1
Q
What is the gastrointestinal (GI) system?
A
A continuous series of hollow, muscular tubes extending from the mouth to the anus, where muscle movement and secretions enable digestion and absorption.
2
Q
What enables digestion and absorption in the GI system?
A
Muscle movements (motility) and the release of various secretions.
3
Q
List the organs/structures of the GI system.
A
Nasal passages
Mouth
Salivary glands
Esophagus
Liver
Stomach
Gallbladder
Pancreas
Small intestine
Colon
Rectum
Anus
4
Q
What is the primary role of the digestive system?
A
To transfer nutrients, water, and electrolytes from food and drinks into the body.
5
Q
Why is digestion essential for the body?
A
For ATP production and the renewal and growth of body tissues.
6
Q
What are the five stages of nutrient breakdown?
A
Ingestion, digestion, absorption, distribution, usage.
7
Q
What is ingestion?
A
The physical act of eating.
8
Q
What is digestion?
A
The breakdown of food into small, absorbable molecules.
9
Q
What is absorption?
A
Movement of nutrients from the digestive tract into the circulatory system.
10
Q
What is distribution?
A
Transport of nutrients through the circulatory system to tissues and cells.
11
Q
What is usage?
A
Movement of nutrients into cells for metabolism or anabolic processes.
12
Q
What are the four basic digestive processes?
A
Motility, secretion, digestion, absorption.
13
Q
What is motility?
A
Muscular contractions that mix and propel contents through the digestive system.
14
Q
What is the role of smooth muscle tone in the GI tract?
A
Maintains constant contraction to prevent overstretching and maintain pressure.
15
Q
What are propulsive movements?
A
Movements that push contents forward through the GI tract.
16
Q
What determines the rate of movement in the GI tract?
A
The segment of the digestive system and its function.
17
Q
What are mixing movements?
A
Movements that mix food with enzymes and promote absorption by increasing contact with GI walls.
18
Q
What do exocrine glands in the GI system do?
A
Secrete digestive juices into the lumen.
19
Q
What do digestive juices contain?
A
Water, electrolytes, enzymes, bile salts, and mucus.
20
Q
Where do secretory cells get materials to produce secretions?
A
From plasma.
21
Q
What triggers secretion release into the lumen?
A
Neural or hormonal signals.
22
Q
What happens to digestive secretions after use?
A
They are normally reabsorbed into the body.
23
Q
What is the role of endocrine cells in the GI tract?
A
They release hormones into the blood to regulate motility and secretion.
24
Q
What is digestion (biochemically)?
A
Enzymatic breakdown of complex food into small absorbable units.
25
What are the three main food groups digested?
Carbohydrates, proteins, fats.
26
What process do all digestive enzymes use?
Hydrolysis (adding water to break bonds).
27
In what forms are carbohydrates ingested?
Polysaccharides (starch, glycogen) and disaccharides (sucrose, lactose).
28
What are carbohydrates broken down into?
Monosaccharides (mainly glucose, also fructose and galactose).
29
Which carbohydrate form can be absorbed?
Only monosaccharides.
30
What are polysaccharides?
Complex carbohydrates made of many glucose molecules.
31
What are monosaccharides?
Simple sugars such as glucose.
32
In what form are dietary fats consumed?
Triglycerides.
33
What happens to triglycerides during digestion?
Two fatty acids are removed, forming free fatty acids and a monoglyceride.
34
What fat components are absorbed?
Free fatty acids and monoglycerides.
35
What are triglycerides?
Three fatty acids attached to a glycerol molecule.
36
What are dietary sources of protein?
Meats, legumes, eggs, grains, dairy.
37
What are proteins broken down into during digestion?
Amino acids and small polypeptides.
38
Where does most absorption occur?
The small intestine.
39
What substances are absorbed in the GI tract?
Nutrients, water, vitamins, and electrolytes.
40
Where do absorbed substances go?
Into the blood and lymph.
41
Which digestive organs or structures use skeletal muscle rather than smooth muscle to move the material within them?
The top of the esophagus, mouth, and external anal sphincter
42
From where to where does the digestive tract share the same wall structure?
From the esophagus to the anus.
43
How many major layers are in the digestive tract wall?
4
44
What are the four layers of the digestive tract wall?
Mucosa, submucosa, muscularis externa, serosa.
45
What is the mucosa?
The innermost layer lining the luminal surface.
46
What is a key structural feature of the mucosa?
It is highly folded to increase surface area (varies by location).
47
How does mucosal folding vary along the GI tract?
Esophagus: little folding
Small intestine: highest folding (for absorption)
48
What is the submucosa made of?
Thick connective tissue.
49
What are the functions of the submucosa?
Supports mucosa, provides distensibility and elasticity.
50
What structures are found in the submucosa?
Larger blood vessels, lymph vessels, and the submucosal plexus.
51
What is the submucosal plexus?
A network of nerves located in the submucosa.
52
What is the muscularis externa?
A smooth muscle layer surrounding the submucosa.
53
What are the two muscle layers in the muscularis externa?
Inner circular layer and outer longitudinal layer.
54
What happens when the circular layer contracts?
Decreases the lumen diameter.
55
What happens when the longitudinal layer contracts?
Shortens the digestive tube.
56
What is the combined function of both muscle layers?
Propulsive and mixing contractions.
57
What nerve network is located between the muscle layers?
The myenteric plexus.
58
What regulates local gut activity?
The myenteric plexus, along with hormones and local chemical mediators.
59
What is the serosa?
The outer connective tissue layer covering the digestive tract.
60
What is the serosa continuous with?
The mesentery (throughout most of the digestive tract).
61
What is the function of the mesentery?
Suspends digestive organs from the abdominal wall while allowing movement.
62
Why is movement of digestive organs important?
For mixing and propulsion of contents.
63
Two defining characteristics of submucosa
- It is made of connective tissues that support the mucosa
- It contains the submucosal plexus, which is a network of nerves
64
Two defining characteristics of serosa
- It is the outermost layer
- It is continuous with the mesentery
65
Two defining characteristics of mucosa
- The innermost layer
- The surface is highly folded to increase its surface area
66
Two defining characteristics of muscularis externa
- It is two layers of smooth muscle layer that surround the submucosa
- Both layers provide the propulsive and mixing contractions
67
Why are digestive motility and secretion regulated?
To maximize digestion and absorption of ingested food.
68
What are the four factors regulating digestive system function?
