Large Intestine Structure & Function Flashcards

1
Q

Order of the large intestine:

A
Caecum (with vermiform appendix coming off)
Ascending Colon
Transverse Colon
Descending Colon
Sigmoid Colon
Rectum
Anal Canal
Anus
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2
Q

What is the caecums function?

A

Its a blind ended sac acting like a big fermentation sac, much bigger in full herbivores who need bacteria to break down cellulose more

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3
Q

Where is the appendix and what does it do?

A

Most often retrocaecal but varies

No real known function- but they are associated with lymph nodes so may have an immune function

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4
Q

How long is the colon?

A

1.5m

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5
Q

Whats different about the muscularis Externa of the large intestine?

A

The longitudinal muscle layer isn’t complete but instead comes in three strips that run the length of the colon called teniae coli

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6
Q

The colon has a quilted or puffa jacket appearance, what produces this?

A

The 3 teniae coli, when they contract the circular muscle layer is forced out the gaps and produces the haustra or sacculations.

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7
Q

Whats different about the mucosa of the large intestine to small?

A

SI has villi

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8
Q

Whats different about the crypts in the large intestine to the small intestine?

A

They’re much longer in the colon and lined with goblet cells to lubricate movement of faeces

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9
Q

What is the rectum?

A

A straight muscular tube connecting the sigmoid colon and anal canal.
It has a thicker muscularis externa than most of the canal

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10
Q

What is the anal canal?

A

A short 2-3cm channel.

Its muscularis externa forms the internal anal sphincter (IAS).

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11
Q

Where is the external anal sphincter, and what is it made from?

A

In the anal canal, distal to the internal anal sphincter.

Its made of skeletal muscle and so is voluntarily controlled

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12
Q

How does epithelium change leaving the anal canal?

A

IT changes from simple columnar to stratified squamous like the skin.

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13
Q

What is the main function of the colon?

A

Actively absorbing sodium in order to take up water.

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14
Q

A huge amount of bacteria exists in the colon, (colonic microflora) why?

A

The long residence time of faeces allows extensive bacterial colonisation

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15
Q

What are the roles of colonic microflora?

A
  • Breakdown undigested carbohydrates (cellulose) to short chain fatty acids which we use for energy
  • Also produce vitamin K which we use for blood clotting
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16
Q

What gasses are there in the colon? (Flatus)

A
Nitrogen
CO2
Hydrogen
Methane
Hydrogen Sulphide
17
Q

What sphincters control defecation and how?

A

Internal Anal Sphincter - Smooth muscle - Autonomic (part of the anal canal)
External Anal Sphincter - Skeletal Muscle - Voluntary

18
Q

What is Mass Movement Contraction?

A

Waves of intense peristaltic contraction from colon to rectum that occur after eating and result in:

  • Rectal wall distends by mass movement of faeces
  • Stimulates mechanoreceptors
  • Initiates defaecation reflex (urge to shit)

Basically making room for fresh food

19
Q

What controls the post-meal defecation reflex?

A

Parasympathetic control via pelvic splanchnic nerves

20
Q

How does defaecation occur?

A
  • Contraction of rectum
  • Relaxation of Internal anal sphincter
  • Increased peristaltic activity in colon -> increased pressure on External Anal Sphincter (EAS)
  • Voluntary Relaxation of EAS
  • Faeces Expulsed
21
Q

As you know defaecation can be voluntarily delayed, why cant babies do this?

A

The descending pathways required for conscious control of defecation dont develop until your around 2. Prior to that potty training wont work because kids cant physically stop

22
Q

What are the symptoms of constipation and why?

A
The build up of material causes rectum distension which can cause:
= Headaches
= Nausea
= Loss of Appetite
= Abdominal Distension
23
Q

Define Diarrhoea

A

Unusually frequent and liquid faeces

24
Q

What are some causes of diarrhoea?

A
  • Pathogenic Bacteria e.g. C.Diff/Vibrio Cholerae
  • Protozoans
  • Viruses
  • Toxins (from bad food or bacteria)
  • Certain foods cause it in certain people
25
Q

How many people die from diarrhoea?

A

About 1/4 of <5yr deaths in the developing world are due to diarrhoea

26
Q

Define an enterotoxin?

A

A toxin produced in or affecting the intestines

27
Q

Name 2 enterotoxigenic bacteria?

A

Vibrio Cholerae

Escherichia Coli

28
Q

How do enterotoxogenic bacteria cause diarrhoea?

A
  • Produce protein enterotoxins
  • Elevates intracellular secondary messengers (e.g. cAMP, calcium etc)
  • Maximally activates intestinal Cl- secretion from crypt cells
  • You passively secrete loads of water
  • Secretion swamps absorptive capacity of villi
  • Diarrhoea
29
Q

How do we treat diarrhoea?

A

Sodium/Glucose solution (Oral Rehydration Salts, ORS)

  • Gut absorbs sodium & glucose
  • Drives H20 absorption
  • Keeps you hydrated
  • Secretion is still ongoing and will wash away the infection eventually