Anatomy Chapter 16: The Digestive System
What are the three general roles of the liver?
(1) metabolic regulation, (2) hematological regulation, and (3) bile production.
What are the six major functions of the digestive system?
1. Ingestion 2. Mechanical digestion 3. Chemical digestion 4. Secretion 5. Absorption 6. Defecation
What are the three phases of The Regulation of Gastric Activity?
1. cephalic phase 2. gastic phase 3. Intestinal phase
What are the lingual tonsils and where are they located?
A pair of prominent lateral swellings at the base of the tongue marks the location of the lingual tonsils, clusters of lymphoid nodules that help resist infections.
What are the four fat-soluble vitamins?
A, D, E, K
What are the accessory organs of the digestive system?
Accessory digestive organs include the teeth, tongue, and glandular organs such as the salivary glands, liver, and pancreas, as well as the gallbladder, which has a storage function.
Which of the following structures covers the dentin of a tooth's root, providing protection and firmly anchoring the periodontal ligament?
Cementum
Bile is released into the duodenum only under the stimulation of which of the following hormones?
Cholecystokinin (CCK)
The digestion of which nutrient would be most impaired by damage to the exocrine pancreas?
Damage to the exocrine pancreas would most impair the digestion of fats (lipids), because that organ is the primary source of lipases. Even though such damage would also reduce carbohydrate and protein digestion, digestive enzymes for these nutrients are also produced by the salivary glands (carbohydrates), the small intestine (carbohydrates and proteins), and the stomach (proteins).
Which of the following structures is retroperitoneal?
Duodenum
In which phase of swallowing is the bolus pushed toward the stomach by peristaltic contractions?
Esophageal phase
Which of the following structures is the longest segment of the small intestine?
Ileum
What is the muscularis mucosae?
In most regions of the digestive tract, the outer portion of the mucosa contains a narrow band of smooth muscle and elastic fibers.
Which of the following activities is a main function of the large intestine?
Preparing fecal matter for elimination
Which enzyme in the mouth breaks carbohydrates into smaller fragments, producing a mixture of disaccharides and trisaccharides?
Salivary amylase
What are the three phases of swallowing?
The buccal, pharyngeal, and esophageal phases
What is the fundus?
The bulge of the stomach superior to the cardia
Which type of tooth is most useful for chopping off bits of raw vegetables?
The incisors are the type of tooth most useful for chopping (or cutting or shearing) pieces of relatively rigid food, such as raw vegetables.
What are some structural differences between the large intestine and the small intestine?
The large intestine is larger in diameter than the small intestine, but its relatively thin wall lacks villi, and it has an abundance of mucous glands.
What is the anal canal?
The last portion of the rectum, the anal canal, contains small longitudinal folds called anal columns. The distal margins of these columns are joined by transverse folds that mark the boundary between the columnar epithelium of the rectum and a stratified squamous epithelium like that found in the oral cavity.
What is the upper esophageal sphincter and the lower esophageal sphincter?
The lower sphincter is normally in active contraction. This condition prevents the backflow of materials from the stomach into the esophagus.
What are villi?
The mucosa of the small intestine is composed of a multitude of fingerlike projections called villi. These structures are covered by a simple columnar epithelium carpeted with microvilli.
What process is occurring when the soft palate and larynx elevate and the glottis closes?
The process being described is swallowing (deglutition).
What is the tooth socket or alveolus?
The root of each tooth sits within this bony cavity or socket
What is the cardia?
The smallest region of the stomach where the esophagus connects
Name the three segments of the small intestine from proximal to distal.
The three segments of the small intestine from proximal to distal are the duodenum, jejunum, and ileum.
In a person suffering from chronic gastric ulcers, why might the branches of the vagus nerves serving the stomach be cut in an attempt to provide relief?
The vagus nerves contain parasympathetic motor fibers that can stimulate gastric secretions even when the stomach is empty (the cephalic phase of gastric secretion). Cutting the branches of the vagus nerves that supply the stomach would prevent this type of secretion from taking place, and reduce the likelihood of new ulcer formation.
What are stellate macrophages, or Kupffer cells?
These cells are part of the monocyte-macrophage system. They engulf pathogens, cell debris, and damaged blood cells.
Which of the following digestive enzymes, produced by the pancreas, produces short peptide chains?
Trypsin
Which of the following vitamins cannot be absorbed by the intestinal mucosa unless it has been bound to intrinsic factor, a protein secreted by parietal cells of the stomach?
