Gastroenterology Flashcards
(244 cards)
1
Q
What is the primary function of the digestive system?
A
Transfer nutrients, water, and electrolytes from ingested food into body’s internal environment
2
Q
What organs are included in the digestive tract?
A
Mouth, pharynx, esophagus, stomach, small intestine, large intestine, and anus
3
Q
What are 4 accessory organs of the digestive tract?
A
Teeth, salivary glands, liver, and pancreas
4
Q
What are the 4 digestive processes?
A
1) Digestion
2) Absorption
3) Motility
4) Secretion
5
Q
What is digestion?
A
The biochemical breakdown of structurally complex food into smaller, absorbable units
6
Q
How is digestion accomplished?
A
By enzymatic hydrolysis
7
Q
What can be absorbed from carbohydrates?
A
Monosaccharides
8
Q
What can be absorbed from proteins?
A
Amino acids
9
Q
What can be absorbed from fats?
A
Glycerol and fatty acids
10
Q
What is absorption?
A
When small units resulting form digestion, along with water, vitamins, and electrolytes are transferred from digestive tract lumen to enterocytes of villi to blood or lymph
11
Q
What is motility?
A
Muscular contractions that mix and move forward he contents of the digestive tract
12
Q
What is peristalsis?
A
Propulsive movements that push contents forward through the digestive tract
13
Q
What are segmentation and churning?
A
Mixing movements
14
Q
What are the 2 functions of segmentation and churning?
A
1) Mixing food with digestive juices to promote digestion
2) Facilitate absorption by exposing all parts of intestinal contents to absorbing surfaces of digestive tract
15
Q
What 3 substances are commonly secreted?
A
Water, electrolytes, and digestive juices
16
Q
Where are secretions released?
A
Into digestive tract lumen
17
Q
What causes secretion?
A
Appropriate neural or hormonal stimulation
18
Q
True or false: most secretions are reabsorbed in one form or another back into blood after their participation in digestion
A
True
19
Q
True or false: digestive system regulates uptake
A
False, it does not
20
Q
What percent of ingested food is made available for the body to use?
A
95%
21
Q
What are 4 regulators of digestive motility and secretion?
A
1) Autonomous smooth muscle function
2) Intrinsic nerve plexuses
3) Extrinsic nerves
4) Gastrointestinal hormones
22
Q
What do autonomous smooth muscle produce?
A
Self-induced electrical activity (slow-wave potentials)
23
Q
What are slow-wave potentials?
A
- Not action potentials
- Bring the membrane closer and further to threshold
24
Q
True or false: when food is present in the digestive tract, membranes are further from threshold than normal
A
False, membranes are closer to threshold
25
What are the 2 networks of nerve fibres that lie within the digestive tract wall?
1) Submucosal plexus
| 2) Myenteric plexus
26
What is a collective term for the submucosal plexus and myenteric plexus?
Enteric nervous system
27
What does the enteric nervous system allow for?
Self-regulation
28
What are extrinsic nerves?
Nerve fibres from both branches of the ANS
29
What effect does the sympathetic nervous system have on digestion?
Inhibits digestion
30
What effect does the parasympathetic nervous system have on digestion?
Stimulates digestion
31
What are 3 functions of extrinsic nerves on digestion?
1) Influence digestive tract motility and secretion
2) Modify activity of the enteric nervous system
3) Alter the level of hormone secretion
32
What is another term for chewing?
Mastication
33
What is the first step in the digestive process?
Chewing
34
What is chewing?
Grinding and breaking food into smaller pieces to make swallowing easier and increase food surface area for salivary enzymes to act on
35
What produces saliva?
3 major pairs of salivary glands
36
What percent of saliva is water?
99.5%
37
What percent of saliva is electrolytes and protein?
0.5%
38
How much saliva is secreted per day?
1 - 1.5 L per day
39
What are 7 functions of saliva?
1) Salivary amylase begins digestion of carbohydrates
2) Facilitates swallowing by moistening food
3) Mucus provides lubrication
4) Antibacterial action
5) Solvent for molecules that stimulate taste buds
6) Aids speech by facilitating movement of lips and tongue
7) Rich in bicarbonate buffers
40
What are some antibacterial actions of saliva?
