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Physiology > Gastrointestinal Physiology > Flashcards

Gastrointestinal Physiology Flashcards

1
Q

Two types of smooth muscle layer

A

Longitudinal smooth muscle layer
Circular smooth muscle layer

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2
Q

What is the function of the longitudinal smooth muscle layer?

A

extends down the GI and contraction moves the food forward

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3
Q

What is the function of the circular smooth muscle layer?

A

extend around the GI tract and contraction squeezes the lumen

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4
Q

What happens to splanchnic blood flow when there is a portal hypertension?

A

increase in the splanchnic flow

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5
Q

List the layers of the gastrointestinal tract form outermost to innermost.

A

◾ Serosa
◾ Longitudinal smooth muscle layer
◾ Circular smooth muscle layer
◾ Submucosa
◾ Mucosa

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6
Q

What is the most basic metabolic substrate utilized by enterocytes to produce energy?

A

glutamine

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7
Q

Briefly discuss how glutamine is used by enterocytes to produce energy.

A

In the mitochondria, glutamine is converted to glutameate, and then to alpha-ketoglutarate, which is then channelled into the Krebs cycle for ATP production.

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8
Q

What is the normal resting membrane potential in the smooth muscle fibers of the gut?

A

between -50 and -60 millivolts

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9
Q

What channels are responsible for action potentials in gastrointestinal smooth muscle fibers?

A

calcium-sodium channels

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10
Q

What are the interstitial cells of cajal?

A

specialized cells mostly in circular smooth muscle layer that act as electrical pacemakers for smooth muscle cells

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11
Q

What factors depolarize the membrane of gastrointestinal smooth muscle cells?

A

◾ stretching the muscle
◾ stimulation by acetylcholine released from endings of parasympathetic nerves
◾ stimulation by several specific GI hormones

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12
Q

What factors hyperpolarize the membrane of gastrointestinal smooth muscle cells?

A

◾ the effect of norepinephrine or epinephrine on the fiber membrane
◾ stimulation of the sympathetic nerves that secrete mainly norepinephrine at their endings

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13
Q

What is the reason of lower motility of the GI tract during exercise?

A

sympathetic stimulation hyperpolarize the GI smooth muscle cells

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14
Q

(a) What are tonic contractions in relation to the GI tract?
(b) How long do they last?
(c) What is their function?

A

(a) These are sustained, long-lasting contractions of the smooth muscle in certain regions of the GI tract.
(b) They can last from minutes to hours.
(c) They help to maintain the closure of sphincters [e.g. the lower esophageal sphincter, teh pyloric sphincter, and ileocecal valve], preventing the backflow of contents and regulating the passage of food and digestive juices between different sections of the GI tract.

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15
Q

What causes tonic contractions?

A

◾ continuous repetitive spike potentials
◾ hormones or other factors that cause continuous depolarization
◾ continuous entry of calcium ions into the interior of the cell

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16
Q

(a) Between which layers is the Myenteric plexus located?
(b) What is the function of the Myenteric plexus/Auerbach’s plexus?

A

(a) It is located between the longitudinal and circular layers of the muscularis externa.

(b) Functions:
(1) It regulates peristalsis.
(2) It influences the secretion of digestive enzymes and other substances by the GI tract.
(3) It responds to the stretching of the GI tract walls, which occurs when food enters, and adjusts the muscle activity accordingly.

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17
Q

(a) Where is the submucosal/Meissner’s plexus located?
(b) What is the function of Meissner’s plexus?

A

(a) It is located in the submucosa layer of the GI tract.

(b) )Functions:
(1) It regulates the secretion of digestive enzymes and other substances by the glands in the mucosa.
(2) It helps in controlling blood flow to the mucosa.
(3) It influences the contraction of the muscularis mucosae, aiding in the movement of the mucosal layer.

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18
Q

What neurotransmitter excites GI activity?

A

acetylcholine

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19
Q

What neurotransmitter inhibits GI activity?

A

norepinephrine and epinephrine

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20
Q

What are the divisions for parasympathetic supply to the gut?

A

cranial and sacral divisions

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21
Q

Where are the cranial parasympathetic nerve fibers primarily located?

A

vagus nerves

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22
Q

Smooth muscle fibers connected together electrically through ___

A

gap junctions

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23
Q

(a) What are slow waves?
(b) Where do slow waves originate from?
(c) What is the function of slow waves?

A

(a) What? Slow waves, also known as basic electrical rhythm (BER), are rhythmic fluctuations in the resting membrane potential of the smooth muscle cells in the gastrointestinal tract.

(b) Origin: Slow waves originate from specialized pacemaker cells called the interstitial cells of Cajal (ICCs), which are located in the walls of the GI tract.

(c) Function: Slow waves set a basic rhythm for GI motility They do not cause muscle contractions directly but create a baseline electrical activity that can be modulated by neural and hormonal inputs to trigger contractions.

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24
Q

A slow wave is an action potential. True or False?

