Chapter 25 (Digestion) Study Guide

Question 1

Why does the digestive system work as a disassembly line? (2 reasons)

Answer 1

1) To break down nutrients into forms that can be used by the body
2) To absorb them so they can be distributed to the tissues

Question 2

What are the five stage of digestion? Where does ingestion usually occur?

Answer 2

1) Ingestion: typically at the oral cavity (mouth)
2) Digestion: mechanical and chemical breakdown of food
3) Absorption
4) Compaction
5) Defecation

Question 3

1) Define mechanical digestion. Where does mechanical digestion occur?
2) Define chemical digestion. Chemical digestion is carried out by enzymes produced by what organs?

Answer 3

1) Mechanical digestion occurs with the grinding of the teeth and churning of the stomach, which break down food into smaller particles.
2) Chemical digestion is the hydrolysis of macromolecules into their monomers, and is carried out by digestive enzymes produced by salivary glands, stomach, pancreas, and small intestine

Question 4

Which nutrients are already present in usable form without digestion and can be directly absorbed?

Answer 4

Vitamins, amino acids, minerals, cholesterol, and water

Question 5

1) What enzyme is used to digest starch? What two organs produce the enzyme?
2) What are the three disaccharides?
3) What 3 enzymes digest disaccharides into monosaccharides? Where are they produced?
4) What are the three monosaccharides?

Answer 5

1) Amylase; produced by the salivary glands and pancreas.
2) Disaccharides: Maltose, sucrose, and lactose
3) Maltase, sucrase, and lactase digest disaccharides into monosaccharides. Produced in the small intestine.
4) Monosaccharides: Glucose, galactose, and fructose.

Question 6

1) What are proteins broken down into?
2) What enzyme breaks down proteins in the stomach? How is that enzyme activated?
3) What enzyme breaks down proteins in the small intestine that was produced by the pancreas? How and where is this enzyme activated?
4) Why must these enzymes be released in an inactive form?

Answer 6

1) Proteins are broken down into large polypeptides, then peptides, then amino acids.
2) Stomach: Pepsin digests proteins; pepsinogen is activated into pepsin by HCl and later by pepsin.
3) Small intestine: Trypsin (produced by the pancreas) digests proteins.Trypsinogen is converted into trypsin, which is activated in the duodenum of the small intestine by enteropeptidase.
4) If released in an active form, these enzymes would begin to digest your own body’s proteins.

Question 7

1) Fats (triglycerides) are broken down into what monomers?
2) What enzyme is used?
3) Why is bile needed?
4) Is bile an example of mechanical digestion or chemical digestion?

Answer 7

1) A monoglyceride and 2 fatty acids (which can then be broken down into a glycerol and 3 fatty acids.)
2) Lipase is the enzyme used
3) Bile is needed for lipase to work well becauses it emulsifies (breaks down) fats.
4) Bile is an example of mechanical digestion.

Question 8

1) What are nucleic acids broken down into?
2) What group of enzymes are used?

Answer 8

1) DNA or RNA is broken down into nucleotides, which are then broken down into pentose sugars, nitrogen bases, and phosphate ions.
2) Nucleases are used

Question 9

Define:
1) Absorption
2) Compaction
3) Defecation

Answer 9

1) Absorption: uptake of nutrients into epithelial cells of GI tract and then into the blood or lymph
2) Compaction: absorbing water and consolidating the indigestible residue into feces
3) Defecation: elimination of feces; usually at anus

Question 10

1) What organs make up the gastrointestinal (GI) tract?
2) What are the accessory organs?

Answer 10

1) GI tract: stomach and intestines
2) Accessory organs: teeth, tongue, salivary glands, liver, gallbladder, and pancreas

Question 11

What are the digestive tract layers from deepest to most exterior? (4)

Answer 11

1) Mucosa
2) Submucosa
3) Muscularis externa
4) Serosa

Question 12

A) Where is the mucosa layer of the digestive tract? What does it line?
B) What are its three layers? Describe them

Answer 12

A) The deepest digestive tract layer that lines the lumen; its 3 layers are:
B)
1) Epithelium: Simple columnar in most of digestive tract, stratified squamous mouth through esophagus, and in lower anal canal
2) Lamina propria: loose connective tissue layer
3) Muscularis mucosa: thin layer of smooth muscle that creates grooves and ridges that enhance surface area and contact with food

Question 13

Define MALT and where it’s found

Answer 13

Mucosa-associated lymphatic tissue (MALT): Found in the mucosa and serves for defense against pathogens

Question 14

What is found in the submucosa layer of the digestive tract? What primary tissue type does it come from?

