Chapter 16- The Digestive System Flashcards
(221 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 are the four general functions of the digestive system?
A
- Motility
- Secretion
3.Digestion
4.Absorption
3
Q
What is motility?
A
Muscular activity to mix and move contents
4
Q
What are the two types of digestive motility?
A
- Propulsive movements
- Mixing movements
5
Q
What are propulsive movements?
A
Push contents forward through the digestive tract
6
Q
What are mixing movements?
A
Have two functions:
1. Mixing food with digestive juices promotes digestion of foods
2. Absorption
7
Q
What do exocrine glands (neural and hormonal stimulation) secrete into the digestive tract lumen?
A
Digestive secretions
8
Q
What are digestive secretions?
A
-Water
-electrolytes
-specific organic constituents
9
Q
What happens to digestive secretions once they have participated in digestion?
A
Reabsorbed in one form or another back into blood
10
Q
What is digestion?
A
Biochemical breakdown of structurally complex foodstuffs into smaller, absorbable units
11
Q
What allows digestion to be accomplished?
A
Digestive enzymes
12
Q
What are carbohydrates absorbable unit?
A
Monosachharides
13
Q
What are proteins absorbable units?
A
Amino acids
14
Q
What are fats absorbable units?
A
Glycerol and fatty acids
15
Q
How are most carbohydrates consumed in one’s diet?
A
As disaccharides or polysaccharides
16
Q
What are examples of disaccharides or polysaccharides?
A
Sucrose
Lactose
Maltose
Starch
Glycogen
Cellulose (not digested –
“fibre”)
17
Q
What kind of carbohydrates are absorbed by the intestinal cells for use in the body?
A
Monosaccharides
18
Q
What must Disaccharides and polysaccharides be digested into before they can be absorbed?
A
Must be digested into monosaccharides
19
Q
What are carbohydrates?
A
Simple sugars
C6H12O6
20
Q
What is the chemical structure of a disaccharide/double sugar?
A
2 monosaccharides linked together
21
Q
What is the chemical structure of a polysaccharide?
A
Many sugar molecules linked together
22
Q
What are proteins first broken down into?
A
peptide fragments
23
Q
What are peptide fragments further digested into?
A
Free amino acids
24
Q
What happens to free amino acids during protein digestion?
A
The free amino acids enter epethial cells to be absorbed along with shorts chains of 2-3 a.a are also absorbed
25
What are most dietary fats?
Triglycerides
Glycerol + 3 fatty acids
26
What does the digestion of triglycerides produce?
2 free fatty acids and a monoglyceride
27
What is absorption?
Occurs in small intestine, small absorbable units along with water, vitamins and electrolytes from digestive tract are transferred into lumen then into blood or lymph.
28
What are the parts of the digestive tract?
Mouth
Pharynx
Esophagus
Stomach
Small intestine
Duodenum
Jejunum
Ileum
Large intestine
Cecum
Appendix
Colon
Rectum
Anus
29
What are the accessory digestive organs?
Salivary glands
Exocrine: pancreas
Bilary system: Liver and gallbladder
30
What are the four major tissue layers of the digestive tract wall? (innermost to outermost)
1. Mucosa
2. Submucosa
3. Muscularis externa
4. Serosa
31
What is the mucosa?
Layer that line the luminal surface
has 3 layers
32
How does the mucosa increase surface area?
It has a highly folded surface
33
What are the 3 layers of the mucosa?
1. Mucous membrane
2. Lamina propria
3. Muscularis mucosa
34
What is the mucosa's mucous membrane function?
-Protection
-Modified for secretion and absorption
35
What does the mucosa's mucous membrane contain?
a. Exocrine gland cells
b. Endocrine gland cells
c. Epithelial cells
36
What is the function of exocrine gland cells (mucous membrane)?
Secrete digestive juices
37
What is the function of endocrine gland cells (mucous membrane)?
