Digestive System

Question 1

Define:

digestion

Answer 1

The mechanical and chemical process in which food is broken down into smaller components.

Question 2

What is the difference between extracellular and intracellular digestion?

Answer 2

• Extracellular digestion occurs outside of cells, as in the chemical digestion of food in the digestive tract.
• Intracellular digestion is the breakdown of molecules within the cytoplasm or lysosomes of cells.

Question 3

Is the breakdown of proteins by trypsin in the small intestine an example of intracellular or extracellular digestion?

Answer 3

The action of trypsin is an example of extracellular chemical digestion. It takes place outside the cells, in the lumen of the duodenum.

Question 4

What is the difference between mechanical and chemical digestion?

Answer 4

• Mechanical digestion is the physical fragmenting of food into pieces. * Chemical digestion splits food into smaller chemical units by breaking bonds.

Question 5

The churning of food in the stomach is an example of what kind of digestion?

Answer 5

Extracellular mechanical digestion.

This activity physically mixes food but does not break any chemical bonds.

Question 6

What is the alimentary canal?

Answer 6

The alimentary canal, or digestive tract, is the tube through which food enters the body and exits as waste.

The digestive tract consists of the mouth, pharynx, esophagus, stomach, small intestine, large intestine, and anus.

Question 7

Define:

absorption

Answer 7

The process by which molecules are taken up from the digestive tract into the cells.

Absorption of nutrients occurs in the small intestine, while absorption of water occurs in the large intestine.

Question 8

What name refers to the ball of food formed by the action of the tongue during ingestion?

Answer 8

bolus

Once formed, the bolus is forced to the back of the oropharynx and swallowed.

Question 9

Why is mastication a useful precursor to the later chemical digestion of food?

Answer 9

Mastication, or chewing, provides an increase in the surface area available for digestion.

The action of digestive enzymes, and thus digestion, is able to proceed more rapidly when the surface area-to-volume ratio of the ingested food particles is increased.

Question 10

Which class of macromolecules is digested by salivary amylase?

Answer 10

Salivary amylase acts on starch, which is a carbohydrate.

This enzyme cleaves certain glycosidic linkages, producing the disaccharide maltose from starch, a polysaccharide.

Question 11

What flap of elastic cartilage, if dysfunctional, could potentially lead to difficulty swallowing?

Answer 11

the epiglottis

One of the cartilaginous structures that constitute the voice box, the epiglottis is attached to the larynx. When elevated during swallowing, it blocks food from entering the trachea and directs it instead into the esophagus.

Question 12

If the epiglottis does not close properly when a person is eating, what can happen?

Answer 12

Food can enter the trachea.

The epiglottis closes off the airway when a person is eating or drinking.

Question 13

In the digestive tract, which structure is positioned between the oral cavity and the esophagus?

Answer 13

the pharynx

The pharnyx is part of both the respiratory and digestive systems. It is divided into three components: the nasopharynx, the oropharynx, and the laryngopharynx.

Question 14

The upper portion of the esophagus is composed of what type of muscle?

Answer 14

striated muscle

The esophagus is a muscular tube through which food passes. The superior portion of the esophagus is surrounded by striated, or skeletal, muscle.

Question 15

What term describes the coordinated muscular action that helps food pass through the digestive tract?

Answer 15

This motion is called peristalsis.

Peristalsis involves a series of muscular contractions throughout the gastrointestinal tract. These contractions are undergone by smooth muscle, meaning that the process is involuntary.

Question 16

The pyloric sphincter separates the stomach from the duodenum. Which similar muscular structure serves to keep the contents of the stomach contained?

Answer 16

the cardiac sphincter

The digestive system contains two main sphincters, or muscular rings composed of smooth muscle. The cardiac sphincter separates the esophagus from the stomach.

Question 17

What name is given to the semi-solid, partially digested food that exists in the stomach?

Answer 17

chyme

Chyme results from the mechanical and chemical breakdown of food in the stomach, and is composed of water, stomach acid, and digestive enzymes.

Question 18

What are the key structural characteristics of the stomach?