Vitamin B12
Bacteria residing within the colon generate which three vitamins?
Vitamin K, a fat-soluble vitamin needed by the liver to synthesize four clotting factors, including prothrombin. Biotin, a water-soluble vitamin important in glucose metabolism. Vitamin B5 (pantothenic acid), a water-soluble vitamin required in the manufacture of steroid hormones and some neurotransmitters.
What is the muscular layer?
a band of smooth muscle cells arranged in an inner circular layer and an outer longitudinal layer. Contractions of these layers agitate and propel materials along the digestive tract.
What is bile?
a bitter greenish-brown alkaline fluid that aids digestion and is secreted by the liver and stored in the gallbladder.
Once material has been shredded or torn by the teeth, moistened with salivary secretions, and accepted by taste receptors, the tongue begins compacting the debris into which of the following?
a bolus
What is deglutition?
a complex process that can be initiated voluntarily but proceeds automatically once it begins. You take conscious control over swallowing when you eat or drink, but swallowing is also controlled at the subconscious level. Before food can be swallowed, it must have the proper texture and consistency.
What is the submucosa?
a layer of dense irregular connective tissue that binds the mucosa to the muscular layer. The submucosa contains numerous blood vessels and lymphatic vessels. Along its outer margin, it contains a network of nerve fibers, sensory neurons, and parasympathetic motor neurons.
What is pancreatic juice?
a mixture of digestive enzymes, water, and buffers
What is the serosa?
a serous membrane, covers the muscular layer along most portions of the digestive tract enclosed by the peritoneal cavity.
What is a diaphragmatic hernia, or hiatal hernia?
abdominal organs slide up into the thoracic cavity through the esophageal hiatus.
What is the function of the large intestine?
absorbing a variety of substances and preparing the fecal material for elimination.
The dense network of collagen fibers covering the muscularis externa of the oral cavity, pharynx, esophagus, and rectum is called the ___________.
adventitia
What is the appendix?
attaches to the cecum, The walls of the appendix are dominated by lymphoid nodules, and it functions primarily as an organ of the lymphatic system.
What are liver lobules?
basic functional units of the liver. Each lobule is roughly 1 mm in diameter.
What is the large intestine?
begins at the end of the ileum and ends at the anus. The large intestine lies inferior to the stomach and liver and almost completely frames the small intestine
What is lingual lipase and where is it secreted?
begins lipid digestion in the oral cavity from glands under the tongue
What is the intestinal phase?
begins when chyme first enters the duodenum of the small intestine. Most of the regulatory controls for this phase (whether neural or endocrine) are inhibitory. By controlling the rate of gastric emptying, they ensure that all functions of the small intestine can proceed efficiently.
What is the gastric phase?
begins when food arrives in the stomach. The stimulation of stretch receptors in the stomach wall and of chemoreceptors in the mucosa triggers local reflexes controlled by the submucosal and myenteric plexuses. The myenteric plexus stimulates mixing waves in the muscular layer of the stomach wall. The submucosal plexus stimulates the parietal cells and chief cells. Both parietal and chief cells respond to the presence of gastrin by accelerating their secretory activities. The effect on the parietal cells is the most pronounced, and the pH of the gastric juice drops sharply. This phase may continue for several hours while the acids and enzymes process the ingested materials. During this period, gastrin also stimulates stomach contractions, which mix the ingested materials with the gastric secretions to form chyme. As mixing proceeds, the contractions begin sweeping down the length of the stomach. Each time the pylorus contracts, a small quantity of chyme squirts through the pyloric sphincter into the small intestine.
What is the cephalic phase?
begins when you sense or think of food. This phase prepares the stomach to receive food. It is directed by different regions of the CNS, including the cerebral cortex and hypothalamus. The neural output proceeds by way of the parasympathetic division of the ANS. The vagus nerves innervate the submucosal plexus of the stomach. Next, postganglionic parasympathetic fibers innervate mucous cells, parietal cells, chief cells, and endocrine cells of the stomach.
Describe bile production in the liver.
bile is synthesized in the liver and ejected into the lumen of the duodenum. Bile consists mostly of water, ions, bilirubin (a pigment derived from hemoglobin), cholesterol, and an assortment of lipids collectively known as bile salts. The water and ions in bile help dilute and buffer acids in chyme as it enters the small intestine. Bile salts are synthesized from cholesterol in the liver. They are required for the normal digestion and absorption of fats.
