FHB Exam 3 > GI: Colonic Phase > Flashcards

GI: Colonic Phase Flashcards

(37 cards)

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1
Q

What are the components of the colon?

A
  • cecum
  • ascending, transverse, descending colon
  • sigmoid
  • rectum
  • anus
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2
Q

What are the functions of the colon?

A
  • water absorption
  • storage of waste products
  • commensal bacteria
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3
Q

Describe how chyme is emptied from the ileum.

A
  1. short-range peristalsis propels chyme through the ileocecal sphincter
  2. once the sphincter is contracted and closed again, no reflux and no electrical connection
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4
Q

Describe the histology of the colon.

A
  • absorptive columnar cells
  • short microvilli, no villi
  • goblet cells
  • crypts of lieberkuhn glands
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5
Q

What muscles make up the colon?

A
  • taeniae coli = 3 longitudinal bands

- circular muscle (when contracted you get haustra)

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6
Q

Describe local reflexes of colonic motility.

A
  1. short bursts of Cl and fluid secretions

2. mediated by 5-HT and ACh

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7
Q

What are the 2 long reflex arcs of colonic motility?

A
  • gastrocolic

- orthocolic

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8
Q

Describe the gastrocolic reflex arc

A
  1. distension of the stomach
  2. increased colonic motility and mass movements
  3. mediated by parasympathetics (afferent) and 5-HT, ACh (CCK, gastrin)
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9
Q

Define the orthocolic reflex arc.

A

urge to defecate when you get out of bed

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10
Q

Describe the effects of peptide YY.

A
  • slows gastric emptying
  • reduces intestinal motility
  • reduces Cl and water secretion
  • reduces gastric propulsion
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11
Q

What causes the secretion of peptide YY?

A
  • presence of lipids in the colonic lumen

- secreted by enteroendocrine cells in the terminal ileum and colon

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12
Q

Describe haustrations and their purpose.

A
  • short duration contractions of the circular muscle
  • segmental contractions that serve to mix the chyme
  • increase exposure of chyme to epithelium to optimize water and salt absorption
  • creates haustra
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13
Q

Describe long duration contractions and their purpose.

A
  • initiated by taeniae coli

- mild propulsion of food forward or backward

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14
Q

Describe high-amplitude propagating contractions and their purpose.

A
  • occur 10x/day
  • clears the colon from the cecum to the rectum
  • fills the rectum, but not necessarily associated with defecation
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15
Q

Describe parasympathetic innervation of the colon.

A
  • enhances motility
  • vagus = cecum, ascending, transverse
  • pelvic = descending, sigmoid, rectum, anal canal
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16
Q

Describe sympathetic innervation of the colon.

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A
  • decreases motility
  • superior mesenteric = cecum, ascending transverse
  • inferior mesenteric = descending, sigmoid
17
Q

Describe short chain FA absorption in the colon.

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A
  1. SCFA is actively transported into the cell via SMCT (sodium monocarboxylate transporters)
  2. SCFA is used for intestinal epithelial metabolism
18
Q

What is an example of an SCFA?

19
Q

Describe Na absorption in the colon.

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A
  1. neurotransmitters activate apical ENaC channels to passively allow Na to enter the cell
  2. absorbed into the blood via Na/K ATPase
20
Q

What is a possible cause of bowel inflammation and diarrhea?

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A

reduced ENaC expression leads to water retained in the lumen

21
Q

Describe Cl absorption in the colon.

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A
  1. passively absorbed via tight junctions
22
Q

Describe water absorption in the colon.

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A
  1. passively absorbed via tight junctions

2. colon has a high water reserve, typically absorbs 1.8L

23
Q

List some functions of the commensal bacteria system.

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A
  1. digestion of endogenous and exogenous substances
  2. protects epithelial lining from bacterial invasion
  3. creates flatulence
24
Q

What is the effect of broad-spectrum antibiotics on the commensal bacteria?

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A
  1. wipes out protective bacteria

2. makes it easy for pathogenic bacteria to colonize

25
What is the purpose of probiotics?
probiotics are intentionally ingested commensal bacteria that can withstand gastric acid and proteolytics - prevents or treats infections
26
For what disorders may a fecal transplant be used?
- infant kwashiorkor | - intestinal infections that are not responsive to antibiotics
27
What is kwashiorkor?
an infection caused by antibiotics mostly in infants predisposes individuals to C. diff
28
What is the mechanism for a fecal transplant?
1. dilute stool with salt water | 2. pump into the intestine of the recipient via enema, colonoscope, or NG/NJ tube
29
What sphincters are found in the anal canal?
- internal anal sphincters = thick, circular | - external anal sphincters = striated
30
What is the purpose of the rectum?
- no circular muscle - acts as waste storage - joins the anal canal
31
What are the steps to defecation?
1. high-amplitude propagating contraction fills the rectum 2. internal sphincter relaxes, releases VIP, and produces NO 3. external sphincter remains tonically contacted until voluntarily relaxed 4. upon relaxation of external sphincter, rectum contracts to push out feces
32
Why is the colon vulnerable to malignancy?
- rapid epithelial turnover | - exposure to bacterial or environmental toxins
33
How prevalent is colon cancer?
2nd in men | 3rd in women
34
How does colon cancer progress?
a polyp becomes invasive and metastatic
35
Describe colon cancer screenings.
- early detection can prevent mortality | - detected via colonoscopy or a CT
36
What causes Hirschsprung's Disease? How is it treated?
Cause = failure of the ENS to develop in a section of the colon leads to a tonically contracted segment that creates an obstruction diagnosed in infants Tx: surgical resection of the afflicted part
37
What are associated manifestations with Hirschsprung's Disease?
- mutations in glial-derived neurotrophic factor and endothelin III
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