Chapter 16 - Digestive System Flashcards
1
Q
What is the primary function of the digestive system?
A
transfer nutrients, water, and electrolytes from ingested food into the body’s internal environment
2
Q
How long is the digestive tract?
A
4.5m
3
Q
What is food broken down into?
A
molecular forms
4
Q
What are the 4 functions of the digestive system?
A
motility, secretion, digestion, absorption
5
Q
Motility
A
the muscular contractions that mix and move forward the contents
6
Q
What kind of muscle makes up the digestive tract?
A
smooth muscle
7
Q
Tone
A
-the constant low level of contraction maintained by smooth muscles
8
Q
What is tone used for?
A
-maintains a steady pressure
-prevents permanent stretching
9
Q
Propulsive Movements
A
-a type of motility
-used to push contents forward through the tract
10
Q
Mixing Movements
A
-a type of motility
-two functions: 1) mixing food with juices 2) absorption
11
Q
Where is skeletal muscle used in digestion?
A
-mouth and anus
-chewing, swallowing, defecation are voluntary
12
Q
What secretes digestive juices?
A
exocrine glands
13
Q
What makes up digestive secretions
A
water, electrolytes, specific organic constituents (enzymes, bile salts, mucus)
14
Q
What monitors the release of secretions?
A
neural or hormonal stimulation
15
Q
When are digestive secretions normally reabsorbed?
A
after their participation in digestion
16
Q
Digestion
A
the biochemical breakdown of structurally complex food into smaller, absorbable units
17
Q
What accomplishes digestion?
A
enzymes
18
Q
What is the absorbable unit of carbohydrates?
A
Monosaccharides (ie. glucose and fructose)
19
Q
What must be done to disaccharides and polysaccharides before they can be absorbed?
A
they must be broken down into monosaccharides
20
Q
What are some polysaccharide examples?
A
starch, glycogen, cellulose
21
Q
What are some disaccharide examples?
A
sucrose, maltose, and lactose
22
Q
What are some monosaccharide examples?
A
glucose, fructose, galactose
23
Q
Disaccharide
A
2 monosaccharides linked together
24
Q
Polysaccharide
A
multiple monosaccharides (glucose) linked together
25
What is the organic composition of single sugars?
C₆H₁₂O₆
26
Sucrose = Glucose + __________
fructose
27
Lactose = Glucose + _________
galactose
28
Maltose = Glucose + _________
glucose
29
What are proteins broken down into?
peptide fragments
30
What are peptide fragments further digested into?
amino acids
31
Where do amino acids go?
epithelial cells
32
Can short amino acid chains be absorbed?
yes
33
What form are dietary fats in?
triglycerides
34
What does fat digestion produce?
2 free fatty acids and monoglyceride
35
Hydrolysis
how the enzymes break bonds to digest contents into smaller molecules
36
Where does most absorption occur?
the small intestine
37
Absorption
of small units resulting from digestion, vitamins, electrolytes, and water into blood or lymph
38
Digestive Tract Organs
-mouth
-pharynx
-esophagus
-stomach
-sm. intestine (duodenum, jejunum, ileum)
-lg. intestine (cecum, appendix, colon, rectum)
-anus
39
Accessory Digestive Organs
-salivary glands
-pancreas (exocrine)
-liver
-gall bladder
40
What are the functions of the mouth and pharynx?
-chewing
-swallowing
41
What are the functions of salivary glands?
-moisten and dissolve food
-lubrication
-polysaccharide digesting enzyme (amylase)
42
What do the salivary glands secrete?
-salt
-water
-mucus
-amylase
43
What does the stomach do?
-store, mix, dissolve
-continue digestion
-regulate emptying into sm. intestine
44
What does the stomach secrete?
-HCl (kill microbes, pepsinogen to pepsin)
-Pepsin (protein digesting enzyme)
-Mucus (lubrication and protection)
45
What does the pancreas do?
-secrete enzyme and bicarbonate
46
What does the pancreas secrete?
