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GASTROENTEROLOGY > Large Bowel > Flashcards

Large Bowel Flashcards

1
Q

What does the large bowel consist of?

A

Large bowel consists of the colon, caecum, appendix, rectum and anal canal.

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2
Q

What is the caecum?

A

The caecum is a blind pouch just distal to the ileocecal valve- larger in herbivores.

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3
Q

What is the appendix?

A

The appendix is a thin, finger-like extension of the caecum - not physiologically relevant in humans.

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4
Q

what are the principal functions of the large bowel?

A

the reabsorption of electrolytes & water, and the elimination of undigested food and waste.

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5
Q

What are the four sections to the colon?

A

Ascending colon, Transverse colon, Descending colon and Sigmoid colon

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6
Q

Where does the ascending colon run from?

A

The caecum to the hepatic flexure

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7
Q

Where does the transverse colon run from?

A

The hepatic flexure to the splenic flexure

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8
Q

Where does the descending colon run from?

A

The splenic flexure to the sigmoid colon

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9
Q

Where does the sigmoid colon run from?

A

from descending colon to the rectum.

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10
Q

Which band of tissue attaches the transverse colon to the stomach?

A

Greater omentum

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11
Q

What is the blood supply of the proximal and distal transverse colon?

A

Proximal - blood from middle colic artery

Distal third - perfused with the inferior mesenteric artery

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12
Q

What is the region between the proximal part and the distal third of the colon sensitive to?

A

ischemia

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13
Q

What is the appendices epiplociae? and what is their suggestive purpose?

A

Fatty tags - protective function against intra-abdominal infections

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14
Q

What is the name given to describe the pouched appearance of the muscle coat of the colon?

A

haustra

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15
Q

What is the taeniae coli?

A

longitudinal muscle - 3 thick bands which are needed for large intestine motility

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16
Q

What immunological tissues are common in the walls of the distal small intestine and large intestines?

A

Small intestine - Peyers Patches

Large Intestine - Solitary nodules

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17
Q

How do haustra form?

A

The taenia cli is shorter than the small intestine which Cause the formation of pouched ovoid segments called haustra

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18
Q

What does the colon reabsorb?

A

Electrolytes and water

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19
Q

In which part of the colon is more water and electrolytes absorbed?

A

More in the proximal colon

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20
Q

How does Na and Cl get absorbed?

A

Through exchange mechanisms and ion channels

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21
Q

How does K+ get reabsorbed?

A

Moves passively into the lumen

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22
Q

What happens when the large intestine absorbs more than 4.5L of water?

A

DIarrhoea

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23
Q

What histological feature distinguishes the rectum from the colon?

A

Transverse rectal folds in its submucosa and absence of taenia coli

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24
Q

Which two muscles surround the anal canal?

A

The internal sphincter and external sphincters

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25
Q

What type of muscle is the internal anal sphincter?

A

Circular muscle

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26
Q

What type of muscle is the external anal sphincter?

A

Striated muscle

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27
Q

What are the mucosal layers of the large bowel, starting with the inner most?

A

Mucosa
Submucosa
Muscularis
Serosa

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28
Q

What does the serosa harbour?

A

Blood vessels and nerve endings

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29
Q

What are found in crypts?

A

Stem cells

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30
Q

Which cells are abundant in the large bowel?

A

Crypts with stem cells
Goblet cells
Enterocytes

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31
Q

Why does the mucosa appear smooth at gross level?

A

No vili

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32
Q

What are enterocytes primarily concerned with?

A

The resorption of salts

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33
Q

What do enterocytes have on their surface?

A

Short, irregular microvilli

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34
Q

Does the large or small bowel contain more goblet cells?

A

Large bowel

35
Q

Which cell dominates inside the crypts?

A

Goblet cells

36
Q

What are the apical ends of the goblet cells packed with?

A

Mucus filled granules awaiting release

37
Q

What is the role of mucus in the large bowel?

A

Mucus - facilitates the passage of the increasingly solid colonic contents and covers bacteria & particulate matter.

38
Q

what neurotransmitter stimulates goblet cell secretion?

A

ACh

39
Q

Are there paneth cells in the large bowel?

A

No

40
Q

Does the glycocalyx of the large bowel contain digestive enzymes?

A

No

41
Q

What makes up the brush border?

A

Microvilli

42
Q

What is the surface of the microvilli covered in?

A

Glycocalyx

43
Q

what does the glycocalyx do?

A

traps a layer of water & mucous known as “unstirred layer” - this regulates the rate of absorption from the intestinal lumen

44
Q

What is the glycocaylx?

A

A rich carbohydrate layer on the apical membrane

45
Q

What does the muscularis externa consist of?

A

an inner circular and outer longitudinal layer

46
Q

How are the circular muscles thickened?

A

Segmentally thickened

47
Q

Where are the longitudinal muscles of the large bowel concentrated?

