Chapter 16 The Digestive System

Question 1

General Aspects of Digestion

• The four basic digestive processes are _____, _____, _____, and _____.

Answer 1

General Aspects of Digestion

• The four basic digestive processes are motility, secretion, digestion, and absorption.

Question 2

General Aspects of Digestion

• Three classes of energy-rich nutrients are digested into absorbable units:
  
  1. ________________________.
  2. ________________________.
  3. ________________________.

Answer 2

General Aspects of Digestion

• Three classes of energy-rich nutrients are digested into absorbable units:
  
  1. Dietary carbohydrates in the form of the polysaccharides starch (amylose and amylopectin) and glycogen are digested into monosaccharides, mostly glucose.
  2. Dietary proteins are digested into amino acids and a few small polypep- tides.
  3. Dietary fats (triglycerides) are digested into monoglycerides and free fatty acids.

Question 3

General Aspects of Digestion

• The digestive system consists of the digestive tract and accessory digestive organs (_________, _________, and _________).

Answer 3

General Aspects of Digestion

• The digestive system consists of the digestive tract and accessory digestive organs (salivary glands, exocrine pancreas, and biliary system).

Question 4

General Aspects of Digestion

• The lumen of the digestive tract (a tube that runs from the mouth to the anus) is _______ with the external environment, so its contents are technically outside the body.
• This arrangement permits digestion of food without _______ occurring in the process.

Answer 4

General Aspects of Digestion

• The lumen of the digestive tract (a tube that runs from the mouth to the anus) is continuous with the external environment, so its contents are technically outside the body.
• This arrangement permits digestion of food without self-digestion occurring in the process.

Question 5

General Aspects of Digestion

• The digestive tract wall has _____ layers.
• From innermost out-ward, they are the _____, _____, __________, and _____.

Answer 5

General Aspects of Digestion

• The digestive tract wall has four layers.
• From innermost out- ward, they are the mucosa, submucosa, muscularis externa, and serosa.

Question 6

General Aspects of Digestion

• Digestive activities are carefully regulated by __________, _____ (both intrinsic and extrinsic), and _____ mechanisms to ensure that ingested food is maximally made available to the body.

Answer 6

General Aspects of Digestion

• Digestive activities are carefully regulated by synergistic autonomous, neural (both intrinsic and extrinsic), and hormonal mechanisms to ensure that ingested food is maximally made available to the body.

Question 7

Mouth

• ______ is when food enters the digestive system through the mouth, where it is chewed and mixed with saliva.

Answer 7

Mouth

• Motility is when food enters the digestive system through the mouth, where it is chewed and mixed with saliva.

Question 8

Mouth

• Secretion and digestion occurs when the salivary enzyme, ______, begins to digest polysaccharides into the disaccharide maltose, a process that continues in the stomach after swallowing.
• Salivary secretion is controlled by a salivary center in the ______, mediated by ______ nerves to the salivary glands.

Answer 8

Mouth

• Secretion and digestion occurs when the salivary enzyme, amylase, begins to digest polysaccharides into the disaccharide maltose, a process that continues in the stomach after swallowing.
• Salivary secretion is controlled by a salivary center in the medulla, mediated by autonomic nerves to the salivary glands.

Question 9

Mouth

• No food is _______ from the mouth.

Answer 9

Mouth

• No food is absorbed from the mouth.

Question 10

Pharynx and Esophagus

• The esophageal secretion, mucus, is _____.
• No nutrient _____ or _____ occurs here.

Answer 10

Pharynx and Esophagus

• The esophageal secretion, mucus, is protective.
• No nutrient digestion or absorption occurs here.

Question 11

Pharynx and Esophagus

• Motility occurs when the tongue propels the ____ of food to the rear of the throat, which initiates the ____ reflex.
• The swallowing center in the ____ coordinates a complex group of activities that result in closure of the ____ passages and propulsion of food through the pharynx and esophagus into the stomach.

Answer 11

Pharynx and Esophagus

• Motility occurs when the tongue propels the bolus of food to the rear of the throat, which initiates the swallowing reflex.
• The swallowing center in the medulla coordinates a complex group of activities that result in closure of the respiratory passages and propulsion of food through the pharynx and esophagus into the stomach.

Question 12

Stomach

• Motility: Gastric motility includes _____, _____, _____, and _____.
• Gastric filling is facilitated by _____ mediated receptive relaxation of the stomach.
• Gastric storage takes place in the body of the stomach, where _____ contractions of the thin muscle walls are too weak to mix the contents.
• Gastric mixing in the thick-muscled _____ results from vigorous peristaltic contractions and _____.