Which of the following vitamins, generated by bacteria in the colon, is a water-soluble vitamin important in glucose metabolism?
biotin
What are incisors?
blade-shaped teeth at the front of the mouth. They are useful for clipping or cutting, as when you nip off the tip of a carrot stick.
What are Cuspids?
canines, are conical, with a sharp ridgeline and a pointed tip. They are used for tearing or slashing. You might weaken a tough piece of celery by the clipping action of the incisors and then take advantage of the shearing action provided by the cuspids.
What is the pancreatic duct?
carries these secretions to the duodenum. The pancreatic duct penetrates the duodenal wall with the bile duct from the liver and gallbladder.
During which phase of gastric secretion does the production of gastric juice accelerate to approximately 500 mL per hour?
cephalic phase
Which of the following cells secrete pepsinogen?
chief cells
What is cement?
covers the dentin of the root, providing protection and firmly anchoring the periodontal ligament. Cement is similar in structure to bone, but softer.
Swallowing is also known as ___________.
deglutition
What is adventitia?
dense connective tissue with collagen fibers that firmly attaches the oral cavity, pharynx, esophagus, and rectum regions of the digestive tract to adjacent structures.
What are gastric pits?
depressions in gastric mucosa
What are mesenteries?
double sheets of serous membrane composed of the parietal peritoneum and visceral peritoneum. The loose connective tissue sandwiched between the epithelial surfaces of the mesenteries provides a pathway for the blood vessels, nerves, and lymphatic vessels servicing the digestive tract. The mesenteries also stabilize the positions of the attached organs. They prevent the intestines from becoming entangled during digestive movements or sudden changes in body position.
What triggers the pancreas?
duodenal hormones
What is the parotid duct?
empties into the vestibule at the level of the second upper molar.
What is the external anal sphincter?
encircles the anus, consists of skeletal muscle fibers and is under voluntary control.
What is the ileocecal valve?
guards the connection between the ileum and the cecum.
Which type of tooth is blade-shaped and useful for clipping or cutting?
incisor
What is the enterogastric reflex?
inhibitory reflex to slow the rate of movement of chyme
What is the mucosa?
inner lining of the digestive tract, is a mucous membrane. It consists of an epithelium moistened by glandular secretions, called the mucosal epithelium, and an underlying layer of areolar tissue, the lamina propria. Along most of the length of the digestive tract, the mucosa has permanent transverse circular folds. The folding increases the surface area available for absorption. In the small intestine, the mucosa forms fingerlike projections, called villi (villus, shaggy hair), that further increase the area for absorption.
What is the submucosal plexus?
involved in controlling contractions of the smooth muscle in the muscularis mucosae. It is also involved in regulating the secretion of digestive glands.
What are deciduous teeth?
known as primary teeth, milk teeth, or baby teeth. Most children have 20 deciduous teeth
In addition to capillaries, each intestinal villus contains nerve endings and which of the following?
lacteal
What is the cystic duct?
leads bile to the gallbladder.
The free anterior portion of the tongue is connected to the underlying epithelium by a thin fold of mucous membrane called the ____________.
lingual frenulum
What component of food would increase the number of chylomicrons in the lacteals?
lipids
What are hepatocytes?
liver cells that adjust the circulating levels of nutrients by selective absorption and secretion.
What are the sublingual salivary glands?
located beneath the mucous membrane of the floor of the mouth. Numerous sublingual ducts open along either side of the lingual frenulum.
What is a lacteal?
lymphatic capillary
What is Segmentation?
mechanical mixing of the material. churn and break up digestive materials. Over time, this action thoroughly mixes the contents with intestinal secretions.
Double sheets of serous membrane that suspend portions of the digestive tract within the peritoneal cavity are called __________.
mesenteries
What is dentin?
mineralized matrix similar to that of bone. Dentin differs from bone in that it does not contain cells.
What is rugae?
prominent longitudinal folds when the stomach is empty. These temporary features let the gastric (gaster, stomach) lumen expand. As the stomach expands, the rugae gradually flatten out until, at maximum distension, they almost disappear.
What is the pulp cavity?
receives blood vessels and nerves
What is the hepatopancreatic sphincter?
regulates what can enter the duodenum
When is secretin released by the small intestine?
released when the pH in the duodenum falls as acidic chyme arrives from the stomach. The primary effect of secretin is to increase the secretion of bile by the liver and buffers by the pancreas.
