Chapter 23: The Digestive System

Check Your Understanding #3 Which digestive system activity actually moves nutrients from the outside to the inside of the body?

The process of absorption moves nutrients into the body.

Check Your Understanding #10 The term "gut brain" does not really mean there is a brain in the digestive system. What does it refer to?

The term "gut brain" refers to the enteric nervous system, the web of neurons closely associated with the digestive organs.

What is produced by the endocrine cells of the pancreas?

insulin (beta cells) and glucagon (alpha cells).

Check Your Understanding #31 What are brush border enzymes?

Brush border enzymes are enzymes associated with the microvilli of the enterocytes of the small intestine mucosa.

Why don't monogycerides and fatty acids need help from proteins to get into epithelial cells?

because they are lipophilic and can diffuse straight through the cell membrane.

What is the "brush border"?

epithelial cell membrane lining the small intestine that houses additional enzymes

Are bile salts hydrophilic or hydrophobic?

they are amphipathic - partlu hydrophilic, partly lipophilic.

Are bile salts enzymes?

no

Review #16 The products of protein digestion enter the bloodstream largely through cells lining ______. (a) the stomach, (b) the small intestine, (c) the large intestine, (d) the bile duct.

(b) the small intestine.

Review #17 Before the blood carrying the products of protein digestion reaches the heart, it first passes through capillary networks in ________. (a) the spleen, (b) the lungs, (c) the liver, (d) the brain.

(c) the liver.

When carbohydrates are digested, what do they turn into?

glucose and other sugars

Review #14 The protein molecule will be digested by enzymes made by ______. (a) the mouth, stomach, and colon (b) the stomach, liver, and small intestine (c) the small intestine, mouth, and liver (d) the pancreas, stomach, and small intestine.

(d) the pancreas, stomach, and small intestine.

Review #15 The protein molecule must be digested before it can be transported to and utilized by the cells because ____. (a) protein is only useful directly (b) protein has a low pH (c) proteins in the circulating blood produce an adverse osmotic pressure (d) the protein is too large to be readily absorbed.

(d) the protein is too large to be readily absorbed.

Chapter Practice Test #16 Name three characteristics of the liver.

1. It is highly regenerative. (It can regenerate to its normal size even after surgical removal or loss of 70% of its normal mass.) 2. It has a role in detoxifying the blood. 3. It stores glucose as glycogen.

Check Your Understanding #9 When sensors in the GI tract are stimulated, they trigger reflexes. What types of digestive activity may be put into motion via those reflexes?

Reflexes associated with the GI tract promote muscle contraction and secretion of digestive juices or hormones.

Define catabolic metabolism.

breaking big molecules down into smaller molecules

Where carboxypeptidase, aminopeptidase and dipeptidase found?

brush border

Where in the small intestine are maltase, sucrase, and kactase found?

in the brush border of the small intestine and produced by those epithelial cells lining the intestine.

What enzyme(s) break proteins into polypeptides?

pepsin

What are the three categories of macro nutrients?

proteins, carbohydrates, and fats

What enzyme(s) break polypeptides into peptides?

trypsin, chymotrypsin, carboxypeptidase

Chapter Practice Test #5 __________ circulation collects nutrient-rich blood from the GI tract and delivers it to the liver. A. Hepatic portal B. Peritoneal C. Aortic D. Cardiac

A. Hepatic portal

Check Your Understanding #41 Suppose you had a patient that was unable to make bile salts. What digestive processes would be affected and what might be some of the consequences?

Lack of bile salts would dramatically decrease both digestion and absorption of fats and fat-soluble vitamins. Without bile salts, you would expect the patient to have fatty stools. The patient might exhibit signs of weight loss and malnutrition. (In children this would be seen as lack of growth and failure to thrive.) The patient may also exhibit signs of deficiency of fat-soluble vitamins.

Which substances do NOT need the help of proteins to get into epithelial cells?

Monoglycerides and fatty acids

Can sugars and amino acids diffuse through cell membranes without protein help?

No, they need transporters to help them across because they're hydrophilic.

Check Your Understanding #26 What is the functional difference between pancreatic acini and islets?

Pancreatic acini produce the exocrine products of the pancreas (digestive enzymes and bicarbonate-rich juice). The islets produce pancreatic hormones, most importantly insulin and glucagon.

Chapter Practice Test #14 Digestion of carbohydrates and proteins by brush border enzymes occurs within the __________ of the small intestine. A. circular folds B. villi C. goblet cells D. microvilli

D. Microvilli The microvilli house brush border enzymes that digest carbohydrates and proteins in the small intestine.

Chapter Quiz #11 What would be the effect of stripping the small intestines of their villi? A. A duodenal ulcer would develop. B. The large intestine would take over as the primary absorptive site. C. Salivary amylase secretion would increase. D. decreased surface area for absorption

D. decreased surface area for absorption Decreased intestinal surface area would lead to decreased absorption, leading to a long list of problems such as malnutrition, dehydration, diarrhea, and electrolyte imbalance.