Answer 18

The stomach is a muscular and elastic sac sealed on both ends by sphincters. Due to a densely folded inner membrane, the stomach can easily stretch.

This organ is the main site of digestion. It secretes hydrochloric acid that facilitates the activity of certain enzymes.

Question 19

Chyme is a product of which type(s) of digestion?

Answer 19

Both mechanical and chemical digestion act together to produce chyme.

Chyme is the mixture of food and fluid that forms in the stomach. Here, mechanical digestion is performed by the stomach musculature, while chemical digestion involves enzymes such as pepsin and gastric lipase.

Question 20

What compounds do chief cells and parietal cells secrete into the stomach?

Answer 20

Chief cells secrete pepsinogen, while parietal cells secrete HCl and intrinsic factor.

Both cell types are located in the gastric glands of the stomach.

Question 21

How does the pH of the stomach lumen change in response to secretion of hydrochloric acid (HCl)?

Answer 21

The pH of the lumen decreases.

HCl, sometimes referred to as gastric acid, is a strong acid. Its secretion from parietal cells keeps the pH of the stomach lumen around 2. Note that the lumen always refers to the inside cavity of an organ.

Question 22

What are zymogens, and what function do they serve in the digestive system?

Answer 22

It is the inactive version of an enzyme, and can usually be activated via cleavage.

Zymogens are also known as proenzymes.

Zymogens are especially prevalent among proteases, or protein-digesting enzymes. The presence of an inactive form prevents these enzymes from breaking down the digestive cells themselves.

Question 23

What zymogen responsible for digestion of proteins in the stomach is secreted by gastric chief cells?

Answer 23

pepsinogen

Pepsinogen is the inactive precursor of the proteolytic enzyme pepsin. When activated by the acidic conditions of the stomach, pepsin acts to digest protein by cleaving specific peptide bonds.

Question 24

In what layer of the stomach are gastric glands located?

Answer 24

In the gastric mucosa.

These glands contain chief and parietal cells, which secrete HCl, mucus, pepsinogen, and hormones. The mucosa is the uppermost layer of the stomach; in other words, it physically contacts the stomach contents.

Question 25

How does the stomach’s mucous membrane work to protect the stomach?

Answer 25

The mucous membrane secretes mucus, an alkaline covering that protects the stomach from the acidity of its contents.

Question 26

Through which structure does food leave the stomach when it passes into the duodenum?

Answer 26

Food passes through the pyloric sphincter.

Sphincters are muscular valves. Upon parasympathetic stimulation, the pyloric sphincter opens to allow chyme into the duodenum of the small intestine.

Question 27

Other than gastrin itself, what chemical or hormone would be over-secreted as a result of a gastrinoma, a gastrin-secreting tumor?

Answer 27

Hydrochloric acid

(HCl)

Gastrin is a hormone that stimulates HCl release and increases stomach motility. Hypersecretion of gastrin would thus lead to a decrease in pH and promotion of peristalsis.

Question 28

Which blood vessels supply the liver?

Answer 28

The liver receives blood from the hepatic portal vein and the hepatic arteries.

Portal circulation carries nutrient-rich blood from the digestive tract for processing, while the hepatic arteries supply oxygenated blood as part of the systemic circulation.

Question 29

In what organ is bile produced?

Answer 29

In the liver.

Bile is an alkaline emulsifying agent that aids in the digestion of fats. Note that while bile is synthesized in the liver, it is stored in the gall bladder.

Question 30

Xenobiotics, or foreign compounds, are modified during hepatic metabolism. What is the ultimate fate of these substances?

Answer 30

They will be excreted.

A main role of the liver involves processing of lipid-soluble drugs and toxins, which arrive from the hepatic portal vein. This modification aids in their removal from the body via excretion.

Question 31

Name the process of glucose synthesis that takes place in the liver and is stimulated by glucagon.

Answer 31

Gluconeogenesis, or the synthesis of glucose from amino acids and other non-carbohydrate substrates, occurs primarily in the liver. This process also takes place in the kidneys.

Glucagon, a pancreatic hormone, acts to increase blood glucose levels. Since gluconeogenesis produces glucose, glucagon would act to stimulate it.

