Large Intestine Structure and Function Flashcards

1
Q

T/F: large intestine has a complete circular muscle layer but incomplete longitudinal muscle layer.

A

True

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2
Q
  1. Entire length of colon has 3 bands, what are they called?

2. When the bands contract, what do they form?

A
  1. Teniae coli

2. pouches called haustra -puckered appearance

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3
Q

What kind of epithelium makeup the mucosa?

A

Simple columnar epithelium (flat)

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4
Q

Large, straight crypts are lined with which cells & what is their function?

A

large number of goblet cells: lubrication for movement of faeces.

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5
Q

Rectum:

  1. What kind of epithelium makeup the mucosa?
  2. Compare the muscularis externa thickness of rectum to other regions of alimentary canal.
A
  1. simple columnar epithelium

2. Thicker compared to other regions

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6
Q

Anal Canal:

  1. What kind of epithelium makeup the mucosa?
  2. Internal anal sphincter is made up of what?
  3. External anal sphincter is made up of what kind of muscle?
A
  1. Goes from simple columnar to stratified squamous.
  2. Thickening of smooth muscle of muscularis externa (thicker than rectum) makes the sphincter.
  3. Skeletal muscle
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7
Q

What role colon plays in nutrient absorption?

A

No important role

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8
Q

What is the function of colon?

A

Actively transports Na from lumen into blood. Creates osmotic gradient so water follows leading to dehydration of chyme resulting in solid faecal pellets.

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9
Q

Why there is long residence time for chyme in colon?

A

To promote bacterial colonisation. Colonic microflora = 10^14 bacteria (1kg).

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10
Q

What is the role of bacteria in the colon?

A

Ferments undigested carbs (e.g. cellulose). Products of fermentation include short chain fatty acids (sometimes only energy source in ruminants such as cows), vitamin K (important in blood clotting), & gas (flatus - N2, CO2, H2, CH4, hydrogen sulphide (characteristic aroma)).

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11
Q

Normally, anus is closed by what?

A

internal anal sphincter & external anal sphincter.

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12
Q

What controls internal & external anal sphincters?

A

Internal = smooth muscle under autonomic control. external = skeletal muscle under voluntary control.

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13
Q

What produces the urge to defaecate?

A

Following a meal: wave of intense contraction (mass movement contraction) movies from colon to rectum. This mass movement of faecal material into rectum results in distension of rectal wall which triggers the mechanoreceptors which then triggers defaecation reflex (urge to defaecate).

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14
Q

Defaecation reflex:

  1. Which nerves controls the reflex?
  2. Does sympathetic system influence reflex?
  3. Outline how the reflex occurs.
  4. Can defaecation be delayed?
A
  1. Under parasympathetic control via pelvis splanchnic nerves.
  2. No
  3. Contraction of rectum. Relaxation of internal & contraction of external anal sphincters. Increased peristaltic activity in colon increases pressure on external anal sphincter which relaxes under voluntary control which leads to expulsion of faeces.
  4. yes, voluntary delay of defaecation due to descending pathways (kick in after you are 2 years of age).
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15
Q

Constipation:

  1. T/F: No absorption of toxins from faecal material following long periods of retention
  2. what are symptoms associated with constipation?
A
  1. True
  2. Headaches, nausea, loss of appetite, abdominal distension. These all are caused by distension of rectum (as lots of material there).
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16
Q

Define diarrhoea.

A

Too frequent passage of faeces which are too liquid.

17
Q

What are the causes of diarrhoea?

A

Pathogenic bacteria, protozoans, viruses, toxins, food, stress?

18
Q

What is the major killer of children <5 in developing countries?

A

Diarrhoea

19
Q

Enterotoxigenic bacteria:

  1. Give some examples that cause diarrhoea.
  2. What do these bacteria produce & what is the consequence of such secretion?
A
  1. Vibrio cholerae, Escherichia coli
  2. Produce protein enterotoxins (don’t damage villus cells) which maximally turn on intestinal Cl secretion from crypt cells leading to increased H2O secretion. These toxins increase intracellular 2nd messengers such as cAMP (V cholerae), cGMP (E coli) & calcium (C difficle).
    H2O secretion swamps absorptive capacity of villus cells: profuse watery diarrhoea (25L/day for cholera).
20
Q

What is the treatment of secretory diarrhoea?

A

Na/glucose solution: drives H2O absorption so rehydrates. Secretion still going so that infection is washed away.
Oral rehydration therapy saves 4 million children’s lives per year.