- Lysozyme destroys bacteria
| - Saliva rinses away material that could serve as food source for bacteria
41
What is the parasympathetic effect on saliva?
Stimulates secretion of an abundant amount of thin, enzyme rich saliva
42
What is the sympathetic effect on saliva?
Decreases volume of saliva
43
What happens to the mouth when the SNS has a higher dominance?
Mouth is drier than usual
44
Why are saliva and gastric juice not essential for digesting and absorbing foods?
Because enzymes produced by the pancreas and small intestine can complete food digestion
45
What is the only digestive secretion that is entirely under neural control?
Salivary secretion
46
What are all digestive secretions (except salivary secretion) regulated by?
Nervous system reflexes and hormones
47
True or false: there is no absorption in the mouth
True
48
Swallowing occurs in __ phases
3
49
What are the 3 phases of swallowing?
1) Buccal phase
2) Pharyngeal phase
3) Esophageal phase
50
Is the buccal phase voluntary or involuntary?
Voluntary
51
What occurs in the buccal phase?
Food is compacted by the tongue into bolus and moves to the pharynx by tongue pressing on hard palate
52
Is the pharyngeal phase voluntary or involuntary?
Involuntary
53
Is the esophageal phase voluntary or involuntary?
Involuntary
54
True or false: the pharyngeal phase is an all-or-none reflex
True
55
What initiates the swallowing reflex?
Swallowing center in the medulla
56
What is the function of the pharyngoesophageal sphincter?
Keeps the entrance to the esophagus closed to prevent air entrance during respiration
57
What is the function of the gastroesophageal sphincter?
Maintains barrier between stomach and esophagus preventing gastric reflux
58
What occurs in the esophageal phase?
Food moves down esophagus by peristalsis
59
What type of neurons control the upper 1/3 of the esophagus?
Somatic motor neurons to skeletal muscle
60
What type of neurons control the lower 1/3 of the esophagus?
Parasympathetic NS (vagus nerve) to smooth muscle
61
What type of neurons control the middle 1/3 of the esophagus?
A mixture of somatic motor neurons and the vagus nerve
62
What happens if a large or sticky piece of food is swallowed and gets stuck?
- Esophagus distends stimulating pressure receptors
| - A second, more forceful, wave is initiated by the intrinsic nerve plexus
63
What are the mechanisms in the different part of the mouth/esophagus that prevent food from entering while swallowing?
- Mouth -- tongue on hard palate
- Nasopharynx -- uvula, soft palate elevated
- Trachea -- epiglottis
64
Esophageal (mucous) secretions are ______
Protective
65
What do esophageal secretions do?
Reduce the likelihood of damage by sharp edges
66
What is the stomach?
J-shaped sac-like chamber lying between esophagus and small intestine
67
What are the 3 sections of the stomach?
1) Fundus
2) Body
3) Antrum
68
What is the function of the pyloric sphincter?
Serves as barrier between stomach and upper part of small intestine
69
What are the 3 main functions of the stomach?
1) Store ingested food until it can be emptied into the small intestine
2) Secrete HCl and enzymes that begin protein digestion
3) Mixing movements convert pulverized food to chyme
70
What does gastric filling involve?
Receptive relaxation
71
What is receptive relaxation?
Smooth muscle relaxes to accommodate the extra volume of food
72
What triggers gastric filling?
Act of eating
73
Where does gastric storage take place?
In body of stomach
74
What occurs in gastric storage?
Carbs are broken down by salivary amylase and gastric mixing takes place in antrum
75
What controls gastric emptying?
Factors in the duodenum
76
What are 4 factors in the duodenum that delay the rate of gastric emptying?
1) Fat
2) Acid
3) Hypertonicity
4) Distension
77
How does fat delay the rate of gastric emptying?
- Fat digestion and absorption takes place only within lumen of small intestine
- When fat is already in duodenum, further gastric emptying of additional fatty stomach contents is prevented
78
How long will fatty meals remain in the stomach?
About 6 hours
79
How long will a meal of lean meat and potatoes remain in the stomach?
3 hours
80
How does acid delay the rate of gastric emptying?
Unneutralized acid in duodenum inhibits further emptying of acidic gastric contents until neutralization can be accomplished by sodium bicarbonate
81
Why does acid delay the rate of gastric emptying?