-enzymes (digestion)
-bicarbonate (neutralize HCl entering sm. intestine)
47
What does the liver do?
-secrete bile
48
What does the liver secrete?
-bile salts (solubilize fats)
-bicarbonate (neutralize HCl)
49
What does the gallbladder do?
store and concentrate bile between meals
50
What does the small intestine do?
-digestion and absorption of most substances
-mixing and propulsion
51
What does the small intestine secrete?
-enzymes (digestion)
-salt and water (fluid balance)
-mucus (lubrication)
52
What does the large intestine do?
-storage
-absorption of salt and water
-mixing and propulsion
-defecation
53
What does the large intestine secrete?
mucus for lubrication
54
What are the 4 major tissue layers of the digestive tract?
from inward to outward: mucosa, submucosa, muscularis externa, serosa
55
Mucosa
-lines luminal surface
-divided into 3 layers: mucous membrane, lamina propria, muscularis mucosa
56
What do the folds of the mucosa do?
increase absorptive surface area
57
Mucous Membrane
-most inward
-exposed to lumen
-serves as a protective surface
-secretion and absorption in certain areas
58
Mucous Membrane: Exocrine Gland Cells
secrete digestive juices
59
Mucous Membrane: Endocrine Gland Cells
secrete blood-borne GI hormones
60
Mucous Membrane: Epithelial Cells
-specialized
-absorb digestive nutrients
61
Lamina Propria
-thin middle layer
-house GALT
62
Gut-Associated Lymphoid Tissue (GALT)
defence against pathogenic bacteria
63
Muscularis Mucosa
-outermost mucosal layer
-sparse layer of smooth muscle
64
Submucosa
-second layer inward
-thick connective tissue layer
65
What is the function of the submucosa?
provides distensibility and elasticity
66
What does the submucosa have?
-larger blood and lymph vessels
-submucosal plexus
67
Submucosal Plexus
nerve network in the submucosa
68
Muscularis Externa
-third layer inward
-the major smooth muscle coat
-2 layers: circular and longitudinal
-myenteric plexus
69
Muscularis Externa: Circular Layer
-inner muscular layer
-controls diameter of lumen
70
Muscularis Externa: Longitudinal Layer
-outer layer
-controls length of the tube
71
What is the function of the muscularis externa?
propulsion and mixing
72
Interstitial Cells of Cajal
-cells between the two muscularis externa layers
-the origin of BER
73
Basic Electrical Rhythm (BER)
-rhythmic electrical activity
-pacemaker cells
-control slow wave cycle activity
-not action potentials, controlled by calcium
74
Myenteric Plexus
-lies btween the two muscularis externa layers
-extensive network of nerve cells
75
What regulates local gut activity?
-submucosal and myenteric plexuses
-hormones
-local chemical mediators
76
Serosa
-outer of the 4 layers
-connective tissue covering
77
What does the serosa secrete?
serous fluid to lubricate and prevent friction with surrounding organs
78
What is the serosa continuous with? Why?
-the mesentery
-suspends GI organs like a sling
-provides fixation and support
79
What regulates motility and secretion?
-autonomic smooth muscle
-BER
-intrinsic nerves plexuses
-extrinsic nerves plexuses
-GI hormones
80
What are the two intrinsic nerve plexuses?
ENS (myentric and submucosal)
81
Enteric Nervous System
-the GI tracts own NS
-mostly self-regulated but receives some ANS input
82
The ENS has ________ and ________ functions
sensory and motor
83
Extrinsic Nerve
-from both ANS branches
-originate outside GI tract
84
Sympathetic NS
-inhibit GI contraction and secretion
-digestion not a priority in an emergency
85
Parasympathetic NS
-dominates when regular activity needed
86
Gastrointestinal Hormones
-carried through blood and exhibit functions
-ie. Gastrin stimulates gastric juice release in stomach
87
Lips
-opening to the digestive tract
-procure, guide, maintain food in mouth
-speech
-tactile sensation
88
Palate
arched roof of the oral cavity
89
Uvula
seals off nasal passages during swallowing
90
Tongue
-floor of oral cavity
-chewing
-swallowing
-speech
-taste
91
What type of muscle is the tongue made of?