What is the difference between digestion and absorption?

Digestion entails chemical breakdown Absorption is the movement of those newly created pieces out of the GI tract, into epithelial cells and then the blood.

Check Your Understanding #32 Distension of the stomach and duodenal walls have different effects on stomach secretory activity. What are these effects?

Distension of stomach walls enhances stomach secretory activity. Distension of the walls of the small intestine reduces stomach secretory activity (to give the small intestine time to carry out its digestive and absorptive activities).

Check Your Understanding #20 How are the respiratory passages blocked during swallowing?

During swallowing the larynx rises and the epiglottis covers its lumen so that foodstuffs are diverted into the esophagus posteriorly.

Chapter Quiz #1 In order to prevent self-digestion of the pancreas, activation of pancreatic proteases occurs in the __________. A. liver B. stomach C. gallbladder D. pancreas E. duodenum

E. Duodenum The pancreatic duct empties into the duodenum, where activation of proteases occurs. Secreting initially inactive forms of proteases prevents self-digestion of the pancreas.

Chapter Quiz #8 Which regulatory chemical stimulates gastric gland activity and motility? A. histamine B. secretin C. CCK D. gastrin E. vasoactive peptide

E. Gastrin Gastrin is the major stomach hormone. Both the stomach and the small intestine produce this chemical.

Check Your Understanding #11 Jerry has been given a drug that inhibits parasympathetic stimulation of his digestive tract. Should he "eat hearty" or temporarily refrain from eating, and why?

He should temporarily refrain from eating because the parasympathetic nervous system stimulates digestive activities.

Where along the digestive tract does most macronutrient absorption occur?

In the small intestine.

Chapter Practice Test #15 Bile is stored and concentrated in the __________. A. gallbladder B. stomach C. liver D. pancreas

A. gallbladder

When proteins are digested, what do they turn into?

amino acids

Where are trypsin, chymotrypsin, and caraboxypeptidase located?

small intestine lumen (near-neutral pH)

Where is pepsin found?

stomach (very acidic)

Where are bile salts made?

the liver, stored in gallbladder, released into small intestine

Why is a triglyceride called a TRIglyceride?

there are 3 fatty acids attached to the glycerol backbone

Define anabolism and give examples.

combining smaller molecules to make bigger molecules Examples: 1. Proteins broken down into amino acids are built back into PROTEINS 2. Carbohydrates digested into glucose and other sugars are built back into GLYCOGEN 3. Fats --> Glycerol + Fatty acids --> TRICLYCERIDES

When fats are digested, what do they turn into?

glycerol and fatty acids

Chapter Quiz #13 The final product of carbohydrate digestion is __________. A. monosaccharides B. glycogen C. polysaccharides D. starch E. disaccharides

A. Monosaccharides With the exception of fatty acids, all macromolecules are broken down to their monomers, such as when enzymes hydrolyze complex carbohydrates into monosaccharides.

Chapter Quiz #6 The main propulsive force that occurs in the majority of the alimentary canal is called __________. A. peristalsis B. ingestion C. segmentation D. defecation E. swallowing

A. Peristalsis Peristalsis occurs as alternating waves of contraction and relaxation and serves to propel food down the tract.

Chapter Quiz #5 What are the main organic molecules digested in the stomach? A. proteins B. lipids C. carbohydrates D. salts E. nucleic acids

A. Proteins The main enzyme produced by the stomach is pepsin, which digests protein (gastric lipases are only of minor importance).

Chapter Practice Test #13 The __________ is the first segment of the small intestine. A. duodenum B. ileum C. jejunum D. colon

A. duodenum

Review #6 The digestive juice product containing enzymes capable of digesting all four major foodstuff categories is ______. (a) pancreatic (b) gastric (c) salivary (d) biliary.

A. pancreatic

Chapter Quiz #28 Which of the following is a function of the gallbladder? A. storing and concentrating bile B. secreting pancreatic juice C. metabolizing carbohydrate D. converting pepsinogen to pepsin

A. storing and concentrating bile Bile that is not immediately needed for digestion is concentrated and stored by the gallbladder.

Review #10 The sphincter between the stomach and duodenum is _____. (a) the pyloric sphincter (b) the gastroesophageal sphincter (c) the hepatopancreatic sphincter (d) the ileocecal valve.

A. the pyloric sphincter

Check Your Understanding #36 What is the result of stimulation of stretch receptors in the rectal walls?

Activation of stretch receptors in the rectal walls initiates the defecation reflex.

Check Your Understanding #30 What common advantage do circular folds, villi, and microvilli provide to the digestive process?