To prevent damage (duodenal peptic ulcers) and to allow pancreatic enzymes to function
82
How does hypertonicity delay the rate of gastric emptying?
Osmolarity of duodenal contents begins to rise as molecules of protein and starch are digested in the duodenal lumen, causing lots of amino acids and glucose to be released
83
What does osmolarity depend on?
The number of molecules present, not on their size
84
How does distension delay the rate of gastric emptying?
Too much chyme in duodenum inhibits emptying of gastric contents
85
What are 2 factors that regulate gastric motility and secretion?
1) Neural response
| 2) Hormonal response
86
How is gastric motility and secretion regulated neurally?
Through intrinsic nerve plexuses and autonomic nerves; collectively called enterogastric reflex
87
How is gastric motility and secretion regulated hormonally?
Through the release of hormones from duodenal mucosa collectively known as enterogastrones
88
What are the 2 most important hormones in the regulation of gastric motility and secretion?
1) Secretin
| 2) Cholecystokinin (CCK)
89
What is gastric dumping syndrome?
Rapid emptying
90
When does early gastric dumping syndrome occur and what are the symptoms?
- During or right after a meal
| - Symptoms -- nausea, vomiting, bloating, diarrhea, dizziness, fatigue
91
When does late gastric dumping syndrome occur and what are the symptoms?
- 1-3 hours post-meal
| - Symptoms -- weakness, sweating, and dizziness
92
True or false: it is uncommon for people to have early and late gastric dumping syndrome
False, it is very common
93
What are some treatments for gastric dumping syndrome?
- Adjust eating habits (avoid certain foods)
- Medications to slow digestion
- Surgery as a last resort
94
What are 3 types of gastric exocrine secretory cells?
1) Parietal cells
2) Chief cells
3) Mucous cells
95
What do parietal cells secrete?
HCl and intrinsic factor
96
What is the importance of the intrinsic factor of parietal cells?
Vitamin B12 can be absorbed only when bound to intrinsic factor; vitamin B12 is essential for formation of RBCs
97
What does HCl do?
Denatures proteins -- causes them to lose their tertiary and secondary structure, allowing digestive enzymes o break down the amino acid chains
98
True or false: HCl kills most of the microorganisms ingested with food
True
99
What does HCl act on?
Pepsinogen
100
What do chief cells secrete?
Pepsinogen
101
What does HCl change pepsinogen into?
Pepsin
102
What does pepsin do?
Turns proteins in small amino acid chains
103
What do mucous cells secrete?
Mucous
104
What is the function of mucous?
Acts as a lubricant and prevents mechanical injury
105
Stomach is protected from self-digestion by ______
Alkaline mucous
106
True or false: mucous cells are replaced about every 3 months
False, they are replaced very rapidly and a new cell lining appears every 3 days
107
What happens if the mucous barrier is broken?
The gastric wall is injured, resulting in a gastric peptic ulcer
108
What does the cephalic phase refer to?
Increased secretion of HCl and pepsinogen that occurs in response to stimuli acting in the head before food reaches the stomach
109
When does the gastric phase begin?
When food actually reaches the stomach; presence of protein increases gastric secretions
110
The intestinal phase is the ______ phase
Inhibitory
111
What is the function of the intestinal phase?
Helps shut off flow of gastric juices as chyme begins to empty into small intestine
112
What are the 3 regulatory phases?
1) Cephalic phase
113
What occurs in the cephalic phase?
Stomach is prepared for food
114
What is the pH of the stomach when it is nearly empty?
3
115
What happens when the pH of the stomach dips below 3?
NS shuts off, causing decreased acid and gastrin decreases, causing decreased acid
116
Does gastrin secretion increase or decrease initially in the intestinal phase?
Increases
117
During the intestinal phase, what do inhibitory signals cause?
- Decreased gastric motility
| - Decreased gastric secretion
118
What causes decreased gastric motility?
1) CCK that is released due to presence of fatty and amino acids
2) Enterogastric reflex
119
What triggers the enterogastric reflex?
- Amino acids/peptides
- Acid
- Duodenal stretch
- Hypertonicity
120
What causes decreased gastric secretion?
1) Secretin released due to acid
| 2) CCK released due to fatty and amino acids
121
Where can ethyl alcohol be absorbed the most quickly?
