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bioregulatory systems 🦠 > large bowel > Flashcards

large bowel Flashcards

1
Q

what does the large bowel consist of

A

colon, caecum, appendix, rectum and anal canal

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2
Q

what is the caecum

A

blind pouch just distal to the ileocecal valve (communicates terminal ileum to colon) which is 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

reabsorption of electrolytes and water

the elimination of undigested food and waste

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5
Q

what is the length and diameter of the large bowel

A

1.5m long - 6cm in diameter

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6
Q

where is the ascending colon

A

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

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7
Q

where is the transverse colon

A

runs from the hepatic flexure to the splenic flexure (the turn of the colon by the spleen), hangs off the stomach, attached by a wide band of tissue called the greater omentum (posterior side, mesocolon)

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8
Q

where is the descending colon

A

runs from the splenic flexure to the sigmoid colon

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9
Q

where is the sigmoid colon

A

(s shaped) colon runs from the descending colon to the rectum

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10
Q

what supplies the proximal transverse colon with blood

A

the proximal transverse colon is supplied with blood by the middle colic artery (branch of the superior mesenteric artery)

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11
Q

what is the distal 3rd of the transverse colon perfused by

A

distal third of transverse colon is perfused by the inferior mesenteric artery

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12
Q

what is the region between the distal and proximal third of the transverse colon sensitive to

A

sensitive to ischemia because blood supply is not as extensive

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13
Q

what does the peritoneum carry

A

the peritoneum carries fatty tags (appendices epiploicae)

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14
Q

how many bands does the muscle coat have

A

3 thick longitudinal bands (taeniae coli)

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15
Q

what is the gut wall like in appearance

A

pouched in appearance (haustra)

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16
Q

what is the structural or functional purpose of the appendices epiploicae

A

unknown - suggested to have a protective function against intra-abdominal infections

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17
Q

what does the taenia coli do

A

necessary for large intestine motility

18
Q

what is present in the walls of the distal small intestine and large intestine

A

nodules of lymphoid tissue are common in the walls of the distal small intestine (Peyer’s patches) and large intestine (solitary nodules)

19
Q

what is the function of the colon

A

colon absorbs electrolytes and water
happens more in proximal colon
Na+ and Cl- absorbed by exchange mechanisms and ion channels
water follows by osmosis
K+ moves passively into the lumen
large intestine can reabsorb approx 4.5 litres water (usually 1.5) - above this threshold = diarrhoea

20
Q

what is the rectum

A

dilated distal portion of the alimentary canal of the large bowel

21
Q

how can you tell the colon and rectum apart

A

histology is similar to the colon but is distinguished by transverse rectal folds in its submucosa and the absence of taenia coli in its muscularis externa

22
Q

what is the anal canal and what is it surrounded by

A

terminal portion is anal canal

surrounded by internal (circular muscle) and external (striated muscle) and sphincters

23
Q

what is the mucosal structure of the large bowel

A 
4 main layers
mucosa
submucosa
muscularis
serosa
24
Q

what is the mucosa

A

most inner layer and contains many glands covered by submucosa which also has many glands

25
Q

what does the muscularis have

A

harbours myenteric plexuses

26
Q

what does the serosa have

A

harbours vessels and nerve endings for large bowel

27
Q

what cells are abundant in the large bowel

A

enterocytes and goblet cells

abundant crypts

28
Q

what types of cells are found in crypts

A

stem cells

29
Q

at the gross level, how does the mucosa appear to look

A

smooth - no villi (smaller SA than small bowel)

30
Q

why do enterocytes have short irregular microvilli

A

concerned with reabsorption of salts

31
Q

how is water absorbed

A

passively as it follows electrolytes - resulting in more solid gut contents

32
Q

what cells are the crypts dominated by

A

goblet cells and stem cells

more in crypts than on surface - no of goblet cells increases distally towards the rectum

33
Q

where are goblet cells most abundant - small or large bowel

A

large bowel

34
Q

what are apical ends packed with

A

with mucus-filled secretion granules awaiting release

35
Q

what does mucus do

A

facilitates the passage of the increasingly solid colonic contents and covers bacteria and particulate matter

36
Q

what stimulates goblet cell secretion

A

acetylcholine (parasympathetic and enteric nervous system) stimulates goblet cell secretion

37
Q

what are the differences between the small and large bowel

A

no paneth cells and enteroendocrine cells are rarer than in the small bowel
glycocalyx does not contain digestive enzymes
crypts are dominated by goblet and stem cells > enterocytes
- movement of large bowel is more complicated than the small intestine

38
Q

describe the muscle layers in the large bowel

A
  • muscularis externa consists of an inner circular and outer longitudinal layer
  • circular muscles segmentally thickened
  • longitudinal layer concentrated in 3 bands - taenia coli
  • between the taenia, longitudinal layer is thin
  • bundles of muscle from the taenia coli penetrate the circular layer at irregular intervals +
    contribute to haustra formation
  • shorter than circular muscle layers are ovoid segments called haustracan contract
    individually
  • apart from rectum and anal canal - substantial and continuous
39
Q

what are colonic contractions

A

kneading process - minimally propulsive ~5-10 cm/hr at most

promotes absorption of electrolytes and water

40
Q

what patterns dominate in the proximal colon to retain chyme

A

anti propulsive patterns dominate to retain chyme

41
Q

what contractions occur in the transverse and descending colon

A

in transverse and descending colon, localised segmental contractions of circular muscle called haustral contractions cause back and forth mixing

42
Q

how often are short propulsive movements

A

short propulsive movements every 30 mins

increase in freq in response to a meal

bioregulatory systems 🦠 (54 decks)

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