A

In three bands - taenia coli

48
Q

What is the thickness of the longitudinal layer between the taenia coli?

A

Thin

49
Q

Where are the ovoid segments of the large bowel not seen?

A

Rectum and anal canal

50
Q

What are haustra?

A

Ovoid segments, which are are shorter than circular muscle layer and can contract individually

51
Q

What large bowel movements dominate in the chyme in order to retain chyme?

A

Anti-propulsive patterns

52
Q

What causes back and forth mixing in the transverse and descending colon?

A

haustral contractions

53
Q

What do colonic contractions promote?

A

Absorption of electrolytes and water

54
Q

How does the motility of the large bowel change following a meal?

A

Increase in the frequency of colonic contractions following a meal in order to promote the reabsorption of electrolytes and water

55
Q

What is mass movement?

A

High amplitude propagated contractios which resemble a peristaltic wave. Can propel the contants 1/3-3/4 of the length of the large intestine in a few seconds

56
Q

What promotes the process of mass movement through the large intestine?

A

Food containing fibre (undigestible material)

57
Q

What is the parasympathetic innervation of the ascending colon?

A

Vagus nerve

58
Q

What is the parasympathetic innervation of most of the transverse colon?

A

Vagus Nerve

59
Q

What is the parasympathetic innervation of the distal colon?

A

Pelvic nerves

60
Q

What is the sympathetic innervation of the large bowel?

A

Lower thoracic and upper lumbar spinal nerves

61
Q

What is the external anal sphincter controlled by?

A

Somatic motor fibres in the pudendal nerves

62
Q

What is Hirschsprung’s disease?

A

Lack of enteric intramural ganglia

63
Q

Where are myenteric plexus ganglia concentrated?

A

Below the taenia coli

64
Q

What can stimulate mass movement?

A

Presence of food in the stomach

65
Q

how does aldosterone promote water and na+ reabsorption?

A

synthesis of Na+ ion channel, Na+/K+ pump)

66
Q

How does the rectum become filled with faeces?

A

Through mass movement in the sigmoid colon

67
Q

What controls the defacation reflex?

A

Sacral spinal cord

68
Q

Describe the defacation reflex?

A
  • Reflex to sudden distension of walls of rectum.
  • Pressure receptors send signals via myenteric plexus to initiate peristaltic waves in descending, sigmoid colon and rectum. Internal anal sphincter inhibited.
  • This weak, intrinsic signal is then augmented by autonomic reflex
69
Q

How is the sensation for defacation able to subside?

A

External anal sphincter under voluntary control, so if the urge is resisted then the sensation subsides

70
Q

Which part of the rectum can distinguish between solids, liquids and gas?

A

The “social” part of the rectum - last few cm of the rectum

71
Q

How many grams of faeces do adults pass a day?

A

150g

72
Q

what proportion of faeces is water?

A

2/3rds

73
Q

What are the solid components of faeces?

A

cellulose, bacteria, cell debris, bile pigments, salts (K+).

74
Q

What gives faeces such a strong odor?

A

Bacterial fermentation

75
Q

Describe he microbiome of an average adult?

A

Diverse, highly metabolically active community.

comprises approximately 1.5 kg of live bacteria, with the active biomass equivalent to a major human organ.

76
Q

What are the 7 roles of the intestinal flora - summary?

A
  1. Synthesize and excrete vitamins
  2. Prevent colonisation by pathogens through competitive inhibition
  3. Produce substances which are toxic to non-indigenous species
  4. Stimulate prouction of cross-reactive antibodies
  5. Stimulate development of some tissues
  6. Break down fibre
  7. Produce short chain fatty acids
77
Q

How do intestinal flora prevent colonisation by pathogens?

A

pathogens by competing for attachment sites or for essential nutrients.

78
Q

How does the production of cross reactive antibodies by intestinal flora prevent infection?

A

Antibodies produced against components of the normal flora can crossreact with certain related pathogens,

79
Q

Which tissues do intestinal flora stimulate the development of?

A

Caecum and lymphatic tissues

80
Q

What i the purpose of intestinal flora producing short chain fatty acids?

A

regulate gut hormone release, or be absorbed to be used as an energy source or to influence functions such as food intake or insulin sensitivity directly

81
Q

Recent research has shown links between gut bacteria and..

A

1) Drug metabolism
2) Insulin resistance
3) Bile acid metabolism
4) Lipid metabolism
5) Obesity

82
Q

What are the most prevalent types of bacteria in the gut?

A

Bacteroides - gram negative, anaerobic and non-spore forming bacteria

83
Q

Describe Bifidobacteria?

A

Gram-positive, non-sporeforming, lactic acid bacteria. Have been described as “friendly” bacteria. Thought to prevent colonization by potential pathogens.

GASTROENTEROLOGY (25 decks)

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