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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
what is the most deep layer
mucosa
26
and most external layer
serosa
27
what strcutures are similar in the large bowel and the small intestines
Enterocytes and goblet cells are abundant. Abundant crypts Stem cells are found in the crypts.
28
why is the mucosa smooth
no villi
29
what do the enterocytes (of the large bowel) have
short, irregular microvilli - primarily concerned with resorption of salts.
30
how is water absorbed
Water is absorbed as it passively follows the electrolytes, resulting in more solid gut contents
31
what is more numerous cypts or goblets
goblet cells
32
do the number of goblet cell increase along the large bowel
yes increases distally towards the rectum
33
function of the mucus
- facilitates the passage of the increasingly solid colonic contents and covers bacteria & particulate matter.
34
how are they stimulated
(parasympathetic and enteric nervous system) stimulates Goblet Cell secretion.
35
how are new cells made in LB
crypt stem cells
36
what cells are found in the SB and not in the LB
No Paneth cells & enteroendocrine cells are rarer than in small bowel
37
do the glycocalyx contain digestive enzymes
nope
38
what makes up the brush border
microvilli
39
what does the glycocalyx control
regulates rate of absorption from intestinal lumen
40
similarly to SB what do the musclaris externa consit of
inner circular and outer longitudinal layer
41
what do the longitudinal muscles have
3 bands formed by the taenia coli
42
how do the teania coli look like when h and e stained
round long circular blobs on the end of the muscles
43
what are the ovoid segments in the circular muscle layer called
haustra
44
what can they do
cintract individually
45
what are the haustra and tenia coli not found
rectum and anal canal
46
what is the colonic contarctions like
kneading process which is minimally propulsive | 5-10cm/hr
47
what does the colonic contraction do
promotes absorption of lectrolytes and water
48
what pattern/contraction occurs at the proximal colon
antipropulsive pattern
49
why
to retain chyme
50
what pattern/contraction in transverse and descending colon
localised segmental contractions of circular muscle called Haustral contractions cause back and forth mixing
51
does it increase in frequency
yes during meal
52
how often do you see mass movement in the LB
1-3x daily | like peristaltic wave
53
what promotes rapid trasnport through colon
Food that contains fibre (indigestible material)
54
how are the ascending colon and travsevrse colon innervayed
vagus nerve | parasympthetic
55
and how is sympathetic innervation done
lower thoracic and upper lumbar spinal cord.
56
how is the external anal sphincter controlled
controlled by somatic motor fibres in the pudendal nerves.
57
what do the afferent sensory nuerons detect
pressure
58
where is the Myenteric plexus ganglia concentrated
below taenia coli
59
hoe is the rectum filled with feaces
by mass movement
60
how is defeaction reflex controlled normally
by sacral spinal cord | ref;ex and voluntray actions
61
describe the nervous pathway for defecation
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
what are the last few c, of the rectum known as
social part
63
what can it do
Can distinguish between solid, liquid and gas.
64
why is it important
That perceptual ability is important in knowing what can be passed appropriately in what circumstance.
65
what gives it colour
bile pigment
66
what smell
bacterial fermentatation
67
what has more bacteria stomach, SB or LB
Stomach and small bowel have few bacteria- protected. Large bowel contains many Essential to normal function.
68
function of teh interstinal flora
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
how are fibres broken down
Fibre (indigestible carbohydrate) can be broken down by colonic bacteria.
70
what do they form once broken down
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
what are the most prevelant bacteria in the normal flora
Most prevalent bacteria are the Bacteroides-
72
what are bacteriodes
Gram-negative, anaerobic, non-spore forming bacteria.  Implicated in the initiation colitis and colon cancer.
73
what are bifidobacteria
are Gram-positive, non-sporeforming, lactic acid bacteria. Have been described as "friendly" bacteria. Thought to prevent colonization by potential pathogens

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