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Patho 2 > 2 - Gastrointestinal 01 > Flashcards

2 - Gastrointestinal 01 Flashcards

1
Q

List the layers of the gastrointestinal wall, from the outside to the inside

A

serosa

longitudinal smooth mm

circular smooth mm

submucosa

mucosa

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2
Q

Gastrointestinal smooth mm fibers are connected by _____ junctions

A

gap

allows low-resistance movement of depolarization between cells

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3
Q

Electrical signals can travel faster along the muscle fiber _____ than _____

A

lengthwise

sideways

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4
Q

Each muscle layer in the GI tract functions as a _______

A

syncitium

when an action potential is elicited anywhere in the muscle mass, it travels in all directions at once

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5
Q

Muscle fibers in the GI smooth muscle have two basic types of electrical waves:

A

slow waves (cause undulating change in membrane potential)

spikes (true action potentials that cause muscle contractions)

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6
Q

What is the average resting and threshold potential in the gut?

A

Resting -50 to -60

Threshold -40

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7
Q

What are factors that depolarize gut membranes?

A

stretching

acetylcholine release from PS

gastrointestinal hormones

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8
Q

What are factors that hyperpolarize the gut membrane?

A

catecholamines

sympathetic nn stim

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9
Q

The GI tract has its own nervous system, called the:

A

enteric nervous system

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10
Q

What are the two plexi of the enteric nervous system, and where are they located?

A

Auerbach’s Plexus (between longitudinal and circular layers)

Meissner’s Plexus (in the submucosa)

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11
Q

The myenteric plexus controls ______,

and the submucosal plexus controls ________

A

GI movement

GI secretion and blood flow

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12
Q

When the myenteric plexus is stimulated, what are its principal effects? (4)

A
  1. increased tone
  2. increased intensity of contraction
  3. increased rate of contraction
  4. increased velocity of conduction within the gut wall
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13
Q

The myenteric plexus inhibits _______

A

sphincters that prevent movement of food

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14
Q

Acetylcholine _______ GI activity

Norepinephrine ______ GI activity

A

excites

inhibits

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15
Q

The two types of movements in the GI tract are:

A
  1. Propulsive movements
  2. Mixing movements
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16
Q

What is the usual stimulus for peristalsis?

A

Distention of the gut

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17
Q

What is the “law of the gut?”

Why is it universally true?

A

All peristaltic movement moves toward the anus with downstream relaxation

The myenteric plexus is polarized in the anal direction

Peristalsis does not occur where the myenteric plexus is not present. Ever.

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18
Q

Blood vessels of the gut are part of the ________ circulation

A

splanchnic

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19
Q

All the venous blood from the gut, pancreas, and spleen empties into the:

A

protal vein

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20
Q

What happens to all the fat absorbed from the intestines?

A

It isn’t put into the portal vein with everything else

It’s absorbed into the intestinal lymphatics and carried to the circulating blood through the thoracic duct

It bypasses the liver

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21
Q

Blood flow to the gut increases with gut activity.

How is this increase stimulated?

A
  1. Vasodilating peptide horomones released from the mucosa
  2. Kinins released from GI glands
  3. Decreased O2 concentration
  4. Increased adenosine
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22
Q

Why are the villi particularly sensitive to low blood flow states?

A

Counter-current flow

At baseline, about 80% of oxygen passes directly from arterioles into adjacent venules without ever going to the tips of the villi

This is adaptive for high absorption, but leaves little wiggle room for hypoxia

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23
Q

What is the difference between hunger and appetite?

A

Hunger is an intrinsic desire for food

appetite is the type of food a person preferentially seeks

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24
Q

Most of the muscles of chewing are innervated by what nerve?

A

motor branch of CN5 (Trigeminal)

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25
Q

Why is chewing so important for digestion?

A

Digestive enzymes only work when they directly contact the surfaces of food particles

the more varied the surfaces, the more digestion occurs

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26
Q

What are the three stages of swallowing?

A
  1. Voluntary
  2. Pharyngeal (involuntary)
  3. Esophageal (involuntary)
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27
Q

Essentially all sensory impulses from the mouth wind up in which area of the brain?

A

tractus solitarius in the medulla

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28
Q

The esophagus exhibits two kinds of peristalsis:

A

Primary (continuation of the wave that began in the pharynx)

Secondary (esophagus initiates additional waves if the primary one is insufficient to move food out)

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29
Q

What kind of muscle controls the pharyngeal wall and the upper 1/3 of the esophagus?

A

Striated!

controlled by skeletal nerves from the glossopharyngeal and vagus nerves

NOT SMOOTH MUSCLE

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30
Q

What happens to the stomach as a wave from the esophagus approaches?

A

It relaxes and is inhibited

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31
Q

Describe the gastroesophageal sphincter

A

Tonically contracted at baseline

receptively Relaxes in response to waves from the esophagus

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32
Q

What prevents stomach reflux?

A
  1. Gastroesophageal Sphincter
  2. The esophagus has a valve like closure at the end
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33
Q

What are the three functions of the stomach?