Secrete blood-borne gastrointestinal hormones
38
What is the functions of epethielial cells (mucous membrane)?
specialized for absorbing digestive nutrients
39
What is the function of the mucosa's lamina propria?
Houses GALT
40
What is GALT?
Gut-Associated Lymphoid Tissue
-Defend against disease-causing intestinal bacteria
41
What is the mucosa's muscularis mucosa?
Sparse layer of smooth muscle
42
What is the anatomy of the Submucosa?
Thick layer of connective tissue
43
What is the function of the submucosa?
Provides digestive tract with distensibility and elasticity
44
What does the submucosa contain?
-Larger blood and lymph vessels
-Nerve network: Submucosal plexus
45
What is the Muscularis Externa?
Major smooth muscle coat of digestive tube
46
What are the 2 layers of the Muscularis externa?
1. Circular layer
2. Longitudinal layer
47
What is the circular layer of the muscularis externa?
-Inner layer
-Contraction ---> decrease diameter of lumen
48
What is the longitudinal layer of the muscularis externa?
-Outer layer
-Contraction ---> shorten the tube
49
Contractile activity of the muscularis externa produces what?
propulsive and mixing movements
50
What cells are found between the two muscle layers of the muscularis externa?
Pacemaker cells called Interstitial cells of Cajal
51
What are Interstitial cells of Cajal?
Origin of rhythmic electrical activity (BER)
-Basic Electrical Rhythm
52
What nerve network lies between the two muscle layers of the muscularis externa?
Myenteric plexus
53
What is the function of the serosa?
Secrete serous fluid
54
What does serous fluid do?
Lubricates and prevents friction between digestive organs and surrounding viscera
55
What is the serosa continuous with throughout most of the tract?
Continous with the mesentery
56
What does the attachment of the serosa and mesentery do?
Provides relative fixation
Supports digestive organs (during mixing/propulsive movements)
57
What is digestive motility and secretion regulated by?
-Autonomous smooth muscle functions
-Intrinsic nerve plexuses
-Extrinsic nerves
-Gastrointestinal hormones
58
What autonomous smooth muscle functions help regulate digestive system functions?
Interstitial cells of Cajal (BER)
59
What are the intrinsic nerve plexuses that help regulate digestive system functions?
Enteric NS= Myenteric + submucosal plexuses
Other sensory and motor functions
60
What extrinsic nerves help regulate digestive system functions?
Nerves from the ANS
61
What gastrointestinal hormones help regulate digestive system functions?
a. Gastrin
b. Other hormones from the brain
62
What parts of the digestive tract do the things regulating digestive system functions act on?
1. Smooth muscle
2. Exocrine gland cells
3. Endocrine gland cells
63
What are the parts of the oral cavity?
-Lips
-Palate
-Tongue
-Pharynx
-Teeth
64
What is the function of the lips?
-Forms an opening
-Helps procure, guide and contains food in the mouth
-Important for speech
-Tactile sensation
65
What is the function of the tongue?
-Forms floor of oral cavity
-Movements of skeletal muscle aid in chewing and swallowing
-Important for speech
-Taste buds
66
What is the function of the palate?
-Forms the roof of the oral cavity
-Contains uvula: seals off nasal passages during swallowing
67
What is the function of the pharynx?
-Passageway for digestive and respiratory systems
-Contains tonsils (lymphoid tissue)
68
What is the function of teeth?
CHEWING:
-Grind, break food into small pieces
-Mix food with saliva
-Stimulate taste buds
69
Why is it important that teeth break food into smaller pieces?
1. Make swallowing easier
2. Increase surface area for salivary enzymes to act on
70
What are the 3 pairs of salivary glands?
1. Parotid
2. Sublingual
3. Submandibualr
71
How do the salivary glands secrete?
Secretion occurs when there's a large increase in blood flow
-Per gram, have the largest secretion of any exocrine gland
72
What is Saliva composed of?
99.5% H2O
0.5% electrolytes and protein
73
What is the 0.5% of saliva composed of specifically?
