Large intestine structure and function Flashcards

1
Q

How does the ileum ultimately connect to the colon?

A

ileum - ileocaecal valve - caecum - vermiform appendix

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2
Q

How long is the colon?

A

1.5-1.8m

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3
Q

Name the 4 parts of the colon

A

ascending, transverse, descending and sigmoid

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4
Q

Is the circular or longitudinal muscle layer incomplete in the colon?

A

longitudinal

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5
Q

What are teniae coli?

A

3 bands spanning the entire length of the colon which is why the longitudinal muscle is disrupted

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6
Q

What are haustra and how are they formed?

A

pouches of the large intestine due to the contractions of the teniae coli

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7
Q

What epithelium is found in the mucosa of the large intestine?

A

simple columnar

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8
Q

Describe the crypts of the large intestine

A

large and straight

large amount of goblet cells to secrete mucus to help with lubrication for the movement of faeces

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9
Q

Where is the rectum anatomically?

A

Between the sigmoid colon and the anal canal

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10
Q

Describe the rectum

A

straight muscular tube with simple columnar epithelium and a thick muscularis externa

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11
Q

Where is the anal canal anatomically?

A

2-3cm between the distal rectum and anus

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12
Q

What epithelium makes up the anal canal?

A

stratified squamous epithelium

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13
Q

How many anal sphincters are there?

A

2 - internal and external which is comprised of skeletal muscle

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14
Q

What is the primary role of the colon?

A

dehydrate chyme

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15
Q

How does the colon dehydrate the chyme?

A

active transport of sodium and the water follows

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16
Q

What are the 2 reasons for the transmit time of the colon being relatively long?

A

bacterial colonisation

ferment undigested carbohydrate

17
Q

What are the 3 products after fermentation of undigested carbohydrates

A

vitamin K
short chain fatty acids
Gas

18
Q

Explain the difference in muscle between the internal and external anal sphincters

A

internal - smooth under autonomic control

external - skeletal under voluntary control

19
Q

Explain how the defaecation reflex comes about

A

following a meal the faeces travels from the colon to the rectum which distends the wall of the rectum which is sensed by mechanoreceptors

20
Q

How is the defaecation reflex controlled by the nervous system?

A

parasympathetically by pelvic splanchnic nerve

21
Q

After the defaecation reflex has begun explain how this leads to faces being expelled

A

MMC in colon increases pressure on external sphincter which you voluntarily relax and pass faeces

22
Q

How can you put off the expulsion of faeces?

A

descending neural pathways

23
Q

Is there absorption of toxins from faecal material due to long retention times in the colon in constipation?

24
Q

What are the symptoms of constipation and what are these due to?

A

headache, nausea, abdominal distension and loss of appetite caused by distension of rectum

25
How can constipation be treated?
laxatives
26
What is the definition of diarrhoea?
Too frequent passage of faeces which are too liquid
27
What are some causes of diarrhoea?
pathogenic bacteria, toxins, viruses, food, nerves, protozoans
28
What do enterotoxigenic bacteria do? plus examples
vibrio cholera, E coli | Produce protein enterotoxins to turn on chloride secretion and therefore promote extreme water loss
29
What do enterotoxigenic bacteria do to intracellular 2nd messengers?
turn them on eg cAMP, cGMP and calcium
30
How is diarrhoea by enterotoxigenic bacteria now treated in developing countries to prevent children dying?
sodium-glucose solution as the villi are not damaged so this will promote rehydration and the washing away of bacteria