skeletal
92
Pharynx
-the cavity at the back of the throat
-passageway for air and food
93
Tonsils
-side walls of pharynx
-lymphoid tissue for immune support
94
Teeth
-functions of chewing
-mechanical digestion
-increases surface area for enzymes to act on
-mix food and saliva and stimulate taste buds
95
What are the 3 pairs of salivary glands?
-parotid
-sublingual
-submandibular
96
How is saliva secretion accomplished?
by a large increase in blood flow
97
Which exocrine has the largest secretion per gram?
salivary glands
98
What is the composition of saliva?
99.5% water and 0.5% electrolytes and proteins (amylase, mucus, lysozyme)
99
Salivary Amylase
-begins the digestion of carbohydrates
-breaks polysaccharides into maltose
100
Antibacterial Action of Saliva
-lysozyme breaks down the cell walls of certain bacteria
-rinse away food that could feed bacteria
101
Lubrication at Oral Cavity
-saliva moistens food
102
How does saliva act as a solvent?
-taste buds need moisture to work
103
Bicarbonate in Saliva
-neutralizes acids to prevent cavities and tooth decay
104
Do sympathetic or parasympathetic NS control saliva release?
both
105
Where is amylase broken down?
stomach
106
Is digestion at the oral cavity essential?
no, most of it is done later on
107
Parasympathetic Salivary Secretion
-low-level
-keeps throat and mouth always moist
108
Simple Salivary Reflex
-controlled by chemoreceptors and pressure receptors responding to presence of food
109
Salivary centre
-located in the medulla
-controls digestive activities
110
Conditioned Salivary Reflex
-occurs without oral stimulation
-thinking about, seeing, smelling, hearing food can activate
111
Is parasympathetic and sympathetic activity at salivary glands antagonistic?
no
112
What motility is associated with the pharynx and esophagus?
swallowing
113
Swallowing is an ______ or _____ reflex.
all or none
114
When is swallowing initiated?
when bolus is forced by tongue into pharynx
115
What is the most complicated reflex in the body?
swallowing
116
Can swallowing be stopped once begun?
no
117
Is swallowing voluntary?
yes
118
Where is the swallowing centre located?
medulla
119
Epiglottis
-small cartilage flap
-protects airways from food
120
Esophagus
-straight muscular tube between pharynx and stomach
121
The esophagus has ________ at each end.
sphincters
122
Pharyngoesophageal Sphincter
-upper esophageal sphincter
-prevents large volumes of air from entering digestive tract during breathing
123
Gastroesophageal Sphincter
-lower esophageal sphincter
-prevents reflux of gastric contents
124
Peristaltic Waves
push food through the esophagus
125
Esophageal secretions are entirely _________
protective (mucus lubricates)
126
What are the 3 sections of the stomach?
1. fundus
2. body
3. antrum
127
Fundus
-lies above esophageal opening
-thin smooth muscle
128
Body (Stomach)
-the middle/main part
-thin smooth muscle
129
Antrum
-lower part
-heavier smooth muscle
130
Pyloric Sphincter
-barrier between stomach and duodenum (sm. intestine)
131
Where are the mucosa located in the stomach?
1. Oxyntic (in the body and fundus)
2. Pyloric Gland Area (in the antrum)
132
What are the 3 main stomach functions?
1. Store ingested food
2. Secrete HCl and enzymes for protein digestion
3. Mixing to convert food to chyme
133
What are the 4 aspects of gastric motility?
1. filling
2. storage
3. mixing
4. emptying
134
Gastric Filling
-stomach has a 50mL capacity at empty but can hold up to 1L
135
Receptive Relaxation
-an aspect of filling
-how the stomach accommodates volume change
-stomach folds relax and get smaller as it fills
-without increasing pressure
136
Where does gastric storage take place?
the body of the stomach
137
What moves contents into the storage area?
