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630: Medical Physiology > Gastrointestinal Physiology > Flashcards

Gastrointestinal Physiology Flashcards

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USMLE® Step 1 flashcards
1
Q

What are the 2 functions of the GI tract?

A

digestions and absorption of nutrients

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2
Q

In order to serve these 2 functions, what are the 4 major activities of the GI tract?

A

(1) Motility propels ingested food from the mouth toward the rectum and mixes and reduces the size of the food
(2) Secretions from the salivary glands, pancreas, and liver add fluid, electrolytes, enzymes, and mucus to the lumen of the gastrointestinal tract
(3) Ingested foods are digested into absorbable molecules
(4) Nutrients, electrolytes, and water are absorbed from the intestinal lumen into the bloodstream

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3
Q

Describe the linear arrangement of the GI tract

A

Mouth –> Esophagus –> Stomach –> Small Intestine (duodenum, jejunum, ileum) –> Large intestine –> Anus

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4
Q

What are the 2 surfaces of the GI wall?

A
  • mucosal

- serosal

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5
Q

The mucosal surface faces the _____ and the serosal surface faces the _____.

A

lumen

blood

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6
Q

What 3 things does the mucosal layer consist of?

A
  • a layer of epithelial cells
  • a lamina propria
  • a muscularis mucosae
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7
Q

What does contraction of the muscularis mucosae do?

A

Changes the shape and surface area of the epithelial cell layer

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8
Q

What lies beneath the mucosal layer?

A

a submucosal layer

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9
Q

What is found between the submucosal layer and the serosal layer?

A

2 layers of smooth tissue: circular and longitudinal muscle

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10
Q

What 2 plexuses contain the nervous system of the GI tract?

A
  • submucosal plexus

- myenteric plexus

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11
Q

The GI tract is regulated by the _____ nervous system

A

autonomic

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12
Q

What are the 2 components of the autonomic nervous system?

A
  • intrinsic component

- extrinsic component

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13
Q

What is the intrinsic component called and what does it do?

A

Enteric system, which is wholly contained within the submucosal and myenteric plexuses. It communicates with the extrinsic component

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14
Q

The extrinsic component is the ________ and _______ innervation of the GI tract

A

parasympathetic

sympathetic

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15
Q

Postganglionic neurons of the parasympathetic nervous system are classified as either _____ or _______.

A

cholinergic

peptidergic

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16
Q

What neurotransmitter do cholinergic neurons release?

A

ACh

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17
Q

Parasympathetic innervation results in what 5 things?

A
  • contraction of smooth muscle in the GI tract wall
  • relaxation of the sphincters
  • increased salivary secretion
  • increased gastric secretion
  • increased pancreatic secretion
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18
Q

Postganglionic neurons of the sympathetic nervous system are classified as _____.

A

adrenergic

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19
Q

What neurotransmitter do adrenergic neurons release?

A

norepinephrine

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20
Q

Sympathetic innervation results in what 5 things?

A
  • relaxation of smooth muscle in the GI tract wall
  • contraction of the sphincters
  • increased salivary secretion
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21
Q

GI peptides are classified as what 3 things?

A
  • hormones
  • neurocrines
  • paracrines
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22
Q

What are hormones?

A

Peptides released from endocrine cells of the GI tract

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23
Q

Describe the path hormones take to reach their target cell

A

They are excreted into portal circulation, pass through the liver, and enter the systemic circulation.
The systemic circulation then delivers the hormone to target cells with receptors for that hormone.

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24
Q

What are paracrines?

A

Peptides released from endocrine cells of the GI tract

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25
Q

How do paracrines differ from hormones?

A

They act locally within the same tissue that secretes them.

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26
Q

Paracrines reach their target cells by way of _____.

A

diffusion

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27
Q

What are neurocrines?

A

Peptides that are synthesized in neurons of the GI tract and released following an action potential

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28
Q

After neurocrines are released following an AP they ______ across the synapse to act on its target cell.

A

diffuse

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29
Q

What does motility refer to?

A

contraction and relaxation of the walls and sphincters of the gastrointestinal tract

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30
Q

What 4 things does motility do to ingested food to prepare it for digestion and absorption?

A
  • grinds
  • mixes
  • fragments
  • propels
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31
Q

All contractile tissue of the GI tract is smooth muscle, except for what 3 structures? What kind of muscle are these?

A
  • the pharynx
  • upper 1/3 of the esophagus
  • external anal sphincter

They are all striated muscle

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32
Q

The smooth muscle cells of the GI tract are coupled via what?

A

gap junctions

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33
Q

Contraction of the circular smooth muscle of the GI tract results in what?

A

shortening of a ring of smooth muscle, which decreases the diameter of that segment

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34
Q

Contraction of the longitudinal smooth muscle of the GI tract results in what?