Answer 14

1) Blood vessels, lymphatic vessels, a nerve plexus, and in some places mucus-secreting glands (dump mucus into lumen).
-MALT extends into submucosa in some GI areas.
2) It’s a thicker layer of loose connective tissue

Question 15

Describe the two layers of the muscularis externa. What is the purposes of sphincters (valves)?

Answer 15

1) Inner circular layer: in some places this layer thickens to form valves (sphincters) that regulate the passage of material through the tract
2) Outer longitudinal layer

Question 16

1) What tissues make up the serosa?
2) When does the serosa become the adventitia?

Answer 16

1) Areolar tissue (thin layer) topped by simple squamous mesothelium
2) The pharynx, esophagus, and rectum have adventitia

Question 17

1) The esophagus, stomach, and intestines have a nervous network called the ________ nervous system.
2) What does the system regulate and how?
3) What are the two plexuses of this nervous system?

Answer 17

1) Enteric
2) Regulates motility, secretions and blood flow. It can be independent of CNS and is primarily parasympathetic stimulated (sympathetic inhibits). It’s a neuronal network in the walls of esophagus, stomach, intestines.
3) Submucosa (Meissner) plexus and Muscularis externa (myenteric) plexus

Question 18

Name and describe the two plexuses of the enteric nervous system

Answer 18

1) Submucosa (Meissner) plexus controls glandular secretions in muscosa and movement of muscularis mucosae
2) Muscularis externa (myenteric) plexus controls peristalsis and other contractions

Question 19

1) What do the mesenteries do and what does it provide?
2) The lesser omentum extends from what?
3) The greater omentum extends from?

Answer 19

1) Mesenteries are connective tissue sheets that hold abdominal viscera in place but allow movement
2) Lesser omentum: extends from lesser curvature of the stomach to the liver
3) Greater omentum: hangs from greater curvature of the stomach; drapes small intestine like an apron

Question 20

1) What is the purpose of the mesentery
2) What is the purpose of the mesocolon?
3) What does it mean to be retroperitoneal?

Answer 20

1) Mesentery: anchors small intestine to posterior wall
2) Mesocolon: anchors the colon to the abdominal wall
3) Retroperitoneal: Behind and outside the peritoneal cavity (ex: duodenum, pancreas, and parts of the large intestine)

Question 21

1) What are short myenteric reflexes triggered by, and what do they do?
2) What are long vagovagal reflexes triggered by, and what do they do?
3) What three hormones are controlling the motility and secretion?

Answer 21

1) Short (myenteric) reflexes: Stretch or chemical stimulation in GI tract; triggers peristaltic contractions of swallowing
2) Long (vagovagal) reflexes: sensory information from GI tract interpreted by CNS. Parasympathetic stimulation of digestive motility and secretion
3) Gastrin, CCK and secretin control motility and secretion

Question 22

1) The mouth is known as what two terms?
2) What extrinsic muscle alters the tongue’s position?

Answer 22

1) The oral or buccal cavity
2) The genioglossus muscle

Question 23

Name the 4 groups of functions of the mouth

Answer 23

1) Ingestion (food intake)
2) Taste and other sensory responses to food
3) Chewing (mastication) and chemical digestion
4) Swallowing, speech, and respiration

Question 24

What type of tissue is the mouth lined with and why is it slightly different in different areas?

Answer 24

Stratified squamous epithelium lines mouth:
-Keratinized in areas subject to food abrasion: gums and hard palate
-Nonkeratinized in other areas: floor of mouth, soft palate, and insides of cheeks and lips

Question 25

1) What is the lingual frenulum?
2) What is the purpose of the lingual glands?

Answer 25

1) Lingual frenulum: secures the tongue to the floor of the mouth
2) Lingual glands: serous and mucous glands amid the extrinsic muscles; secrete a portion of the saliva

Question 26

List the 4 functions of the tongue

Answer 26

1) Speech
2) Taste
3) Chewing
4) Swallowing

Question 27

1) What does the palate separate?
2) What does it make it possible to do?
3) Where is the uvula located?

Answer 27

1) Palate separates the oral and nasal cavities
2) To breathe while chewing food
3) At the end of the soft palate

Question 28

1) Define dentition.
2) What are the incisors used for?
3) What are canines used for?
4) What are premolars and molars used for?

Answer 28

1) Dentition: The teeth
2) Incisors: act to cut, nip or bite off food
3) Canine: act to puncture and shred food
4) Premolars and molars: broad surface for crushing, shredding, and grinding

Question 29

1) How many adult teeth are there?
2) What is a dental caries?
3) What is gingivitis?
4) What is periodontal disease?

Answer 29

1) 32 adult teeth
2) Dental caries: Also called cavities, bacteria metabolize sugars and release acids that dissolve the minerals of enamel and dentin.
3) Gingivitis: inflammation of the gums
4) Periodontal disease: destruction of the supporting bone around the teeth which may result in tooth loss

Question 30

1) What is mastication? What is it the first step of?
2) What two muscles are involved in chewing?

