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Physiology 216 > Module 6: Gastrointestinal Physiology > Flashcards

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

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2
Q

What are the 5 stages of nutrient breakdown?

A

Ingestion
Digestion
Absorption
Distribution
Usage

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3
Q

Describe ingestion

A

The physical act of eating

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4
Q

Describe digestion

A

The breakdown of food into small molecules that can be absorbed

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5
Q

Describe absorption

A

The movement of nutrients from the digestive tract into the circulatory system

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6
Q

Describe distribution

A

The movement through the circulatory system for delivery to the tissues and cells

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7
Q

Describe usage

A

The movement of the nutrients into cells for the metabolism or anabolic process

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8
Q

Describe motility

A
  • The muscular contractions that both mix and propel the contents of the digestive system
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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

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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

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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

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12
Q

Each digestive juice secretion contains a unique mixture of what?

A

Electrolytes, water, enzymes, bile salts, mucus

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13
Q

What happen to secretions once they have completed their role in digestion

A

They are absorbed back into the body

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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

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15
Q

What is digestion?

A

The biochemical process of the enzymatic breakdown of foods into small absorbable units

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16
Q

Describe how carbohydrates are digested

A

Most enter as polysaccharides
They are broken down into monosaccharides - mainly glucose, fructose and galactose

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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

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18
Q

How are proteins digested?

A

They are broken down into single amino acids or into small polypeptides for absorption

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19
Q

Where does absorption occur?

A

In the small intestine

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20
Q

What are the four major layers of the digestive tract walls?

A

The mucosa
Submucosa
Muscularis Externa
Serosa

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21
Q

Describe the mucosa

A

The innermost layer
Lines the luminal space
Highly folded surface to increase SA, but this varies

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22
Q

T/F
The esophagus has less folding of the mucosa than the small instestine

A

True

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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

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24
Q

In what digestive tract wall layer contains the submucosal plexus

A

The submucosa layer

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25
Q

Describe the muscularis externa

A

The smooth muscle layer that surrounds the submucosa
Contains two layers
Provide propulsive and mixing contractions

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26
Q

What does contraction of the inner circular layer of the muscularis externa do?

A

Decreases the lumen diameter

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27
Q

What does contraction of the outer longitudinal layer of the muscularis externa do?

A

Shortens the tube

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28
Q

where is the myenteric plexus located?

A

Between the inner circular layer and outer longitudinal layer of the muscularis externa

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29
Q

Describe the serosa

A

The outer connective tissue layer that covers the digestive tract
Helps to suspend the digestive organs from the inner wall of the abdominal cavity

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30
Q

What are the four factors that regulate digestive system function?

A

The autonomous smooth muscle function
The intrinsic nervous plexuses
The extrinsic autonomic nerves
The gastrointestinal hormones

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31
Q

What is another name for the enteric nervous system (ENS)

A

The intrinsic nerve plexuses

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32
Q

What is the ENS?

A

Is the submucosal plexus and the myenteric plexus

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33
Q

T/F
The ENS is completely self-regulated

A

False
It is mostly self-regulated, but receives significant input from the ANS

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34
Q

T/F
The ENS is made up of sensory neurons

A

True

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35
Q

Describe the extrinsic autonomic nerves

A

Made up of nerve fibres from both the sympathetic and parasympathetic nervous systems that innervate digestive organs

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36
Q

How does the ANS influence motility and secretion

A

It modifies the activity of the ENS, regulating GI hormone secretion, and can directly innervate some smooth muscle and glands

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37
Q

How does the sympathetic system impact digestive tract contractions and secretions

A

It slows them down

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38
Q

How does the parasympathetic system impact digestive tract contractions and secretion

A

It increases them

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39
Q

T/F
Gastrointestinal hormones only have excitatory actions on motility and exocrine gland secretions

A

False
They have both excitatory and inhibitory

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40
Q

What are the non-contractile interstitial cells of Cajal?

A

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

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41
Q

How do the muscles in the stomach coordinate an in-sync contraction?

