that aid in the digestion of carbohydrates, proteins, and fats, the initial chemical digestion of carbohydrates primarily occurs in the oral cavity with the action of salivary amylase.
. Parietal cells secrete ________.
A. gastrin
B. hydrochloric acid
C. pepsin
D. pepsinogen
The Correct Answer is B.b) hydrochloric acid
- Correct: Parietal cells, also known as oxyntic cells, secrete hydrochloric acid (HCl) into the stomach lumen. HCl plays a critical role in the digestive process by creating an acidic environment necessary for the activation of pepsinogen to pepsin and for the breakdown of food proteins. Parietal cells also secrete intrinsic factor, which is essential for the absorption of vitamin B12 in the small intestine.
a) gastrin
- Incorrect: Gastrin is a hormone secreted by G cells in the gastric glands of the stomach. It stimulates the secretion of gastric acid (HCl) by parietal cells and promotes gastric motility and emptying.
c) pepsin
- Incorrect: Pepsin is an enzyme that digests proteins by breaking them down into smaller peptides. Pepsin is formed from the precursor molecule pepsinogen, which is secreted by chief cells in the gastric glands. Parietal cells do not directly secrete pepsin.
d) pepsinogen
- Incorrect: Pepsinogen is the inactive precursor of pepsin. It is secreted by chief cells in the gastric glands of the stomach. Pepsinogen is activated to pepsin by the acidic environment created by hydrochloric acid secreted by parietal cells.
In which organ of the human body is urea produced as a result of the breakdown of amino acids?
A. liver
B. pancreas
C. stomach
D. small intestine
The Correct Answer is A.A) liver
- Correct: Urea is produced in the liver as a result of the breakdown of amino acids. Amino acids are the building blocks of proteins, and when proteins are metabolized for energy or other purposes, their constituent amino acids are broken down in a process called deamination. During deamination, the amino groups (-NH2) are removed from the amino acids, forming ammonia (NH3). The liver converts ammonia into urea through a series of biochemical reactions known as the urea cycle. Urea is then excreted by the kidneys in the urine, helping to remove nitrogenous waste from the body.
B) pancreas
- Incorrect: The pancreas is an organ involved in the production of digestive enzymes and hormones such as insulin and glucagon. It is not primarily responsible for the production of urea from the breakdown of amino acids.
C) stomach
- Incorrect: The stomach is primarily involved in the mechanical and chemical digestion of food, particularly proteins. While protein digestion begins in the stomach with the action of gastric juices containing enzymes such as pepsin, urea production from the breakdown of amino acids occurs mainly in the liver.
D) small intestine
- Incorrect: The small intestine is primarily involved in the absorption of nutrients from digested food, rather than the production of urea from the breakdown of amino acids. While some amino acids may be absorbed in the small intestine, urea production primarily occurs in the liver.
Where are most fat-digesting enzymes produced?
A. small intestine
B. gallbladder
C. liver
D. pancreas
The Correct Answer is D.d) pancreas
- Correct: Most fat-digesting enzymes, such as pancreatic lipase, are produced in the pancreas. Pancreatic lipase is secreted by the pancreas into the small intestine, specifically the duodenum, where it plays a crucial role in the digestion of dietary fats. Additionally, other enzymes involved in fat digestion, such as pancreatic colipase and phospholipase, are also produced by the pancreas.
a) small intestine
- Incorrect: While some fat-digesting enzymes are present in the small intestine, the majority of these enzymes are produced by the pancreas and delivered to the small intestine via the pancreatic duct.
b) gallbladder
- Incorrect: The gallbladder stores and concentrates bile produced by the liver, but it does not produce fat-digesting enzymes. Bile stored in the gallbladder contains bile salts, which aid in the emulsification and digestion of fats, but they are not enzymes themselves.
c) liver
- Incorrect: The liver produces bile, which contains bile salts that aid in fat digestion by emulsifying large fat globules into smaller droplets, but it does not produce fat-digesting enzymes. The liver also plays a role in lipid metabolism and the synthesis of lipoproteins but does not produce enzymes directly involved in fat digestion.
Which of these statements about reflexes in the GI tract is false?
A. Short reflexes are provoked by nerves near the GI tract.
B. Short reflexes are mediated by the enteric nervous system.
C. Food that distends the stomach initiates long reflexes.
D. Long reflexes can be provoked by stimuli originating outside the GI tract.
The Correct Answer is C.c) Food that distends the stomach initiates long reflexes.
- False: This statement is false. Food that distends the stomach initiates short reflexes, not long reflexes. Short reflexes are local reflexes that are mediated by the enteric nervous system, which consists of a network of neurons within the walls of the digestive tract. When food stretches or distends the stomach, sensory neurons in the stomach wall detect this mechanical stimulus and initiate short reflexes that regulate local gastrointestinal functions, such as gastric motility and secretion.
Most of the nutrient absorption along the alimentary canal occurs in the
A. ascending colon
B. stomach
C. jejunum
D. ileum
The Correct Answer is C.C. jejunum
- Correct: Most of the nutrient absorption along the alimentary canal occurs in the jejunum, which is the middle segment of the small intestine. The jejunum has a highly folded inner surface covered with finger-like projections called villi and even smaller microvilli. These structures greatly increase the surface area available for absorption. The epithelial cells lining the villi contain numerous transport proteins and enzymes responsible for absorbing nutrients such as carbohydrates, proteins, fats, vitamins, and minerals into the bloodstream for distribution to the body's cells.
A. ascending colon
- Incorrect: The ascending colon is part of the large intestine (colon) where water and electrolytes are primarily absorbed, but it is not a major site of nutrient absorption.
B. stomach
- Incorrect: While some substances, such as water, electrolytes, alcohol, and certain drugs, can be absorbed in small amounts in the stomach, the stomach is not a major site of nutrient absorption. Its main function is to begin the digestion of proteins and store food temporarily.
D. ileum
- Incorrect: The ileum is the final segment of the small intestine, and while it does participate in nutrient absorption, the majority of nutrient absorption occurs in the jejunum, which precedes the ileum along the alimentary canal. The ileum primarily absorbs bile salts, vitamin B12, and some remaining nutrients not absorbed in the jejunum.
The pancreas, liver, and gallbladder help digestion in these ways, respectively:
A. making enzymes; making bile and processing nutrients; and storing bile
B. producing saliva; digesting carbohydrates; and eliminating waste
C. producing hormones; producing enzymes; and eliminating waste
D. making acids; producing digestive juices; and storing enzymes
The Correct Answer is A.a. making enzymes; making bile and processing nutrients; and storing bile
- Correct: The pancreas, liver, and gallbladder help digestion in the following ways:
1. The pancreas produces and secretes digestive enzymes into the small intestine to aid in the breakdown of carbohydrates, proteins, and fats. These enzymes include amylase (for carbohydrates), proteases (for proteins), and lipases (for fats).
2. The liver produces bile, a digestive fluid that emulsifies fats by breaking them down into smaller droplets, which increases the surface area for enzymes to act upon. The liver also processes nutrients absorbed from the small intestine, including carbohydrates, proteins, and fats.
3. The gallbladder stores and concentrates bile produced by the liver. When needed for digestion, the gallbladder releases bile into the small intestine via the common bile duct to aid in the emulsification and digestion of fats.
Therefore, option a accurately describes the roles of the pancreas, liver, and gallbladder in digestion.