Gastrointestinal Tract Structure
What hormone stimulates digestive enzyme secretion by the pancreas, relaxation of the sphincter of Oddi, and contraction of the gallbladder?
cholecystokinin
What type of cells or tissue make up the serosa of the wall of the gastrointestinal tract?
connective tissue
The wall of most of the intestinal tract
contains convolutions that increase the surface area for absorption
In passing from the thoracic cavity to the abdominal cavity, the esophagus passes through a large muscle called the
diaphragm
The process of dissolving and breaking-down macromolecules within the GI tract is referred to as
digestion
The primary functions of the digestive system are
digestion and absorption of ingested food
The ______ consists of neurons that are located within the organs of the digestive tract, and control reflexes associated with digestive secretion and motility.
enteric nervous system
Amylase, protease, and lipase are ____ produced by the digestive system to help break down specific kinds of food molecules
enzymes
Which two of the following, when present in chyme, are mainly responsible for stimulating the secretion of cholecystokinin (CCK) by the small intestine?
free fatty acids and amino acids
Which of these hormones is not predominantly secreted from the small intestine?
gastrin
Billions of bacteria are present in the ______, which doesn't cause harm because that space is part of the ______
gastrointestinal tract lumen; external environment
Billions of bacteria are present in the ______, which doesn't cause harm because that space is part of the ______.
gastrointestinal tract lumen; external environment
What are the four best-understood gastrointestinal tract hormones?
glucose-dependent insullinotropic peptide cholecytokinin gastrin secretin
After a bolus has entered the stomach, the esophagus is protected from gastric juice by continued constriction of the
lower esophageal sphincter
Which of these are functions of chewing?
mixing food with saliva to create the subjective pleasure of taste breaking up large pieces of food into smaller particles creating a bolus that can be more easily swallowed
Because the lower esophageal sphincter is located ______ the diaphragm, when the pressure in the abdominal cavity increases the lower esophageal sphincter is
Below, prevented from opening
The epithelial cells lining the gastrointestinal tract are completely replaced about once every 5
Days
Which of these accurately describe general features of the gastrointestinal tract wall from the stomach to the anus?
most of the luminal surface is highly convoluted, which increases the surface area available for absorption; epithelial cells are joined by tight junctions; invaginations of the epithelium form exocrine glands; the lumen is lined by a single layer of epithelial cells
Of the four histological layers that make up the wall of the intestinal tract, the one closest to the lumen is called the
mucosa
The ____ is the layer of the digestive tract that is composed of epithelium, the lamina propria, and the muscularis mucosa.
mucosa
The ______ is the layer of the digestive tract that is composed of epithelium, the lamina propria, and the muscularis mucosa.
mucosa
The innermost layer of the four histological layers making up the wall of the small intestine (facing the lumen) is called the
mucosa
In the digestive system, the general term describing the transport of digestive products across the mucosal layer from the lumen of the tract into the blood or lymph is
absorption
The entry of products of chemical digestion from the lumen of the gastrointestinal tract into blood or lymph is called ______.
absorption
The molecules produced by digestion then move from the lumen of the gastrointestinal tract across a layer of epithelial cells and enter the interstitial fluid. This process is called
absorption
Which of these are stimuli that initiate the intestinal phase of gastrointestinal regulation?
acidity of contents in the small intestine distension of the small intestine osmolarity in the lumen of the small intestine digestive products in the small intestine.
Collectively, the tubular organs through which food passes during the digestive process are referred to as the
alimentary canal, gastrointestinal tract
Partial digestion of starch, a complex dietary carbohydrate, begins in the oral cavity through the action of the salivary enzyme called
amylase
Which of the following are not part of the gastrointestinal tract, but are accessory organs that secrete substances into it?
salivary glands, liver, pancreas
Digestive enzymes are released from exocrine glands into the lumen of the GI tract through the process of
secretion
The movement of chemicals and enzymes from exocrine glands into the digestive tract lumen is referred to as
secretion
Which of these are stimuli that initiate salivation?