Amylase
Mucous
Lysozyme
74
What does amylase do?
Begins digestion of carbs
Polysaccharides ---> Disaccharides
75
What does mucus (in saliva) do?
Provides lubrication
76
What does lysozyme do?
-Antibacterial action by destroying bacteria
77
What antibacterial action does saliva have other than lysozyme?
Saliva rinses away material that could be a food source for bacteria
78
How does saliva stimulate taste buds?
Is a solvent for molecules that stimulate taste buds
79
What other functions does saliva have?
-Moistens food making it easier to swallow
-Makes movements of lips/tongue easier for speech
-helps keep mouth and teeth clean
-Rich in bicarbonate buffers
80
What stimulates saliva secretion?
1. Presssure receptors and chemoreceptors in the mouth
2. Thinking, seeing and smelling food signals the cerebral cortex
-triggers salivary centre in medulla
81
What is swallowing?
Motility associated with pharynx and esophagus
82
What kind of reflex is swallowing?
Sequentially programmed all-or-none reflex
-Most complex reflex
83
How is swallowing initiated?
When bolus is voluntarily forced by tongue to rear of mouth into pharynx
-Once initiated cannot be stopped
84
What is the esophagus?
Fairly straight muscular tube extending between the pharynx and stomach
85
What does the esophagus have at each end?
Sphincters
86
What are the two sphincters of the esophagus?
1. Pharyngoesophageal sphincter
2. Gastroesophageal sphincter
87
What is the function of the Pharyngoesophageal sphincter?
Prevents large volumes of air from entering esophagus and stomach during breathing
88
What is the Gastroesophageal sphincter?
Prevents reflux of gastric contents
89
What pushes food through the esophagus?
Peristaltic waves
90
How is the esophagus protected?
Mucus secretions
91
What is the stomach?
J-shaped sac-like chamber lying between esophagus and small intestine
92
What are the 3 sections the stomach is divided into?
1. Fundus
2. Body
3. Antrum
93
What are the two areas of the mucosa of the stomach?
1. Oxyntic
2. Pyloric gland area
94
What re the 3 main functions of the stomach?
1. Store food before it goes into S.I
2.Secrete HCl and enzymes to digest proteins
3. Mixing movements to make chyme
95
What are the four aspects of gastric motility?
1. Filling
2. Storage
3. Mixing
4. Emptying
96
What volume can the stomach fill up to?
50ml- 1L
97
How does the stomach accommodate extra volume of food without rising stomach pressure?
Receptive relaxation
98
What part of the stomach is responsible for storage?
Body
99
What part of the stomach is responsible for mixing?
Antrum
-Because its a thicker muscle
100
How is emptying of the stomach controlled?
1. Largely by factors in duodenum
2. Stomach peristalsis
101
What are the factors in the duodenum?
1. Acid
2. Hypertonicity
3. Distention
102
How is acid a factor in the duodenum?
acid in duodenum inhibits further emptying of acidic gastric contents
103
How is hypertonicity a factor in the duodenum?
Gastric emptying is reflexly inhibited when osmolarity of duodenal contents starts to rise
104
How is distention a factor in the duodenum?
Too much chyme in duodenum inhibits emptying of even more gastric contents
105
What can the factors in the duodenum trigger?
1. Neural response
2. Hormonal response
106
What is the neural response triggered by factors in the duodenum?
Enterogastric reflex
107
What collectively mediates the enterogastric reflex?
Mediated through both:
1. intrinsic nerve plexuses (short
reflex)
2. autonomic nerves (long reflex)
108
What is the hormonal response triggered by factors in the duodenum?
Enterogastrones hormones released from duodenal mucosa
109
What are enterogastrones?
Secretin
Cholecystokinin (CCK)
110
What additional factors can influence gastric motility?
a. Emotions
b.Intense pain
111
How do emotions influence gastric motility?
Sadness and fear – tend to decrease motility
Anger and aggression – tend to increase motility
112
How does intense pain influence gastric motility?