- Autonomous smooth muscle function
- Intrinsic nerve plexuses (ENS)
- Extrinsic autonomic nerves
- Gastrointestinal hormones
69
What is the ENS?
The intrinsic nerve plexuses of the digestive system.
70
What are the two intrinsic nerve plexuses?
Submucosal plexus and myenteric plexus.
71
What is the primary role of the ENS?
Self-regulation of digestive tract function.
72
Does the ENS function independently?
Mostly yes, but it receives significant input from the autonomic nervous system (ANS).
73
What functions is the ENS involved in?
All aspects of digestive tract function (motility and secretion).
74
What do sensory neurons in the ENS do?
Detect local stimuli within the digestive tract.
75
What do other ENS neurons innervate?
Smooth muscle cells, exocrine glands, and endocrine glands.
76
What is the role of interneurons in the ENS?
Connect neurons, similar to the CNS.
77
What are extrinsic autonomic nerves?
Sympathetic and parasympathetic nerve fibers that innervate digestive organs.
78
How does the ANS influence digestion?
- Modifies ENS activity
- Regulates GI hormone secretion
- Directly innervates smooth muscle and glands
79
What is the effect of the sympathetic system on digestion?
Slows contractions and secretions.
80
What is the effect of the parasympathetic system on digestion?
Increases smooth muscle contraction and promotes secretion.
81
What is unique about parasympathetic postganglionic fibers in the digestive system?
They are part of the intrinsic nervous system (ENS).
82
Where are gastrointestinal hormones produced?
Endocrine glands in the mucosa of the digestive tract.
83
How are GI hormones transported?
Through the blood to other parts of the digestive system.
84
What effects do GI hormones have?
Can be excitatory or inhibitory on motility and secretion.
85
Where else are GI hormones found?
In other parts of the body, including the brain.
86
What is the role of GI hormones in the brain?
Act as neurotransmitters and neuromodulators.
87
What special property do some smooth muscle cells have?
Pacemaker-like spontaneous rhythmic changes in membrane potential.
88
What are slow-wave potentials?
Rhythmic electrical activity in smooth muscle cells.
89
Where do slow-wave potentials originate?
Interstitial cells of Cajal (ICC).
90
Where are interstitial cells of Cajal located?
Between the circular and longitudinal muscle layers.
91
Do slow waves directly cause contractions?
No, they are not action potentials.
92
How does membrane potential behave in smooth muscle cells?
It oscillates toward and away from threshold.
93
When do contractions occur?
When slow waves reach threshold and trigger action potentials.
94
Why can smooth muscle contract as a unit?
Cells are connected by gap junctions, forming a functional syncytium.
95
What factors influence whether action potentials are triggered?
Mechanical, neural, and hormonal factors.
96
How do these factors affect contraction?
They shift membrane potential closer to or further from threshold.
97
What happens when membrane potential is closer to threshold?
Slow-wave peaks can trigger action potentials → contractions.
98
What happens to muscle activity when food is present in the digestive tract?
Increased activity for mixing and propulsion.
99
What would occur if a large piece of food was to get stuck in the esophagus?
If a large piece of food was to get stuck in the esophagus, sensory receptors within the enteric nervous system would detect this blockage. These sensory neurons would relay their signals to interneurons, which would coordinate a response in local motor neurons to induce contraction of smooth muscle cells, thus increasing motility to push food forward.
100
Beyond general sympathetic and parasympathetic effects, what else can the autonomic nervous system (ANS) do?
It can perform discrete (specific) activation to modify digestive activities.
101
What is the purpose of discrete activation of extrinsic innervation?
To coordinate activity between multiple regions of the digestive system.
102
Why is coordination between digestive regions important?
To prepare different organs for digestion and ensure efficient processing of food.
103
What happens during chewing in terms of autonomic regulation?
It reflexively activates digestive secretions in multiple organs.
104
Which secretions are stimulated during chewing?
Salivary enzymes
Stomach secretions
Pancreatic secretions
Liver secretions
105
What type of reflex coordinates these secretions during chewing?
Vagal reflexes.
106
What is the purpose of activating these secretions during chewing?
To prepare the digestive system for the arrival of food.
107
What is the vagus nerve?
An autonomic nerve with parasympathetic activity.
108
What role does the vagus nerve play in digestion?
It mediates reflexes that stimulate digestive secretions and coordination between organs.
109
When can the cephalic phase of digestion begin?
Before food enters the mouth.
110
What stimuli trigger the cephalic phase?
Thought, sight, and smell of food.
111
What brain areas are activated during the cephalic phase?
Cerebral cortex and appetite centres.
112
Which system is activated during the cephalic phase?
Parasympathetic nervous system.
113
How are signals sent to the stomach during the cephalic phase?
Via the vagus nerve.
114
What is the main purpose of the cephalic phase?
Anticipatory preparation of the stomach for incoming food.
115
What is the oral cavity?
The entry point of food into the body.
116
What structures in the oral cavity aid digestion?
Palate, tongue, pharynx, teeth.
117
What is the palate?
The roof of the oral cavity separating it from the nasal cavity.
118
What is the function of the palate?
Allows breathing while chewing.
119
What is the tongue made of?
Voluntarily controlled skeletal muscle.
120
What are the functions of the tongue?
Chewing, swallowing, speech.
121
Where are taste buds located?
On the tongue.
122
What is the pharynx?
A cavity connecting the nose and mouth to the esophagus.
123
What systems share the pharynx?
Digestive and respiratory systems.
124
What are teeth used for?
Mastication (grinding food and mixing it with saliva).
125
What is saliva?
Secretion from salivary glands.
126
How many major salivary glands are there?
Three pairs.
127
Where are salivary glands located?
Outside the oral cavity, secreting into the mouth via ducts.
128
How much saliva is produced daily?
About 1–1.5 L.
129
What is saliva composed of?
99.5% water and 0.5% electrolytes, enzymes, and proteins.
130
What are the main proteins in saliva?
Amylase, mucus, lysozyme.
131
What does amylase do?
Begins carbohydrate digestion by breaking polysaccharides into maltose.
132
What is the role of mucus in saliva?
Moistens food to facilitate swallowing.
133
What does lysozyme do?
Acts as an antibacterial agent.
134
Why is saliva important for taste?
Only dissolved molecules can activate taste buds.
135
How does saliva aid speech?
Lubricates tongue and lips.
136
What is the role of bicarbonate in saliva?
Neutralizes acids from food and bacteria.
137
How do sympathetic and parasympathetic systems affect salivary glands?