-peristalsis
-BER
138
Where does gastric mixing take place?
antrum of the stomach
139
How is food mixed? What does it turn into?
food is mixed by strong peristaltic waves and is turned into chyme
140
Factors that influence gastric emptying: Stomach
-amount of chyme
-Gastrin
-fluidity of the chyme
141
Factors that influence gastric emptying: Duodenum
-*primary controls
-duodenum must be ready
-presence of fat, acid, hypertonicity, distention
142
How does ACID affect emptying in duodenum?
-acid in duodenum inhibits further emptying of acidic contents
143
How does HYPERTONICITY affect emptying in duodenum?
-emptying is inhibited when osmolarity starts to rise
144
How does DISTENSION affect emptying in duodenum?
-too much chyme inhibits emptying
145
How does FAT affect emptying in duodenum?
-fat digestion and absorption only occur in sm. intestine
-when fat is already present, emptying is inhibited
146
Emptying: Neural Response (Enterogastric Reflex)
-mediated by intrinsic nerve plexuses (short) and autonomic nerves (long)
147
Emptying: Hormonal Response (Enterogastrones)
-released from duodenal mucosa
-secretin and cholecystokinin
148
Effect of emotions and pain on emptying:
-decrease motility - sadness, fear, pain (SNS)
-increase motility - anger, aggressioon
149
What are the 3 types of secretory cells in oxyntic mucosa?
1. Parietal (oxyntic) Cells
2. Chief Cells
3. Mucous Cells
150
Parietal (Oxyntic) Cells
-secrete HCl and intrinsic factor
151
Intrinsic Factor
used for vitamin B₁₂ absorption
152
Chief Cells
secrete pepsinogen, an enzyme precursor
153
Mucous Cells
-line gastric pits and gland entrances
-secrete watery mucus for lubrication and HCl and pepsin protection
154
HCl Functions
-activates pepsinogen into pepsin
-provides acid medium for optimal pepsin activity
-breakdown of connective tissue and muscle fibres
-denatures proteins
-kills microorganisms
155
Gastric Pits
invaginations in the stomach wall
156
Gastric Glands
lie at the base of gastric pits
157
The entire stomach mucosa is replaced every ___ days by means of _________ cells.
3 days; stem cells
158
Surface Epithelial Cells
-cover gastric mucosa
-secrete thick alkaline mucus
-forms visible layer for protection
159
Pepsinogen (inactive)
the major digestive constituent of gastric secretion
160
Pepsin (active)
splits certain amino acid chains into smaller chains
161
Where is pepsinogen stored and how is it activated?
-stored in secretory vesicles called zymogen granules
-HCl activates pepsinogen
162
Autocatalytic ("self-activating") Process of Pepsin
-process by which pepsin activates other pepsinogen molecules to create more pepsin
163
Why is pepsin stored in its inactive form?
so it doesn't digest the proteins of the cells that create it
164
What secretes 'gastrin' into the blood?
-endocrine 'G cells' found in gastric PGA pits
165
What secretes 'histamine' into the blood?
-Enterochromaffin-like (ECL) cells
-dispersed among parietal and chief cells
166
What secretes 'somatostatin'?
-D cells
-in glands near pylorus and duodenum
167
What 4 substances control secretion of gastric juices?
-gastrin
-histamine
-ACh
-somatostatin
168
What does ACh do?
-stimulates parietal, chief, G cells, and ECL cells to secrete
169
What does Gastrin do?
-stimulates parietal and chief cells
-stimulates ECL cells to release histamine to bring about HCl
170
What does histamine do?
-acts locally to speed up HCl secretion
171
What does somatostatin do?
-acts as a paracrine gland locally
-negative feedback fashion on G cells and ECL cells to inhibit HCl secretion
172
What does the pyloric gland area (PGA) secrete?
gastrin and somatostatin
173
What are the 3 phases of gastric secretion?