Answer 30

1) Mastication: Chewing; breaks food into smaller pieces to be swallowed and exposes more surface to digestive enzymes. The first step of mechanical digestion.
2) The masseter and temporalis perform the the raising and lowering of the jaw in chewing.

Question 31

What are the 6 functions of saliva?

Answer 31

1) Moistens mouth
2) Begins starch and fat digestion
3) Cleanses teeth
4) Inhibits bacterial growth
5) Dissolves molecules so they can stimulate the taste buds
6) Moistens food and binds it together into bolus to aid in swallowing

Question 32

1) What is the composition of saliva?
2) What does salivary amylase do and when?
3) What does lingual lipase do and when?

Answer 32

1) Saliva is a hypotonic solution of 97.0% to 99.5% water and the solutes salivary amylase, lingual lipase, mucus, lysozyme, IgA, and electrolytes.
2) Salivary amylase: begins starch digestion in the mouth
3) Lingual lipase: enzyme that is activated by stomach acid and digests fat after food is swallowed

Question 33

1) What does the mucus in saliva do?
2) What does lysozyme in saliva do?
3) What does the IgA in saliva do?

Answer 33

1) Mucus: binds and lubricates a mass of food, aids swallowing
2) Lysozyme: enzyme that kills bacteria
3) Immunoglobulin A (IgA): antibody that inhibits bacterial growth
pH range: 6.8 to 7.0

Question 34

1) What are the two types of salivary glands?
2) What is the purpose of intrinsic salivary glands?

Answer 34

1) Intrinsic and extrinsic
2) Intrinsic salivary glands all secrete saliva at a fairly constant rate, keeps your mouth moist throughout the day.

Question 35

Name the 4 intrinsic salivary glands and where they’re located

Answer 35

1) Lingual glands: in tongue
2) Labial glands: in lips
3) Palatine glands: in roof of mouth
4) Buccal glands: in cheeks

Question 36

There are three pairs of extrinsic salivary glands, name them and where they’re located. include which is related to mumps.

Answer 36

1) Parotid: located beneath the skin anterior to earlobe. Mumps is an inflammation and swelling of this gland caused by a virus.
2) Submandibular gland: located halfway along the body of the mandible; its duct empties at the side of the lingual frenulum
3) Sublingual gland: located in the floor of the mouth; has multiple ducts that empty into the floor of the mouth

Question 37

1) Define salivation.
2) About how much saliva is produced per day by the extrinsic salivary glands?
3) Salivary amylase begins to digest what?
4) What is a bolus?

Answer 37

1) Salivation: The secretion of saliva
2) Extrinsic salivary glands secrete about 1 to 1.5 L of saliva per day
3) Salivary amylase begins to digest starches into sugars.
4) Bolus: A mass swallowed as a result of saliva binding food particles into a soft, slippery, easily swallowed ball

Question 38

1) What drives the production of saliva, is it sympathetic or parasympathetic?
2) If you are have less and thicker mucus, is it sympathetic or parasympathetic?

Answer 38

1) Parasympathetic fibers stimulate the glands to produce an abundance of thin, enzyme-rich saliva (from either ingested food or the thought or smell of food)
2) Less, and thicker, saliva with more mucus: Sympathetic

Question 39

1) When food is not being swallowed, what sphincter is contracted? Why?
2) What tissue lines the esophagus?
3) What is the outmost layer called in the esophagus?

Answer 39

1) The upper esophageal sphincter remains contracted when food isn’t being swallowed to keep air out of the esophagus.
2) It’s made of nonkeratinized stratified squamous epithelium
3) Adventitia

Question 40

1) What is the name of the sphincter that opens into the stomach?
2) Why is that sphincter necessary?
3) Define heartburn.
4) Define deglutition; what coordinates it?

Answer 40

1) The lower esophageal (cardiac) sphincter.
2) Food pauses at the cardiac sphincter because of constriction to prevent stomach contents from regurgitating into the esophagus, which protects esophageal mucosa from erosive stomach acid
3) Heartburn: burning sensation produced by acid reflux into the esophagus
4) Deglutition: Swallowing, coordinated by the medulla oblongata

Question 41

Name and describe the 3 phases of swallowing. Include what type of control is in each phase and what happens to food during each phase.