Both stimulate salivation (not opposing).
138
What type of saliva does the parasympathetic system produce?
Large volume, watery, enzyme-rich saliva.
139
What type of saliva does the sympathetic system produce?
Smaller volume, thick, mucus-rich saliva.
140
Why does stress cause a dry mouth?
Sympathetic stimulation produces less saliva.
141
What is basal salivary secretion?
Constant low-level secretion to keep mouth and throat moist.
142
What triggers simple salivary reflexes?
Chemoreceptors and mechanoreceptors responding to food.
143
Where is the salivary centre located?
Medulla of the brainstem.
144
How do simple reflexes increase saliva?
Via autonomic nerve signals to salivary glands.
145
What are conditional salivary reflexes?
Learned “mouth-watering” responses.
146
What brain area is involved in conditional reflexes?
Cerebral cortex.
146
What triggers conditional reflexes?
Thinking about, seeing, smelling, or hearing food.
147
What is swallowing?
The process of moving food from the mouth through the esophagus to the stomach.
148
Is swallowing only oral?
No, it involves both oral and esophageal phases.
149
How is swallowing initiated?
Voluntarily by pushing the bolus to the back of the mouth.
150
What triggers the swallowing reflex?
Pressure of the bolus on the pharynx.
151
Is swallowing voluntary or involuntary?
Both—starts voluntary, then becomes involuntary.
152
How complex is the swallowing reflex?
One of the most complex reflexes, involving 25 pairs of muscles.
153
Where is the swallowing centre located?
Medulla of the brainstem.
154
What do afferent signals do in swallowing?
Send sensory information to the swallowing centre.
155
What do efferent signals do in swallowing?
Control timing of muscle activation.
156
What does “all-or-none” mean in swallowing?
Once started, the process cannot be stopped.
157
What is a bolus?
A ball-like mixture of food and saliva formed during chewing.
158
How many phases does swallowing have?
Two phases: oropharyngeal phase and esophageal phase.
159
What is the first phase of swallowing?
The oropharyngeal phase.
160
How long does the oropharyngeal phase last?
About 1 second (very rapid).
161
What must happen when the bolus enters the pharynx?
It must be directed to the esophagus and prevented from entering other openings.
162
How is food prevented from re-entering the mouth during swallowing?
The tongue presses against the palate.
163
How are the nasal passages blocked during swallowing?
The uvula elevates.
164
What happens to breathing during swallowing?
The respiratory centre is inhibited, stopping airflow.
165
How is food prevented from entering the trachea?
Larynx elevates
Vocal folds tighten
166
What happens after the bolus enters the esophagus?
The esophageal phase begins.
167
What happens to the upper esophageal sphincter (UES)?
It closes.
168
What happens to oropharyngeal structures after swallowing begins?
They return to normal position.
169
What happens to breathing after the oropharyngeal phase?
Inhibition is removed and breathing resumes.
170
What is peristalsis?
Ring-like contractions of circular smooth muscle that move contents forward.
171
What initiates the primary peristaltic wave?
The swallowing centre.
172
What does the primary peristaltic wave do?
Moves from the beginning to the end of the esophagus, pushing the bolus to the stomach.
173
When does secondary peristalsis occur?
When the bolus is not cleared by the primary wave.
174
What triggers secondary peristalsis?
Distension of the esophagus.
175
How is secondary peristalsis different from primary?
- More forceful
- Controlled by intrinsic nerve plexus (not swallowing centre)
176
What happens to the LES during peristalsis?
It relaxes to allow the bolus into the stomach.
177
What is the normal state of the LES?
Tightly contracted.
178
Why is the LES normally contracted?
To prevent gastric reflux.
179
What is gastric reflux?
Backflow of acidic stomach contents into the esophagus.
180
What is secreted throughout the esophagus?
Mucus
181
What are the functions of esophageal mucus?
- Lubricates for easier movement of the bolus
- Protects against gastric juices
182
What is the sequence of events in swallowing?
1. Oropharyngeal phase (protection of openings)
2. Bolus enters esophagus
3. Primary peristalsis moves bolus
4. Secondary peristalsis if needed
5. LES relaxes → bolus enters stomach
183
The thought, sight, smell, and taste of food stimulates cerebral cortex
Cephalic phase
184
The uvula elevates and blocks the nasal passages
Oropharyngeal phase
185
The upper esophageal sphincter (UES) closes and the inhibition on
breathing is removed
Esophageal phase
186
The larynx elevates and the vocal folds tighten to prevent food from
entering the trachea
Oropharyngeal phase
187
Anticipatory in preparing the stomach for the arrival of food
Cephalic phase
188
Peristaltic waves relax the lower esophageal sphincter (LES) and allow the
bolus into the stomach
Esophageal phase
189
What is the stomach?
A J-shaped chamber where the bolus enters after the esophagus.
190
What separates the stomach from the small intestine?
The pyloric sphincter.
191
What are the three regions of the stomach?
Fundus, body, antrum.
192
What is the fundus?
The portion above the esophageal opening.
193
What is the body of the stomach?
The main central region.
194
What is the antrum?
The muscular lower portion of the stomach.
195
What are the three main functions of the stomach?
- Store food
- Secrete HCl and enzymes for protein digestion
- Mix food into chyme
196
What is chyme?
A thick fluid formed by mixing food with gastric secretions.
197
What are the four aspects of gastric motility?
Gastric filling
Gastric storage
Gastric mixing
Gastric emptying
198
What is the volume of an empty stomach?
About 50 mL.
199
How much can the stomach expand?
- ~1000 mL for a meal
- Up to ~4000 mL maximum
200
How does the stomach expand without increasing pressure?
Folds flatten out.
201
What is receptive relaxation?
Vagus-mediated relaxation allowing expansion without pressure increase.
202
Where are pacemaker cells located in the stomach?
In the fundus.
203
What do pacemaker cells generate?
Slow-wave potentials (~3 per minute).
204
When do peristaltic waves occur in the stomach?
When slow waves reach threshold.
205
Where is most food stored in the stomach?
In the body.
206
Where does mixing mainly occur?
In the antrum.
207
What happens during gastric mixing?
Chyme is pushed toward the pyloric sphincter.
208
Why doesn’t most chyme pass through the pyloric sphincter immediately?
It is usually almost closed.
209
What is retropulsion?
Chyme is pushed back and forth for thorough mixing.
210
Why is retropulsion important?
Ensures particles are small enough for emptying.
211
What happens during gastric emptying?
