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BRS Term 2 > The large bowel (40) > Flashcards

The large bowel (40) Flashcards

1
Q

What is the main function of the large bowel?

A

reabsorption of electrolytes and water AND elimination of undigested food and waste

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2
Q

What is the structure of the large bowel?

A

1.5m long, 6cm diameter
ileocaecal valve, caecum (appendix attached), ascending colon, transverse colon, descending colon, sigmoid colon, rectum, anus

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3
Q

Where is the ascending colon located?

A

on the right side of the abdomen, runs from caecum to hepatic flexure (the turning of the colon by the liver)

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4
Q

Where is the transverse colon located?

A

runs from hepatic flexure to the splenic flexure (the turn of the colon by the spleen)
- hangs off stomach, attached by a wide band of tissue, the lesser omentum

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5
Q

Where is the descending colon located?

A

runs from the splenic flexure to the sigmoid colon

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6
Q

Where is the sigmoid colon located?

A

s-shaped, runs from descending colon to the rectum

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7
Q

What is the blood supply to the large bowel?

A

mainly supplied by superior mesenteric artery and inferior mesenteric artery

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8
Q

What are the appendices epiploicae?

A
  • fatty tags of visceral peritoneum that hang from teniae coli (thick, longitudinal bands of muscle on colon, necessary for large intestine motility)
  • suggested to have protective function against intra-abdominal infections
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9
Q

Why are haustra present in the large bowel?

A

bc teniae coli are shorter than in the small intestine, so pouched ovoid segments are formed

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10
Q

What is the rectum?

A
  • dilated distal portion of alimentary canal

- similar histology to colon, but no teniae coli, and has transverse rectal folds in submucosa

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11
Q

What is the anal canal?

A
  • the terminal portion of bowel

- surrounded by internal circular muscle and external striated muscle and anal sphincters

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12
Q

What are the layers in the large bowel?

A
  • mucosa: epithelium, lamina propria, muscularis mucosae
  • submucosa
  • muscularis: circular and longitudinal
  • serosa: connective tissue and epithelium
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13
Q

What cells are present in the mucosa of the large bowel?

A
  • goblet cells for mucus–> sliding for hard faeces to move
  • enterocytes
  • no paneth cells or enteroendocrine cells
  • no villi, but microvilli for water absorption
  • stem cells in crypts
  • glycocalyx (unstirred layer) for protecting surface of bowel
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14
Q

What is the difference in the presence of goblet cells in the large bowel vs small bowel?

A
  • higher # of goblet cells in large bowel
  • more prevalent in crypts than along surface
  • no. inc. distally towards rectum
  • apical ends packed w/ mucus-filled secretion granules –> to facilitate passage of increasingly solid colonic contents and to cover bacteria
    N.B. ACh stimulates goblet cell secretion
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15
Q

What is the structure of the muscle layers in the large bowel?

A
  • muscularis externa consists of an inner circular and outer longitudinal layer like the small bowel
  • circular muscles segmentally thickened
  • longitudinal layers concentrated in 3 bands- teniae coli (between these bands, layer is thin)
  • teniae coli penetrate circular layer at irregular intervals
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16
Q

What is the motility in the large bowel like during the day?

A
  • segmenting contractions- kneading
  • minimally propulsive- 5-10cm/hr at most –> promotes absorption of electrolytes and water
  • anti-propulsive patterns in proximal colon to retain chyme
  • localised segmental contractions of circular muscle cause mixing in transverse and descending colon
  • short, propulsive movements every 30 mins
17
Q

What is mass movement in the large bowel?

A
  • resembles peristaltic wave
  • 1-3 times a day
  • propels contents up to 3/4 length of large intestine in a few seconds
  • fibre (indigestible material) promotes rapid transport through colon
18
Q

What is the nervous supply to the large bowel?

A
  • parasympathetic: vagus nerve innervates ascending colon and most of transverse colon…pelvic nerves innervate more distal parts
  • sympathetic (stops motility): lower thoracic and upper lumbar spinal cord
  • external anal sphincter controlled by somatic motor fibres in pudendal nerves (voluntarily controlled)
  • afferent sensory neurons detect pressure, esp. w/in rectum
  • enteric nervous system important (Hirschsprung’s disease)
  • myenteric plexus ganglia below teniae coli
19
Q

What is the function of the interstitial cells of cajal?

A

act as pacemaker of GI smooth muscle

20
Q

What is Hirschsprung’s disease?

A
  • absence of ganglion cells in bowel–> causes the muscles in the bowels to lose their ability to move stool through the intestine (peristalsis)
  • presents w/ constipation in infants
21
Q

Where is stool stored until convenient to void?

A

rectum- filled w/ faeces by mass movement in the sigmoid colon

22
Q

What controls the defecation reflex?

A

primarily the sacral spinal cord (both reflex and voluntary- external sphincter)

23
Q

How does defecation occur?

A
  • faeces in the rectum expand the rectal walls
  • stretch/pressure receptors send signals via myenteric plexus–> initiates peristaltic waves in descending, sigmoid colon and rectum
  • internal anal sphincter controlled by parasympathetic fibres which relax involuntarily
  • external anal sphincter= skeletal muscle controlled by a somatic nerve supply–> allows conscious control of defecation
  • if urge is resisted, the sensation subsides
24
Q

What is the function of the “social part” of the rectum?

A
  • to distinguish between solid, liquid and gas

- to know what can be passed appropriately in what circumstance

25
Q

What gives the odour of faeces?

A

bacterial fermentation

26
Q

What solids are present in faeces?

A
  • cellulose
  • bacteria
  • cell debris
  • bile pigments
  • salts
27
Q

What are the roles of intestinal flora?

A
  • synthesise and excrete vitamins e.g. Vit K
  • prevent colonisation by pathogens by competing for attachment sites or essential nutrients
  • antagonise other bacteria through the production of substances that inhibit/kill non-indigenous species
  • stimulate production of cross-reactive antibodies (that will prevent infection/invasion)
  • stimulate development of certain tissues: caecum and lymphatic tissues
  • digest fibre (BAD)
  • produce short chain FAs that regulate gut hormone release
  • be absorbed and used as an energy source
28
Q

What types of normal flora are usually found in the bowel?

A
  • Bacteroides (gram -ve, anaerobic, non-spore forming bacteria, implicated in colitis and colon cancer)
  • Bifidobacteria (gram +ve, non-spore forming, lactic acid bacteria, prevents colonisation by potential pathogens)

BRS Term 2 (36 decks)

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