A

shortening in the longitudinal direction, which decreases the length of that segment

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35
Q

Contractions of the GI smooth muscle can be either _____ or _____.

A

phasic

tonic

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36
Q

Describe phasic contraction of smooth muscle

A

Periodic contractions followed by relaxation

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37
Q

Where are phasic contractions found?

A
  • the esophasgus
  • gastric antrum
  • small intestine
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38
Q

Describe tonic contraction of smooth muscle

A

Sustained contraction at a constant level or tone without regular periods of relaxation

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39
Q

Where are tonic contractions found?

A
  • upper region of the stomach
  • lower esophageal sphincter
  • iliocecal sphincter
  • internal anal sphincter
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40
Q

What are the first steps in the processing of ingested food?

A

chewing and swallowing

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41
Q

What are the 3 functions of chewing?

A
  • it mixes food with saliva, lubricating it to facilitate swallowing
  • it reduces the size of food particles, which facilitates swallowing
  • it mixes ingested carbohydrates with salivary amylase to begin carbohydrate digestion
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42
Q

What are the 2 types of chewing?

A
  • voluntary

- involuntary

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43
Q

What does the involuntary component of chewing involve?

A

Reflexes initiated by food in the mouth

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44
Q

Swallowing is initiated ______ in the mouth, but thereafter it is under _____ control

A

voluntarily

reflex (involuntary)

45
Q

The reflex portion of swallowing is control by what?

A

the swallowing center located in the medulla

46
Q

What are the 3 phases of swallowing?

A
  • oral phase
  • pharyngeal phase
  • esophageal phase
47
Q

When is the oral phase initiated? What does it result in?

A

when the tongue forces a bolus of food back toward the pharynx, this activates the receptors which initiate the involuntary reflex

48
Q

What is the purpose of the pharyngeal phase?

A

To propel the food bolus from the mouth through the pharynx to the esophagus

49
Q

Describe the 4 steps of the pharyngeal phase

A

1) the soft palate is pulled upward
2) the epiglottis moves to cover the larynx
3) the upper esophageal sphincter relaxes, allowing food to pass into the esophagus
4) a peristaltic wave of contraction propels the food through the open sphincter

50
Q

Breathing is _______ during the pharyngeal phase.

A

inhibited

51
Q

The esophageal phase is controlled by what 2 things?

A
  • the swallowing reflex

- enteric nervous system

52
Q

What occurs during the esophageal phase?

A

Food is propelled through the esophagus to the stomach

53
Q

Primary and secondary _____ waves travel down the esophagus propelling the food toward the stomach

A

peristaltic

54
Q

Emptying of the gastric contents to the duodenum takes approximately _ hours.

A

3

55
Q

In order to enter the duodenum, solids must be reduced to particles that are how small?

A

at least 1mm cubed

56
Q

What are 2 factors that slow or inhibit gastric emptying (increase gastric emptying time)?

A
  • the presence of fat

- the presence of H+ ions

57
Q

The effect of fat in the duodenum is mediated by what?

A

CCK

58
Q

How does CCK mediate the presence of fat?

A

It slows gastric emptying, ensuring the gastric contents are delivered slowly to the duodenum which provides adequate time for fat to be digested and absorbed

59
Q

The effect of H+ in the duodenum is mediated by what?

A

reflexes in the enteric system

60
Q

How do reflexes in the enteric system mediate the presence of H+?

A

H+ receptors in the duodenal mucosa detect low pH of the intestinal contents and relay this information to the gastric smooth muscle. This permits enough time for neutralization of H+ by pancreatic HCO3-

61
Q

Small intestinal motility serves what 3 functions?

A
  • to mix the chyme with digestive enzymes and pancreatic secretions
  • expose the nutrients to the intestinal mucosa for absorption
  • propel the unabsorbed chyme along the small intestine into the large intestine
62
Q

What innervates the small intestine?

A

both sympathetic and parasympathetic nervous systems

63
Q

Parasympathetic stimulation ______ contraction of intestinal smooth muscle, whereas sympathetic stimulation _______ it.

A

increases

decreases

64
Q

What are contents of the large intestine called?

A

feces

65
Q

Where do segmentation contractions occur?

A

in the cecum and proximal colon

66
Q

In the large intestine, segmentation contractions are associated with characteristic saclike segments called what?

A

haustra

67
Q

Where do mass movements occur?

A

In the colon

68
Q

A final mass movement propels fecal contents into what?

A

Into the rectum, where they are stored until defecation occur

69
Q

As the rectum fills with feces, the smooth muscle wall of the rectum contracts and the internal anal sphincter relaxes via what reflex?