1. cephalic
2. gastric
3. intestinal
174
Cephalic Phase
-acts in the head before food reaches the stomach
175
What happens during cephalic phase?
-increased HCl and pepsinogen secretion
-a) thinking about food increases ACh action on these cells
-b) stimulation of G cells enhances HCl and pepsinogen secretion
176
Gastric Phase
-begins when food reaches stomach (ie. proteins)
177
What happens during gastric phase?
-proteins stimulate nerve pathways and gastrin release
178
Intestinal Phase
-the inhibitory phase
179
What happens during the intestinal phase?
when chyme begins to empty the flow of gastric juices is shut off
180
Which nerve controls all these actions?
vagus
181
What 3 things reduce gastric secretion?
1. as the food empties into duodenum
2. fall in pH triggers somatostatin release
3. enterogastric reflex and enterogastrones suppress secretory cells
182
Tight Junctions
line mucosa to prevent leaking acid
183
Gastric Mucosal Barrier
-lubricant, prevention of mechanical injury, protects from self digestion
184
Peptic Ulcers
-when barrier is broken and gastric wall is injured by acid
185
Where does alcohol and aspirin absorption occur?
-stomach
186
Where does 95% of absorption occur?
small intestine
187
Pancreas
-below stomach and above duodenum
-has endocrine and exocrine functions
188
Islets of Langerhans
secrete insulin and glucagon in pancreas
189
Acini
-secretory cells in the pancreas
-connect to ducts and eventually empty into duodenum
190
Exocrine Pancreas
-secretes pancreatic juice that consists of 1) pancreatic enzymes secreted by acinar cells 2) aqueous alkaline solution secreted by duct cells
191
Where are pancreatic enzymes stored?
zymogen granules (inactive precursors)
192
What is the alkaline solution rich in?
sodium bicarbonate NaHCO3
193
What do proteolytic enzymes do?
digest proteins
194
What are the 3 proteolytic enzymes?
trypsin, chymotrypsin, carboxypeptidase
195
Trypsinogen is converted to ______
trypsin
196
Chymotrypsinogen is converted to ______
chymotrypsin
197
Procarboxypeptidase is converted to _______
carboxypeptidase
198
What 3 pancreatic enzymes are secreted by acinar cells?
1. Proteolytic enzymes
2. Pancreatic amylase
3. Pancreatic lipase
199
Pancreatic Amylase
-converts polysaccharides into maltose (disaccharide)
200
Pancreatic Lipase
-only enzyme that can digest fat
201
What activated trypsinogen?
enterokinase in duodenum
202
Secretin acts on the ____ cells of the pancreas.
duct
203
CCK acts on the ______ cells of the pancreas.
acinar
204
What is the purpose of the alkaline fluid secreted?
-duodenum can be damaged by acid
-pancreatic enzymes don't work in acidic conditions
205
Action of Secretin
-release is stimulated by acid in duodenum
-secretin carried by blood to pancreas
-stimulates duct cells to make alkaline fluid
-acid in duodenum is neutralized
206
Action of CCK
-presence of fat and protein in duodenum stimulate CCK release
-CCK carried by blood to pancreas
-acts of acinar cells to increase digestive enzyme secretion
-fat and proteins are digested
207
How are digestive enzymes released?
all of them are grouped together in zymogen granules and release together
208
What is the largest and most important metabolic organ in the body?
liver
209
Where are bile salts secreted from?
the liver via gallbladder and ducts
210
What are bile salts used for?
fat digestion and absorption
211
Where is bile stored?
gallbladder
212
What makes up bile?
-bile salts
-cholesterol
-lecithin
-bilirubin (yellow)
213
When does bile enter the duodenum?
after a meal
214
What does the hepatic portal vein carry? What does it connect?
-carries newly absorbed nutrients to liver for processing
-from sm. intestine to liver
215
What is bile salt?
