what’s the L intestine made up of?
- cecum
- appendix
- colon
appendix
a small finger like projection of lymphoid tissue projecting from bottom of cecum
cecum
the blind ended pouch below the junction of the small and large intestines
colon
majority of L intestine
3 parts of L intestine
- ascending colon
- transverse colon
- descending colon
what does the end part of the descending colon form?
sigmoid colon that straightens to form rectum
what is chyme mainly have when reaching L intestine?
- indigestible food elements
– eg, celluslose - unabsorbed biliary secretions
- some fluid
what can upper half of colon absorb a bit of?
salt and water
what are the SM layers in colon?
circular and longitudinal
do longituinal layers of SM completely wrap around L intestine?
NO
- they are organized into 3 bands called taenia coli
length of taenia coli
shorter than large intestine so it can bunch up and make haustra
are haustra in a fixed location?
no they change locations as a result of circular SM contractions
mass movements
several times a day after meals there’s an increase in haustral contractions to move feces 1/3-3/4 the length of colon in a few seconds
colon motitlity
- haustra contractions is main form
– slow non propulsive - generated by autonomous rhythmicity of colon SM cells
- analogous to segmentation
- 2/hour
- controlled by locally mediated reflexes involving intrinsic plexus
what are mass movements driven and mediated by?
driven= gastrocolic reflex
mediated= stomach by release of gastrin
defecation reflex
1) when fecal matter fills rectum, stretch receptors send impulses to spinal cord, which sends reflex signal via parasympathetic NS to distal colon
2) causes internal anal sphincter (SM involuntary) to relax and cause contractions in sigmoidal colon and rectum
3) if external anal sphincter (skeletal voluntary) is relaxed, deification will occur) if timing isn’t right voluntary control will keep it closed
what happens to abdominal pressure when deification occurs?
it increases to expel feces
does the colon secrete antibacterial agents?
NO
- it favours bacterial growth
- 1000s of bacteria makeup microbiome in colon
microbiome
all microbes within a particular environment
roles of microbiome in gut
- enhance intestinal immunity by competing with potentially pathogenic microbes for nutrients and space
- promote colon motility
- make nutritional contributions as a result of their metabolism
- help maintain integrity of colon mucosa
what part of the body has the most bacteria?
the gut microbiome
when is gut flora established
2yo
what does intestinal epithelium and intestinal mucosa do?
co-develop
- provides barrier to pathogenic organisms and supports gut flora
whats is the surface of lumen of colon like?
smooth so low SA for absorption
- absorbs water and salt only
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Module 4: Section 136
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Module 4: Section 228
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Module 4: Section 454
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Module 4: Section 516
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Module 4: Section 637
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Module 5: Section 115
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Module 5: Section 223
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Module 5: Section 321
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Module 5: Section 427
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Module 6: Section 146
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Module 6: Section 229
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Module 6: Section 351
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Module 6: Section 450
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Module 6: Section 629