Which gastric secretion, found in newborns, coagulates milk, thereby slowing its passage through the stomach and allowing more time for digestion?
rennin
Which of the following hepatic structures is a fibrous remnant of the fetal umbilical vein?
round ligament
What are pancreatic islets?
secrete the hormones insulin and glucagon.
Which of the following gastrointestinal hormones stimulates the production of alkaline buffers and increases the rate of bile secretion?
secretin
Movements that churn and fragment digestive materials are called ____, which occurs in the ____.
segmentation; small intestine
What are micelles?
small lipid-bile salt complexes
A narrowing of the ileocecal valve would hamper movement of chyme between what two organs?
small to large intestine
Absorption of which of the following ions is the most important factor promoting water movement in the digestive tract?
sodium and chloride
The space between the cheeks or lips and the teeth is called the ___________.
vestibule
What are bile canaliculi?
where bile enters the bile ducts of the liver cells which unite to form larger ducts and merge to form the hepatic duct
List some effects of aging on the digestive system.
1. The division rate of epithelial stem cells declines. 2. Smooth muscle tone decreases. 3. The effects of cumulative damage become apparent. 4. Cancer rates increase. 5. Dehydration is common among the elderly. 6. Changes in other systems have direct or indirect effects on the digestive system.
What is the duodenum?
25 cm (10 in.) in length, is the segment closest to the stomach. This portion of the small intestine is the "mixing bowl." It receives chyme from the stomach and digestive secretions from the pancreas and liver.
How many permanent teeth are there?
32
What makes up saliva?
99.4 percent water, plus mucins and an assortment of ions, buffers, waste products, metabolites, and enzymes. Mucins are glycoproteins that absorb water and form mucus. Buffers in the saliva keep the pH of your mouth near 7. They prevent the buildup of acids produced by bacteria. Salivary antibodies (IgA) and lysozyme help control populations of oral bacteria.
What is a bolus?
A ball of food that is formed.
Does a high-fat meal raise or lower the level of cholecystokinin (CCK) in the blood?
A high-fat meal would increase cholecystokinin (CCK) level in the blood.
What is the jejunum?
At this site, the small intestine reenters the peritoneal cavity, supported by a sheet of mesentery. The jejunum is about 2.5 meters (8 ft) long. The bulk of chemical digestion and nutrient absorption takes place in the jejunum.
What are the water soluble vitamins?
B and C
Which of the following gastrointestinal hormones stimulates the production of pancreatic enzymes?
CCK (cholecystokinin)
What is included in pancreatic enzymes?
Carbohydrases, lipases, nucleases, and proteases
Which of the following intestinal hormones is secreted when chyme (especially chyme containing lipids and partially digested proteins) enters the duodenum?
Cholecystokinin (CCK)
Which of the following enter a lacteal after they are secreted by exocytosis into interstitial fluid of the intestine?
Chylomicrons
What are chylomicrons?
Chylomicrons are tiny fatty droplets composed of triglycerides, small amounts of phospholipids, cholesterol, free fatty acids, and some protein.
Describe carbohydrate digestion and absorption.
DIGESTION: Carbohydrate digestion begins in the mouth during mastication, through the action of salivary amylase. This enzyme breaks down complex carbohydrates into smaller fragments, producing a mixture primarily composed of disaccharides (two simple sugars) and trisaccharides (three simple sugars). Salivary amylase continues to digest the starches and glycogen in the meal for an hour or two before stomach acids render it inactive. In the duodenum, the action of pancreatic amylase breaks down the remaining complex carbohydrates. Brush border enzymes on the surfaces of the intestinal microvilli break disaccharides and trisaccharides into monosaccharides (simple sugars). ABSORPTION: The intestinal epithelium then absorbs the resulting simple sugars through carrier-mediated transport processes, such as facilitated diffusion or cotransport. Simple sugars entering an intestinal cell diffuse through the cytoplasm and cross the basement membrane by facilitated diffusion to enter the interstitial fluid. They then enter intestinal capillaries for delivery to the hepatic portal vein and liver.
Describe lipid digestion and absorption.
DIGESTION: Lipid digestion involves lingual lipase from glands of the tongue and pancreatic lipase from the pancreas. Fats, or triglycerides, are the most abundant dietary lipids. Triglycerides and other dietary fats are relatively unaffected by conditions in the stomach and enter the duodenum in the form of large lipid droplets. Recall that bile salts emulsify these drops into tiny droplets that can be more efficiently attacked by pancreatic lipase. This enzyme breaks apart the triglycerides. Micelles form. ABSORPTION: When a micelle contacts the intestinal epithelium, the enclosed lipids diffuse across the plasma membrane and enter the cytoplasm. The intestinal cells manufacture new triglycerides from the arriving fatty acids and monoglycerides. They are then coated with proteins. secreted by exocytosis into the interstitial fluids. From there, they enter intestinal lacteals through large gaps between adjacent lacteal endothelial cells. From the lacteals they proceed along lymphatic vessels and through the thoracic duct. They enter the bloodstream at the left subclavian vein.