sight of food, stimulation of mechanoreceptors in the mouth, smell of food, increased parasympathetic nerve activity
What is the main efferent signal pathway mediating chewing reflexes?
somatic nerves
The digestive organ connecting the esophagus and the small intestine is the
stomach
The histological layer of the gastrointestinal tract wall immediately outside of the mucosa is the
submucosa
Stimuli included in cephalic phase control of gastrointestinal function include
the taste of food the sight of food the smell of food
The esophageal phase of swallowing begins when the ______ relaxes, permitting entry of the bolus into the esophagus.
upper esophageal sphincter
Which of the following do NOT need to be digested into smaller forms before the GI tract can absorb them?
vitamins and minerals
Of the approximately 8 L of fluid entering the gastrointestinal tract by ingestion or secretion each day, approximately what fraction is excreted in the feces?
1%
Arrange in order the events of a local reflex coordinating intestinal motility and secretion. Start with the earliest at the top of the list.
1. Stretch and food particles occur inside the GI tract lumen. 2. Chemoreceptors and mechanoreceptors in the tract wall are activated 3. Receptor activity stimulates neurons in the myenteric plexus and submucosal plexus 4. Smooth muscle and exocrine glands act as effectors
Place the segments of the small intestine in the order of which food travels. Start with the earliest at the top.
1. duodenum 2. Jejunum 3. Ileum
Approximately how long does it take a peristaltic wave to travel the length of the esophagus after swallowing?
9 seconds
With a few exceptions, the digestive system will _____ all of a particular nutrient that is ingested. Therefore, the digestive system is not generally responsible for the homeostatic control of nutrient concentrations in the internal environment.
Absorb
The phase that is initiated when sensory receptors in the head are stimulated by sight, smell, taste, and chewing is the ___ phase.
Cephalic
Within the gastrointestinal tract, macromolecules are broken down into smaller units via a process called
Digestion
Breaking down food and absorbing the resulting molecules into the body are the functions of the ___ system.
Digestive
Which four stimuli initiate gastric phase reflexes of the gastrointestinal tract?
Distension, acidity, amino acids, peptides
The small intestine consists of three sections. As food passes from the stomach through the small intestine, it first passes through the ___, then through the ___, and finally the ___.
Duodenum, jejunum, ileum
Small amounts of certain metabolic end products are excreted via the gastrointestinal tract, primarily by way of the liver. This process, which represents a relatively minor function of the GI tract, is termed
Elimination
Which of the following are true statements about the elimination process of digestion?
Elimination of waste products from the internal environment is a minor role of the digestive tract. The kidneys are more responsible for elimination of wastes from the internal environment of the body than the digestive system. Feces eliminated from the digestive tract are composed mainly of bacteria and ingested material that was not absorbed.
The submucous plexus and the myenteric plexus are components of the
Enteric nervous system
During swallowing, the bolus of food forces a flap of tissue called the ___ backward to cover the entrance to the airway and prevent food from entering the trachea.
Epiglottis
Which of these accurately describe general features of the gastrointestinal tract wall from the stomach to the anus?
Epithelial cells are joined by tight junctions Invaginations of the epithelium form exocrine glands The lumen is lined by a single layer of epithelial cells Most of the luminal surface is highly convoluted, which increases the surface area available for absorption
True or False: All neural GI reflexes are initiated by receptors within the gastrointestinal tract.
False
True or False: Some digestive enzymes are secreted from exocrine glands into the lumen of the GI tract, while others are located on the basolateral membranes of the intestinal epithelium.
False
True or False: The neural and hormonal control of the digestive system is, in large part, divisible into two phases—gastric, and intestinal—according to where the stimulus is perceived.
False
The phase of digestive regulation that is responsive to the distension and acidity of the stomach as well as the presence of amino acids and peptides, is the ___ phase.
Gastric
During the last half of pregnancy, increased pressure in the abdominal cavity and movement of the lower esophagus into the thoracic cavity can result in
Gastroesophageal reflux
Entry of gastric juice into the esophagus causes a painful sensation commonly referred to as
Heartburn
Why does pregnancy sometimes result in reflux of gastric chyme through the lower esophageal sphincter?