Small amounts of chyme pass into the small intestine.
212
How much chyme is typically in the antrum?
About 30 mL.
213
How much chyme passes per wave?
Only a few mL.
214
What increases gastric emptying?
Stronger peristaltic waves.
215
What factors influence contraction strength in the stomach?
- Volume of chyme (distension)
- Fluidity of chyme
216
How does volume affect gastric emptying?
More volume → more distension → stronger contractions.
217
How does fluidity affect gastric emptying?
More liquid chyme empties faster.
218
Does the duodenum affect gastric emptying?
Yes, it can slow it down.
219
What is the enterogastric reflex?
Neural signals (intrinsic + autonomic) that reduce gastric emptying.
220
What hormones regulate gastric emptying from the duodenum?
Secretin and cholecystokinin (CCK).
221
What are the four main duodenal stimuli that slow gastric emptying?
Fat, acid, hypertonicity, distension.
222
How does fat affect gastric emptying?
Strongly inhibits it (most potent factor).
223
Why does fat slow gastric emptying?
Takes longer to digest and absorb.
224
How long can high-fat meals stay in the stomach?
Up to 6 hours.
225
How long do high protein/carbohydrate meals take to empty?
About 3 hours.
226
Why must acid be regulated in the duodenum?
To prevent tissue damage and protect enzymes.
227
How is acid neutralized in the duodenum?
By NaHCO₃ (mainly from the pancreas).
228
What effect does high acid have on gastric emptying?
Decreases it.
229
What causes increased osmolarity in the duodenum?
Breakdown of proteins and carbohydrates.
230
What happens when osmolarity increases?
Water moves into the lumen by osmosis.
231
Why does hypertonicity inhibit gastric emptying?
Prevents excessive fluid shifts and plasma volume loss.
232
How does duodenal distension affect gastric emptying?
Increased distension slows emptying.
233
What is the overall control principle of gastric emptying?
The stomach empties based on its contents and the readiness of the duodenum.
234
What is vomiting also called?
Emesis.
235
Where is vomiting coordinated?
The vomiting centre in the medulla of the brainstem.
236
What is the first step in vomiting?
Deep inspiration.
237
What happens to the glottis during vomiting?
It closes to prevent aspiration into the lungs.
238
What happens to the uvula during vomiting?
It closes to prevent entry into the nasal cavity.
239
What happens to the diaphragm during vomiting?
It contracts downward.
240
What happens to the abdominal muscles during vomiting?
They contract inward.
241
What happens to the stomach during vomiting?
It becomes flaccid and is compressed.
242
How do stomach contents exit during vomiting?
Forced upward through relaxed esophageal sphincters and out the mouth.
243
How long does vomiting continue?
Until the stomach is empty.
244
What symptoms often precede vomiting?
Sweating
Salivation
Increased heart rate
Nausea
245
Why do these symptoms occur?
Due to autonomic nervous system involvement.
246
What are common triggers of vomiting?
Multiple physiological and reflex causes
247
How can throat stimulation cause vomiting?
Touching the back of the throat triggers the reflex.
248
How does GI irritation trigger vomiting?
Irritation or distension of the stomach or duodenum.
249
How can brain-related issues cause vomiting?
Elevated intracranial pressure (e.g., head injury).
250
How does motion cause vomiting?
Rotation or acceleration of the head (motion sickness).
251
What role do chemicals/drugs play in vomiting?
Stimulate the chemoreceptor trigger zone.
252
Where is the chemoreceptor trigger zone located?
Near the vomiting centre in the brainstem.
253
What is psychogenic vomiting?
Vomiting triggered by psychological factors.
254
What is the protective role of vomiting?
Removes harmful (noxious) substances from the digestive tract.
255
What is a potential consequence of excessive vomiting?
Disruption of acid-base balance.
256
What systems are involved in vomiting?
Nervous (reflex + autonomic), muscular, and digestive systems.
257
What are the two secretion regions in the gastric mucosa?
- Oxyntic mucosa
- Pyloric gland area
258
Where is the oxyntic mucosa located?
In the fundus and body of the stomach.
259
Where is the pyloric gland area located?
In the antrum.
260
What are gastric pits?
In-foldings of the gastric mucosa on the luminal surface.
261
What is located at the bottom of gastric pits?
Gastric glands.
262
What are the three types of secretory cells in the oxyntic mucosa?
Mucous cells
Chief cells
Parietal cells
263
Where are mucous cells located?
Lining gastric pits and gland entrances.
264
What do mucous cells secrete?
Watery mucus.
265
What do chief cells secrete?
Pepsinogen
266
Are chief cells numerous?
Yes, they are the most numerous in gastric glands.
267
What do parietal cells secrete?
Hydrochloric acid (HCl) and intrinsic factor.
268
What do surface epithelial cells secrete?
Thick, viscous, alkaline mucus.
269
What is the function of this mucus layer?
Protects the gastric mucosa from acid.
270
What do pyloric glands secrete?
Mucus and a small amount of pepsinogen.
271
Do pyloric glands secrete HCl?
No
272
What pH can HCl lower the stomach to?
As low as pH 2
273
What are the four functions of HCl?
- Activates pepsinogen → pepsin
- Breaks down connective tissue and muscle fibers
- Denatures proteins
- Kills microorganisms
274
What happens to water (H₂O) inside parietal cells?
It splits into H⁺ and OH⁻.
275
How is H⁺ secreted into the stomach lumen?
Via H⁺-K⁺ ATPase (active transport).
276
What happens to OH⁻ inside the cell?
Combines with H⁺ from H₂CO₃ to form water.
277
What enzyme is abundant in parietal cells for this process?
Carbonic anhydrase.
278
What reaction does carbonic anhydrase facilitate?
CO₂ + H₂O → H₂CO₃ → H⁺ + HCO₃⁻.
279
What happens to HCO₃⁻ in parietal cells?
Transported into plasma via Cl⁻/HCO₃⁻ exchanger.
280
What happens to Cl⁻ in parietal cells?
Accumulates and diffuses into the lumen.
281
What combines in the lumen to form HCl?
H⁺ and Cl⁻.
282
Why must HCl secretion be tightly regulated?
To prevent damage to the gastric mucosa.
283
Where is pepsinogen stored?
In secretory vesicles within chief cells
284
When is pepsinogen released?
Upon appropriate stimulation into the stomach lumen.
285
Where is pepsinogen activated?
In the lumen of the stomach.
286
What initiates the activation of pepsinogen?