List the digestive system functions that are related to the cardiovascular system.
Digestive system functions related to the cardiovascular system include absorption of water to maintain blood volume, absorption of vitamin K produced by intestinal bacteria (vital to blood clotting), excretion of bilirubin (a breakdown product of the heme portion of hemoglobin) by the liver, and synthesis of blood clotting factors by the liver.
Which segment of the small intestine is known as the "mixing bowl" because it receives chyme from the stomach and secretions from the pancreas and liver?
Duodenum
What are haustra?
Haustra permit the colon to expand and elongate
Which of the following groups of structures constitute a portal triad at each corner of a liver lobule?
Hepatic artery, hepatic portal vein, bile duct
What is chyme?
Ingested substances mix with secretions of the glands of the stomach. viscous, highly acidic, soupy mixture of partially digested food
What is intestinal juice?
Intestinal juice moistens the intestinal contents, helps buffer acids, and keeps both the digestiveenzymes and the products of digestion in solution.
Which of the following statements accurately describes the effects of decreased gastrointestinal motility and weaker peristaltic contractions in the elderly?
Intestinal movement slows, and constipation occurs.
Which of the following structures is normally in active contraction, preventing the backflow of materials from the stomach into the esophagus?
Lower esophageal sphincter
What is the colon?
Major characteristics of the colon are a lack of villi and an abundance of mucous cells.
What is the cecum?
Material arriving from the ileum first enters an expanded pouch, the cecum. Compaction begins there.
What is the parotid salivary gland?
On each side, a large parotid salivary gland lies under the skin covering the lateral and posterior surface of the mandible.
Which of the following pancreatic enzymes catabolizes carbohydrates?
Pancreatic amylase
Which of the following cells of the digestive system secrete hydrochloric acid?
Parietal cells
Which of the following ducts empties into the vestibule at the level of the second upper molar?
Parotid duct
Which of the following enzymes complete the process of protein digestion?
Peptidases
In which phase of swallowing does the bolus come into contact with structures that initiate the involuntary swallowing reflex?
Pharyngeal phase
Which of the following structures regulates the flow of chyme between the stomach and small intestine?
Pyloric sphincter
Removal of the stomach would impair the absorption of which vitamin?
Removal of the stomach would interfere with the absorption of vitamin B12. Parietal cells of the stomach are the source of intrinsic factor, which is required for the vitamin's absorption.
What are the four segments of the colon?
The ascending colon begins at the ileocecal valve. It ascends along the right side of the peritoneal cavity until it reaches the inferior margin of the liver. It then turns horizontally, becoming the transverse colon. The transverse colon continues toward the left side, passing below the stomach and following the curve of the body wall. Near the spleen, it turns inferiorly to form the descending colon. The descending colon continues along the left side until it curves and forms the S-shaped sigmoid colon. The sigmoid colon empties into the rectum.
What is the internal anal sphincter?
The circular muscle layer of the muscular layer in this region forms the internal anal sphincter. The smooth muscle cells of this sphincter are not under voluntary control.
The digestion of which nutrient would be affected by damage to the parotid salivary glands?
The digestion of carbohydrates would be affected by damage to the parotid salivary glands, because these glands secrete salivary amylase, the enzyme that digests complex carbohydrates (starches).
Identify the functional relationships between the digestive system and other body systems presented so far.
The digestive system absorbs the organic substrates, vitamins, ions, and water needed by cells of all the body's systems.
Describe the movement through the large intestine.
The gastroileal and gastroenteric reflexes move material into the cecum while you eat. Movement from the cecum to the transverse colon is very slow, allowing hours for the reabsorption of water. Powerful peristaltic contractions called mass movements take place a few times a day. They move material from the transverse colon through the rest of the large intestine. The normal stimulus is distension of the stomach and duodenum. The commands are over the intestinal nerve plexuses. The contractions force feces into the rectum and produce the conscious urge to defecate.
What are circular folds, or plicae circulares?