Answer 41

1) Oral phase: under voluntary control
-Tongue collects food, presses it against palate forming bolus, and pushes it posteriorly
2) Pharyngeal phase: involuntary
-Prevents food and drink from reentering mouth or entering the nasal cavity, so breathing is suspended when the vocal cords and epiglottis close airway.
-The upper esophagus widens and the food bolus is driven downward by constriction of the upper, then middle, and finally the lower pharyngeal constrictors.
3) Esophageal phase: peristalsis: involuntary wave of muscular contraction that pushes the bolus ahead of it
-When it reaches lower end of the esophagus, the lower esophageal sphincter relaxes to let food pass into the stomach

Question 42

1) What is the stomach and what does it do? What chemical and mechanical digestion occurs in the stomach?
2) Is gastric juice, alkaline, neutral or acidic?
3) What does the stomach convert the bolus into?

Answer 42

1) It primarily functions as a food storage organ and mechanically breaks up food (churning); liquefies it, and begins chemical digestion of protein (and fat; minor importance).
2) Gastric juice is acidic
3) The stomach converts the bolus into chyme.

Question 43

1) The stomach has what tissue covering the mucosa?
2) When will the stomach have rugae?
3) What is unique about the muscularis externa of the stomach?

Answer 43

1) Simple columnar epithelium cover the stomach’s mucosa.
2) The mucosa and submucosa of the stomach have rugae when stomach is empty
3) The stomach’s muscularis externa has three layers (has 2 layers in all other places)

Question 44

1) What are gastric pits of the stomach and what are they lined with?
2) Why are tight junctions located here?

Answer 44

1) Gastric pits: depressions in the gastric mucosa lined with simple columnar epithelium
2) They have tight junctions to prevent seepage of acid and enzymes to deeper tissue

Question 45

Describe what the following cells of the stomach secrete or function as:
1) Mucous cells
2) Regenerative (stem) cells
3) Parietal cells
4) Chief cells
5) Enteroendocrine cells

Answer 45

1) Mucous cells: secrete thick mucus (alkaline) for protection
2) Regenerative (stem) cells: create constant supply of new cells
3) Parietal cells: secrete hydrochloric acid (HCl), intrinsic factor, and ghrelin
4) Chief cells: secrete gastric lipase and pepsinogen
5) Enteroendocrine cells: secrete hormones (Gastrin and secretin)

Question 46

1) What is the purpose of HCl?
2) What is the purpose of gastric lipase?
3) Why is intrinsic factor essential?
4) What forms pepsin, and what converts pepsinogen into pepsin?

Answer 46

1) HCl: activates pepsin and lingual lipase, kills ingested pathogens, unfolds (denatures proteins)
2) Gastric lipase (and lingual lipase) play a minor role in digesting dietary fats
3) Intrinsic factor: used in small intestine for vitamin B12 (needed to make RBCs)
4) Initially pepsin is formed by HCl, later the existing pepsin converts more pepsinogen into pepsin

Question 47

1) Define gastritis. What is a peptic ulcer?
2) What are treatment options?

Answer 47

1) Gastritis, inflammation of the stomach, can lead to a peptic ulcer as pepsin and hydrochloric acid erode the stomach wall.
2) Most ulcers are caused by acid-resistant bacteria Helicobacter pylori, that can be treated with antibiotics and Pepto-Bismol

Question 48

1) Explain what controls peristaltic contractions.
2) Where are contractions stronger, at the pyloric region or at the cardiac region of the stomach?
3) Where does the chyme go after leaving the stomach and how much leaves at a time?

Answer 48

1) The rhythm of peristaltic contractions (mixing waves) is controlled by pacemaker cells in muscularis externa; a ring of constriction every 20 seconds
2) Becomes stronger contraction at pyloric region
3) 3 mL of chyme is squirted into the duodenum of the small intestine at a time; this allows duodenum to neutralize the stomach acid and digest nutrients little by little

Question 49

1) What digestion is going on in the stomach?
2) What nutrients if any get absorbed?

Answer 49

1) Salivary and gastric enzymes partially digest protein and lesser amounts of starch and fat in the stomach
2) Stomach does not absorb any significant amount of nutrients; only water, alcohol, and aspirin

Question 50

Name and describe the 3 phases of gastric activity.

Answer 50

1) Cephalic phase: stomach controlled by brain
2) Gastric phase: stomach controlling itself
3) Intestinal phase: stomach controlled by small intestine

Question 51

The cephalic phase is the stage in which the stomach does what 5 steps? Include which nerve is involved and if it’s parasympathetic or sympathetic.

Answer 51

1) Sight, smell, taste, or thought of food (cerebral cortex) occurs
2) Sensory and mental inputs converge to hypothalamus
3) Hypothalamus relays to medulla oblongata
4) Parasympathetic stimulation (vagus nerve; parasympathetic) occurs (controlled by brain)
5) Stomach starts secretion of gastric juices and contraction of muscles

Question 52

1) The gastric phase is a period in which what happens?
2) What chemicals are involved during this phase and what cells do they stimulate? Are there any feedback loops during this time? If so, what are they?