All of these modifications increase the surface area of the small intestine.

Where in the small intestine is amylase found?

Amylase comes from the pancreas to digest in the small intestine lumen.

Chapter Quiz #17 Emulsification of which organic molecules would be most affected if the liver were severely damaged? A. carbohydrates B. lipids C. nucleic acids D. proteins

B. Lipids Fat emulsification occurs by the detergent action of bile salts from the liver.

Chapter Practice Test #23 Pepsin enzymatically digests __________. A. fat B. protein C. carbohydrate D. nucleic acids

B. Protein Lipases digest fats, amylases digest carbohydrates, proteases (such as pepsin) digest proteins, and nucleases digest nucleic acids such as DNA and RNA.

Chapter Practice Test #2 The major site for nutrient absorption is the __________. A. stomach B. small intestine C. large intestine D. mouth

B. small intestine

Review #5 The parasympathetic nervous system influences digestion by ______. (a) relaxing smooth muscle (b) stimulating peristalsis and secretory activity (c) constricting sphincters (d) none of these.

B. stimulating peristalsis and secretory activity

Review #7 The site of production of cholecystokinin is ____. (a) the stomach (b) the small intestine (c) the pancreas (d) the large intestine.

B. the small intestine

Review #8 Which of the following is not characteristic of the colon? (a) It is divided into ascending, transverse, and descending portions (b) it contains abundant bacteria, some of which synthesize certain vitamins (c) it is the main absorptive site (d) it absorbs much of the water and salts remaining in the wastes.

C. it is the main absorptive site;

Review #9 The gallbladder _____. (a) produces bile (b) is attached to the pancreas (c) stores and concentrates bile (d) produces secretin.

C. stores and concentrates bile

Check Your Understanding #28 What stimulates CCK release and what are its effects on the digestive process?

CCK is secreted in response to the entry into the duodenum of chyme rich in protein and fat. It causes the pancreatic acini to secrete digestive enzymes, stimulates the gallbladder to contract, and relaxes the hepatopancreatic sphincter.

What is the difference between chewing/churning/segmentation and digestion?

Chewing is part of the PHYSICAL (not chemical) breakdown of food. Digestion is the CHEMICAL changes (breaking of individual MOLECULES into smaller molecules - e.g., protein gets chopped into pieces), catalyzed by enzymes.

Review #25 Explain why fatty stools result from the absence of bile or pancreatic juice.

The absence of bile (which causes fat emulsification) and/or pancreatic juice (which contains essentially the only important source of lipase) causes fat absorption to be so slow as to allow most of the fat to remain unabsorbed and be passed into the large intestine.

Review #19 Lara was on a diet but she could not eat less and kept claiming her stomach had a mind of its own. She was joking, but indeed, there is a "gut brain" called the enteric nervous system. Is it part of the parasympathetic and sympathetic nervous system? Explain.

The digestive system does contain local nerve plexuses known as the local (enteric) nervous system. This is composed of nerve plexuses in the wall of the alimentary canal that extend the entire length of the GI tract, and is the major nerve supply supplying the GI tract. The enteric system does link to the CNS, however, by afferent visceral fibers and autonomic branches.

Check Your Understanding #19 What is the functional significance of the epithelial change seen at the esophagus-stomach junction?

The esophagus is merely a chute for food passage and is subjected to a good deal of abrasion, which a stratified squamous epithelium can withstand. The stomach mucosa is a secretory mucosa served well by a simple columnar epithelium.

Chapter Practice Test #18 Most digestion occurs in the small intestine. True False

True. Almost all digestion and nutrient absorption occur in the small intestine. The stomach has a role in the initial breakdown of protein, but very little nutrient absorption occurs in the stomach. Water, electrolytes, and some vitamins are absorbed in the large intestine. The liver can store nutrients, but it does not absorb nutrients from the GI tract into the blood.

In this picture, the blue arrows stand for catabolism. the blue arrows stand for anabolism.

What do the blue and purple arrows stand for in this picture?

[Switch card for picture] Lipase; mostly produced by pancreas and found in small intestine lumen

What is the enzyme that catalyzes the reaction shown here? Where is it made, and where does it do its job?

[Flip card for question and picture] Bottom right: secondary active transport/cotransport. Uses ATP indirectly. One substance goes down its gradient (possible because of primary active transport, which used ATP to create that gradient) while another goes against its gradient. Called "cotransport" because two substances are always transported together.

Which one of these is secondary active transport? Why is it also known as cotransport?

Name the four individual enzyme names important to digestion.

amylase, lipase, pepsin, trypsin

What enzyme(s) break peptides into amino acids?

carboxypeptidase, aminopeptidase, and dipeptidase

What is produced by the exocrine cells of the pancreas?

digestive enzymes (for carbs, lipids, and proteins), HCO3- (for neutralizing stomach acid)