Module 6: Gastrointestinal Physiology Flashcards
1
Q
Name the 12 organs and structures of the GI system
A
Nasal passages
Esophagus
Gallbladder
Colon
Mouth
Liver
Pancreas
Rectum
Salivary Glands
Stomach
Small intestine
Anus
2
Q
What are the 5 stages of nutrient breakdown?
A
Ingestion
Digestion
Absorption
Distribution
Usage
3
Q
Describe ingestion
A
The physical act of eating
4
Q
Describe digestion
A
The breakdown of food into small molecules that can be absorbed
5
Q
Describe absorption
A
The movement of nutrients from the digestive tract into the circulatory system
6
Q
Describe distribution
A
The movement through the circulatory system for delivery to the tissues and cells
7
Q
Describe usage
A
The movement of the nutrients into cells for the metabolism or anabolic process
8
Q
Describe motility
A
- The muscular contractions that both mix and propel the contents of the digestive system
9
Q
T/F
The rate of movement is the same throughout the entirety of the digestive system
A
False
It depends on the segment of the digestive system
Contents are moved at an appropriate speed to allow each segment to do its job
10
Q
Why are the contents of the stomach mixed?
A
To help mix the food with digestive enzymes and to promote absorption by making sure all the contents eventually make contact with the digestive system walls
11
Q
What are the three digestive structures that use skeletal muscle instead of smooth?
A
The mouth
Top of the esophagus
External anal sphincter
12
Q
Each digestive juice secretion contains a unique mixture of what?
A
Electrolytes, water, enzymes, bile salts, mucus
13
Q
What happen to secretions once they have completed their role in digestion
A
They are absorbed back into the body
14
Q
What are the role of endocrine cells in the digestive tract?
A
To secrete gastrointestinal hormones into the blood that help control motility and exocrine gland secretion
15
Q
What is digestion?
A
The biochemical process of the enzymatic breakdown of foods into small absorbable units
16
Q
Describe how carbohydrates are digested
A
Most enter as polysaccharides
They are broken down into monosaccharides - mainly glucose, fructose and galactose
17
Q
How are fats digested?
A
They are consumed as triglycerides and are broken down by releasing two of the fatty acids, leading a monoglyceride
The monoglyceride and fatty acids can be absorbed
18
Q
How are proteins digested?
A
They are broken down into single amino acids or into small polypeptides for absorption
19
Q
Where does absorption occur?
A
In the small intestine
20
Q
What are the four major layers of the digestive tract walls?
A
The mucosa
Submucosa
Muscularis Externa
Serosa
21
Q
Describe the mucosa
A
The innermost layer
Lines the luminal space
Highly folded surface to increase SA, but this varies
22
Q
T/F
The esophagus has less folding of the mucosa than the small instestine
A
True
23
Q
Describe the submucosa
A
Thich
Made up of connective tissue that support the mucosa
Provides distensibility and elasticity to the digestive tract
Contains larger blood and lymph vessels
24
Q
In what digestive tract wall layer contains the submucosal plexus
A
The submucosa layer
25
Describe the muscularis externa
The smooth muscle layer that surrounds the submucosa
Contains two layers
Provide propulsive and mixing contractions
26
What does contraction of the inner circular layer of the muscularis externa do?
Decreases the lumen diameter
27
What does contraction of the outer longitudinal layer of the muscularis externa do?
Shortens the tube
28
where is the myenteric plexus located?
Between the inner circular layer and outer longitudinal layer of the muscularis externa
29
Describe the serosa
The outer connective tissue layer that covers the digestive tract
Helps to suspend the digestive organs from the inner wall of the abdominal cavity
30
What are the four factors that regulate digestive system function?
The autonomous smooth muscle function
The intrinsic nervous plexuses
The extrinsic autonomic nerves
The gastrointestinal hormones
31
What is another name for the enteric nervous system (ENS)
The intrinsic nerve plexuses
32
What is the ENS?
Is the submucosal plexus and the myenteric plexus
33
T/F
The ENS is completely self-regulated
False
It is mostly self-regulated, but receives significant input from the ANS
34
T/F
The ENS is made up of sensory neurons
True
35
Describe the extrinsic autonomic nerves
Made up of nerve fibres from both the sympathetic and parasympathetic nervous systems that innervate digestive organs
36
How does the ANS influence motility and secretion
It modifies the activity of the ENS, regulating GI hormone secretion, and can directly innervate some smooth muscle and glands
37
How does the sympathetic system impact digestive tract contractions and secretions
It slows them down
38
How does the parasympathetic system impact digestive tract contractions and secretion
It increases them
39
T/F
Gastrointestinal hormones only have excitatory actions on motility and exocrine gland secretions
False
They have both excitatory and inhibitory
40
What are the non-contractile interstitial cells of Cajal?