Answer 52

1) The stomach is controlling itself
2) Gastric secretion is stimulated by the hormone gastrin and other chemicals, which stimulates the stomach to release HCl and enzymes. As peptides and amino acid levels increase, more gastrin secreted in positive feedback loop.

Question 53

How is the gastric phase of gastric activity stimulated by ingested food? (2 ways)

Answer 53

1) By stretching the stomach
2) By raising the pH of its contents

Question 54

What 3 conditions of the duodenum trigger the intestinal phase of gastric activity?

Answer 54

1) Stretching of duodenum
2) Presence of low pH chyme in duodenum
3) Presence of partially digested food in duodenum

Question 55

A) The duodenum enhances what at the beginning of the intestinal phase of gastric activity?
B) What 2 things are triggered by the intestinal phase? What two hormones are released by the enteroendocrine cells of the duodenum?

Answer 55

A) Initially stimulate the stomach to mix more and secrete more, then inhibits stomach
B) The intestinal phase triggers:
1) The enterogastric reflex
2) Causes release of two hormones from enteroendocrine cells of duodenum: Cholecystokinin (CCK) and secretin

Question 56

1) When does CCK (cholecystokinin) get released? CCK is secreted by?
2) What does CCK stimulate?
3) What does CCK inhibit?
4) What does CCK induce with regards to the gallbladder?
5) What does CCK induce the relaxation of?

Answer 56

1) Cholecystokinin (CCK) is secreted by enteroendocrine cells of the duodenum in response to arrival of fats in small intestine
2) Stimulates enzyme-rich pancreatic juice
3) Inhibits the stomach
4) Strongly stimulates contraction of gallbladder
5) Induces relaxation of hepatopancreatic sphincter

Question 57

1) Secretin is produced where and in response to what?
2) What does it do to the pancreas?
3) What does it do in regards to the liver?
4) What does it do to the stomach?

Answer 57

1) Secreted by enteroendocrine cells of the duodenum in response to acidic chyme from the stomach
2) Stimulates pancreas to secrete bicarbonate-rich juice
3) Stimulates liver to produce more bile
4) Inhibits stomach

Question 58

1) What does the liver secrete?
2) What does the falciform ligament separate?
3) What did the round ligament use to be?

Answer 58

1) Bile (contributes to digestion)
2) The left and right lobes of the liver anteriorly
3) The round ligament is a remnant of the fetal umbilical vein, which carries blood from umbilical cord to liver of the fetus

Question 59

Define in regards to the liver:
1) Hepatic lobules and triad
2) Hepatocytes
3) Hepatic sinusoids
4) Hepatic macrophages

Answer 59

1) Hepatic lobules: microscopic hexagonal shaped lobules of the liver. There’s a triad at each of the 6 corners that contains a branch of hepatic artery, a branch of hepatic portal vein, and bile ductules.
2) Hepatocytes (cuboidal) arranged around a central vein
3) Hepatic sinusoids: blood-filled channels that fill spaces between the plates
4) Hepatic macrophages: phagocytic cells in sinusoids that remove bacteria and debris from the blood

Question 60

What are major functions of hepatocytes? Include what substances are secreted into the blood that were made by the liver

Answer 60

1) After a meal, hepatocytes absorb from the blood: glucose, amino acids, iron, vitamins, and other nutrients for metabolism or storage
2) Between meals, hepatocytes break down stored glycogen and release glucose into the blood
3) Remove and degrade: hormones, toxins, bile pigments, and drugs
4) Secrete into the blood: albumin, lipoproteins, clotting factors, angiotensinogen, and other products

Question 61

1) The right and left hepatic ducts merge to form which duct?
2) Which two ducts merge to form the bile duct?
3) Which two ducts merge at the hepatopancreatic sphincter?

Answer 61

1) Common hepatic duct
2) Common hepatic duct and cystic duct form bile duct
3) Bile duct and pancreatic duct merge

Question 62

A) The gallbladder is a pear-shaped sac on the underside of the liver that does what?
B) What are the two parts of the gallbladder?

Answer 62

A) Serves to store and concentrate bile by absorbing water and electrolytes
B) 2 parts:
1) Head (fundus) usually projects slightly beyond inferior margin of liver
2) Neck (cervix) leads into the cystic duct

Question 63

What two categories of things does bile contain? Describe them

Answer 63

1) Contains waste products: Bilirubin, cholesterol, triglycerides and ions
2) Contains digestive products called bile acids/salts from cholesterol derivatives from the emulsification of fat

Question 64

1) What do bile salts help with?
2) What happens to most of the bile acid, is it excreted or reabsorbed?

