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Systems: Alimentary AB > Large Intestine Structure and Function > Flashcards

Large Intestine Structure and Function Flashcards

1
Q

How long is the colon?

A

1.5-1.8m

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2
Q

What are the 4 parts of the colon?

A
  • Ascending
  • Transverse
  • Descending
  • Sigmoid
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3
Q

How do the longitudinal and circular muscle layers differ?

A

Circular muscle layers is complete by longitudinal muscle layer is incomplete

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4
Q

What are the 3 bands of the colon called?

A

Teniae coli

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5
Q

What does contraction of the teniae coli result in?

A

Pouches (haustra) resulting in a puckered appearance

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6
Q

What is the mucosa of the large intestine composed of?

A

Simple columnar epithelium

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7
Q

What provides lubrication for movement of faeces?

A

Large straight crypts lined with large numbers of goblet cells

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8
Q

What is the rectum?

A

Straight, muscular tube between end of sigmoid colon and anal canal

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9
Q

What is the mucosa of the rectum?

A

Simple columnar epithelium

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10
Q

How does the muscularis externa of the rectum compare to that of other regions of the alimentary canal?

A

Thicker

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11
Q

What is the anal canal?

A

2-3cm between distal rectum and anus

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12
Q

How does the muscularis of the anal canal compare to that of the rectum?

A

Thicker, contains internal anal sphincter

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13
Q

What is the external anal sphincter?

A

Skeletal muscle

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14
Q

How does the epithelium of the anal canal transition?

A

Simple columnar to stratified squamous

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15
Q

What nutrient absorption role does the colon play?

A

No important role

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16
Q

What is the result of the active transport of sodium from the lumen into the blood?

A
  • Osmotic absorption of water
  • Dehydration of chyme
  • Production of solid faecal pellets
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17
Q

What does the long residence time in the colon lead to?

A

Bacterial colonisation

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18
Q

How much colonic microflora is there?

A

10^14 bacteria (~1kg)

19
Q

What does the bacterial fermentation of undigested carbohydrate lead to?

A
  • Short chain fatty acids
  • Vitamin K
  • Gas
20
Q

What are the components of flatulence?

A
  • Nitrogen
  • CO2
  • Hydrogen
  • Methane
  • Hydrogen sulphide
21
Q

Why is the anus normally closed?

A

Closed by internal anal sphincter and external anal sphincter

22
Q

What is the control of the internal anal sphincter?

A

Smooth muscle under autonomic control

23
Q

What is the control of the external anal sphincter?

A

Skeletal muscle under voluntary control

24
Q

Describe the production of the urge to defecate.

A
  • Following meal wave of intense contraction (MMC) from colon through to rectum
  • Distension of rectal wall produced by mass movement of faecal matter into rectum
  • Stimulates mechanoreceptors
  • Defaecation reflex
  • Urge
25
Q

What is the control of the defecation reflex?

A

Under parasympathetic control via pelvic splanchnic nerves

26
Q

What influence does the sympathetic system have on the defecation reflex?

A

No influence

27
Q

What are the components defecation reflex?

A
  • Contraction of rectum
  • Relaxation of internal and contraction of external anal sphincters
  • Increased peristaltic activity in colon
28
Q

What is the result of the defecation reflex?

A
  • Increased pressure on external anal sphincter
  • Relaxes under voluntary control
  • Expulsion of faeces
29
Q

What is voluntary delay of defecation due to?

A

Descending pathways

30
Q

Describe the frequency of bowel movements?

A

Varies considerably from person to person

31
Q

What is the absorption of toxins from faecal material following long periods of retention?

A

No absorption

32
Q

What are the symptoms associated with constipation?

A
  • Headaches
  • Nausea
  • Loss of appetite
  • Abdominal distension
33
Q

What is constipation due to?

A

Distension of rectum

34
Q

What is diarrhoea?

A

Too frequent passage of faeces which are too liquidy

35
Q

What are the causes of diarrhoea?

A
  • Pathogenic bacteria
  • Protozoans
  • Viruses
  • Toxins
  • Food
36
Q

How many deaths a year is diarrhoea responsible for?

A

2.5 million of the 1,500 million cases a year

37
Q

Give 2 examples of enterotoxigenic bacteria.

A
  • Vibrio cholerae

- Escherichia coli

38
Q

What doe enterotoxigenic bacteria produce?

A

Produce protein enterotoxins which maximally turn on intestinal chloride secretion from crypt cells which leads to increased H2O secretion

39
Q

How do enterotoxigenic bacteria act?

A

Elevate intracellular second messengers:

  • cAMP
  • cGMP
  • Calcium
40
Q

How does H2O secretion lead to profuse watery diarrhoea?

A

H2O secretion swamps absorptive capacity of villus cells

41
Q

What damage do enterotoxins do to villus cells?

A

No damage

42
Q

What is the treatment for secretory diarrhoea?

A
  • Give sodium/glucose solution

- Oral rehydration therapy

43
Q

What does sodium/glucose solution do?

A

Drives H2O absorption leading to rehydration

Systems: Alimentary AB (37 decks)

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