Answer 12

Stomach

• Motility: Gastric motility includes filling, storage, mixing, and emptying.
• Gastric filling is facilitated by vagally mediated receptive relaxation of the stomach.
• Gastric storage takes place in the body of the stomach, where peristaltic contractions of the thin muscle walls are too weak to mix the contents.
• Gastric mixing in the thick-muscled antrum results from vigorous peristaltic contractions and retropulsion.

Question 13

Stomach

• Gastric emptying is influenced by factors in both the ____ and ____.
  1. Increased volume and fluidity of ____ in the stomach promote emptying.
  2. Fat, acid, hypertonicity, and distension in the ____ (the dominant factors controlling gastric emptying) delay gastric emptying until the ____ is ready to process more chyme. They do so by inhibiting stomach peristaltic activity via the ____ reflex and the enterogas- trones, ____ and ________, which are secreted by the duodenal mucosa.

Answer 13

Stomach

• Gastric emptying is influenced by factors in both the stomach and duodenum.
  1. Increased volume and fluidity of chyme in the stomach promote emptying.
  2. Fat, acid, hypertonicity, and distension in the duodenum (the dominant factors controlling gastric emptying) delay gastric emptying until the duodenum is ready to process more chyme. They do so by inhibiting stomach peristaltic activity via the enterogastric reflex and the enterogas- trones, secretin and cholecystokinin (CCK), which are secreted by the duodenal mucosa.

Question 14

Stomach

• Secretion: Gastric secretions into the stomach lumen include
  
  1. HCl (from the parietal cells), which activates ______;
  2. pepsinogen (from the chief cells), which, once activated, initiates ______
  3. mucus (from the mucous cells), which provides a ______; and
  4. intrinsic factor (from the parietal cells), which is needed for ______ absorption.

Answer 14

Stomach

• Secretion: Gastric secretions into the stomach lumen include
  
  1. HCl (from the parietal cells), which activates pepsinogen;
  2. pepsinogen (from the chief cells), which, once activated, initiates protein digestion
  3. mucus (from the mucous cells), which provides a protective coating; and
  4. intrinsic factor (from the parietal cells), which is needed for vitamin B12 absorption.

Question 15

Stomach

• The stomach also secretes the hormone _____, which plays a dominant role in stimulating gastric secretion, and the paracrines _____ and _____, which stimulate and inhibit gastric secretion, respectively.

Answer 15

Stomach

• The stomach also secretes the hormone gastrin, which plays a dominant role in stimulating gastric secretion, and the paracrines histamine and somatostatin, which stimulate and inhibit gastric secretion, respectively.

Question 16

Stomach

• Gastric secretion is increased before and during a meal via excitatory ____ and intrinsic nerve responses along with the stimulatory actions of ____ and ____.
• After the meal empties, gastric secretion is reduced by withdrawal of ________, release of inhibitory ____, and inhibitory actions of the ____ reflex and enterogastrones.

Answer 16

Stomach

• Gastric secretion is increased before and during a meal via excitatory vagal and intrinsic nerve responses along with the stimulatory actions of gastrin and histamine.
• After the meal empties, gastric secretion is reduced by withdrawal of stimulatory factors, release of inhibitory somatostatin, and inhibitory actions of the enterogastric reflex and enterogastrones.

Question 17

Stomach

• Digestion and absorption: Carbohydrate digestion continues by swallowed salivary ____ in the body of the stomach.
• Protein digestion is initiated by ____ in the antrum of the stomach, where vigorous peristaltic contractions mix the food with ____ secretions, converting it to a thick liquid mixture known as ____.
• No nutrients are ____ from the stomach.

Answer 17

Stomach

• Digestion and absorption: Carbohydrate digestion continues by swallowed salivary amylase in the body of the stomach.
• Protein digestion is initiated by pepsin in the antrum of the stomach, where vigorous peristaltic contractions mix the food with gastric secretions, converting it to a thick liquid mixture known as chyme.
• No nutrients are absorbed from the stomach.

Question 18

Pancreatic and Biliary Secretions

• Pancreatic exocrine secretions and bile from the liver both enter the _______.

Answer 18

Pancreatic and Biliary Secretions

• Pancreatic exocrine secretions and bile from the liver both enter the duodenal lumen.