Answer 64

1) Bile salts aid in fat and cholesterol absorption and help dissolve cholesterol
2) 80% of bile is reabsorbed, 20% is secreted

Question 65

1) What is the endocrine function of the pancreas?
2) What is the exocrine function of the pancreas?
3) What release their secretions into small ducts that converge on the main pancreatic duct?
4) What enzymes does the pancreas produce?

Answer 65

1) Endocrine: secretion of insulin and glucagon
2) Exocrine: secretion of 1,200 to 1,500 mL of pancreatic juice per day
3) Acini release their secretion into small ducts
4) Pancreatic enzymes: amylase, lipase, ribonuclease and deoxyribonuclease, trypsinogen, chymotrypsinogen, procarboxypeptidase

Question 66

1) Why does the pancreas produce sodium bicarbonate?
2) What is the purpose of the accessory duct?
3) What enzyme activates chymotrypsinogen and procarboxypeptidase?

Answer 66

1) Pancreatic juice is alkaline because it contains sodium bicarbonate to neutralize the acidic chyme
2) To be a backup for the main pancreatic duct and prevent a buildup of pressure
3) Trypsin activates chymotrypsinogen and procarboxypeptidase

Question 67

Where does nearly all chemical digestion and nutrient absorption occur?

Answer 67

In the small intestine

Question 68

1) What are the three regions of the small intestine in order?
2) What valve leads into the beginning of the small intestine?
3) What takes place in the duodenum in terms of chemical digestion?
4) What is inactivated in the duodenum?
5) What other mechanical digestion occurs in the duodenum?

Answer 68

1) Duodenum, jejunum, and ilium
2) The pyloric sphincter leads to the duodenum
3) Chemical digestion in the duodenum: Stomach acid is neutralized here because of the bicarbonate-rich mucus of the duodenal cells, which allows pancreatic enzymes to perform chemical digestion
4) Pepsin is inactivated due to increased pH
5) Fats are physically broken up (emulsified) by bile acids

Question 69

1) What actual portion of the small intestine provides the most digestion and nutrient absorption?
2) What are Peyer patches?
3) What valve regulates passage into the large intestine?
4) What tissue lines the lumen of the small intestines?

Answer 69

1) Jejunum
2) Prominent lymphatic nodules
3) Ileocecal valve
4) Simple columnar epithelium

Question 70

What three structures create the large internal surface area of the small intestines? Describe how much each affects the surface area.

Answer 70

1) Circular folds (plicae circulares): increase surface area by a factor of 2 to 3
2) Villi: increase surface area by a factor of 10
3) Microvilli: increase surface area by a factor of 20

Question 71

1) Where do the circular folds occur and what do they promote?
2) What two kinds of epithelial cells cover the finger-like projections of the small intestine?
3) What is the brush border made of and what does it do to surface area?

Answer 71

1) Circular folds occur from duodenum to middle of ileum and promote more thorough mixing and nutrient absorption because they cause chyme flow in spiral path causing more contact with mucosa
2) Villi are finger-like projections that are made of absorptive cells and goblet cells joined by tight junctions
3) Made of microvilli on the apical surface of each absorptive cell, they increase surface area.

Question 72

1) What do microvilli contain?
2) What is the purpose of the brush border enzymes?
3) Can you explain what is meant by “contact digestion”?

Answer 72

1) The plasma membrane of microvilli contains brush border enzymes
2) Brush border enzymes carry out some of the final stages of enzymatic digestion; they aren’t released into the lumen, instead, they require contact through intestinal churning.
3) Contact digestion: chyme must contact the brush border for digestion to occur

Question 73

1) What are intestinal crypts?
2) What is their purpose?
3) Is the fluid produced by the intestinal crypts enzyme rich?

Answer 73

1) They’re numerous pores of glands on the floor of the small intestine between bases of the villi
2) They secrete 1 to 2 L of alkaline intestinal juice (water, mucus, little enzyme)
3) No; the pancreas provides the enzymes

Question 74

What 3 purposes are associated with the contractions of the small intestines?

Answer 74

1) To mix chyme with intestinal juice, bile, and pancreatic juice
2) To churn chyme and bring it in contact with the mucosa for contact digestion and nutrient absorption
3) To move residue toward large intestine

Question 75

Can you explain the difference between segmentation and peristalsis?

Answer 75

1) Segmentation: Movement in which stationary ring-like constrictions appear in several places along the intestine; rhythm is set by pacemaker cells.
-Purpose is to churn.
2) Peristalsis: Moving contractions that involve the migrating motor complex
-Purpose is to move things along the tract.

Question 76

1) What is the purpose of pacemaker cells?
2) What is the purpose of the migrating motor complex?
3) When does peristalsis begin in the small intestines?