The intestinal lining bears a series of transverse folds called circular folds, or plicae circulares. The circular folds are permanent features. They do not disappear when the small intestine fills.
Describe the hematological regulation of the liver.
The liver is the largest blood reservoir in the body. It receives about 25 percent of cardiac output. As blood passes through the liver, stellate macrophages remove aged or damaged red blood cells, debris, and pathogens. Stellate macrophages are antigen-presenting cells that can stimulate an immune response. Hepatocytes also synthesize the plasma proteins. These molecules determine the osmotic concentration of the blood, transport nutrients, and make up the clotting and complement systems.
Describe the metabolic regulation of the liver.
The liver is the primary organ involved in regulating the composition of circulating blood. All blood leaving the absorptive areas of the digestive tract flows through the liver before reaching the general circulation. For this reason, hepatocytes are well positioned to (1) extract absorbed nutrients or toxins from the blood before they reach the rest of the body and (2) monitor and adjust the circulating levels of organic nutrients. The liver removes and stores excess nutrients. It corrects nutrient deficiencies by mobilizing stored reserves or synthesizing necessary compounds
Discuss the significance of the low pH in the stomach.
The low pH in the stomach creates an acidic environment that kills most microorganisms ingested with food, denatures proteins and inactivates most enzymes in food, helps break down plant cell walls and meat connective tissue, and activates pepsin.
What is the enteric nervous system (ENS)?
The myenteric and submucosal plexus. The myenteric plexus contains parasympathetic ganglia, sensory neurons, interneurons, and sympathetic postganglionic fibers. Parasympathetic stimulation increases muscular tone and activity. Sympathetic stimulation promotes muscular inhibition and relaxation.
What is salivary amylase?
The parotid glands produce a secretion rich in salivary amylase, an enzyme that breaks down starches (complex carbohydrates) into smaller molecules that can be absorbed by the digestive tract.
Which ring of muscle regulates the flow of chyme from the stomach to the small intestine?
The pyloric sphincter is the ring of muscle that regulates the flow of chyme into the small intestine.
How is the small intestine adapted for the absorption of nutrients?
The small intestine has several adaptations that increase its surface area and thus its absorptive capacity for nutrients. Its walls have permanent circular folds (plicae circulares), each of which is covered by fingerlike projections called villi. The epithelial cells covering the villi have an exposed surface covered by small fingerlike projections, the microvilli. In addition, the small intestine has a very rich supply of blood vessels and lymphatic vessels that transport the absorbed nutrients.
Describe the defecation reflex.
This reflex involves two positive feedback loops: In the shorter feedback loop, stretch receptors in the rectal walls stimulate a series of increased local peristaltic contractions in the sigmoid colon and rectum. The contractions move feces toward the anus and increase distension of the rectum. The stretch receptors in the rectal walls also stimulate parasympathetic motor neurons in the sacral spinal cord. These neurons stimulate increased peristalsis (mass movements) in the descending colon and sigmoid colon that push feces toward the rectum, further increasing distension there.
Which of the following is not an age-related change that affects digestion and absorption?
Tightening of the haustra
Why is it that diarrhea is potentially life threatening but constipation is not?
When someone with diarrhea loses fluid and electrolytes faster than they can be replaced, the resulting dehydration can be fatal.
What are sinusoids?
Within a lobule, specialized and highly permeable capillaries form passageways between the adjacent plates that empty into the central vein. Sinusoids permit the free exchange of water and solutes as large as plasma proteins between blood and interstitial fluid.
What is the gallbladder?
a muscular sac that stores and concentrates bile before it is ejected into the small intestine.
What is the esophagus?
a muscular tube that conveys solid food and liquids to the stomach. It begins at the pharynx, runs posterior to the trachea in the neck, and passes through the mediastinum in the thoracic cavity. It then enters the abdominopelvic cavity through the esophageal hiatus, an opening in the diaphragm. Finally it empties into the stomach. The esophagus is lined with a stratified squamous epithelium that resists abrasion, hot or cold temperatures, and chemical attack. The secretions of esophageal mucous glands lubricate this epithelial surface and prevent materials from sticking to it during swallowing. The upper third of its muscular layer contains skeletal muscle, the lower third contains smooth muscle, and a mixture of each makes up the middle third.
Which phase of gastric secretion is directed by the CNS and prepares the stomach to receive food?
cephalic phase
What is mastication?
chewing. Mastication breaks down tough connective tissues in meat and the plant fibers in vegetables. It also helps saturate the food with salivary secretions.