Question 19

Pancreatic and Biliary Secretions

• Pancreatic exocrine secretions include
  
  1. Potent digestive enzymes from the ____ cells, which digest all three categories of foodstuff
  2. an aqueous ____ solution from the ____ cells, which neutralizes the acidic contents emptied into the duodenum from the stomach.
• ____ stimulates the pancreatic duct cells, and ____ stimulates the acinar cells.

Answer 19

Pancreatic and Biliary Secretions

• Pancreatic exocrine secretions include
  
  1. Potent digestive enzymes from the acinar cells, which digest all three categories of foodstuff
  2. an aqueous NaHCO3 solution from the duct cells, which neutralizes the acidic contents emptied into the duodenum from the stomach.
• Secretin stimulates the pancreatic duct cells, and CCK stimulates the acinar cells.

Question 20

Pancreatic and Biliary Secretions

• The pancreatic digestive enzymes include
  
  1. the proteolytic enzymes ______, ______, and ______, which are secreted in inactive form and are activated in the duodenal lumen on exposure to ______ and activated ______
  2. pancreatic ______, which continues carbohydrate digestion; and
  3. ______, which accomplishes fat digestion.

Answer 20

Pancreatic and Biliary Secretions

• The pancreatic digestive enzymes include
  
  1. the proteolytic enzymes trypsinogen, chymotrypsinogen, and procarboxypeptidase, which are secreted in inactive form and are activated in the duodenal lumen on exposure to enteropeptidase and activated trypsin
  2. pancreatic amylase, which continues carbohydrate digestion; and
  3. lipase, which accomplishes fat digestion.

Question 21

Pancreatic and Biliary Secretions

• The liver performs many metabolic functions. Its contribution to digestion is secretion of bile-salt containing ____.
• Bile salts aid ____ digestion through their detergent action (forming a ________) and facilitate fat absorption by forming water-soluble micelles that carry the water-insoluble products of ________ to their absorption site.

Answer 21

Pancreatic and Biliary Secretions

• The liver performs many metabolic functions. Its contribution to digestion is secretion of bile-salt containing bile.
• Bile salts aid fat digestion through their detergent action (forming a lipid emulsion) and facilitate fat absorption by forming water-soluble micelles that carry the water-insoluble products of fat digestion to their absorption site.

Question 22

Pancreatic and Biliary Secretions

• Between meals, bile is stored and concentrated in the _______, which is stimulated by _______ to contract and empty into the _______ during meal digestion.
• After participating in fat digestion and absorption, bile salts are reabsorbed and returned via the ______________ to the liver, where they are resecreted and also act as a potent _______ to stimulate secretion of more bile.

Answer 22

Pancreatic and Biliary Secretions

• Between meals, bile is stored and concentrated in the gall- bladder, which is stimulated by CCK to contract and empty into the duodenum during meal digestion.
• After participating in fat digestion and absorption, bile salts are reabsorbed and returned via the hepatic portal system to the liver, where they are resecreted and also act as a potent choleretic to stimulate secretion of more bile.

Question 23

Pancreatic and Biliary Secretions

• Bile also contains _____, a derivative of degraded _____, which is the major excretory product in the feces.

Answer 23

Pancreatic and Biliary Secretions

• Bile also contains bilirubin, a derivative of degraded hemoglobin, which is the major excretory product in the feces.

Question 24

Small Intestine

• Motility: _______, the small intestine’s primary motility during digestion of a meal, thoroughly mixes the _______ with digestive juices to facilitate digestion
• It also exposes the products of digestion to the absorptive _______.
• Between meals, the ______________ sweeps the lumen clean.

Answer 24

Small Intestine

• Motility: Segmentation, the small intestine’s primary motility during digestion of a meal, thoroughly mixes the chyme with digestive juices to facilitate digestion
• It also exposes the products of digestion to the absorptive surfaces.
• Between meals, the migrating motility complex (MMC) sweeps the lumen clean.

Question 25

Small Intestine

• Secretion: The juice secreted by the small intestine does not contain any _________.
• The enzymes synthesized by the small intestine act within the __________ of the epithelial cells.

Answer 25

Small Intestine

• Secretion: The juice secreted by the small intestine does not contain any digestive enzymes.
• The enzymes synthesized by the small intestine act within the brush-border membrane of the epithelial cells.

Question 26

Small Intestine

• Digestion: The small intestine is the main site for _____ and _____.
• _____ and _____ digestion continues in the small-intestine lumen by the _____ enzymes and is completed by the small-intestine __________ enzymes (disaccharidases and aminopeptidases, respectively).
• Fat is digested entirely in the small-intestine lumen, by pancreatic _____.