Answer 76

1) Pacemaker cells: Set the rhythm of segmentation (faster in duodenum and slower in ilium).
2) Migrating motor complex: Successive, overlapping waves of contraction that milk chyme toward colon, involved with peristalsis
3) When most nutrients have been absorbed segmentation declines and peristalsis begins

Question 77

1) Is the ileocecal valve normally open or closed?
2) What triggers the change in the valve?
3) Why does the cecum promote one-way flow?

Answer 77

1) Normally closed
2) Food in stomach triggers gastroileal reflex that enhances segmentation in the ileum and relaxes the valve
3) As cecum fills with residue, pressure pinches the ileocecal valve shut

Question 78

1) Where does starch digestion start and using what enzyme produced by what gland?
2) When does that initial enzyme get denatured and digested?
3) What resumes carbohydrate digestion in the small intestines?

Answer 78

1) Starts in the oral cavity with amylase produced by the salivary glands
2) Amylase gets denatured in the stomach by acid and digested
3) Pancreatic amylase resumes carbohydrate digestion in the small intestines

Question 79

1) Which 3 brush border enzymes are involved in carbohydrate digestion?
2) What cells are used to absorb the monosaccharides into the blood?
3) What structure houses these blood capillaries that take up monosaccharides?

Answer 79

1) Maltase, sucrase, and lactase are brush border enzymes that continue carbohydrate digestion
2) Absorptive cells’ plasma membranes take up monosaccharides into blood
3) The villus contains capillaries that take up monosaccharides

Question 80

What are the three protein sources for amino acids?

Answer 80

1) Dietary proteins
2) Digestive enzymes digested by each other
3) Sloughed epithelial cells digested by enzymes

Question 81

1) Where does protein digestion start and with what enzyme?
2) When is this enzyme inactivated? What takes over the process after?
3) What cells are used to absorb the amino acids into the blood? What structure houses these blood capillaries?

Answer 81

1) In the stomach with pepsin
2) It continues in the small intestine until it is inactivated by pancreatic juice’s high pH. Pancreatic enzymes trypsin and chymotrypsin take over, and brush border enzymes finish the task.
3) Intestinal epithelial cells absorb amino acids into blood capillaries in the villus

Question 82

1) What is used to emulsify fats and why is this needed?
2) After the first step, is fat hydrolysis, what enzyme digests fats?
3) What two sources combined will digest only 10 to 15% of lipids?

Answer 82

1) Fat is emulsified by vigorous muscular contractions of stomach and small intestines and the bile salts/acids released by liver and gallbladder
2) Pancreatic lipase breaks down triglyceride to monoglyceride and two free fatty acids
3) Lingual lipase and gastric lipase digest 10-15% before reaching the duodenum

Question 83

1) What are micelles?
2) What do they do?
3) Are micelles reusable?

Answer 83

1) Micelles: Fatty acids, monoglycerides, fat-soluble vitamins and other lipids coated by bile acids to allow for absorption
2) Micelles transport lipids to the surface of the intestinal absorptive cells. Lipids leave the micelles and diffuse through the plasma membrane into the cells
3) Micelles are reused, picking up another cargo of lipid, transporting them to the absorptive cells

Question 84

1) What happens after the lipids from the micelles is released?
2) What is resynthesized?
3) They get coated with a protein-coated film to form droplets called what?

Answer 84

1) Lipids leave the micelles and diffuse through the plasma membrane into the cells
2) Within the intestinal cell, triglycerides are resynthesized in the smooth ER
3) Golgi complex coats the triglycerides with phospholipids and protein to form chylomicrons

Question 85

1) If the protein-coated structure is too large to penetrate the endothelium of blood capillaries, they are taken up by what? Use an example.
2) How does this enter the bloodstream?

Answer 85

1) Chylomicrons (lipid digestion) are packaged into secretory vesicles that leave via exocytosis and are taken up by lacteal into lymph.
2) They enter the bloodstream when lymphatic fluid enters the subclavian vein via the thoracic duct.

Question 86

1) What enzyme digests nucleic acids? What is the source of the enzyme?
2) What enzymes complete their digestion?
3) What structure houses these blood capillaries?

Answer 86

1) Digestion occurs in small intestines with pancreatic nucleases
2) Brush border enzymes (nucleosidases and phosphatases) further split them of into phosphate ions, ribose or deoxyribose sugar, and nitrogenous bases
3) Absorbed by blood capillaries in the villus

Question 87

1) Do vitamins have to be digested to be absorbed?
2) What happens if the fat-soluble vitamins A, D, E, and K are ingested without fat-containing food, what happens to them?
3) How are minerals absorbed?