-derivatives of cholesterol
216
What does bile salt do?
convert large fat globules into a liquid emulsion
217
What happens to bile salts after participating in fat digestion and absorption?
it is reabsorbed into the blood
218
Where are bile salts reabsorbed?
terminal ileum
219
Secreted bile salts are ____% recycled, ___% new.
95; 5
220
What % of bile salts are lost in feces?
5%
221
How do bile salts help lipase?
increase surface area for the enzyme to act on
222
Enterohepatic Circulation
mechanism that recycles bile salts
223
Micelle
-water soluble structures critical component for fat absorption
224
What do micelles do?
-transport digested free fatty acids, monoglycerides, fat soluble vitamins, cholesterol in their hydrophobic centre
225
Structure of a Micelle
-hydrophilic shell (water loving)
-hydrophobic centre (water fearing)
226
Bilirubin
-no role in digestion
-waste product excreted in bile
-pigment derived from breakdown of RBCs
227
How is bile concentration controlled?
-salt actively transported out of gallbladder and water osmotically follows
228
After luminal contents pass beyond the sm. intestine, _____ and _____ no longer occur
digestion and absorption (except salt and water)
229
What are the motility components of the sm. intestine?
-segmentation
-migrating motility complex
230
Segmentation
-the sm. intestines primary method of motility
-ring-like contractions
231
What does segmentation do?
-mix chyme
-expose chyme to absorptive surfaces in mucosa
-move chyme along lumen
232
What initiates segmentation?
-pacemaker cells that produce BER
233
Is segmentation frequency constant?
no, it is slower in the ileum
234
When do segmentation contractions cease?
when most of the meal has been absorbed
235
What replaces segmentation?
migrating motility complex (MMC)
236
When does the MMC act?
between meals
237
What does the MMC do?
-uses peristaltic waves to sweep from the stomach to the intestine
-get rid of meal debris and bacteria and push towards colon
238
Which hormone regulates MMC?
motilin, secreted by intestinal mucosa
239
Ileocecal Valve
-keeps ileal contents moving forward
240
The ileocecal juncture function
barrier between the sm. and lg. intestines
241
Ileocecal Sphincter
-remains mostly constricted
-mediated by intrinsic plexus and gastrin secretion
242
Does the juice secreted by sm. intestine contain digestive enzymes?
no
243
Succus Entericus
-aqueous salt and mucous solution secreted by sm. intestine
-lubricates and protects
-provides water to help with digestion (hydrolysis)
244
Where do synthesized enzymes in sm. intestine act?
within brush-border membrane of epithelial cells
245
What forms the brush border?
microvilli that line the intestinal lumen
246
What are the 3 brush border enzymes?
1. enterokinase
2. disaccharidases
3. aminopeptidases
247
Enterokinase
activates trypsinogen to trypsin
248
Disaccharidases
-maltase, sucrase, or lactase convert disaccharides to monosaccharides
249
Aminopeptidases
convert peptides to amino acids
250
What continues carb and protein digestion in the sm. intestine?
pancreatic enzymes
251
What completes carb and protein digestion in sm. intestine?
brush border enzymes
252
Where and by what is fat ENTIRELY digested by?
-within small intestine by pancreatic lipase
253
What 2 enzymes digest carbohydrates?
-amylase (1st by salivary glands and in stomach: poly to di)
-disaccharidases (2nd by pancreas and sm. intestine: di to mono)
254
What are the absorbable nutrients of carbohydrates?
monosaccharides (esp. glucose)
255
What 3 enzymes digest proteins?
-pepsin (stomach antrum: peptide fragments)
-Trypsin, chymotrypsin, carboxypeptidase (pancreas: attack different fragments)
-Aminopeptidases (sm. intestine: peptide fragments to amino acids)
256
What are the absorbable nutrients of proteins?
amino acids (+ some small peptides)
257
What are the 2 enzymes for digesting fat?