Question 32

Vitamins stored in the liver display what level of affinity for water?

Answer 32

Vitamins within the liver may be hydrophobic or hydrophilic, meaning that their affinity for water varies.

While the liver is the primary storage site for hydrophobic, fat-soluble vitamins, including A, D, and K, the water-soluble vitamin B₁₂ is stored there as well.

Question 33

In a portal system, one capillary bed drains directly into another without going through the heart. What does hepatic portal circulation accomplish?

Answer 33

Hepatic portal circulation drains blood from the gastrointestinal tract directly into blood vessels that feed the liver.

Question 34

Digestion of what type of macromolecule is aided by bile?

Answer 34

lipids

Amphipathic bile salts serve to emulsify the hydrophobic component of dietary fats. While emulsification does not break chemical bonds, it does increase the surface area of fats available for contact with pancreatic lipase.

Question 35

Liver dysfunction can cause decreased synthesis of albumin. What effect would this abnormality have on peripheral tissue?

Answer 35

Edema, or swelling, would occur.

Albumin, the most abundant human blood protein, acts mainly to maintain osmotic pressure in the capillaries. A decrease in albumin concentration would cause circulatory osmotic (or more specifically, oncotic) pressure to become lower as well. With decreased fluid resportion into capillaries, fluid would remain in the tissue, causing edema.

Question 36

What substance does the gallbladder release, and in which part of the digestive tract does it act?

Answer 36

Bile is stored and concentrated in the gallbladder. When released, it acts on the duodenum of the small intestine.

Remember that the gallbladder stores, but does not produce, bile. When stimulated by the hormone cholecystokinin (CCK), this bile is released into the small intestine, where it emulsifies fats to assist in their digestion.

Question 37

What effect will a malfunctioning gallbladder have on digestion?

Answer 37

It will lead to improper digestion of fats.

The gallbladder stores and releases bile, which emulsifies fats, increasing the rate of their digestion. An impaired gallbladder would result in slow or incomplete lipid breakdown.

Question 38

Which structure of the digestive system serves both an endocrine and an exocrine function?

Answer 38

pancreas

Endocrine organs release hormones into the blood, while exocrine structures secrete enzymes or other substances through ducts. The pancreatic hormones insulin, glucagon, and somatostatin contribute to its endocrine function, while digestive enzymes such as pancreatic amylase are part of its exocrine role.

Question 39

What chemical bonds does carboxypeptidase cleave?

Answer 39

carboxy-terminal peptide bonds

Carboxypeptidase is one of a number of pancreatic digestive enzymes that selectively hydrolyzes certain chemical bonds. Since it assists in the breakdown of proteins, it is classified as a protease.

Question 40

Name three proteases produced by the pancreas.

Answer 40

• trypsinogen
• chymotrypsinogen
• carboxypeptidase

Note that both trypsinogen and chymotrypsinogen are zymogens, or inactive forms. Trypsinogen is converted to active trypsin, and chymotrypsinogen is converted to active chymotrypsin.

Question 41

Which pancreatic secretion neutralizes acidic chyme?

Answer 41

Bicarbonate, or HCO₃^-, neutralizes stomach acid in the small intestine. Its release is promoted by the hormone secretin.

As a base, bicarbonate raises the pH of the duodenum to around 6, in comparison to the stomach pH of 2.

Question 42

How does increased insulin secretion affect blood glucose levels in a healthy individual?

Answer 42

Insulin release decreases blood glucose concentration.

Insulin, a peptide hormone, is released in response to elevated blood glucose levels (after meals). By increasing uptake of glucose into the cells and promoting its storage as glycogen, this activity lowers blood glucose concentrations to normal levels.

Question 43

What is the most likely treatment for type I diabetes, an autoimmune destruction of pancreatic beta islet cells?

Answer 43

insulin administration

The loss of beta islet cell function results in reduced production of insulin. Administration of exogenous insulin is required to manage blood glucose concentrations in affected individuals. This differs from type II diabetes, in which cells become less responsive to insulin.

Question 44

What part of the brain, in addition to its role in regulating endocrine function, is involved in the hunger response?

Answer 44

The hypothalamus is involved in hunger, as well as hormone synthesis and thermoregulation.