A

the rectosphincteric reflex

70
Q

Once the rectum fills to __% of its capacity, there is an urge to defecate

A

25

71
Q

Distention of the stomach by food increases the motility of the colon and increases the frequency of mass movements in the large intestine via which reflex?

A

the gastrocolic reflex

72
Q

What are the functions of saliva?

A
  • initial digestion of starches and lipids
  • dilution and buffering of ingested foods
  • lubrication of ingested food with mucus to aid its movement through the esophagus
73
Q

What are the 3 anatomic divisions of the stomach?

A
  • fundus
  • body
  • antrum
74
Q

What are the 4 kinds of cells that are contained in the gastric mucosa?

A
  • parietal cells
  • chief cells
  • G cells
  • mucous cells
75
Q

The body of the stomach contains _____ glands. What do they do?

A

oxyntic glands

76
Q

What are the 2 cell types found in oxyntic glands?

A
  • parietal cells

- chief cells

77
Q

What do the parietal cells secrete?

A

HCl and intrinsic factor

78
Q

Describe the process behind HCl secretion in the parietal cells

A

1) CO2 combines with H20 to form H2CO3 which is broken down into H+ and HCO3-
2) H+ is secreted
3) Cl- which is reabsorbed from the blood is secreted with H+

79
Q

What are 3 substances that alter HCl secretion?

A
  • ACh
  • histamine
  • gastrin
80
Q

ACh binds to _____ receptors on the parietal cells.

A

M3

81
Q

Histamine binds to _____ receptors on the parietal cells.

A

H2

82
Q

Gastrin binds to _____ receptors on the parietal cells.

A

cholecystokinin B

CCK(B)

83
Q

Both ACh and gastrin stimulate H+ secretion via which second messenger?

A

IP3/Ca2+

84
Q

Histamine stimulates H+ secretion via which second messenger?

A

cAMP

85
Q

What do the chief cells secrete?

A

pepsinogen

86
Q

The antrum of the stomach contains ______ glands.

A

pyloric

87
Q

What are the 2 cell types found in pyloric glands?

A
  • G cells

- mucous neck cells

88
Q

What do the G cells secrete?

A

gastrin into the circulation

89
Q

What do the mucous neck cells secrete?

A
  • mucus
  • HCO3-
  • pepsinogen
90
Q

Pepsinogen is important in the digestion of what?

A

proteins

91
Q

What is the only essential secretion of the stomach?

A

intrinsic factor

92
Q

What is intrinsic factor required for?

A

absorption of vitamin B12 in the ileum

93
Q

What occurs in the absence of intrinsic factor?

A

pernicious anemia

94
Q

The pancreas secretes approximately how many liters of fluid per day? Where does it secrete it?

A

1 L into the lumen of the duodenum

95
Q

Pancreatic secretions consist of what 2 components?

A

aqueous and enzymatic

96
Q

The aqueous component is high in what? What is the significance behind this?

A

HCO3-

Which functions to neutralize the H+ delivered to the duodenum from the stomach

97
Q

What is the function of the enzymatic component of pancreatic secretions?

A

to digest carbs, proteins, and lipids into absorbable molecules

98
Q

Describe the structure of the pancreatic exocrine glands

A

It resembles a bunch of grapes, with each grape corresponding to a single acinus

99
Q

What is an acinus? What lines it?

A

The blind end of a branching duct system that is lined with acinar cells

100
Q

What do acinar cells do?

A

secrete the enzymatic portion of the pancreatic secretion

101
Q

What are the ducts of the pancreas lined with?

A

ductal cells

102
Q

These ductal cells extend into a special region of _____ cells in the acinus

A

centroacinar

103
Q

What do the ductal and centroacinar cells do?

A

Secrete the aqueous HCO3- component of the pancreatic secretion

104
Q

What innervates the exocrine pancreas?

A

both parasympathetic and sympathetic nervous systems

105
Q

Parasympathetic activity ______ pancreatic secretion, and sympathetic activity _____ it.

A

stimulates

inhibits

106
Q

What is bile necessary for?

A

the digestion and absorption of lipids in the small intestine

107
Q

What are the components of the biliary system?

A
  • liver
  • gallbladder and bile duct
  • ileum
  • portal circulation
108
Q

Describe the steps involved in bile production and secretion

A

1) hepatocytes of the liver synthesize and secrete bile
2) bile flows out of the liver through the bile duct and fills the gallbladder
3) CCK acts on the gall bladder allowing the bile to flow into the lumen of the duodenum
4) bile salts are recirculated to the liver via the enterohepatic circulation
5) bile salts are delivered back to the liver

109
Q

What are the components of the bile salts?

A
  • Bile salts (including bile acids)
  • Bile pigments like bilirubin
  • Cholesterol
  • Phospholipids
  • Electrolytes
  • Water

630: Medical Physiology (24 decks)

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