They are smooth muscle cells that have slow-wave, pacemaker like changes in membrane potential
The slow waves are not action potentials in that they cannot induce contractions
41
How do the muscles in the stomach coordinate an in-sync contraction?
The cells are connected by gap junctions, so an action potential can move between cells and allow for them to contract as a unit
42
T/F
Mechanical, neural, and hormonal factors module the membrane potential around which the slow-waves oscillate
True
43
When does the cephalic phase of digestion begin
Before the food enters your mouth
44
What is the purpose of the cephalic phase of digestion?
To prepare the stomach prior to the arrival of food
45
What cranial nerve signals the stomach to cause gastric secretions during the cephalic phase
The vagus nerve
46
Where does the oral phase occur?
In the oral cavity
47
What oral cavity structures aid in digestion?
The palate
Tongue
Pharynx
Teeth
48
What is the palate?
How does it help in digestion?
It is the "roof" of the mouth
It separates the oral cavity from the nasal cavity and allows breathing while chewing
49
What is the tongue?
How does it help in digestion?
The "floor" of the oral cavity
Important for chewing, swallowing, tasting, and speech
50
What is the pharynx
How does it help in digestion?
The cavity behind the nose and mouth
Connects them to the esophagus
51
T/F
The pharynx is part of both the digestive system and the respiratory system
True
52
What are the teeth
How do they help with digestion?
External bones embedded in the jaw bone
Used for chewing and mixing food with saliva
53
What is saliva made of?
99.5% water
0.5% electrolytes, enzymes, and proteins
54
What are the three major proteins of saliva?
Amylase, mucus, and lysozyme
55
What does amylase in saliva do?
Begins the breakdown of carbohydrates
56
What does mucus in saliva do?
Moistens the food to facilitate swallowing
57
What does lysozyme in saliva do?
Destroys bacteria
58
How does saliva play a role in speech?
It lubricates the tongue and lips
59
Compare sympathetic vs parasympathetic innervation on salivary secretion
Sympathetic:
- Less saliva
- Thick and rich in mucus
Parasympathetic:
- Fast flow of saliva
- Watery and rich in enzymes
60
What are simple salivary reflexes? When does it occur?
Occur when chemoreceptors and mechanoreceptors in the oral cavity respond to the presence of food
Promotes increased salivation
61
What are conditional salivary reflexes?
The "mouth watering" effect that happens when thinking about, seeing, smelling, or hearing the preparation of yummy food
Is a conditioned response
62
Describe the neural process of swallowing
Pressure sensors in the pharynx send afferent signals to the swallowing centre, located in the medulla
Efferent signals from the centre control the timing and muscle activation for swallowing
63
T/F
Swallowing is a voluntary process
False
The first part of swallowing is voluntary, but once it starts, it cannot be stopped (aka, involuntary)
64
What are the two phases of swallowing?
The orthopharyngeal phase
The esophageal phase
65
How long does the orthopharyngeal phase last?
About a second
66
Describe the orthopharyngeal phase
Bolus enters the pharynx, and needs to be directed to the esophagus
67
Describe how the bolus is prevented from entering the mouth in swallowing
After swallowing is initiated, the tongue positions itself against the palate to keep food from coming back into the mouth
68
Describe how the bolus is prevented from entering the nasal passages in swallowing
The uvula elevates and blocks the nasal passages
69
Describe how the bolus is prevented from entering the respiratory passages in swallowing
The respiratory centre in the brain stem is inhibited so there is no movement of air
The larynx elevates and the vocal folds tighten to prevent food from entering the trachea
70
Describe what happens in the esophageal phase of swallowing
The swallowing center activates a primary peristaltic wave that moves from the beginning of the esophagus to the end
71
What is peristalsis?
The ring-like contractions of the circular smooth muscle found in the digestive tract
72
What happens if the bolus does not enter the stomach with the primary peristaltic wave?
The distension of the esophagus initiates a more powerful second wave
73
T/F
The secondary peristaltic wave is initiated from the swallowing centre in the medulla
False
It is initiated by the intrinsic nerve plexus
74
How does the stomach prevent gastric reflux?
The lower esophageal sphincter remains tightly contracted when swallowing is not occurring to prevent stomach acids from coming up into the esophagus
75
What are the three areas of the stomach?