A

False

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25
Are tonic contractions associated with slow waves?
No
26
What are the 3 types of GI reflexes?
(1) **Short reflexes**: These are reflexes that are integrated entirely within the gut wall enteric nervous system. They do not involve the central nervous system. (2) **Long reflexes**: These are reflexes from the gut to the prevertebral sympathetic ganglia and then back to the gastrointestinal tract. They coordinate activities over longer distances within the GI tract. An example is the gastrocolic reflex, which stimulates the colon to move contents toward the rectum in response to food entering the stomach. (3) **Vagovagal reflexes**: These are reflexes from the gut to the spinal cord or brain stem and then back to the gastrointestinal tract. An example is the receptive relaxation reflex, where the stomach relaxes to accomodate incoming food.
27
What are the excitatory functions of the mesenteric plexus when stimulated?
◾ Increases tonic contraction (tone) of the gut wall ◾ Increased intensity of the rhythmic contractions ◾ Slightly increased rate of the rhythm of contraction ◾ Increased velocity of conduction of excitatory waves along the gut wall, causing more rapid movement of the gut peristaltic waves
28
Where is gastrin produced?
G cells of stomach
29
What is the function of gastrin?
◾ stimulation of gastric acid secretion ◾ promotes pepsin secretion ◾ enhances gastric motility ◾ stimulates growth of gastric mucosa ◾ causes contration of the muscle at the gastro-esophageal junction ◾ it has a trophic effect on colonic mucosa
30
What happens if there is abnormal secretion of gastrin in a patient?
can lead to peptic ulcer
31
Where is cholecystokinin produced?
I cells in the mucosa of duodenum and jejunum
32
What stimulates the production of CCK?
the presence of fats and proteins in the small intestine
33
What is the function of cholecystokinin?
◾ it stimulates gallbladder contraction and hence the release of bile into the small intestine ◾ it stimulates pancreatic enzyme secretion. ◾ It slows down the emptying of the stomach, allowing more time for the digestion and absorption of nutrients in the small intestine. ◾ It acts on the brain to promote satiety, helping to regulate food intake.
34
Where is secretin produced?
S cells in the mucosa of the duodenum
35
What hormones control GI motility?
◾ Gastrin ◾ Cholecystokinin ◾ Secretin ◾ Gastric inhibitory peptide ◾ Motilin
36
What is the function of secretin?
◾ It stimulates the pancreas to release bicarbonate-rich fluid, which neutralizes the acidic chyme entering the small intestine from the stomach. ◾ It inhibits gastric acid secretion. ◾ It stimulates the liver to produce bile. ◾ It promotes the secretion of digestive enzymes from the pancreas.
37
Where is gastric inhibitory peptide produced?
K cells in the mucosa of the duodenum and jejunum
38
What is the function of gastric inhibitory peptide?
◾ Inhibition of gastric acid secretion ◾ Stimulation of insulin release ◾ Promotion of fat storage
39
Where is motilin produced?
M cells in the mucosa of the duodenum and jejunum
40
What is the function of motilin?
◾ Stimulates gastric emptying ◾ Regulates migrating motor complex (MCC) ◾ Enhances intestinal motility
41
What is the gastrocolic reflex?
This is a reflex that occurs when the stomach stretches due to ingestion of food, triggering increased peristalsis in the colon.
42
What is the enterogastric reflex?
This is a feedback loop where the small intestine signals the stomach to slow down gastric emptying when chyme enters the duodenum. This slowing allows for more efficient digestion and absorption in the small intestine.
43
What is the usual stimulus for peristalsis of the gut?
distension of the gut wall
44
What is the "Law of the Gut"?
This refers to the principle that peristalsis always proceeds in an oral-to-aboral direction.
45
What is the stimulus for secretion of gastrin?
(1) Presence of amino acids and peptides in the stomach lumen (2) Stomach distension (3) Vagal stimulation
46
What is the stimulus for secretion of CCK?
presence of fats and proteins in the duodenum
47
What is the stimulus for secretion of secretin?
low pH in the duodenum
48
What is the stimulus for secretion of GIP?
presence of glucose and fats in the small intestine
49
What stimulates the secretion of motilin?
fasting or the absence of food in the stomach and small intestine
50
Explain the physiology of the peristaltic reflex.
(1) **Stimulus**: the presence of a bolus in the digestive system stretches the gut wall (2) **Sensory activation**: stretch receptors in the gut wall are activated and send signal to the ENS. (3) **Ascending excitation (oral contration)**: the ENS triggers muscle contraction behind the bolus; circular muscles contract, squeezing the bolus forward. (4) **Descending inhibition (caudal relaxation)**: simultaneously, the ENS causes muscle relaxation ahead of the bolus (caudal to it). Longitudinal muscles relax, allowing the gut to widen and receive the bolus. This is the "descending relaxation. (5) The end result is **propulsion** of the bolus foward through the digestive tract.
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59