Hydrochloric acid (HCl)
287
How does HCl activate pepsinogen?
By cleaving off a portion of the molecule to form pepsin.
288
What role does pepsin play in its own production?
It activates more pepsinogen into pepsin.
289
What type of mechanism is this activation process?
Positive feedback.
290
What does pepsin do?
Begins protein digestion.
291
How does pepsin digest proteins?
Splits specific amino acid linkages.
292
What are the products of pepsin activity?
Smaller amino acid chains (polypeptides).
293
What condition is required for pepsin activity?
An acidic environment.
294
Why is stomach acidity important for protein digestion?
It enables both activation and function of pepsin.
295
What are the steps of pepsin activation and function?
1. Pepsinogen released from chief cells
2. HCl activates it to pepsin
3. Pepsin activates more pepsinogen
4. Pepsin digests proteins into smaller chains
296
Why pepsin is stored in the chief cells as pepsinogen?
Since pepsin is able to digest protein, it must be stored in an inactive form to prevent it from digesting the proteins within the chief cells in which it is formed. Therefore, it is stored in an inactive form, such that it is harmless to the cell, until it reaches the gastric lumen and is activated by HCl .
297
What forms the protective barrier in the stomach?
Mucus secreted by surface epithelial cells.
298
What are the three main protective functions of gastric mucus?
- Protects against mechanical injury
- Protects against acid
- Prevents self-digestion
299
How does mucus protect against mechanical injury?
Acts as a lubricant.
300
How does mucus protect against acid?
It is alkaline and neutralizes HCl near the mucosa.
301
What is the pH difference between the stomach lumen and mucus layer?
Lumen: ~pH 2
Mucus layer: ~pH 7
302
How does mucus prevent self-digestion?
Inactivates pepsin by maintaining a less acidic environment.
303
Which cells secrete intrinsic factor?
Parietal cells.
304
What is the function of intrinsic factor?
Enables absorption of vitamin B12.
305
Why is vitamin B12 important?
Essential for normal red blood cell function.
306
How is vitamin B12 absorbed?
- Binds intrinsic factor
- Complex binds receptors in the distal small intestine
- Absorbed via receptor-mediated endocytosis
307
Where are G cells located?
Pyloric gland area.
308
What do G cells secrete?
Gastrin.
309
What stimulates gastrin release?
- Protein in the stomach
- Acetylcholine (ACh)
310
What does gastrin do?
Stimulates chief and parietal cells to increase secretion.
311
Where are ECL cells located?
In oxyntic mucosa among chief and parietal cells.
312
What do ECL cells secrete?
Histamine.
313
What is the role of histamine?
Increases HCl secretion (paracrine effect)
314
What stimulates histamine release?
Gastrin and ACh.
315
Where are D cells located?
Near the pylorus and in the duodenum.
316
What do D cells secrete?
Somatostatin.
317
What stimulates somatostatin release?
Acid.
318
What is the function of somatostatin?
Inhibits parietal, G, and ECL cell secretion.
319
What are the three phases of gastric secretion?
Cephalic, gastric, intestinal.
320
What stimulates the gastric phase?
Protein
Distension
Caffeine
Alcohol
321
What is the most potent stimulus for gastric secretion?
Protein
322
How does protein stimulate secretion?
- Activates chemoreceptors → intrinsic plexus
- Directly stimulates gastrin release
323
How do distension, caffeine, and alcohol affect secretion?
Increase acid secretion, even without food.
324
What is the intestinal phase?
Regulation of gastric secretion by the small intestine.
325
What is the general effect of the intestinal phase?
Inhibits gastric secretion.
326
Why does the intestinal phase inhibit secretion?
To reduce gastric activity as chyme enters the small intestine.
327
What triggers the cephalic phase?
Sight
Smell
Taste
Thought of food
Chewing/swallowing
328
Which system mediates the cephalic phase?
Parasympathetic nervous system
329
What nerve is involved in the cephalic phase?
Vagus nerve.
330
How does vagal stimulation increase gastric secretion?
- Stimulates intrinsic plexuses → ACh release
- Increases HCl and pepsinogen secretion
331
How does the vagus nerve affect G cells?
Stimulates gastrin release → further increases secretion.
332
What is the overall control of gastric secretion?
A combination of neural (ENS + ANS), hormonal, and local mechanisms across three phases.
333
What processes occur in the stomach after motility and secretion?
Gastric digestion and absorption.
334
What happens to food in the body of the stomach?
It remains mostly in a semi-solid state.
335
Why does food remain semi-solid in the stomach body?
Peristaltic contractions are not strong enough for full mixing.
336
Is food or water significantly absorbed in the stomach?
No
337
What types of substances can be absorbed in the stomach?
Certain lipid-soluble substances (e.g., alcohol, weak acids like aspirin).
338
Where does most protein digestion occur in the stomach?
In the antrum.
339
Why is protein digestion limited in the stomach body?
Food is not well mixed with gastric juices.
340
What enzyme continues carbohydrate digestion in the stomach?
Salivary amylase.
341
Why can salivary amylase still function in the stomach?
The interior of the food mass is not exposed to acid.
342
What inhibits salivary amylase activity?
Acidic environment (HCl).
343
Why can alcohol be absorbed in the stomach?
It is somewhat lipid-soluble
344
Where is alcohol absorbed faster: stomach or intestine?
Intestine (greater surface area).
345
How can alcohol absorption be slowed?
By consuming high-fat foods beforehand.
346
Why do high-fat foods slow alcohol absorption?
They slow gastric emptying.
347
What type of compound is aspirin (acetylsalicylic acid)?
A weak acid.
348
What happens to weak acids in the acidic stomach environment?
They become unionized.
349
Why does unionization matter for absorption?
Unionized molecules are lipid-soluble.
350
How does aspirin cross the stomach wall?
Diffuses across epithelial cell membranes.
351
What determines whether a substance can be absorbed in the stomach?
Lipid solubility and ionization state.
352
What enters the duodenum from the stomach?
Chyme.
353
What secretions are added to chyme in the duodenum?
Pancreatic secretions and biliary secretions
354
What are biliary secretions?
Secretions from the liver, gallbladder, and associated ducts.
355
What are the two main components of pancreatic juice?
- Pancreatic enzymes
- Aqueous alkaline secretion
356
What is the function of pancreatic enzymes?
Digest food almost completely, even without gastric secretions.
357
Why is the alkaline secretion important?
Neutralizes stomach acid for optimal enzyme activity.
358
What is the main component of the aqueous secretion?