Leptin, an appetite-inhibiting hormone, is produced by adipose cells in response to increased body fat. This hormone stimulates the production of neuropeptide Y, which in turn prevents the release of hunger-inducing orexins from the hypothalamus.

Question 45

What digestive organ synthesizes cholecystokinin (CCK)?

Answer 45

small intestine

This peptide hormone facilitates digestion in the duodenum. Its effects include inhibited gastric acid production, reduced or slowed gastric motility, and increased release of pancreative digestive enzymes and bile.

Question 46

What hormone is secreted in response to the acidity of the contents entering the small intestine?

Answer 46

Secretin, a pancreatic hormone, responds to excessive acidity in the duodenum.

Secretin slows gastric emptying, decreases HCl secretion in the stomach, increases the release of stomach bicarbonate, and promotes the secretion of enzymes through the pancreatic duct.

Question 47

In what organ does most absorption of dietary nutrients occur?

Answer 47

The small intestine.

Remember that both digestion and absorption occur in the small intestine, while only digestion occurs in the stomach.

Question 48

Which segment of the small intestine precedes the jejunum?

Answer 48

The duodenum, or first segment, precedes the jejunum. It is the site of most chemical digestion.

In the order that material passes through them, the segments of the small intestine are the duodenum, jejunum, and ileum.

Question 49

The majority of ingested ions and water are absorbed in which segment(s) of the small intestine?

Answer 49

Water and ions are absorbed in both the jejunum and the ileum.

These segments contain enterocytes that are specialized for, among other things, absorption of ions, water, and vitamin B₁₂, and resorption of bile salts.

Question 50

What term refers to the small, finger-like protrusions from the small intestinal wall that aid in digestion?

Answer 50

Intestinal villi

In the digestive system, villi are tube-shaped projections of the intestinal epithelium. These structures increase the total surface area available for nutrient absorption.

Question 51

What is the purpose of microvilli?

Answer 51

To further increase the surface area of the small intestine, allowing for more effective absorption of nutrients.

Microvilli are small projections that extend from the surface of larger villi.

Question 52

What is the digestive role of a lacteal?

Answer 52

This is a small lymphatic vessel within a villus, which absorbs lipids from the small intestine in the form of chylomicrons.

After briefly entering the lymphatic system, chylomicrons are brought to venous circulation by passing through the thoracic duct.

Question 53

In the gastrointestinal tract, which type of muscle is responsible for the mixing and propulsion of digestive contents?

Answer 53

Smooth muscle lines the human digestive tract. Its contraction propels the tract’s contents via peristalsis and mixes these contents within the stomach.

Since smooth muscle is innervated by the autonomic nervous system, this digestive activity is involuntary.

Question 54

What function of the small intestine would be most impaired by blockage of the pancreatic duct?

Answer 54

chemical digestion

The small intestine aids in both digestion and absorption. However, the pancreatic duct is only involved in the release of pancreatic enzymes, which contribute to the chemical digestion of lipids, proteins, and carbohydates.

Question 55

Which digestive organ is primarily involved in the absorption of water?

Answer 55

large intestine, or colon

The large intestine also absorbs salt, but all other biologically useful molecules are absorbed earlier, in the small intestine.

Question 56

What organisms are responsible for the production of flatus (gas) within the large intestine?

Answer 56

Bacteria

Gut flora, or bacteria that reside in the large intestine, act symbiotically to ferment undigested polysaccharides that arrive in the large intestine. This process produces small amounts of several gases.

Question 57

What pressure gradient drives absorption of water from the lumen of the colon?

Answer 57

The osmotic pressure gradient.

Waste within the colon possesses relatively large amounts of both sodium and water. Epithelial cells actively absorb sodium, which establishes an osmotic gradient; water then follows sodium out of the intestinal lumen.

Question 58

What segment of the gastrointestinal tract immediately precedes the anus?

Answer 58

The rectum.

After waste passes through the rest of the large intestine, it moves to the rectum, or final segment. From the rectum, waste enters the anal canal and is expelled.

Question 59

Into which segment of the large intestine does chyme from the ileum first pass?

