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Alimentary System > Large Intestine Structure and Function > Flashcards

Large Intestine Structure and Function Flashcards

1
Q

What valve is between the ileum and the caecum?

A

Ileocaecal valve

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2
Q

What is the length of the colon?

A

Ranges from 1.5 to 1.8m

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3
Q

What are the 4 parts of the large intestine?

A

Ascending colon

Transverse colon

Descending colon

Sigmoid colon

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4
Q

Explain how the circular and longitudinal muscles of the colon are different from the small intestine?

A

Circular muscle is complete but the longitudinal is not

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5
Q

What are the three bands present along the entire length of the colon?

A

Teniae coli

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6
Q

What are tenaei coli?

A

Three seperate longitudinal ribbons of smooth muscle running through the entire colon

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7
Q

What are the pouches present throughout the colon called?

A

Haustra

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8
Q

What produces haustra?

A

Contractions of the teniae coli

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9
Q

What is the classification of the mucosa in the colon?

A

Simple columnar epithelium that is flat

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10
Q

What is contained in the crypts within the colon?

A

Goblet cells

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11
Q

Why are goblet cells present in the colon?

A

Secrete mucous that is used as lubrication for faeces to move

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12
Q

What is the rectum?

A

Straight, muscular tube between the end of sigmoid colon and anal canal

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13
Q

What is the classification of the mucosa of the rectum?

A

Simple columnar epithelium

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14
Q

How does the muscularis externa of the rectum compare to other regions of the alimentary canal?

A

It is thicker

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15
Q

What is the anal canal?

A

2-3cm between distal rectum and anus

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16
Q

How does the muscularis externa of the anal canal compare to the rectum?

A

Is thicker forming the internal anal sphincter

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17
Q

What is the internal anal sphincter formed from?

A

Muscularis externa (smooth muscle)

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18
Q

What is the external anal sphincter formed from?

A

Skeletal muscle

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19
Q

How does the epithelium change in the anal canal?

A

Changes from simple columnar to stratified squamous

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20
Q

Does the colon have an important nutrient absorpion role?

A

Not in humans

21
Q

What is the function of the colon?

A

Actively transport sodium from lumen into the blood, causing osmotic absorption of water

This causes dehydration of chyme causing solid faecal pellets

22
Q

What cause faeces to be solid?

A

Water is absorbed, causing dehydration of faeces, due to the colon transporting sodium from the lumen to the blood creating an osmotic difference

23
Q

What causes bacterial colonisation of the colon?

A

Large residence time

24
Q

How much bacteria is present in the colonc microflora?

A

1014 (about 1kg)

25
Q

What happens to undigested carbohydrates in colon?

A

Bacterial fermentation

26
Q

What are consequences of bacterial colonisation of the colon?

A

Bacterial fermentation of undigested carbohydrates, short chain fatty acids and vitamin K

Production of gas

27
Q

Why does defaecation not occur passively?

A

Anus is closed by internal anal sphincter (smooth muscle under autonomic control) and external anal sphincter (skeletal muscle under voluntary control)

28
Q

Explain the mechanism that occurs following a meal that leads to defaecation?

A

1) Wave of intense contraction (mass movement contraction) from the colon into the rectum
2) Distension of rectal wall produced by mass movement of faecal material into rectum
3) Activated mechanoreceptors activate the defaecation reflex
4) Causes urge to defaecate

29
Q

What controls the defaecation reflex?

A

Parasympathetic nervous system (via pelvic splanchnic nerves) with no sympathetic influence

30
Q

How can defaecation be voluntary delayed?

A

By descending neural pathways

31
Q

Explain the mechanism of the defaecation reflex under parasympathetic control?

A

1) Contraction of rectum
2) Relaxation of internal and contraction of external anal sphincters
3) Increased peristaltic activity in colon (increased pressure on external anal sphincter causing expulsion of faeces)

32
Q

What is constipation?

A

Condition where there is difficulty emptying the bowels

33
Q

Does constipation lead to absorption of toxins?

A

No, there is no absorption of toxins from faecal material following long periods of retention

34
Q

How does frequency of bowel movements vary from person to person?

A

Vary considerably

35
Q

What are some symptoms associated with constipation?

A

Headaches

Nausea

Loss of appetite

Abdominal distension

36
Q

Why does constipation cause symptoms?

A

It causes distension of the rectum

37
Q

What is diarrhoea?

A

Too frequent passage of faeces which are too liquid

38
Q

What are some causes of diarrhoea?

A

Pathogenic bacteria

Protozoans

Viruses

Toxins

Food

39
Q

How much deaths occur per year due to diarrhoea?

A

0.5 million deaths/year, mostly children under 5

40
Q

What is E-coli an example of?

A

Enterotoigenic bacteria that normally lives in the intestines

41
Q

What are examples of enterotoxigenic bacteria?

A

Vibrio cholerae

Escherichia coli

42
Q

What does enterotoxigenic bacteria produce that causes diarrhoea?

A

Enterotoxins that maximally turn on intestinal chloride secretion from crypt cells, increasing H2O secretion

43
Q

How does enterotoxigenic bacteria maximally turn on intestinal chloride secretion from crypt cells?

A

Enterotoxins that they produce elevate the levels of intracellular second messengers like:

cAMP
cGMP
Calcium

44
Q

Why does excess H2O secretion in the colon lead to diarrhoea?

A

It swamps absorptive capacity of villus cells leading to profuse watery diarrhoea

45
Q

How much water per day is lost in diarrhoea due to cholerae?

A

25L

46
Q

Do enterotoxins damage villus cells?

A

No

47
Q

What is the treatment of secretory diarrhoea?

A

Sodium/glucose solution which drives H2O absorption leading to rehydration

48
Q

What is the administration of sodium/glucose solutions to people suffering from secretory diarrhoea called?

A

Oral rehydration therapy (ORT)

49
Q

What does ORT stand for?

A

Oral rehydration therapy

Alimentary System (41 decks)

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