A
  1. Storage of food until space opens up in the intestines
  2. mixing of food with secretions until it forms chyme
  3. Slow emptying of chyme into SI at a rate the intestines can handle
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34
Q

What is the capacity of a fully relaxed stomach?

A

0.8-1.5 L

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35
Q

The distal opening of the stomach is called the ______

A

pylorus

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36
Q

When a large amount of fats enters the duodenum, how does it communicate with the stomach to inhibit gastric emptying?

A

Hormones!

The fats extract these hormones from the wall of the duodenum

the hormones are carried via the blood to the stomach, where they inhibit the pyloric pump and increase the tone of the pyloric sphincter

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37
Q

Why do fats in particular play a role in inhibit gastric empyting?

A

They take the longest time to digest

they are the rate limiting factor, so the amount of fat should determine the speed of digestion

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38
Q

The number one hormone that inhibits gastric emptying is:

A

Cholecystokinin

Inhibits the motility caused by gastrin

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39
Q

Gastric inhibitory peptide (GIP) is also released when fat enters the duodenum. What does it do?

A

inhibits gastric motility slightly

mainly stimulates secretion of insulin from the pancreas

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40
Q

What chyme characteristics prevent further emptying into the duodenum?

A

Hyper or hypotonic

Excessively acidic

Too much unprocessed protein or fat

Highly irritating (for whatever reason)

41
Q

The frequency of segmentation contractions in the small intestines is determined by:

A

the frequency of slow waves

maximum frequency is about 12 per minutes (but this is extreme)

42
Q

What drug would cause profound inhibition of SI peristalsis?

A

Anything that block acetylcholine

esp. Atropine

43
Q

What is the rate of net movement along the small intestines?

A

1 cm/min

3-5 hours to get from the pylorus to the ileocecal valve

44
Q

Which hormones enhance intestinal motility?

A

gastrin

CCK

insulin

motilin

serotonin

45
Q

Which hormones inhibit intestinal peristalsis?

A

secretin

glucagon

46
Q

What is the gastroileal reflex?

A

when someone eats a meal, it triggers release from the ileum into the cecum of the large intestines (making room)

47
Q

What is peristaltic rush?

A

powerful and rapid peristalsis caused by irritation of the bowel

goal is to sweep the irritant out of the SI and into the colon

48
Q

The villi in the mucosa have tiny muscles that contract. Why is this important?

A

milk the villi so that lymph flow freely into the lympatic system

49
Q

Which valve prevents backflow from the colon to the SI?

A

ileocecal

50
Q

How much chyme normally empties into the cecum each day?

A

1500-200ml

51
Q

Someone with an inflamed appendix will have almost no passage of chyme from the ileum to the LI. Why?

A

Inflammation and irritation in the LI inhibit the ileocecal sphincter and ileal peristalsis

52
Q

In the colon, mixing movements are known as _______

and propulsive movements are known as ________

A

haustrations

mass movements

53
Q

How long does it usually take to move chyme from the ileocecal valve to the rectum?

A

8-15 hours

54
Q

Series of mass movement usually persist for ______ minutes

A

10-30

55
Q

What reflexes initiate mass movements in the colon?

A

Gastrocolic and duodenocolic

Also: massive irritation in the colon

56
Q

Why do patients with ulcerative colitis have frequent bowel movements?

A

The irritation causes almost perpetual mass movements in the colon

57
Q

The internal anal sphincter is composed of _______ muscle

the external anal sphincter is composed of ______ muscle

A

smooth

striated

58
Q

The external anal sphincter is innervated by what nerves?

A

Pudendal

59
Q

To effectively lead to defecation, two reflexes are generally necessary:

A

myenteric defecation reflex

parasympathetic defecation reflex

need innervation from both nervous systems

60
Q

Why does putting off pooping lead to severe constipation?

A

It’s not very effective to poop without reflexes

If you wait to poop until the reflexes are gone, it’s really difficult

so the poop just sits there and gets harder

61
Q

What is the peritoneointestinal reflex?

Renointestinal reflex?

Vesicointestinal reflex?

A

If the peritoneum is irritated, it inhibits enteric excitation

kidney irritation inhibits enteric excitation

bladder irritation inhibits enteric excitation

62
Q

What are the four types of alimentary glands?

A
  1. Goblet cells (single celled mucous glands)
  2. Pits (invaginations that contain specialized secretory cells)
  3. Tubular glands (stomach and upper duodenum)
  4. Complex glands (salivary, pancreas)
63
Q

What types of stimuli activate the enteric nervous system?

A

tactile stimulation

chemical irritation

distention of the gut wall

64
Q

What is the effect of parasympathetic stimulation on alimentary tract glandular secretion rate?

This is primarily true in which portions of the gut?

A

Increases

upper portions of the SI and some in distal large intestines

65
Q

Secretion in the lower SI and the first 2/3 of the LI occurs in response to:

A

local neural and hormonal stimuli

not a whole lot of PS stimulation

66
Q

How does sympathetic stimulation effect glandular secretion rate?