Answer 59

Chyme first enters the cecum, the initial segment of the large intestine.

In order, the remaining segments of the large intestine are the ascending, transverse, descending, and sigmoid colon, followed by the last structure, the rectum.

Question 60

Relaxation of which two structures permits feces stored in the rectum to exit the anal canal?

Answer 60

The internal and external anal sphincters.

Question 61

What small structure attached to the cecum has little, if any, current function?

Answer 61

The appendix.

The appendix is a functionless, blind pouch found at the intersection of the large and small intestine. It is a frequent site of bacterial infection.

Question 62

Which vitamins are fat-soluble and which are water-soluble?

Answer 62

• Fat-soluble: Vitamins A, D, E, and K
• Water-soluble: Vitamins B and C

Water-soluble vitamins can easily be excreted in the urine, while fat-soluble vitamins tend to persist in the body’s adipose cells.

Question 63

Name the common enzymes that digest carbohydrates.

Answer 63

• salivary amylase
• pancreatic amylase
• maltase
• sucrase
• lactase

In biology, the “-ase” ending generally denotes an enzyme. With digestive enzymes, the part of the word that precedes “-ase” often refers to the substance that is broken down. For example, lactase breaks down lactose into glucose and galactose.

Question 64

Name the common enzymes that digest proteins.

Answer 64

• pepsin
• trypsin
• chymotrypsin
• carboxypeptidase

Aminopeptidase, dipeptidase, and enterokinase also cleave peptide bonds but are less commonly tested.

Pepsin is found in the stomach, while trypsin, chymotrypsin, and carboxypeptidase act in the small intestine.

Question 65

Name the enzyme class that digests fats.

Answer 65

lipase

Lipases hydrolyze triglycerides, usually at a specific site on the glycerol backbone. Note that although bile helps to emulsify fats, it is not an enzyme; it breaks lipid particles into smaller droplets but does not perform catalysis.

Question 66

A patient is found to have impaired water absorption in his GI tract. Damage to which structure(s) could potentially produce this effect?

Answer 66

Impairment of either the small or large intestine could affect water absorption.

The small intestine absorbs both nutrients and water, while the large intestine absorbs the water that remains.

Question 67

How does blood flow in intestinal capillary beds promote absorption of simple sugars and amino acids?

Answer 67

Capillary flow promotes absorption by establishing a concentration gradient.

Due to the constant influx of blood to capillaries in the villi, the plasma concentration of amino acids and simple carbohydrates remains low compared to their concentration in intestinal cells. This establishes a concentration gradient that promotes nutrient diffusion from the intestinal epithelium into the bloodstream.

Question 68

A condition causes obstruction of the lymphatic vessels that drain the small intestine. Absorption of which macromolecule would be most altered by this disorder?

Answer 68

Absorption of fats would be most impaired.

Lymphatic vessels within villi, called lacteals, are only vital to the absorption of fats. Fatty acids are absorbed directly into intestinal cells. From there, triglycerides and esterified cholesterol molecules, in the form of chylomicrons, enter lymphatic circulation through lacteals.

Question 69

Digestion of which macromolecule would be most affected by a significant increase in the pH of the stomach?

Answer 69

An increased pH would most strongly affect protein digestion.

Breakdown of proteins in the stomach is carried out by pepsin. Pepsin activity, as well as its activation from pepsinogen, is optimized for the extremely low pH of the stomach. Any increase in pH that significantly exceeds 2 would result in lowered enzyme activity.

Question 70

Impaired secretion from which type of cell could potentially lead to erosion of the stomach’s mucosal lining?

Answer 70

Reduced secretion from goblet cells could damage the stomach lining.

Gastric goblet cells secrete mucus, which protects the stomach epithelium from the acidic contents of the lumen. When mucus is absent or reduced, damage to the epithelium can occur, leading to an erosive gastric ulcer.

Question 71

What property of amino acids requires their absorption from the small intestine via transport proteins?

Answer 71

They are polar molecules.

Polar molecules are unable to pass through the hydrophobic plasma membrane of intestinal cells. As a result, their absorption from the lumen of the small intestine requires specific transporter proteins.