-bile salts - *not an enzyme (liver: emulsification for attack by lipase)
-lipase (pancreas: triglycerides to fatty acids & monoglycerides)
258
What are the absorbable nutrients of fat?
fatty acids and monoglycerides
259
What does the small intestine absorb?
almost everything presented to it
260
Where does most absorption occur at the sm. intestine?
duodenum and jejunum
261
Where is absorption of bile salts and vit. B12 done?
ileum
262
Specialized Absorptive Sm. Intestine Surfaces
-folds to increase surface area
-microvilli
-600x greater than if it was flat
263
Villus Structure
-epithelial cells cover surface
-connective tissue core
-capillary netwrok
-terminal lymphatic vessel (central lacteal)
264
Crypts of Lueberkühn
-invaginations between villi
-don't secrete digestive enzymes
-secrete water and electrolytes
-stem cells for new epithelial cells
265
The lining of the sm. intestine is replaced every ___ days
3
266
Protein and carb end products need _______ to cross the membrane during absorption.
cell-mediated transport systems
267
How are the products of fat absorbed?
broken down and passively absorbed then enter lymph
268
Carbohydrate Absorption (Glucose and Galactose)
-active transport by a) Na+ monosaccharide co transport or b) Na+ independent facilitated diffusion
269
Carbohydrate Absorption (Fructose)
facilitated diffusion
270
Carbs and proteins _____ into blood
diffuse
271
How are proteins absorbed?
Na+ depended transport
272
Free Ride
glucose, galactose, amino acids get a free ride on the energy expended for Na+ transport
273
How do the Micelle contents enter epithelial cells?
passive transport
274
Once entered epithelial cells, monoglycerides and fatty acids are...
resynthesized into triglycerides and packaged into chylomicrons
275
Chylomicrons
-packaged triglycerides coated in a lipoprotein that makes them water soluble
276
Do chylomicrons enter the blood?
no, they go to the central lacteal in the villus (lymph vessel)
277
The large intestine is primarily a ______ and _______ organ.
drying (salt and water absorption) and storage (of feces)
278
What does the lg. intestine receive from the sm. intestine?
-indigestible food residue
-unabsorbed biliary components
-remaining fluid
279
Taeniae Coli
-longitudinal bands of muscle in the lg. intestine
280
Haustra
-pouches or sacs on the lg. intestine
-actively change location due to smooth muscle contraction
281
What is the main motility of the colon?
haustral contractions
282
How fast are haustral contractions? What regulates them?
-slow
-the autonomic rhythmicity of sm. muscle cells
283
Mass Movements
-massive contractions of the colon to move contents into distal part
-stored until defecation
284
Gastrocolic Reflex
-from stomach to colon
-regulated by ANS and gastrin
-followed by urge to defecate
-evident after 1st meal of the day
-used to make room for new meals
285
What initiates the defecation reflex?
stretch receptors in the rectal wall
286
Where are the sensory receptors sent?
sacral portion of the spinal cord
287
Does the parasympathetic or sympathetic NS initiate the reflex?
parasympatheic
288
What type of muscle is the internal anal sphincter?
smooth muscle
289
What type of muscle is the external anal sphincter?
skeletal muscle
290
Does the lg. intestine secrete digestive enzymes?
no
291
What does the lg. intestine secrete?
-alkaline mucous solution
-lubrication and neutralizing acid produced by bacteria
292
Gastrin Summary
-stimulated by presence of proteins in the stomach
-inhibited by acid accumulation in stomach
-increase HCl and pepsinogen secretion
-enhances motility, mass movements
-GI tract lining maintenance
293
Secretin Summary
-stimulated by presence of acid is duodenum
-inhibits emptying into sm. intestine when acid already present
-stimulates duct cells to excrete alkaline solution
-stimulates bile secretion
-trophic to exocrine pancreas
294
CCK Summary
-inhibits motility and secretion
-stimulates acinar cells to secrete pancreatic enzymes
-gallbladder contraction
-trophic to exocrine pancreas