NaHCO₃-rich fluid.
359
How much pancreatic fluid is secreted daily?
About 1–2 L.
360
What are acini?
Grape-like clusters of secretory cells.
361
Where do acini drain?
Into ducts that empty into the duodenum.
362
What are the major pancreatic proteolytic enzymes?
- Trypsinogen
- Chymotrypsinogen
- Procarboxypeptidase
363
In what form are proteolytic enzymes secreted?
Inactive (zymogens).
364
How is trypsinogen activated?
By enterokinase in the duodenal mucosa → trypsin.
365
What protects the pancreas from premature activation of trypsin?
Trypsin inhibitor in secretory vesicles
366
How is chymotrypsinogen activated?
By trypsin.
367
How is procarboxypeptidase activated?
By trypsin.
368
What does pancreatic amylase do?
Converts polysaccharides into maltose.
369
What carbohydrates can pancreatic amylase digest?
Starch, glycogen, most carbohydrates.
370
What carbohydrate cannot be digested by pancreatic amylase?
Cellulose
371
What is unique about pancreatic lipase?
It is the only enzyme that digests fats.
372
What does pancreatic lipase break down?
Triglycerides → monoglycerides + free fatty acids.
373
When does pancreatic secretion begin?
- Small amount in cephalic phase
- Increased slightly in gastric phase
374
What primarily controls pancreatic secretion?
Hormones
375
What triggers pancreatic hormone release?
Presence of chyme in the duodenum.
376
What stimulates secretin release?
Acid in the duodenum
377
Where is secretin released from?
Duodenal and jejunal mucosa.
378
What does secretin do?
Stimulates pancreatic duct cells to secrete NaHCO₃-rich fluid
379
What determines the amount of secretin released?
Amount of acid entering the duodenum.
380
What primarily stimulates CCK release?
Fats (and to a lesser extent proteins).
381
What does CCK stimulate?
Pancreatic acinar cells → enzyme secretion.
382
Do carbohydrates stimulate CCK release?
No
383
Does a high-protein meal selectively release proteolytic enzymes?
No, all pancreatic enzymes are released together.
384
How are pancreatic secretions coordinated?
- Secretin → bicarbonate (neutralization)
- CCK → enzymes (digestion)
385
↑ Secretion of aqueous Na HCO3 solution into duodenal lumen
Secretin
386
It hydrolyzes triglycerides into monoglycerides and free fatty acids
Pancreatic Lipase
387
↑ Secretion of pancreatic digestive enzymes into duodenal lumen
CCK
388
It converts polysaccharides into the disaccharide maltose
Pancreatic Amylase
389
A proteolytic enzyme converted to its active form by enterokinase
Trypsinogen
390
What is the most important digestive role of the liver?
Production of bile salts for fat digestion and absorption.
391
What are the major functions of the liver?
- Metabolism of fats, carbohydrates, proteins
- Detoxification of wastes, drugs, hormones
- Synthesis of plasma proteins
- Storage of glycogen, fats, iron, copper, vitamins
- Activation of vitamin D
- Removal of old RBCs and bacteria
- Excretion of cholesterol and bilirubin
392
What is a hepatocyte?
A liver cell that performs all liver functions.
393
What must hepatocytes be in contact with?
Both arterial and venous blood.
394
How much venous blood enters the liver per minute?
About 1 L via the hepatic portal vein.
395
What does portal blood deliver?
Absorbed nutrients from the digestive system.
396
How much arterial blood enters the liver?
About 350 mL via the hepatic artery.
397
What does arterial blood supply to the liver?
Oxygen and metabolites.
398
What is the functional unit of the liver?
Lobule.
399
What shape are liver lobules?
Hexagonal.
400
What is located at each corner of a lobule?
- Hepatic artery branch
- Portal vein branch
- Bile duct
401
Where do bile ducts lead?
To the common bile duct → duodenum.
402
What are sinusoids?
Capillary-like channels in the liver.
403
How does blood flow in a lobule?
From periphery → sinusoids → central vein.
404
What do central veins form?
Hepatic vein.
405
What are Kupffer cells?
Macrophages lining sinusoids.
406
What do Kupffer cells do?
Remove old RBCs and bacteria.
407
What are bile canaliculi?
Channels between hepatocytes carrying bile.
408
How does bile flow?
From hepatocytes → canaliculi → bile ducts.
409
What is unique about hepatocyte structure?
- One side faces sinusoids (blood)
- One side faces canaliculi (bile)
410
Is bile continuously produced?
Yes
411
When is bile released into the duodenum?
During active digestion.
412
What controls bile entry into the duodenum?
Sphincter of Oddi.
413
What happens when the sphincter of Oddi is closed?
Bile is stored in the gallbladder.
414
How much bile can the gallbladder store?
About 50 mL.
415
How much bile is produced daily?
About 250 mL.
416
What are the main components of bile?
Bile salts
Cholesterol
Lecithin
Bilirubin
Aqueous fluid
417
What is enterohepatic circulation?
Recycling of bile salts between intestine and liver.
418
Where are bile salts reabsorbed?
Terminal ileum.
419
What percentage of bile salts are recycled?
95%
420
What percentage of bile salts are newly synthesized?
5%
421
What percentage of bile salts are lost in feces?
5%
422
What do bile salts do to fats?
Emulsify them into small droplets.
423
Why is emulsification important?
Increases surface area for lipase.
424
What property allows bile salts to emulsify fats?
Amphipathic structure (lipid + water soluble ends).
425
What prevents fat droplets from rejoining?
Repulsion of polar ends of bile salts.
426
Why can’t lipase act alone on fat droplets?
Bile salts block access.
427
What is the role of colipase?
Anchors lipase to fat droplets.
428
What are micelles?
Clusters of lipid-soluble substances surrounded by bile salts.
429
What do micelles transport?
Digested fats and lipid-soluble compounds
430
What is the structure of a micelle?
Lipophilic core
Hydrophilic outer shell
431
What is bilirubin?
A waste product from hemoglobin breakdown.
432
What is bilirubin’s role in digestion?
None (excretory function only).
433
What color is bilirubin?
Yellow
434
What happens to bilirubin in the intestine?
Converted to brown pigments by bacteria.
435
Why are feces brown?
Due to modified bilirubin.
436
What happens if bile is not secreted?
Feces become grey-white.
437
What happens to some bilirubin after reabsorption?
Excreted in urine.
438
Why is urine yellow?
Due to bilirubin derivatives.