Answer 26

Small Intestine

• Digestion: The small intestine is the main site for digestion and absorption.
• Carbohydrate and protein digestion continues in the small-intestine lumen by the pancreatic enzymes and is completed by the small-intestine brush-border enzymes (disaccharidases and aminopeptidases, respectively).
• Fat is digested entirely in the small-intestine lumen, by pancreatic lipase.

Question 27

Small Intestine

• Absorption: The small-intestine lining is remarkably _____ to its digestive and absorptive function.
• Its folds bear a rich array of fingerlike projections, the _____, which have a multitude of even smaller hairlike protrusions, the _____ (brush border).
• Together, these surface modifications tremendously increase the _____ available to house the membrane-bound _____ and to accomplish _____.
• This lining is replaced about every _____ days to ensure it is optimally healthy despite harsh lumen conditions.

Answer 27

Small Intestine

• Absorption: The small-intestine lining is remarkably adapted to its digestive and absorptive function.
• Its folds bear a rich array of fingerlike projections, the villi, which have a multitude of even smaller hairlike protrusions, the microvilli (brush border).
• Together, these surface modifications tremendously increase the area available to house the membrane-bound enzymes and to accomplish absorption.
• This lining is replaced about every three days to ensure it is optimally healthy despite harsh lumen conditions.

Question 28

Small Intestine

• The energy-dependent process of Na+ absorption provides the driving force for ____, ____, ____, and ____ absorption.
• All these absorbed products enter the ____.

Answer 28

Small Intestine

• The energy-dependent process of Na+ absorption provides the driving force for Cl-, water, glucose, and amino acid absorption.
• All these absorbed products enter the blood.

Question 29

Small Intestine

• Because they are not soluble in water, the products of _____ digestion must undergo a series of transformations that enable them to be _____ absorbed, eventually entering the _____.

Answer 29

Small Intestine

• Because they are not soluble in water, the products of fat digestion must undergo a series of transformations that enable them to be passively absorbed, eventually entering the lymph.

Question 30

Small Intestine

• The small intestine absorbs almost everything presented to it, from ingested food to digestive secretions to sloughed ______ cells.
• In contrast to the almost complete, unregulated absorption of ingested nutrients, water, and most electrolytes, the amount of ______ and ______ absorbed is variable and subject to control.
• Only a small amount of fluid and indigestible food residue passes on to the ____________.

Answer 30

Small Intestine

• The small intestine absorbs almost everything presented to it, from ingested food to digestive secretions to sloughed epithelial cells.
• In contrast to the almost complete, unregulated absorption of ingested nutrients, water, and most electrolytes, the amount of iron and calcium absorbed is variable and subject to control.
• Only a small amount of fluid and indigestible food residue passes on to the large intestine

Question 31

Large Intestine

• Motility: The colon concentrates and stores undigested food residues ( ____—that is, plant ____) and ____ until they can be eliminated in the feces.
• ____ contractions slowly shuffle the colonic contents back and forth to mix and facilitate absorption of most of the remaining ____ and ____.
• Mass movements several times a day, usually ____ meals, propel the feces long distances.
• Movement of feces into the rectum triggers the ____ reflex.

Answer 31

Large Intestine

• Motility: The colon concentrates and stores undigested food residues ( fiber—that is, plant cellulose) and bilirubin until they can be eliminated in the feces.
• Haustral contractions slowly shuffle the colonic contents back and forth to mix and facilitate absorption of most of the remaining fluid and electrolytes.
• Mass movements several times a day, usually after meals, propel the feces long distances.
• Movement of feces into the rectum triggers the defecation reflex.

Question 32

Large Intestine

• Secretion, digestion, and absorption: The _____ mucus secretion is protective.
• The colon secretes no _____ enzymes.
• However, colonic _____ (the microbiota) ferment for their own use some of the fiber that cannot be digested by human digestive enzymes.
• The _____ absorbs some of these bonus nutrients.
• Absorption of some of the remaining salt and water converts the colonic contents into _____.

Answer 32

Large Intestine

• Secretion, digestion, and absorption: The alkaline mucus secretion is protective.
• The colon secretes no digestive enzymes.
• However, colonic bacteria (the microbiota) ferment for their own use some of the fiber that cannot be digested by human digestive enzymes.
• The colon absorbs some of these bonus nutrients.
• Absorption of some of the remaining salt and water converts the colonic contents into feces.

Question 33

Overview of the GI Hormones