The Fundus
The body
The antrum
76
Describe the Fundus
The part of the stomach that lies above the esophageal opening
77
Describe the body
The main part of the stomach
78
Describe the antrum
The muscular lower section of the stomach
79
What are 3 functions of the stomach
- To store ingested food until it is ready to be released into the small intestine
- To secrete HCl and enzymes needed for protein digestion
- To mechanically mix the food with gastric secretions to produce chyme
80
What is the volume of the stomach while empty?
50mL
81
What volume can the stomach expand up to?
4000mL
82
What allows for the stomach to expand
Deep folds that can get smaller and flatter as needed
83
In what area is food stored in the stomach?
In the body
84
Where does mixing occur in the stomach?
In the antrum
85
With each peristaltic wave, the chyme is pushed towards where?
The pylonic sphincter
86
What is retropulsion?
The act of pushing chyme against the pylonic sphincter, only for it to fold back upon itself, and again propelled forward, etc., to mix it
87
If a very strong peristaltic wave occurs, how much chyme will pass through the pylonic sphincter?
A great volume, but then it will tighten up again
88
T/F
A little bit of chyme is released through the pylonic sphincter each time a peristaltic wave occurs?
True!
89
The intensity of the peristaltic wave is influenced by what?
The amount of chyme in the antrum and its fluidity
90
How does the duodenum influence the rate of gastric emptying?
If it is not ready to receive chyme, it will send signals to reduce gastric emptying
91
What four duodenum stimuli affect gastric emptying?
Which is the most potent
Fat - most potent
Acid
Hypertonicity
Distention
92
How does fat impact gastric emptying?
It takes a long time for fat to be digested and absorbed in the lumen of the small intestine, so the presence of fat reduced gastric emptying to allow more time to process it
93
How does acid impact gastric emptying?
The duodenum has to neutralize it to prevent damage to the tissue
94
How does the body neutralize acid leaving the stomach?
It releases NaHCO3 from the pancreas
95
How does hypertonicity impact gastric emptying
The breakdown of proteins and carbs causes increases in osmolarity, which then means more water will be brought in, which needs to be reabsorbed
96
How does distention impact gastric emptying
The more the duodenum is distended, the slower the rate of gastric emptying
97
What is another word for emesis
Vomiting
98
Describe the process of vomiting
Starts with a closure of the glotis, and uvula. The diaphragm then contracts downwards and the abdominal muscles contract inwards. The stomach is compressed and the contents are forced upwards
This repeats until the stomach is empty
99
What is the oxyntic mucosa?
Lines the fundus and body of the stomach
100
What is the pyloric gland?
Lines the antrum
101
What are gastric pits?
The pockets formed by the in-foldings of the gastric mucosa
102
What are the three types of secretory cells in the oxyntic mucosa
Mucous cells
Chief cells
Parietal cells
103
Describe mucous cells
Line the puts and enterance to the glands secrete a watery mucus
104
Describe chief cells
Secrete pepsinogen
105
Describe parietal cells
In the gastric glands
Secrete HCl and intrinsic factor
106
What are the four functions of HCl in the stomach?
1) activates pepsinogen to the active form of pepsin
2) Helps break down CT and muscle fibres
3) Denatures protein
4) Kills most microorganisms ingested with food
107
Describe the mechanism of HCl secretion
In the parietal cells, H2O is broken down into H+ and OH-
The H+ is secreted into the lumen by the H+-K+ATPase transport, and HCO3- also leaks out into the lumen
The HCO3- is meoved into the plasma by a Cl- -HCO3- exchanger, creating a buildup of Cl- within the partietal cells, which move through their electrochemical gradient into the gastric lumen
108
Describe how pepsinogen is converted to its active form: pepsin
HCl cleaves off a small part of the protein to release the active form of pepsin
pepsin then cleaves more pepsinogen to form more pepsin
109
T/F
Pepsin function is dependent on the acidity of the stomach
True
110
List the three ways mucus serves as a protective barrier in the stomach
1) acts as a lubricant and protects gastric mucosa against mechanical injury
2) Protects the stomach wall from the acid environment due to its alkalinicity that can neutralize it
3) It protects the stomach from self-digestion. Bc pepsin requires an acidic environment, the basicity of the mucus inhibits its function
111
What is intrinsic factor important for?
The absorption of B12
112
What are G cells?
Where are they located?
What do they secrete?
What stimulates it?
What does it stimulate?
Endocrine cells in the pylonic gland area that secrete the hormone gastrin
Its release is stimulated by protein in the stomach and ACh from the intrinsic nerve plexus
It stimulates chief and parietal cells to increase their function
113
What are enterochromaffin-like cells?
Where are they located?
What do they secrete?