Inhibits motility via the SNS
113
What do the two area of gastric mucosa secrete?
Gastric juice
114
What does the Oxyntic mucosa of the stomach line?
Lines the body and fundus
115
What does the pyloric gland area of the stomach mucosa line?
Line the antrum
116
What are at the bases of gastric glands?
Gastric pits
117
What 3 gastric exocrine secretory cells does the Oxyntic mucosa have?
1. Parietal oxyntic cells
2. Chief cells
3. Mucous cells
118
What do parietal oxyntic cells secrete?
1. HCl
2. Intrinsic factor (B12 absorption)
119
What do Chief cells (oxyntic) secrete?
Enzyme precursor: Pepsinogen
120
What do mucous cells (oxyntic) secrete?
Thin, watery mucous
121
What do mucous cells line?
Gastric pits and entrance of glands
122
What is the purpose of the mucous cells secretion?
-Covers gastric mucosal barrier
-Lubricant
-Prevents mechanical injury
-Protects against self-digestion via HCl and pepsin
123
What are the functions of Hydrochloric acid?
1. Pepsinogen--->Pepsin
2. Breakdown connective tissues+muscle fibres
3.Denatures proteins via pepsin
4. Antibacterial properties
124
What does Pepsin do?
Splits certain amino acid linkages in proteins into small a.a chains
125
What does the Pyloric gland area secrete?
Hormones/paracrine substances
1. Gastrin
2. Somatostatin
126
What can gastrin stimulate to release from ECL cells?
Histamine
127
What are the 3 phases of Gastric secretion?
1. Cephalic phase
2. Gastric phase
3. Intestinal phase
128
What is the Cephalic phase of gastric secretion?
Increased secretion of HCl and pepsinogen that occurs in response to stimuli acting in the head before food reaches stomach
129
What is the Gastric phase of gastric secretion?
Begins when food reaches stomach
-Presence of protein increases gastric secretion
130
What is the Intestinal phase of gastric secretion?
aka Inhibitory phase
Shuts off flow of gastric juices as chyme begins to empty into small intestine
131
What is the pancreas?
Elongated gland begins and below stomach containing exocrine and endocrine tissue
132
What is the endocrine function of the pancreas?
Islets of Langerhans
133
What is the exocrine function of the pancreas?
Secrete pancreatic juice
134
What does pancreatic juice consist of?
3 different types of enzymes
Aqueous alkaline solution
(NaHCO3 + HCl → CO2 + NaCl + H2O)
135
What cells secrete enzymes in the exocrine pancreas?
Acinar cells
136
What cells secrete an aqueous alkaline solution in the pancreas?
Duct cells
(line pancreatic ducts)
137
What are the 3 enzymes acinar cells secrete?
1. proteolytic
2. Pancreatic amylase
3. Pancreatic lipase
138
What are proteolytic enzymes?
Digest protein
139
What are 3 proteolytic enzymes (inactive forms)?
Trypsinogen
Chymotrypsinogen
Procarboxypeptidase
140
What are the 3 proteolytic enzymes called when converted to their active form?
Trypsinogen ----> Tripsin
Chymotrypsinogen ----> Chymotripsin
Procarboxypeptidase ----> Carboxypeptidase
141
What is the function of pancreatic amylase?
Converts polysaccharides ---> Disaccharide maltose
142
What is the function of pancreatic lipase?
Only enzyme in digestive system that can digest fat
143
What is the function of the Aqueous NaHCO3 solution secreted by pancreatic duct cells?
Secretes into the duodenal lumen to neutralise acid
144
What is the liver?
Largest and most important metabolic organ in the body
-Body’s major biochemical factory
145
How is the liver important to the digestive system?
Secretes bile salts via gallbladder and ducts
146
What is bile?
Stubstance secreted by liver, diverted to gallbladder between meals
147
What does the gallbladder do?
Stores and concentrates bile
50mL capacity
148
What are bile salts?