A

The cells are connected by gap junctions, so an action potential can move between cells and allow for them to contract as a unit

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42
Q

T/F
Mechanical, neural, and hormonal factors module the membrane potential around which the slow-waves oscillate

A

True

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43
Q

When does the cephalic phase of digestion begin

A

Before the food enters your mouth

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44
Q

What is the purpose of the cephalic phase of digestion?

A

To prepare the stomach prior to the arrival of food

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45
Q

What cranial nerve signals the stomach to cause gastric secretions during the cephalic phase

A

The vagus nerve

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46
Q

Where does the oral phase occur?

A

In the oral cavity

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47
Q

What oral cavity structures aid in digestion?

A

The palate
Tongue
Pharynx
Teeth

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48
Q

What is the palate?
How does it help in digestion?

A

It is the “roof” of the mouth
It separates the oral cavity from the nasal cavity and allows breathing while chewing

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49
Q

What is the tongue?
How does it help in digestion?

A

The “floor” of the oral cavity
Important for chewing, swallowing, tasting, and speech

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50
Q

What is the pharynx
How does it help in digestion?

A

The cavity behind the nose and mouth
Connects them to the esophagus

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51
Q

T/F
The pharynx is part of both the digestive system and the respiratory system

A

True

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52
Q

What are the teeth
How do they help with digestion?

A

External bones embedded in the jaw bone
Used for chewing and mixing food with saliva

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53
Q

What is saliva made of?

A

99.5% water
0.5% electrolytes, enzymes, and proteins

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54
Q

What are the three major proteins of saliva?

A

Amylase, mucus, and lysozyme

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55
Q

What does amylase in saliva do?

A

Begins the breakdown of carbohydrates

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56
Q

What does mucus in saliva do?

A

Moistens the food to facilitate swallowing

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57
Q

What does lysozyme in saliva do?

A

Destroys bacteria

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58
Q

How does saliva play a role in speech?

A

It lubricates the tongue and lips

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59
Q

Compare sympathetic vs parasympathetic innervation on salivary secretion

A

Sympathetic:
- Less saliva
- Thick and rich in mucus
Parasympathetic:
- Fast flow of saliva
- Watery and rich in enzymes

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60
Q

What are simple salivary reflexes? When does it occur?

A

Occur when chemoreceptors and mechanoreceptors in the oral cavity respond to the presence of food
Promotes increased salivation

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61
Q

What are conditional salivary reflexes?

A

The “mouth watering” effect that happens when thinking about, seeing, smelling, or hearing the preparation of yummy food
Is a conditioned response

62
Q

Describe the neural process of swallowing

A

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
Q

T/F
Swallowing is a voluntary process

A

False
The first part of swallowing is voluntary, but once it starts, it cannot be stopped (aka, involuntary)

64
Q

What are the two phases of swallowing?

A

The orthopharyngeal phase
The esophageal phase

65
Q

How long does the orthopharyngeal phase last?

A

About a second

66
Q

Describe the orthopharyngeal phase

A

Bolus enters the pharynx, and needs to be directed to the esophagus

67
Q

Describe how the bolus is prevented from entering the mouth in swallowing

A

After swallowing is initiated, the tongue positions itself against the palate to keep food from coming back into the mouth

68
Q

Describe how the bolus is prevented from entering the nasal passages in swallowing

A

The uvula elevates and blocks the nasal passages

69
Q

Describe how the bolus is prevented from entering the respiratory passages in swallowing

A

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
Q

Describe what happens in the esophageal phase of swallowing

A

The swallowing center activates a primary peristaltic wave that moves from the beginning of the esophagus to the end

71
Q

What is peristalsis?

A

The ring-like contractions of the circular smooth muscle found in the digestive tract

72
Q

What happens if the bolus does not enter the stomach with the primary peristaltic wave?