What is the periodontal ligament?
collagen fibers that extend from the dentin of the root to the surrounding bone
What are the gastric glands?
connects gastric pits. dominated by two types of secretory cells: parietal cells and chief cells. Together, they secrete about 1500 mL of gastric juice each day.
What is the pylorus?
connects the stomach with the small intestine.
What is the frenulum?
connects tongue to floor of mouth
What does the digestive system consist of?
consists of a muscular tube, the digestive tract, and various accessory organs. The digestive tract is also called the gastrointestinal (GI) tract or alimentary canal. It begins with the oral cavity (mouth) and continues through the pharynx (throat), esophagus, stomach, small intestine, and large intestine. It ends at the rectum and anus.
What is the enamel?
covers the crown. Enamel contains a crystalline form of calcium phosphate. Enamel is the hardest biologically manufactured substance. Adequate amounts of calcium, phosphate, and vitamin D3 during childhood are essential for an enamel coating that is complete and resistant to decay.
Which portion of the large intestine continues along the left side of the body until it curves to form the sigmoid colon?
descending colon
The chemical breakdown of food into small organic fragments that can be absorbed by the digestive epithelium is called __________.
digestion
What is hydrolysis?
digestive enzymes break the chemical bonds between the component molecules of carbohydrates, lipids, proteins, and nucleic acids
What are Bicuspids and molars?
flattened crowns with prominent ridges. They are used for crushing, mashing, and grinding. You might shift a tough nut or piece of meat to the premolars and molars for crushing.
What are the hard palate and soft palate?
form the roof for the oral cavity.
What is the greater omentum?
forms an enormous pouch that hangs over and protects the abdominal viscera
What is the rectum?
forms the last 15 cm (6 in.) of the digestive tract. It is an expandable organ for the temporary storage of feces.
Which of the following hormones is secreted by duodenal cells in response to large quantities of incompletely digested proteins?
gastrin
What is the gingivae?
gums, are pink ridges of oral mucosae that surround the bases of the teeth. They cover the tooth-bearing surfaces of the upper and lower jaws.
The characteristic pouches of the colon are called ___________.
haustra
Bile contains bilirubin, a pigment derived from __________.
hemoglobin
What is the portal triad?
hepatic artery, portal vein, bile duct
What are the submandibular salivary glands?
in the floor of the mouth along the inner surfaces of the mandible. Their ducts open into the mouth behind the teeth on either side of the lingual frenulum.
What are the three layers of the stomach?
longitudinal layer, a circular layer, and an inner oblique layer. The extra layer of smooth muscle strengthens the stomach wall and assists in the mixing and churning essential to forming chyme.
What is the myenteric plexus?
neural network that controls the muscular layer's functions.
What is the small intestine?
plays a key role in digesting and absorbing nutrients. Ninety percent of nutrient absorption takes place there.
Which of the following substances account for approximately 70 percent of total pancreatic enzyme production?
proteases
Which of the following nutrients does pepsin in the stomach digest?
proteins
What are root canals?
receives blood vessels and nerves through one to four narrow root canals at the root (base) of the tooth.
What is the pyloric sphincter?
regulates the flow of chyme between the stomach and small intestine.
What are G cells?
release the hormone gastrin into the bloodstream.
When is Gastric inhibitory peptide (GIP) released by the small intestine?
released when fats and carbohydrates (especially glucose) enter the small intestine. GIP inhibits gastric activity and causes the release of insulin from the pancreatic islets.
What is the gastroileal reflex?
response to circulating levels of the hormone gastrin. The entry of food into the stomach triggers the release of gastrin, which relaxes the ileocecal valve at the entrance to the large intestine. With the valve relaxed, peristalsis pushes materials from the ileum into the large intestine.
What are teniae coli?
run along the outer surface of the colon just beneath the serosa. Muscle tone within these bands creates the haustra.
What are pancreatic acini?
saclike pouches of the pancreas. The acinar cells of these pouches secrete digestive enzymes.
What are chief cells?
secrete a protein called pepsinogen into the stomach lumen. When pepsinogen contacts the hydrochloric acid released by the parietal cells, it is converted to pepsin, a proteolytic (protein-digesting) enzyme.
What are parietal cells?
secrete intrinsic factor and hydrochloric acid (HCl). Intrinsic factor aids the absorption of vitamin B12 across the intestinal lining. Hydrochloric acid lowers the pH of the gastric juice, keeping the stomach contents at a pH of 1.5-2.0. The acidity of gastric juice kills microorganisms, breaks down plant cell walls and connective tissues in meat, and activates enzymes secreted by chief cells.