439
What is the overall role of bile?
- Aid fat digestion (bile salts)
- Transport lipids (micelles)
- Excrete waste (bilirubin)
440
What mechanisms regulate bile secretion?
Chemical, hormonal, neural
441
What is the most potent chemical stimulus for bile secretion?
Bile salts
442
How do bile salts regulate bile secretion?
Reabsorbed bile salts return via enterohepatic circulation and stimulate further bile release.
443
Which hormone affects bile secretion?
Secretin
444
What does secretin stimulate in bile secretion?
Aqueous alkaline component.
445
Does secretin stimulate bile salt secretion?
No
446
When does neural stimulation of bile secretion occur?
During the cephalic phase.
447
What nerve mediates neural bile secretion?
Vagus nerve.
448
What is the effect of vagal stimulation on the liver?
Promotes bile release before food reaches the intestine.
449
What happens to bile when the sphincter of Oddi is closed?
It is stored in the gallbladder
450
How is bile concentrated in the gallbladder?
Active salt transport + osmotic water reabsorption.
451
How much can bile be concentrated in the gallbladder?
5–10 times
452
What triggers bile release into the duodenum?
Fat in the duodenum
453
Which hormone mediates bile release?
Cholecystokinin (CCK)
454
What are the two actions of CCK on bile flow?
- Contracts gallbladder
- Relaxes sphincter of Oddi
455
What is the result of CCK action?
Bile flows into the duodenum.
456
Why can gallstones form?
Bile salts precipitate due to concentration in the gallbladder.
457
What are gallstones?
Solid precipitates formed from bile components.
458
Can the gallbladder be removed without affecting digestion?
Yes
459
What happens to bile after gallbladder removal?
It is still produced by the liver.
460
Where is bile stored after gallbladder removal?
In the dilated common bile duct.
461
How is bile secretion and release coordinated?
- Bile salts → stimulate production
- Secretin → increases alkaline fluid
- Vagus nerve → early release
- CCK → triggers gallbladder contraction and bile delivery
462
Where is the small intestine located in the GI tract?
Between the stomach and the large intestine.
463
What are the three segments of the small intestine?
Duodenum, jejunum, ileum.
464
What four processes are used to study small intestine function?
Motility, secretion, digestion, absorption.
465
What is the term for motility in the small intestine?
Segmentation
466
What does segmentation do?
Mixes chyme and slowly propels it forward
467
How does segmentation occur?
- Localized concentric contractions trap chyme in relaxed areas.
- Contracted areas relax, new rings appear in previously relaxed areas.
- Chyme moves back and forth, ensuring mixing and slow forward movement
468
What reflex stimulates segmentation in the ileum?
Gastroileal reflex, triggered by gastrin from chyme in the stomach
469
What initiates segmentation contractions?
Pacemaker cells generating the basic electrical rhythm (BER)
470
How fast is the BER in the duodenum/jejunum vs. terminal ileum?
Duodenum/jejunum: ~12/min
Terminal ileum: ~9/min
471
What enhances smooth muscle excitability in the small intestine?
Distention, gastrin, extrinsic nerve activity
472
When is segmentation absent?
Between meals
473
What replaces segmentation after most of a meal is absorbed?
Migrating motility complex (MMC)
474
What is the pattern of the MMC?
Weak peristaltic waves that travel short distances before dying out
475
What is the purpose of the MMC?
Moves remnants of the meal, mucosal debris, and bacteria toward the colon
476
Where does the MMC start and how does it progress?
Starts at the stomach, slowly moves down the intestine, restarts at the duodenum when it reaches the ileum
477
What do exocrine glands in the small intestine secrete?
Mucus
478
How much mucus is secreted daily in the small intestine?
About 1.5 L/day
479
What are the functions of mucus in the small intestine?
- Lubrication
- Protection
- Provides water for hydrolytic reactions
480
Are digestive enzymes secreted into the lumen by the small intestine?
No (digestion is mainly by pancreatic enzymes)
481
What are microvilli?
Hair-like projections forming the brush border
482
What is the brush border?
Luminal epithelial surface with microvilli and enzymes for absorption
483
What types of enzymes are found in the brush border?
- Enterokinases
- Disaccharidases
- Aminopeptidases
484
What is the function of enterokinase?
Converts trypsinogen → trypsin.
485
What do disaccharidases do?
Convert disaccharides → monosaccharides
486
What do aminopeptidases do?
Break peptides into amino acids
487
What enzyme is deficient in lactose intolerance?
Lactase
488
What happens to undigested lactose?
- Draws water into lumen (osmotic effect)
- Fermented by bacteria → gas
489
What symptoms result from lactose intolerance?
Cramping and diarrhea
490
What is the primary function of the small intestine?
Absorption
491
What substances are absorbed in the small intestine?
Carbs, proteins, fats, electrolytes, vitamins, water
492
Where does most absorption occur?
Duodenum and jejunum
493
What is the ileum especially important for absorbing?
Vitamin B12 and bile salts
494
Approximate daily absorption amounts?
Carbs: ≥200 g
Fat: ≥100 g
Amino acids: ≥50 g
Water: 7–8 L
495
What regulates absorption of some minerals?
Body needs (e.g., calcium, iron).
496
How much is surface area increased in the small intestine?
~600-fold
497
What structures increase surface area?
Circular folds (3x)
Villi (10x)
Microvilli (20x)
498
What forms are proteins absorbed as?
Amino acids and small peptides
499
How are amino acids absorbed?
Secondary active transport
500
How are small peptides processed?
Broken down by brush border & intracellular enzymes.
501
What are three sources of protein in the intestine?
- Digestive enzymes
- Sloughed epithelial cells
- Plasma proteins
502
How is sodium absorbed?
Both passive and active transport.
503
How does passive sodium absorption occur?
Through leaky tight junctions down gradient
504
How does active sodium absorption occur?
- Enters via channels or cotransport
- Pumped out by Na⁺-K⁺ ATPase
505
What follows sodium absorption?
- Chloride (electrical gradient)
- Water (osmotic gradient)
506
In what form are carbohydrates absorbed?
Monosaccharides
507
How is galactose absorbed?
Secondary active transport (Na⁺ cotransport)
508
How is glucose absorbed?
Secondary active transport (Na⁺ cotransport)
509
How is fructose absorbed?
Facilitated diffusion (no Na⁺ required)
510
What is the first step in fat digestion?
Emulsification by bile salts
511
What does pancreatic lipase produce?
