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large bowel Flashcards

1
Q

what does the Large bowel consists of

A

the colon, caecum, appendix, rectum and anal canal.

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2
Q

what is the caceum

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

function of the large bowel

A

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

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5
Q

how many parts to the colons

A 
4 
ascending 
transverse 
descending 
sigmoid
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6
Q

what is the transverse colon attached to

A

Hangs off the stomach, attached by a wide band of tissue called the greater omentum (posterior side, mesocolon).

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7
Q

the middle colic artery is a branch off which artery

A

superior mesenteric artery

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8
Q

what is the proximal trasberse colon supplied with

A

middle colic artery

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9
Q

Distal third of transverse colon is perfused by

A

the inferior mesenteric artery.

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10
Q

how many logitudinal bands do the muscles have in the colon

A

and the muscle coat has 3 thick longitudinal band

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11
Q

Structural or functional purpose of appendices epiploica

A

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

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12
Q

function of Taenia coli

A

necessary for large intestine motility.

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13
Q

what is the special secondary lymph tissue in the small intestines

A

payers patches

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14
Q

and in the large

A

solitary nodules

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15
Q

how is the haustra formed

A

by the teania coli

Cause the formation of pouched ovoid segments called haustra

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16
Q

what is the function of the colon

A

reabsorption
Colon absorbs electrolytes & water. (More in proximal colon)

Na+ and Cl- absorbed by exchange mechanisms and ion channels.

Water follows by osmosis.

K+ moves passively into lumen.

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17
Q

what structure follows teh sigmoid colon

A

rectum

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18
Q

what is the rectum a portion of

A

Dilated distal portion of the alimentary canal.

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19
Q

how can you distinguish between the colon and rectus

A

but distinguished by transverse rectal folds in its submucosa and the absence of taenia coli in its muscularis externa.

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20
Q

what strcuture follows the rectum

A

anal canal

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21
Q

what are the sorrounding structures to the anal canal

A

internal and external anal sphincters

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22
Q

what is the internal anal sphincter

A

circular muscle

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23
Q

and external

A

striated muscle

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24
Q

how many layers to the mucosal stucture of the large bowel

A 
4 (order from most internal to external)
mucousa (glands in it)
submucousa (glands in it)
muscularis   
serosa (blood vessels and nerve ending)
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25
Q

what is the most deep layer

A

mucosa

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26
Q

and most external layer

A

serosa

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27
Q

what strcutures are similar in the large bowel and the small intestines

A

Enterocytes and goblet cells are abundant.
Abundant crypts
Stem cells are found in the crypts.

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28
Q

why is the mucosa smooth

A

no villi

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29
Q

what do the enterocytes (of the large bowel) have

A

short, irregular microvilli - primarily concerned with resorption of salts.

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30
Q

how is water absorbed

A

Water is absorbed as it passively follows the electrolytes, resulting in more solid gut contents

31
Q

what is more numerous cypts or goblets

A

goblet cells

32
Q

do the number of goblet cell increase along the large bowel

A

yes increases distally towards the rectum

33
Q

function of the mucus

A
  • facilitates the passage of the increasingly solid colonic contents and covers bacteria & particulate matter.
34
Q

how are they stimulated

A

(parasympathetic and enteric nervous system) stimulates Goblet Cell secretion.

35
Q

how are new cells made in LB

A

crypt stem cells

36
Q

what cells are found in the SB and not in the LB

A

No Paneth cells & enteroendocrine cells are rarer than in small bowel

37
Q

do the glycocalyx contain digestive enzymes

A

nope

38
Q

what makes up the brush border

A

microvilli

39
Q

what does the glycocalyx control

A

regulates rate of absorption from intestinal lumen

40
Q

similarly to SB what do the musclaris externa consit of

A

inner circular and outer longitudinal layer

41
Q

what do the longitudinal muscles have

A

3 bands formed by the taenia coli

42
Q

how do the teania coli look like when h and e stained

A

round long circular blobs on the end of the muscles

43
Q

what are the ovoid segments in the circular muscle layer called

A

haustra

44
Q

what can they do

A

cintract individually

45
Q

what are the haustra and tenia coli not found

A

rectum and anal canal

46
Q

what is the colonic contarctions like

A

kneading process which is minimally propulsive

5-10cm/hr

47
Q

what does the colonic contraction do

A

promotes absorption of lectrolytes and water

48
Q

what pattern/contraction occurs at the proximal colon

A

antipropulsive pattern

49
Q

why

A

to retain chyme

50
Q

what pattern/contraction in transverse and descending colon

A

localised segmental contractions of circular muscle called Haustral contractions cause back and forth mixing

51
Q

does it increase in frequency

A

yes during meal

52
Q

how often do you see mass movement in the LB

A

1-3x daily

like peristaltic wave

53
Q

what promotes rapid trasnport through colon

A

Food that contains fibre (indigestible material)

54
Q

how are the ascending colon and travsevrse colon innervayed

A

vagus nerve

parasympthetic

55
Q

and how is sympathetic innervation done

A

lower thoracic and upper lumbar spinal cord.

56
Q

how is the external anal sphincter controlled

A

controlled by somatic motor fibres in the pudendal nerves.

57
Q

what do the afferent sensory nuerons detect

A

pressure

58
Q

where is the Myenteric plexus ganglia concentrated

A

below taenia coli

59
Q

hoe is the rectum filled with feaces

A

by mass movement

60
Q

how is defeaction reflex controlled normally

A

by sacral spinal cord

ref;ex and voluntray actions

61
Q

describe the nervous pathway for defecation

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.

Weak intrinsic signal augmented by autonomic reflex.

External anal sphincter under voluntary control.

Urge resisted, sensation subsides

62
Q

what are the last few c, of the rectum known as

A

social part

63
Q

what can it do

A

Can distinguish between solid, liquid and gas.

64
Q

why is it important

A

That perceptual ability is important in knowing what can be passed appropriately in what circumstance.

65
Q

what gives it colour

A

bile pigment

66
Q

what smell

A

bacterial fermentatation

67
Q

what has more bacteria stomach, SB or LB

A

Stomach and small bowel have few bacteria- protected.

Large bowel contains many

Essential to normal function.

68
Q

function of teh interstinal flora

A

Synthesize and excrete vitamins e.g. Vitamin K- germ-free animals can have clotting problems.

Prevent colonization by pathogens by competing for attachment sites or for essential nutrients.

Antagonize other bacteria through the production of substances which inhibit or kill non-indigenous species.

Stimulate the production of cross-reactive antibodies. Antibodies produced against components of the normal flora can crossreact with certain related pathogens, and thereby prevent infection or invasion.

Stimulate the development of certain tissues, including caecum and lymphatic tissues

69
Q

how are fibres broken down

A

Fibre (indigestible carbohydrate) can be broken down by colonic bacteria.

70
Q

what do they form once broken down

A

Produces short chain fatty acids which can 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

71
Q

what are the most prevelant bacteria in the normal flora

A

Most prevalent bacteria are the Bacteroides-

72
Q

what are bacteriodes

A

Gram-negative, anaerobic, non-spore forming bacteria. Implicated in the initiation colitis and colon cancer.

73
Q

what are bifidobacteria

A

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

nuero (36 decks)

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