Cells found in the oxyntic mucosa
Secrete histamine, which increases HCl secretion
114
Where are D cells located?
What do they secrete?
Found near the pylorus and in the duodenum
Secrete somatostatin in response to acid, which inhibits the secretion of parietal cells, G cells, and ECL cells
115
What are the three phases of gastric secretion
Gastric phase
Intestinal phase
Cephalic phase
116
What type of stimuli increase gastric secretion?
Protein, distention, caffeine, alcohol
117
What is the intestinal phase
Factors originating in the small intestine that affect gastric secretion
118
T/F
Factors of the intestinal phase can be both inhibitory and excitatory
False
They are all inhibitory to help turn off the flow of gastric juices as chyme starts to move into the small intestine
119
What two contents can the stomach itself absorb?
Alcohol
Aspirin
120
What part of the digestive system are pancreatic and biliary secretions added to?
The small intestine
121
What are the exocrine functions of the pancreas?
Secretes pancreatic juice
122
What is pancreatic juice?
It is a mixture of pancreatic enzymes and aqueous alkaline secretion
123
What are the grape-like secretory cell clusters on the pancreas called?
Acini
124
Acinar cells secrete what types of pancreatic enzymes?
Proteolytic enzymes
Pancreatic amylase
Pancreatic lipase
125
Name the major proteolytic enzymes secreted
Trypsinogen
Chymotripsinogen
Procarboxypeptidase
126
T/F
All proteolytic enzymes are secreted in their inactive form
True
127
What is the function of pancreatic amylase?
Converts polysaccharides into disaccharide maltose
Hydrolyzes starches, glycogen, and carbohydrates
128
What is the function of pancreatic lipase?
To digest fats
Hydrolyzes triglycerides into monoglycerides and free fatty acids, which can then be absorbed
Only enzyme in the entire digestive system that can do this
129
Identify three ways pancreatic exocrine secretion is controlled
Via the parasympathetic system
Gastrin
Hormones
Presence of chyme in the doudenum
130
Secretin secretion is stimulated from what?
The presence of acid causes the duodenal and jejunal mucosa to release it
131
What does secretin stimulate?
The duct cells to increase their secretions of the NaHCO3- rich fluid
132
What causes the release of CCK
In response to the presence of fats or proteins in the duodenum
133
What does the CKK stimulate?
Pancreatic acinar cells to increase digestive enzyme secretion
134
With respect to digestion, what is the most important function of the liver?
The production of bile salts
135
Name three other functions of the
liver
1) Metabolic processing of fats, carbs, proteins
2) Detoxification of wastes
3) Synthesizing plasma proteins
4) Storage of glycogen, fats, iron, copper, vitamins
5) Involved in Vit. D activation
6) Removal of old red blood cells and bacteria
7) Excreting chloesterol and bilirubin
136
What is the liver cell called?
A hepatocyte
137
T/F
Each hepatocyte has to be in contact with both arterial blood and venous blood
true
138
Where does venous blood flow through from the digestive system into the liver?
Via the hepatic portal vein
139
Via what structure does the arterial blood enter the liver?
Via the hepatic artery
140
What is the functional unit of the liver?
The lobules
141
Describe the lobules
Are hexagonal in shape
Surround the central vein
At each of the six outer corners, a branch of the hepatic artery, a branch of the hepatic portal vein, and a bile duct are locatd
142
The bile ducts converge to form what?
What does it do?
The common bile duct
Transports bile from the liver to the duodenum
143
What are sinusoids?
Capillary like structures that run between rows of liver cells towards the central vein that carry blood from the hepatic artery and portal vein
144
What are Kupfer cells?
Macrophages that line the sinusoids
145
The thin-bile-carrying channels located between hepatic cells are called what?
Bile canaliculus
146
T/F
Hepatocytes secrete bile into the canaliculus while under hormonal control
False
They do it all the time - constant
147
T/F
Each hepatocyte is in contact with two sinusoids on one side and a bile canaliculus on the other side
WRONGG
It has contact with ONE sinusoid on one side and a bile canaliculus on the other side
148
T/F
Bile secretion, while constantly produced, doesn't enter the duodenum unless active digestion is occuring?
True
149
The opening of the bile duct into the duodenum is guarded by what?
The sphincter of Oddi
150
What happens to bile that is not needed?
It is diverted back up into the common bile duct and into the gallbladder for storage
151
What is bile composed of?
Bile is composed mainly of bile salts, cholesterol, lecithin, and bilirubin
152
What affects do bile salts have on chyme
They convert large fat globules in the chyme into a lipid emulsion of numerous small fat droplets