By the small intestine mucosa
122
What effect does gastric emptying have on absorption?
It slows it
123
What is the small intestine the site of?
Most digestion and absorption
124
What are the 3 segments of the small intestine?
1) Duodenum
2) Jejunum
3) Ileum
125
What does motility of the small intestine include?
- Segmentation
| - Migrating motility complex
126
What is the primary method of motility in the small intestine?
Segmentation
127
What does segmentation consist of in the small intestine?
Ring-like contractions along the length of the small intestine
128
What does segmentation action do?
Mixes chyme throughout small intestine lumen
129
How is segmentation initiated?
By pacemaker cells in small intestine which produce basic electrical rhythm
130
How is segmentation controlled?
Circular smooth muscle responsiveness is influenced by distension of intestine, gastrin, and extrinsic nerve activity
131
What are 2 functions of segmentation?
1) Mixing chyme with digestive juices into small intestine lumen
2) Exposing all chyme to absorptive surfaces of small intestine mucosa
3) Slowly move chyme through digestive tract
132
The frequency of segmentation _______ along the length of the small intestine
Declines
133
How long does it take food to get through the small intestine?
3-5 hours
134
What happens when most of the meal has been absorbed?
Segmentation contractions cease and are replaced by migrating motility complex
135
What is migrating motility complex?
Slow, weak peristaltic waves
136
What is the function of migrating motility complex?
Sweeps intestines clean between meals
137
The pancreas is a mixture of ____ and ______ tissue
Exocrine and endocrine
138
Where is the pancreas located?
Behind and below the stomach
139
What is the endocrine function of the pancreas?
Islets of Langerhans found throughout the pancreas secrete insulin and glucagon
140
What are 2 exocrine functions of the pancreas?
1) 3 different pancreatic enzymes actively secreted by acinar cells that form the acini
2) Aqueous alkaline solution actively secreted by duct cells that line pancreatic ducts (contains sodium bicarbonate)
141
What are the 3 exocrine steps of digestion?
1) Neutralize acid
2) Pancreatic enzymes
3) Intestinal wall
142
Why must stomach acid be neutralized?
So pancreatic enzymes can work
143
How is stomach acid neutralized?
Secretin secretion is increased, which causes increased bicarbonate and decreased gastric acid secretion
144
Where is alkaline fluid secreted from?
Duct cells of pancreas and gall bladder
145
Describe the process of carbohydrate breakdown
Polysaccharides are broken down into disaccharies by pancreatic amylase
146
Is amylase secreted in an active or inactive form, and why?
Active form so that it doesn't endanger the secretory cells
147
Describe the process of protein breakdown (3 pathways)
1) Trypsinogen is broken down into trypsin by enteropeptidase on intestinal wall
2) Chymotrypsinogen is broken into chymotrypsin
3) Procarboxypeptidase is broke into carboxypeptidase
148
Where are pancreatic enzymes secreted?
Into intestinal lumen from pancreatic acinar cells
149
What does proteases do?
Breaks down dietary protein into peptides and amino acids
150
What is special about pancreatic lipase?
Only enzyme secreted throughout the entire digestive system that can digest fat
151
What does pancreatic lipase do?
Breaks triglycerides into fatty acids and monoglycerides
152
What happens when pancreatic enzymes are deficient?
Serious maldigestion of fats
153
What does the presence of fatty acids and amino acids in the duodenum cause?
Increased cholecystokinin (CCK)
154
True or false: carbs do not have any direct influence on pancreatic digestive enzyme secretion
True
155
What are 3 effects of CCK with respect to digestion?
1) Increases pancreatic enzyme secretion
2) Stimulates gallbladder contractions, causing release of bile
3) Decreases gastric motility (slows emptying) and decrease gastric secretions
156
True or false: small intestine secretions do not contain any digestive enzymes, they are mostly salt and mucous solutions
True
157
What occurs in the intestinal wall during digestion?
Synthesized enzymes act within brush-border membrane of epithelial cells to complete digestion of carbs and proteins
158
Which 3 synthesized enzymes act on the intestinal wall during digestion?
1) Disaccharidases
2) Enterokinase
3) Aminopeptidases
159
What does disaccharidases do?