Answer 87

1) No, vitamins can be absorbed unchanged
2) Then they are not absorbed at all, but are passed in the feces (use micelles, chylomicrons, and lacteals)
3) All along small intestine by blood capillaries; iron and calcium absorbed as needed

Question 88

1) How is water absorbed?
2) When does diarrhea occur?
3) When does constipation occur?

Answer 88

1) Absorbed by osmosis following the absorption of salts and organic nutrients
2) When large intestine absorbs too little water
3) When fecal movement is slow, too much water gets reabsorbed, and feces become hardened

Question 89

1) What are the four regions of the large intestine?
2) The large intestine begins with what structure?
3) Where is the appendix, and what is it a source of?

Answer 89

1) Ascending colon, transverse colon, descending colon, sigmoid colon
2) Begins with the cecum
3) Attached to the lower end of the cecum; contains lymphocytes

Question 90

1) Define defecation.
2) How much residue is received per day?
3) How much is actually eliminated as feces?

Answer 90

1) Defecation: The elimination of feces
2) Large intestine receives about 500 mL of indigestible residue per day
3) Reduces it to about 150 mL of feces by absorbing water and salts

Question 91

1) What flexure is next after the ascending colon?
2) After the transverse colon, what is the name of the next flexure?
3) What is the S-shaped portion of the colon called?

Answer 91

1) Right colic (hepatic) flexure
2) Left colic (splenic) flexure
3) S-shaped: Sigmoid colon.

Question 92

The ______ has three infoldings called transverse rectal folds (rectal valves), which allow what?

Answer 92

rectum; enables it to retain feces while passing gas

Question 93

1) What is the taenia coli?
2) What is the haustra?

Answer 93

1)Taenia coli: longitudinal fibers concentrated in three thickened, ribbon-like strips, part of large intestine muscularis externa
2) Haustra: pouches in the colon caused by the muscle tone of the taenia coli, part of large intestine muscularis externa

Question 94

1) The anus, like the urethra, is regulated by two sphincters.
2) What are these two sphincters and what are they composed of? Are they voluntary or involuntary?

Answer 94

1) Internal anal sphincter: smooth muscle, involuntary
2) External anal sphincter: skeletal muscle, voluntary

Question 95

In terms of microscopic anatomy, the mucosa of the large intestine has a ______ _________ epithelium in all regions except the lower half of the anal canal, where it has what type of tissue?

Answer 95

-simple columnar epithelium
-Nonkeratinized stratified squamous epithelium

Question 96

1) In terms of microscopic anatomy, what type of cells are seen in the intestinal crypts? What is their purpose?
2) Why would the lamina propria and submucosa have an abundance of lymphatic tissue?

Answer 96

1) Intestinal crypts have a high density of mucus-secreting goblet cells
2) Provides protection from large population of bacteria in large intestine

Question 97

1) What is the gut microbiome?
2) What vitamins do they synthesize?
3) How long does it take the large intestine reduce the residue of a meal to feces?
4) Does the large intestine change the chemical composition of the residue?

Answer 97

1) About 800 species of bacteria that populate the large intestine and digest cellulose, pectin, and other carbohydrates for which our cells lack enzymes
2) Vitamins B and K
3) Large intestine takes about 36 to 48 hours to reduce residue of a meal to feces; most time in transverse colon
4) Does not chemically change the residue

Question 98

1) What absorption can occur in the large intestine?
2) What does feces consist of?

Answer 98

1) Absorbs water and electrolytes
2) Feces consist of about 75% water and 25% solids
-Solids: bacteria, undigested fiber, fat, small amount of mucus, proteins, salts, digestive secretions, and sloughed epithelial cells

Question 99

1) How often do haustral contractions occur?
2) What two reflexes trigger the mass movements seen one to three times a day? What are mass movements?

Answer 99

1) Every 30 minutes
2) Mass movements triggered by: Gastrocolic and duodenocolic reflexes; filling of the stomach and duodenum stimulates motility of the colon, move residue several centimeters

Question 100

1) What gets stretched to stimulate the defecation reflexes?
2) Which reflex (intrinsic or parasympathetic) involves the spinal cord?
3) Explain how it works.

Answer 100

1) Stretching of rectum stimulates intrinsic defecation reflex and parasympathetic defecation reflex.
2) Parasympathetic defecation reflex involves spinal cord
3) Stretching of rectum sends sensory signals to spinal cord, then parasympathetic nerves produce peristalsis of rectum and relaxation of the internal anal sphincter

Question 101

1) Which defecation reflex (intrinsic or parasympathetic) produces a weak response?
2) Explain how it works.

Answer 101

1) Intrinsic defecation reflex produces relatively weak response
2) Stretch signals travel to the muscularis, causing it to contract and the internal sphincter to relax