Increased abdominal mass from the fetus forces the lower esophageal sphincter to move from below the diaphragm to above the diaphragm.
Neural and hormonal control of the gastrointestinal tract occurs in three different phases. What are they?
Intestinal phase Cephalic phase Gastric phase
The ___ phase of regulation is mediated by both short and long neural reflexes and by the hormones ___, CCK, and GIP, which are secreted by enteroendocrine cells of the small intestine.
Intestinal, secretin
Triglycerides are digested by the enzyme
Lipase
Where is smooth muscle found in the esophagus?
Lower two-thirds
The ___ of the tract is continuous with the external environment, which means that its contents are technically outside the body.
Lumen
Unlike control systems that regulate variables in the internal environment, the control mechanisms of the digestive system primarily regulate conditions in the ___ and ___ of the GI tract.
Lumen, wall
Protection from potentially harmful bacteria is provided by salivary ___, an antibacterial enzyme also found in tears and nasal secretions.
Lysozyme
Protection from potentially harmful bacteria is provided by salivary ____, an antibacterial enzyme also found in tears and nasal secretions.
Lysozyme
Mixing and peristalsis are subtypes of what property of the gastrointestinal tract?
Motility
Surrounding the submucosa are layers of smooth muscle called the ___ ___. Contractions of these muscles provide the forces for moving and mixing the gastrointestinal contents.
Muscularis externa
The ______ has both circular and longitudinal muscle layers, which can contract to change the circumference and length of the gastrointestinal tract.
Muscularis externa
The cells of the enteric nervous system include the ___ plexus, which mainly regulates motility functions, and the ___ plexus, which mainly influences secretory activity
Myenteric, submucosal
If a large food bolus does not reach the stomach during a given swallowing sequence, stretch of the esophagus initiates reflexive motility known as
Secondary peristalsis
Digestive enzymes are released from exocrine glands into the lumen of the GI tract through the process of
Secretion
The outermost surface of the intestinal tract wall is a thin layer of connective tissue called the
Serosa
The saclike organ that functions to store, dissolve, and partially digest the macromolecules in food, is the
Stomach
The histological layer of the gastrointestinal tract wall immediately outside of the mucosa is the
Submucosa
The lumen of the gastrointestinal tract is part of
The external environment
Which of these helps prevent the reflux of gastric material into the esophagus during respiratory cycles and abdominal muscle contractions?
The terminal segment of the esophagus is in the abdominal cavity, so increased pressure in that space forces the sphincter closed.
Put the typical daily volumes of these fluid movements in descending order, with the largest volume at the top.
Total amount of fluid absorbed by the gastrointestinal tract in a day. Amount of fluid secreted by exocrine glands into the gastrointestinal tract in a day. Amount of fluid in foods and liquids ingested in a day.
True or False: For most ingested substances, the digestive tract will absorb as much of any particular substance that is ingested and thus it does not regulate the total amount of nutrients absorbed or their concentrations in the internal environment.
True
Swallowing is a reflex regulated by
a swallowing center in the medulla oblongata of the brainstem
Feces eliminated from the body consist mainly of
bacteria and ingested material that was neither digested nor absorbed
Differentiated cells of the intestinal mucosa are completely replaced every 4-5 days, the result of constant division of epithelial cells located in what region of the wall?
base of villi
There are three pairs of salivary glands, the ___, ___, and ___ glands.
parotid, sublingual, submandibular
Moving, wave-like contraction of the smooth muscles of the gastrointestinal tract is known as
peristalsis
What term is used to describe the wave-like moving contractions that occur along segments of the gastrointestinal tract?
peristalsis
Food particles on the way from the mouth to the stomach pass through the
pharynx and esophagus
Which stimuli initiate local reflexes that regulate intestinal motility and secretion?
receptors that detect chyme osmolarity, receptors that detect nutrients such as monosaccharides, fatty acids and amino acids, GI tract wall stretch receptors, receptors that detect chyme acidity