Monoglycerides + free fatty acids
512
How do fats enter epithelial cells?
Diffuse from micelles.
513
What happens to fats inside epithelial cells?
Re-formed into triglycerides
514
What are chylomicrons?
Lipid droplets coated with protein (water-soluble).
515
How do chylomicrons leave cells?
Exocytosis into lymphatic system
516
Why is iron important?
Required for hemoglobin production
517
Which form of iron is best absorbed?
Ferrous (Fe²⁺)
518
What happens to absorbed iron?
Used → bound to transferrin → blood
Stored → ferritin
519
What happens if iron levels are high?
Secreted back into lumen.
520
How is stored iron eventually lost?
Sloughed epithelial cells → feces
521
What completes digestion and absorption?
Small intestine (before chyme enters cecum)
522
What is diarrhoea in the context of digestion?
A major mechanism of water loss from the body.
523
How does diarrhoea affect acid-base balance?
Disrupts it by causing loss of bicarbonate (HCO₃⁻)
524
When is diarrhoea beneficial?
When it helps remove harmful substances quickly from the intestine.
525
When is diarrhoea harmful?
When excessive or prolonged
526
What are the negative consequences of prolonged diarrhoea?
- Dehydration
- Loss of nutrients
- Metabolic acidosis (due to HCO₃⁻ loss)
527
What are the three main causes of diarrhoea?
- Excessive motility
- Osmotic particles
- Toxins
528
What causes excessive intestinal motility?
- Local irritation (bacterial/viral)
- Emotional stress
529
How does increased motility cause diarrhoea?
Reduces time for water absorption.
530
What causes osmotic diarrhoea?
Presence of non-absorbed, osmotically active substances
531
How do osmotic particles cause diarrhoea?
Draw water into the intestinal lumen.
532
What is a classic example of osmotic diarrhoea?
Lactose intolerance
533
Which organism is a classic cause of toxin-induced diarrhoea?
Vibrio cholerae
534
How do toxins cause diarrhoea?
Stimulate excessive fluid secretion by intestinal mucosa
535
What is the underlying issue in all types of diarrhoea?
Imbalance between fluid secretion and absorption
536
Which enzymes are involved in the digestion of proteins?
Chymotrypsin, enterokinase, trypsin, aminopeptidase, carboxypeptidase
537
Which enzymes are involved in the digestion of carbohydrates?
Amylase, disaccharidase
538
Which enzymes are involved in the digestion of fats?
Lipase
539
What structures make up the large intestine?
Cecum, appendix, and colon
540
What are the three main parts of the colon?
Ascending, transverse, and descending colon
541
What is the sigmoid colon?
The terminal part of the descending colon that leads to the rectum
542
What is the rectum?
The final straight portion of the large intestine before the anus
543
What is the cecum?
A blind-ended pouch below the junction of the small and large intestines
544
What is the appendix?
A finger-like projection of lymphoid tissue from the cecum
545
What is the colon?
The majority of the large intestine
546
How much chyme enters the large intestine daily?
500–1500 mL
547
What does this chyme mainly contain?
- Indigestible food (e.g., cellulose)
- Unabsorbed bile
- Fluid
548
What happens to chyme in the large intestine?
- Upper colon absorbs some salt and water
- Lower colon stores feces
549
What muscle layers are present in the colon?
Circular and longitudinal smooth muscle
550
What are taenia coli?
Three distinct bands of longitudinal smooth muscle
551
Why do haustra form?
Because taenia coli are shorter than the colon wall → causes sac-like pouches
552
What are haustra?
Sac-like pouches in the colon that shift with contractions.
553
What is the main motility pattern in the colon?
Haustral contractions
554
What are haustral contractions?
Slow, non-propulsive contractions for mixing
555
How frequent are haustral contractions?
As few as 2/hour.
556
How are haustral contractions controlled?
Intrinsic nerve plexus (local reflexes)
557
How does small intestine motility differ from colon motility?
- Small intestine: faster, more frequent segmentation (~12/min)
- Colon: slower haustral contractions (~2/hour)
558
What is the purpose of small intestine motility?
Move remnants, debris, and bacteria toward the colon.
559
What are mass movements?
Strong contractions that move feces long distances quickly
560
When do mass movements typically occur?
After meals
561
What reflex controls mass movements?
Gastrocolic reflex
562
What stimulates the gastrocolic reflex?
- Gastrin
- Autonomic nerves
563
What is the gastroileal reflex?
Moves contents from small intestine to large intestine.
564
What triggers the defecation reflex?
Stretching of the rectum by feces
565
What happens when rectal stretch receptors are activated?
Signals sent to spinal cord → parasympathetic response.
566
What happens to the internal anal sphincter?
Relaxes (involuntary)
567
What type of muscle is the internal anal sphincter?
Smooth muscle (involuntary)
568
What type of muscle is the external anal sphincter?
Skeletal muscle (voluntary)
569
When does defecation occur?
When the external anal sphincter is voluntarily relaxed
570
What assists defecation?
- Abdominal muscle contraction
- Forced expiration against closed glottis
571
Does digestion occur in the large intestine?
No
572
What does the colon secrete?
Alkaline mucus (NaHCO₃)
573
Functions of colonic mucus?
- Lubrication
- Protection
- Neutralizes acids from bacteria
574
Does the colon secrete antibacterial agents?
No
575
What is the microbiome?
All microbes in a specific environment
576
How many bacterial species are in the colon?
Over 10,000
577
Functions of the gut microbiome?
- Compete with pathogens
- Promote motility
- Contribute nutrients
- Maintain mucosal integrity
578
When is gut microbiome established?
Around age 2
579
What develops alongside gut flora?
Intestinal epithelium and mucosal barrier
580
Why is microbiome research important?
It influences digestion and disease processes
581
What does the colon mainly absorb?
Salt and water
582
How is sodium absorbed in the colon?
Actively
583
What follows sodium absorption?
Chloride and water
584
Does the colon have a large surface area?
No, relatively low
585
Why is colon absorption limited?
Lacks specialized transporters
586
How is feces formed?
Through absorption of salt and water → solid mass
587
Is the large intestine a major waste elimination route?
No
588
What is Irritable Bowel Syndrome (IBS)?
A common chronic disorder affecting the large intestine
589
Symptoms of IBS?
- Cramping
- Abdominal pain
- Bloating
- Gas
- Diarrhea and/or constipation
590
What is known about the cause of IBS?
Unknown
PHGY 216
flashcards
Decks in class (6)
# Cards