When is gastrin released by the small intestine?
secreted by duodenal cells in response to large quantities of incompletely digested proteins. Gastrin promotes increased stomach motility and stimulates the production of acids and enzymes.
When is Cholecystokinin (CCK) released by the small intestine?
secreted when chyme arrives in the duodenum, especially when it contains lipids and partially digested proteins. CCK also targets the pancreas and gallbladder. In the pancreas, CCK speeds up the production and secretion of all types of digestive enzymes. At the gallbladder, it causes the ejection of bileinto the duodenum. The presence of either secretin or CCK in high concentrations also reduces gastric motility and the rates of secretions.
The building blocks of typical dietary carbohydrates are _________.
simple sugars
What is the vestibule?
space between the cheeks (or lips) and the teeth.
The loose connective tissue layer of the digestive tract, which contains blood and lymph vessels as well as sensory and parasympathetic motor neurons, is the __________.
submucosa
What are the three segments of the small intestine?
the duodenum, the jejunum, and the ileum
What is the anus?
the exit of the anal canal, the epidermis becomes keratinized and identical to that on the skin surface.
What is the ileum?
the final segment of the small intestine, is also the longest. It averages 3.5 m (12 ft) in length. The ileum ends at the ileocecal valve. This sphincter controls the flow of material from the ileum into the cecum, the first portion of the large intestine.
What are the lobes of the liver?
the large left and right lobes and the smaller caudate and quadrate lobes
What are the labia?
the lips
What are the four major layers of the digestive tract?
the mucosa, the submucosa, the muscular layer, and the serosa
Which of the following types of teeth are the last teeth of the permanent (secondary) dentition to appear?
third molars (wisdom teeth)
What is the pharynx?
throat, serves as a common passageway for solid food, liquids, and air. Food normally passes through the oropharynx and laryngopharynx on its way to the esophagus. Both of these regions of the pharynx have a stratified squamous epithelium similar to that of the oral cavity. The underlying lamina propria contains mucous glands plus the pharyngeal, palatal, and lingual tonsils. The pharyngeal muscles cooperate with muscles of the oral cavity and esophagus to begin the process of swallowing
What are the three most abundant proteases?
trypsin, chymotrypsin, and carboxypeptidase. Together, they break down complex proteins into a mixture of short peptide chains and amino acids.
What is Peristalsis?
waves of muscular contractions that move along the digestive tract and move material along the tract. During a peristaltic movement, the circular muscles first contract behind the digestive contents, such as a bolus (food mass). Then longitudinal muscles contract, shortening adjacent segments of the tract. A wave of contraction in the circular muscles then forces the materials in the desired direction.
What are the three ways of production of acid and enzymes by the stomach mucosa?
(1) controlled by the central nervous system, (2) regulated by reflexes of the enteric nervous system coordinated in the wall of the stomach, and (3) regulated by hormones of the digestive tract.
What are the 3 primary functions of the tongue?
(1) mechanical digestion by compression, abrasion, and distortion; (2) manipulation to assist in chewing and to prepare food for swallowing; and (3) sensory analysis by touch, temperature, and taste receptors.
What are the main functions of the large intestine?
(1) reabsorption of water and compaction of the intestinal contents into feces, (2) absorption of important vitamins freed by bacterial action, and (3) storage of fecal material prior to defecation.
What are the 4 functions of the oral/buccal cavity?
(1) senses and analyzes food before swallowing; (2) mechanically digests food through the actions of the teeth, tongue, and surfaces of the palate; (3) lubricates food by mixing it with mucus and salivary gland secretions; and (4) begins limited chemical digestion of carbohydrates and lipids with salivary enzymes.
What are the 4 primary functions of the stomach?
(1) storage of ingested food; (2) mechanical digestion of ingested food; (3) disruption of chemical bonds in food through the action of acids and enzymes; and (4) production of intrinsic factor, a compound necessary for the absorption of vitamin B12 in the small intestine.
What are the three parts of the large intestine?
(1) the pouchlike cecum, the first portion; (2) the colon, the largest portion; and (3) the rectum, the last 15 cm (6 in.) of the large intestine and the end of the digestive tract.
What is rennin and gastric lipase?
(found only in infants) Rennin coagulates milk proteins, thus slowing their passage through the stomach and allowing more time for its digestion. Gastric lipase begins the digestion of milk fats.