Breaks down disaccharides into monosaccharides
160
What breaks down glucose and what does it produce?
- Sucrase
| - Produces glucose and fructose
161
What breaks down maltose and what does it produce?
- Maltase
| - Produces 2 glucose molecules
162
What breaks down lactose and what does it produce?
- Lactase
| - Produces glucose and galactose
163
What causes lactose deficiency?
Lactose intolerance -- lactose remains undigested and therefore bacteria in large intestine ferment the lactose into gas, which is why cramping and diarrhea are symptoms
164
What does aminopeptidases do?
Breaks peptides into smaller peptides and amino acids
165
True or false: there is no digestion of lipids in the large intestine
True
166
Where is fat digested and how?
Entirely in small intestine lumen by pancreatic lipase
167
What does the small intestine absorb?
- All products of carb, protein, and fat digestion
| - Most ingested electrolytes, vitamins, and water
168
Where does most absorption of the small intestine occur?
In duodenum and jejunum
169
True or false: the more food consumed the less that will be digested and absorbed
False, more food consumed = more digested and absorbed
170
Absorption of ___ and ____ are adjusted to the body's needs
Calcium and iron
171
True or false: the small intestine absorbs almost everything presented to it
True
172
Why is the small intestine the main site of absorption?
1) Large surface area
| 2) Nutrients are small molecules
173
Why does the small intestine have such a large surface area?
Because of folds, villi and microvilli
174
How often does the lining of the small intestine replace itself and why?
- About every 3 days
| - Because of the harsh environment
175
True or false: small intestine cells can withstand radiation and anti-cancer drugs
False, they are very sensitive to it
176
What can cause malabsorption in the small intestine?
Damage to or reduction of the surface area
177
What does absorption of the broken down carbs and proteins involve?
Carrier-mediated secondary active transport mechanisms
178
What are end products of carb and protein digestion absorbed into?
Blood
179
Are fats absorbed into the blood and why?
No because they aren't water soluble
180
How do glucose and galactose enter enterocytes?
Secondary active transport
181
How do glucose and galactose leave enterocytes?
Facilitated transport
182
How does fructose enter enterocytes?
Facilitated transport
183
How does fructose leave enterocytes?
Facilitated transport
184
How do amino acids enter enterocytes?
Secondary active transport
185
How do amino acids leave enterocytes?
Facilitated transport
186
How do di and tripeptides enter enterocytes?
Secondary active transport
187
What happens to di and tripeptides when they enter enterocytes?
Converted to amino acids by cytosolic enzymes
188
How do monoglycerides and long fatty acids enter enterocytes?
Diffusion
189
How do monoglycerides and long fatty acids leave enterocytes?
Exocytosis from enterocyte, diffusion into lymph lacteal
190
How do short fatty acids enter enterocytes?
Diffusion
191
How do short fatty acids leave enterocytes?
Diffusion into blood
192
How does water enter enterocytes?
Osmosis
193
How does water leave enterocytes?
Osmosis into blood and lymph
194
How much water is ingested from food and drink per day?
About 2000 mL
195
How much water is absorbed in the small intestine from secretions per day?
About 7000 mL
196
Where do absorbed nutrients go?
1) Liver
| 2) Lacteals (lymph)
197
How do absorbed nutrients enter the liver?
Via hepatic portal vein
198
How do absorbed nutrients enter lacteals?
Via thoracic duct which goes into left subclavian vein
199
What does fat digestion and absorption require and where does this come from?
Requires bile from liver and gall bladder
200
The liver _____ bile
Synthesizes
201
The gall bladder _____ bile
Stores
202
What is the most important metabolic organ in the body?
Liver
203
Why is the liver important to digestive system?
Secretes bile salts
204
What are 6 functions of the liver that ARE NOT related to digestion?
1) Metabolic processing of nutrients
2) Detoxifying or degrading body wastes and foreign compounds
3) Synthesizes plasma proteins
4) Stores glycogen, fats, iron, copper, and many vitamins
5) Activates vitamin D
6) Excretes cholesterol and bilirubin
205
What performs the functions of the liver that are not related to digestion?
Hepatocytes
206
What function is not accomplished by hepatocytes, and what cell performs this function?
- Removal of bacteria and worn-out RBCs
| - Kupffer cells
207
What does bile consist of?