Derivatives of cholesterol that play a role in digestion and absorption of fats
149
What does bile consist of?
1. Bile salts
2. Cholesterol
3. Lecithin (phospholipid)
4. Bilirubin
150
After a meal where does bile go?
It enters the duodenum
151
What do bile salts convert?
Convert large fat globules into a liquid emulsion
152
What are the functions of bile salts?
1. Break up large fat droplets with intestinal mixing
2. Increase surface area for lipase
153
What is a Micelle?
Water soluble structure that is a loosely bound aggregation of several tens or hundreds of atoms
154
What happens to bile salts and lecithin in micelle formation?
Aggregate into small clusters where the fat soluble part shuttle together to form a hydrophobic core
155
What is the function of micelles?
-Fat absorption
-Transport digested fats
156
What digested fats do Micelle's transport?
-Monoglycerides
-Free fatty acids
-Also fat soluble vitamins e.g; Vitamin K
157
Where are monoglycerides + fatty acids located in a micelle?
At the centre
158
How does the gallbladder concentrate bile?
Salt is actively transported out, and water follows osmotically
159
What is the small intestine?
Site where most digestion and absorption take place
160
What are the 3 segments of the small intestine?
1. Duodenum
2. Jejunum
3. Ileum
161
What does small intestine motility include?
-Segmentation
-Migrating motility complex
162
What is segmentation?
Primary method of motility
-Consists of ring-like contractions along length of small intestine
163
What is the action of segmentation?
Within seconds, contracted segments relax and previously relaxed areas contract to mix chyme throughout small intestine
164
What cells initiate segmentation in the small intestine?
Pacemaker cells that produce basic electrical rhythm (BER)
165
What are the frequencies of BER in the duodenum and ileum?
Duodenum ~12/min
Ileum ~9/min
166
What is the function of segmentation?
1. Mix chyme with small intestine digestive juices
2. Expose chyme to absorptive surfaces of mucosa
3. Slowly move chyme through digestive tract
167
What happens to S.I motility when most of a meal has been absorped?
Segmentation contractions stop and migrating motility complex starts
168
What is migrating motility complex (MMC)?
Peristaltic wave sweeps intestines clean between meals
169
What does the small intestine secrete?
A juice without digestive enzymes
170
What is the purpose of small intestine secretion?
1. Lubrication
2. Salt solution
171
What synthesised enzymes act within brush-border membrane of epithelial cells of the small intestine?
1. Enterokinase
2. Disaccharidases
3. Aminopeptidases
172
What does enterokinase do?
converts trypsinogen to trypsin
173
What does disaccharidase do?
converts disaccharides to monosaccharides
174
What are some examples of disaccharidases?
maltase, sucrase, lactase
175
What does aminopeptidase do?
converts peptide fragments to amino acids
176
What is the function of brush-border enzymes?
Complete digestion of carbohydrates and protein after pancreatic enzymes
177
Where is fat entirely digested by pancreatic lipase?
Within the small intestine lumen
178
What does the small intestine absorb?
Almost everything (in the ingested liquids and solids) presented to it
179
Where in the small intestine does most absorption occur?
Duodenum and jejunum
180
Where is Vit B12 and bile salts absorbed in the small intestine?
ileum
181
How does the small intestine adapt to increase surface area?
a. Inner surface has circular folds
b. Villi
c. Brush border microvilli
182
What are found at the base of villi that play a role in absorption? (small intestine)
Crypt
183
What do crypt secrete?
Water solution and new epithelial cells
184
How often is the lining of the S.I replaced?
Every 3 days
185
What molecules are reabsorbed in the S.I that is similar to a nephron?
Na+ and H2O
186
How is fat able to passively absorbed in the S.I?
undergo transformations
187
How are carbohydrates digested?
Broken down into monosaccharides via brush-border enzymes
188
How is glucose and galactose transported into epithelial cells?
Via Na-dependent transporters
189
How is fructose transported into epithelial cells?