A

If only sympathetic: increases secretion

If superimposed of PS stimulation: reduces secretions due to vasoconstriction of blood supply to the gland

67
Q

How do hormones regulate the secretion rate of alimentary glands?

A

Released from the GI mucosa in response to presence of food

absorbed into the blood and carried to the glands, where they stimulate secretions

68
Q

Chemically, all GI hormones are ________

A

peptide/polypeptide

(water soluble)

69
Q

How do gland cells develop their secretory products?

A

Just like any other protein

Ribosomes in the ER -> Golgi -> Vesicle Storage ->

Calcium mediated exocytosis

70
Q

What’s so special about mucus?

A
  1. adheres tightly to food
  2. has enough body to coat the wall and prevent contact of food with the mucosa
  3. very slippery, allowing particles to slide along the epithelium
  4. makes feces adhere to itself
  5. Resistant to digestion
  6. amphoteric: can buffer small amounts of acid, and contains enough bicarb to neurtalize acids
71
Q

What are the principal glands of salivation?

A

Parotid

Submandibular

Sublingual

72
Q

Daily secretion of saliva is between ______ and _____ ml

A

800

1500

73
Q

Saliva contains two major types of protein secretion:

A
  1. serous secretion (digests starches)
  2. mucus secretion (lubricates and protects)
74
Q

Which salivary glands secrete serous substance?

Which secrete serous and and mucus substance?

A

Parotid

Submandibular and sublingual

75
Q

Saliva contains large quantities of _____

and relatively low quantities of ______

A

K and HCO3

Na and Cl

76
Q

The salivary glands are primarily controlled by _______ nervous signals from _______

A

parasympathetic

salivatory nuclei in the brainstem

77
Q

Do smooth or rough objects in the mouth cause more salivation?

A

Smooth

78
Q

Why do you salivate so much when you’re feeling nauseated?

A

when irritating foods are swallowed or there’s something wrong in the gut, saliva is producted

when swallowed, it helps to distance the irritating factor from the intestinal wall and dilute it

79
Q

Esophageal secretions are entirely ______

A

mucus

80
Q

In the stomach, oxyntin tubular glands produce which substances?’

Which substances do the pyloric glands produce?

A

Hydrochloric acid

pepsinogen

intrinsic factor

mucus

mucus and gastrin

81
Q

A stomach oxyntic gland contains which three types of cells?

A
  1. Mucus neck cells
  2. Peptic (or chief)
  3. Parietal (or oxyntic)
82
Q

What prevents hydrochloric acid from backing up into the stomach wall?

A

alkaline mucus

tight junctions in epithelial cells

83
Q

The basic factors that stimulate gastric secretion are:

A
  1. acetylcholine
  2. gastrin
  3. histamine
84
Q

Acetylcholine excites secretion of _______

Gastrin and histamine excite secretion of _______

A

pepsinogen, acid, and mucus

acid only

85
Q

When does inactivate pepsinogen become activated into pepsin?

A

When it contacts hydrochloric acid

86
Q

What does pepsin do?

A

proteolytic

only works in an extremely acidotic environment (pH 1.8-3.5)

87
Q

Intrinsic factor is essential for absorption of ______

A

Vitamin B12

88
Q

Why does chronic gastritis lead to pernicious anemia?

A

destroys parietal cells, which secrete intrinsic factor

Vit B12 can’t be absorbed and bone marrow won’t be stimulated to form RBCs

89
Q

________ are the only cells that secrete hydrochloric acid

A

parietal cells of the oxyntic glands

90
Q

What factors stimulate gastric secretion?

A

Acetylcholine

gastrin

histamine

91
Q

What are the primary roles of gastrin and histamine

A

Strongly stimulate acid secretion by parietal cells,

but have little effect on the other cells

92
Q

Describe the cephalic phase of gastric secretion

A

occurs before food enters stomach

sparked by sight, smell, thought or taste of food

30% of the gastric secretion associated with eating a meal

93
Q

Describe the gastric phase of secretion

A

Vasovagal reflexes, enteric reflexes, and gastrin all cause secretion of gastric juice while food is in the stomach

60% of gastric secretion

94
Q

Describe the intestinal phase?

A

presence of food in the upper portion of the small intestines continues to cause stomach secretion

Accounts for 10% of secretion

95
Q

The most abundant enzyme found in pancreatic secretions is:

A

Trypsin

96
Q

What is the role of trypsin and chymotrypsin?

A

split whole and partially digested proteins into peptides

do not cause the release of individual amino acids

97
Q

Trace the pathway for pancreatic secretions leaving the pancrease

A

Produced in the acini

long pancreatic duct

joins up with the hepatic duct immediately before emptying into the duodenum

through the papilla of Vater

Which is surrounded by the sphincter of oddi

98
Q

What prevents the pancreas from autodigesting?

A

The same cells that secrete proteolytic enzymes also secrete trypsin inhibitor

prevents activation of trypsin inside the cells

Since it inhibits trypsin, and trypsin activates all of the other proteolytic enzymes, trypsin inhibitor effectively inhibits them all

Patho 2 (24 decks)

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