A

The distension of the esophagus initiates a more powerful second wave

73
Q

T/F
The secondary peristaltic wave is initiated from the swallowing centre in the medulla

A

False
It is initiated by the intrinsic nerve plexus

74
Q

How does the stomach prevent gastric reflux?

A

The lower esophageal sphincter remains tightly contracted when swallowing is not occurring to prevent stomach acids from coming up into the esophagus

75
Q

What are the three areas of the stomach?

A

The Fundus
The body
The antrum

76
Q

Describe the Fundus

A

The part of the stomach that lies above the esophageal opening

77
Q

Describe the body

A

The main part of the stomach

78
Q

Describe the antrum

A

The muscular lower section of the stomach

79
Q

What are 3 functions of the stomach

A
  • 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
Q

What is the volume of the stomach while empty?

A

50mL

81
Q

What volume can the stomach expand up to?

A

4000mL

82
Q

What allows for the stomach to expand

A

Deep folds that can get smaller and flatter as needed

83
Q

In what area is food stored in the stomach?

A

In the body

84
Q

Where does mixing occur in the stomach?

A

In the antrum

85
Q

With each peristaltic wave, the chyme is pushed towards where?

A

The pylonic sphincter

86
Q

What is retropulsion?

A

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
Q

If a very strong peristaltic wave occurs, how much chyme will pass through the pylonic sphincter?

A

A great volume, but then it will tighten up again

88
Q

T/F
A little bit of chyme is released through the pylonic sphincter each time a peristaltic wave occurs?

A

True!

89
Q

The intensity of the peristaltic wave is influenced by what?

A

The amount of chyme in the antrum and its fluidity

90
Q

How does the duodenum influence the rate of gastric emptying?

A

If it is not ready to receive chyme, it will send signals to reduce gastric emptying

91
Q

What four duodenum stimuli affect gastric emptying?
Which is the most potent

A

Fat - most potent
Acid
Hypertonicity
Distention

92
Q

How does fat impact gastric emptying?

A

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
Q

How does acid impact gastric emptying?

A

The duodenum has to neutralize it to prevent damage to the tissue

94
Q

How does the body neutralize acid leaving the stomach?

A

It releases NaHCO3 from the pancreas

95
Q

How does hypertonicity impact gastric emptying

A

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
Q

How does distention impact gastric emptying

A

The more the duodenum is distended, the slower the rate of gastric emptying

97
Q

What is another word for emesis

A

Vomiting

98
Q

Describe the process of vomiting

A

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
Q

What is the oxyntic mucosa?

A

Lines the fundus and body of the stomach

100
Q

What is the pyloric gland?

A

Lines the antrum

101
Q

What are gastric pits?

A

The pockets formed by the in-foldings of the gastric mucosa

102
Q

What are the three types of secretory cells in the oxyntic mucosa

A

Mucous cells
Chief cells
Parietal cells

103
Q

Describe mucous cells

A

Line the puts and enterance to the glands secrete a watery mucus

104
Q

Describe chief cells

A

Secrete pepsinogen

105
Q

Describe parietal cells

A

In the gastric glands
Secrete HCl and intrinsic factor

106
Q

What are the four functions of HCl in the stomach?

A

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
Q

Describe the mechanism of HCl secretion

A

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
Q

Describe how pepsinogen is converted to its active form: pepsin

A

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
Q

T/F
Pepsin function is dependent on the acidity of the stomach

A

True

110
Q

List the three ways mucus serves as a protective barrier in the stomach

A

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
Q

What is intrinsic factor important for?

A

The absorption of B12

112
Q

What are G cells?
Where are they located?
What do they secrete?
What stimulates it?
What does it stimulate?

A

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
Q

What are enterochromaffin-like cells?
Where are they located?
What do they secrete?

A

Cells found in the oxyntic mucosa
Secrete histamine, which increases HCl secretion

114
Q

Where are D cells located?
What do they secrete?

A

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
Q

What are the three phases of gastric secretion

A

Gastric phase
Intestinal phase
Cephalic phase

116
Q

What type of stimuli increase gastric secretion?