The motor activity of the muscularis externa is primarily controlled by the ________. (a) motilin (b) myenteric plexus (c) migrating motor complex (d) extrinsic neurons (e) submucosal plexus
(b) myenteric plexus
60
Sandwiched between the layer of circular and longitudinal muscle in the muscularis externa is the ________. (a) myenteric plexus (b) submucosa (c) mucosa (d) submucosal plexus (e) muscularis mucosa
(a) myenteric plexus
61
The myenteric plexus is ________. (a) the mucus secreting layer of the digestive tract (b) a layer of circular smooth muscle (c) primarily composed of connective tissue (d) a layer of longitudinal smooth muscle (e) a network of sensory, interneurons and motor neurons
(e) a network of sensory, interneurons and motor neurons
62
Slow waves are ________. (a) cycles of depolarization and repolarization (b) reflexes that originate and are integrated in the enteric nervous system (c) peristaltic contractions (d) segmental contractions (e) cycles of smooth muscle contraction and relaxation
(a) cycles of depolarization and repolarization
63
G cells of the stomach secrete ________. (a) cholecystokinin (b) gastrin (c) somatostatin (d) enterokinase (e) secretin
(b) gastrin
64
The actions of gastrin include all but ________. (a) stimulating pepsin secretion (b) stimulating insulin secretion in response to a carbohydrate meal (c) contraction of muscle at the gastro-oesophageal junction (d) a trophic effect on colonic mucosa (e) a trophic effect on gastric mucosa
(b) stimulating insulin secretion in response to a carbohydrate meal
65
Which of the following hormones is released by the presence of fat and protein in the small intestine and has a major effect to decrease gastric emptying? (a) Secretin (b) Motilin (c) Glucose-dependent insulinotropic peptide (GLIP) (d) Cholecystokinin (CCK) (e) Gastrin
(d) Cholecystokinin (CCK)
66
Congenital absence of the myenteric plexus would most likely lead to which of the following effects in gastrointestinal function? (a) Bloating (b) Sluggish peristalsis in the segment of the gastrointestinal tract involved (c) Chronic diarrhea (d) Hypersecretion of acid by the stomach. (e) Excess saliva production
(b) Sluggish peristalsis in the segment of the gastrointestinal tract involved
67
Which of the following is the sequence of layers from the lumen to the outer wall of the digestive tract? (a) serosa, submucosa, mucosa, muscularis externa (b) submucosa, mucosa, serosa, muscularis externa (c) mucosa, submucosa, muscularis externa, serosa (d) submucosa, muscularis externa, serosa, mucosa (e) mucosa, submucosa, serosa, muscularis externa
(c) mucosa, submucosa, muscularis externa, serosa
68
Contraction of the ________ alters the surface area by moving villi. (a) muscularis mucosae (b) adventitia (c) submucosa (d) submucosal plexus (e) mucosa
(a) muscularis mucosae
69
The gastrointestinal functions that are most closely coordinated and regulated are ________. (a) digestion and motility (b) motility, secretion, and digestion (c) absorption and motility (d) motility and secretion (e) secretion and digestion
(b) motility, secretion, and digestion
70
Which of the following is **true** regarding gastric motility? (a) the intragastric pressure rises and remains elevated following an enjoyable moderately large meal. (b) BER (Basal Electrical Rhythm) originating on the superior curvature can be increased in frequency by the vagus. (c) hypertonic chyme leaves the stomach more rapidly than chyme which is isotonic to plasma (d) intraduodenal lipids inhibit gastric emptying partly by releasing CCK which contracts the pyloric sphincter (e) the motility patterns are independing of gastric filling
(d) intraduodenal lipids inhibit gastric emptying partly by releasing CCK which contracts the pyloric sphincter
71
Mass movements constitute an important intestinal event that lead to bowel movements. Mass movements cause which of the following? (a) contraction of the anal sphincter (b) duodenal peristalsis (c) gastric retropulsion (d) hunger sensations (e) rectal distension
(e) rectal distension
72
Migrating motility complexes (MMC) occur about every 90 min between meals and are thought to be stimulated by the gastrointestinal hormone, motilin. An absence of MMCs causes an increase in which of the following? (a) Mass movements (b) Intestinal bacteria (c) Swallowing (d) Duodenal motility (e) Gastric emptying
(b) Intestinal bacteria
73
The layer of connective tissue between the digestive epithelium and a layer of smooth muscle is the ________. (a) muscularis mucosae (b) submucosa (c) lamina propria (d) submucosal plexus (e) myenteric plexus
(c) lamina propria
74
The lamina propria and mucous epithelium are components of the ________. (a) adventitia (b) muscularis mucosae (c) serosa (d) submucosa (e) mucosa
(e) mucosa
75
Which of the following structures undergoes receptive relaxation when a bolus of food is swallowed? (a) thoracic esophagus (b) orad stomach (c) pharynx (d) palatopharyngeal folds (e) upper esophageal sphincter
(b) orad stomach *Further notes:* The orad stomach refers to the upper portion of the stomach, which includes the fundus and the upper part of the body of the stomach.

Physiology (27 decks)

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