Via Facilitated diffusion
190
Once inside epithelial cells, how do monosaccharides and amino acids move out of a cell to be diffused into blood?
Via carriers
191
How are amino acids transported into epithelial cells?
Via Na-dependent transporters
192
What structures help transport eructs of fat digestion (triglycerides)?
Micelles
193
How are fats transported to epithelial cells?
Passively
194
Inside epithelial cells what happens to components of triglycerides?
They reform to make intact triglycerides
195
What happens to the reformed triglycerides?
Packaged into larger particles called Chylomicrons
196
Where do Chylomicrons enter?
Centreal lacteal of the lymphatic vessel of villus
197
What is the large intestine?
Primarily a drying and storage organ
198
What are the parts of the large intestine?
Colon
Cecum
Appendix
Rectum
199
What are the contents that the large intestine receives from the S.I?
1. Indigestible food residues
2. Unabsorbed binary components
3. Remaining fluid
200
What is the colon?
Extracts more water and salt from contents
Forms feces
201
What 2 structures does the large intestine have?
Teniae coli
Haustra
202
What are teniae coli?
Longitudinal bands of muscle
203
What are Haustra?
Pouches or sacs that actively change location as a result of contraction of circular smooth muscle layer
204
What are haustra contractions?
Main motility (slow)
Intimated by autonomous rhythmicity of colonic smooth muscle cells
205
What are mass movements of the large intestine?
Massive contractions that move colonic contents into distal part of large intestine
-2 reflexes
206
What are the 2 reflexes contributing to mass movements or the large intestine?
1. Gastrocolic reflex
2. Defecation reflex
207
What is the Gastrocolic reflex?
Stimulate from stomach to colon by gastrin and by autonomic nerves
-most evident after first meal of the day
-often followed by urge to defecate
208
What stimulates the defecation relflex?
Stretch receptors in the rectal wall stimulated by distention
209
What does the stimulation of the defecation reflex cause?
Causes internal anal (smooth muscle) sphincter to relax and rectum and sigmoid colon to contract more via Parasympathetic NS
210
When does defecation occur?
If external anal sphincter is voluntarily also relaxed
(Micturition)
211
What does the large intestine secrete?
-Alkaline mucous solution
-Has good bacteria
NO DIGESTIVE ENZYMES
212
What does the Colon normally absorb?
Salt and water
213
What are some issues related to the colon?
A. Constipation
B. Diarrhea (not always a colon issue)
214
What is constipation?
Large amount of dry feces
Blockages causing discomfort
Decreased motility due to age, low-bulk diet
215
What is diarrhoea?
Loss of watery material – colon cannot absorb it all
Fluid bulk – not increased motility
Increased secretion
eg cholera: NaCl loss (therefore H2O), K+ and HCO3 - (metabolic acidosis)
216
What is gastrin stimulated by?
Presence of protein in stomach
217
What is gastrin secretion inhibited by?
When acid in stomach accumulates
218
What are the functions of gastrin?
1. Increase HCl and pepsinogen secretion
2. Enhances gastric motility
3. Stimulates ideal motility
4. Relaxes ileocecal sphincter
5. Induces mass movements in the colon
6. Helps maintain viable digestive tract lining
219
What stimulates the secretion of Secretin?
Presence of acid in duodenum
220
What are the functions of secretin?
1. Stops gastric emptying from entering duodenum, until acid already in duodenum is neutralised
2. Inhibits gastric secretion to reduce amount of acid produced
3. Stimulates duct cells to secrete NaHCO3
4. Stimulates liver to secrete NaCO3 rich bile for neutralization
5.Trophic to exocrine pancreas (along with CCK)
221
What are the functions of CCK?
1. Inhibits gastric motility and secretion
2. Stimulates acinar cells to increase enzyme secretion
3. Contracts gallbladder
4. Relaxes sprinter of oddi
5.Trophic to pancreas
6. Long-term adaptive changes to prolonged diet changes
7. Regulator of food intake