A

Protein, distention, caffeine, alcohol

117
Q

What is the intestinal phase

A

Factors originating in the small intestine that affect gastric secretion

118
Q

T/F
Factors of the intestinal phase can be both inhibitory and excitatory

A

False
They are all inhibitory to help turn off the flow of gastric juices as chyme starts to move into the small intestine

119
Q

What two contents can the stomach itself absorb?

A

Alcohol
Aspirin

120
Q

What part of the digestive system are pancreatic and biliary secretions added to?

A

The small intestine

121
Q

What are the exocrine functions of the pancreas?

A

Secretes pancreatic juice

122
Q

What is pancreatic juice?

A

It is a mixture of pancreatic enzymes and aqueous alkaline secretion

123
Q

What are the grape-like secretory cell clusters on the pancreas called?

A

Acini

124
Q

Acinar cells secrete what types of pancreatic enzymes?

A

Proteolytic enzymes
Pancreatic amylase
Pancreatic lipase

125
Q

Name the major proteolytic enzymes secreted

A

Trypsinogen
Chymotripsinogen
Procarboxypeptidase

126
Q

T/F
All proteolytic enzymes are secreted in their inactive form

A

True

127
Q

What is the function of pancreatic amylase?

A

Converts polysaccharides into disaccharide maltose
Hydrolyzes starches, glycogen, and carbohydrates

128
Q

What is the function of pancreatic lipase?

A

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
Q

Identify three ways pancreatic exocrine secretion is controlled

A

Via the parasympathetic system
Gastrin
Hormones
Presence of chyme in the doudenum

130
Q

Secretin secretion is stimulated from what?

A

The presence of acid causes the duodenal and jejunal mucosa to release it

131
Q

What does secretin stimulate?

A

The duct cells to increase their secretions of the NaHCO3- rich fluid

132
Q

What causes the release of CCK

A

In response to the presence of fats or proteins in the duodenum

133
Q

What does the CKK stimulate?

A

Pancreatic acinar cells to increase digestive enzyme secretion

134
Q

With respect to digestion, what is the most important function of the liver?

A

The production of bile salts

135
Q

Name three other functions of the
liver

A

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
Q

What is the liver cell called?

A

A hepatocyte

137
Q

T/F
Each hepatocyte has to be in contact with both arterial blood and venous blood

A

true

138
Q

Where does venous blood flow through from the digestive system into the liver?

A

Via the hepatic portal vein

139
Q

Via what structure does the arterial blood enter the liver?

A

Via the hepatic artery

140
Q

What is the functional unit of the liver?

A

The lobules

141
Q

Describe the lobules

A

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
Q

The bile ducts converge to form what?
What does it do?

A

The common bile duct
Transports bile from the liver to the duodenum

143
Q

What are sinusoids?

A

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
Q

What are Kupfer cells?

A

Macrophages that line the sinusoids

145
Q

The thin-bile-carrying channels located between hepatic cells are called what?

A

Bile canaliculus

146
Q

T/F
Hepatocytes secrete bile into the canaliculus while under hormonal control

A

False
They do it all the time - constant

147
Q

T/F
Each hepatocyte is in contact with two sinusoids on one side and a bile canaliculus on the other side

A

WRONGG
It has contact with ONE sinusoid on one side and a bile canaliculus on the other side

148
Q

T/F
Bile secretion, while constantly produced, doesn’t enter the duodenum unless active digestion is occuring?

A

True

149
Q

The opening of the bile duct into the duodenum is guarded by what?

A

The sphincter of Oddi

150
Q

What happens to bile that is not needed?

A

It is diverted back up into the common bile duct and into the gallbladder for storage

151
Q

What is bile composed of?

A

Bile is composed mainly of bile salts, cholesterol, lecithin, and bilirubin

152
Q

What affects do bile salts have on chyme

A

They convert large fat globules in the chyme into a lipid emulsion of numerous small fat droplets

Physiology 216 (5 decks)

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