Bile salts, cholesterol, lecithin and bilirubin, detoxified drugs, toxins, and hormones in an aqueous alkaline fluid
208
What does bile do AFTER a meal?
Enters duodenum
209
Describe the enterohepatic circulation
Bile salts in liver --> common bile duct --> stomach or gall bladder --> in stomach, sphincter of Oddi --> duodenum --> terminal ileum --> hepatic portal vein --> liver
210
Bile salts are derivatives of _____
Cholesterol
211
What are 2 functions of bile salts?
1) Convert large fat globules into a liquid emulsion
| 2) Micelle formation
212
True or false: after bile salts participate in fat digestion and absorption, most are excreted
False, most are reabsorbed into the blood
213
What does CCK do with respect to bile?
Stimulates contraction of the gall bladder and relaxation of the hepatopancreatic sphincter
214
How do bile salts form micelles?
Bile salts and lecithin aggreagate in small clusters with their fat-soluble parts huddled together in the middle to form a hydrophobic core while their water-soluble parts form an out hydrophilic shell
215
What is found within the core of bile salt micelles?
Products of fat digestion and fat-soluble vitamins
216
With respect to micelle formation, where does cholesterol dissolve?
In the core
217
What is the function of bilirubin?
Gives bile and urine their colour
218
True or false: some bilirubin is reabsorbed into the blood
True
219
What happens to bilirubin in the intestinal tract?
It is modified by bacteria, giving feces it's brown colour
220
What occurs in the lumen with respect to fat digestion and absorption?
- Lipid globule is converted to fatty acids and monoglycerides by emulsification and lipase
- Fatty acids and monoglycerides diffuse from micelle into enterocytes
221
What occurs in the enterocyte with respect to fat digestion and absorption?
- Monoglycerides and fatty acids are converted to diglycerides and fatty acid
- Diglycerides are converted to triglycerides
- Triglycerides are converted to a chylomicron with cholesterol, proteins, and phospholipids
- Chylomicron moves to interstitial by exocytosis, and then to lymph by diffusion
222
What primarily happens in the large intestine?
Drying and storage
223
What does the large intestine consist of?
- Colon
- Cecum
- Appendix
- Rectum
224
What does the large intestine receive from the small intestine?
Indigestible food residues, unabsorbed biliary components, and remaining fluid
225
Where is the ileococcal valve found?
Between ileum and large intestine
226
What surrounds the ileococcoal valve?
Thickened smooth muscle, the ileocecal sphincter
227
What does pressure on the cecal side do to the ileococcal valve?
Pushes it closed and contracts the sphincter, preventing the bacteria-laden colonic contents from contaminating the nutrient-rich small intestine
228
What does pressure on the ideal side do to the ileococcal valve?
Opens the valve/sphincter, allowing ileal contents to enter the large intestine and gastrin to be secreted
229
What causes the motility of the large intestine?
1) Haustral contractions
| 2) Mass movements
230
What are Haustral contractions?
- Main motility
| - Slow and weak contractions initiated by autonomous rhythmicity of colonic smooth muscle cells
231
What are mass movements?
Massive contractions mediated from stomach to colon by gastrin and autonomic nerves
232
What causes mass movements?
Food in the stomach (gastrocolic reflex)
233
What is the gastrocolic reflex?
Powerful waves of contractions from transverse colon to rectum
234
What stimulates the defecation reflex?
Feces in rectum
235
What part of the CNS is responsible for the defecation reflex?
Sacral segment of spinal cord (para NS)
236
What is the effect of the defecation reflex?
Smooth muscle of rectum contracts and internal anal sphincter relaxes
237
True or false: external anal sphincter is under voluntary control
True
238
True or false: no digestive enzymes are secreted into the large intestine
True
239
What is secreted into the large intestine?
- Alkaline mucous secretions
| - K and bicarbonate
240
What occurs in the large intestine?
Bacterial fermentation of undigested nutrients
241
How does the large intestine absorb water?
Osmosis
242
What 3 hormones are secreted from the stomach and duodenum?
1) Gastrin
2) Secretin
3) CCK
243
What is the function of gastrin?
Increases acid and gastric enzyme secretion
244
What is the function of secretin?
- Increases alkaline fluid secretion
| - Decrease gastric secretion
