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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

No important nutrient absorption role in humans

21
Q

What is the function of the colon?

A

Actively transports sodium from lumen into blood ⇒ osmotic absorption of water ⇒ dehydration of chyme ⇒ solid faecal pellets

22
Q

What cause faeces to be solid?

A

sodium from lumen into blood ⇒ osmotic absorption of water ⇒ dehydration of chyme ⇒ solid faecal pellets

23
Q

What causes bacterial colonisation of the colon?

A

Long residence time in colon

24
Q

How much bacteria is present in the colonc microflora?

A

1014 bacteria (~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

Short chain fatty acids (energy source in ruminants)

Vitamin K (blood clotting)

Gas (flatus) - nitrogen, CO2, hydrogen, methane, hydrogen sulphide

27
Q

Why does defaecation not occur passively?

A

Normally, anus closed by internal anal sphincter (smooth muscle under automatic 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

Wave of intense contraction (Mass Movement Contraction) - colon → rectum

Distension of rectal wall produced by mass movement of faecal material into rectum → mechanoreceptors → defaecation reflex → urge to defaecate

29
Q

What controls the defaecation reflex?

A

Distension of rectal wall produced by mass movement of faecal material into rectum → mechanoreceptors → defaecation reflex → urge to defaecate

30
Q

How can defaecation be voluntary delayed?

A

Voluntary delay of defaecation - descending pathways

31
Q

Explain the mechanism of the defaecation reflex under parasympathetic control?

A

Under parasympathetic control – via pelvic splanchnic nerves (no sympathetic influence)

Contraction of rectum

Relaxation of internal and contraction of external anal sphincters

Increased peristaltic activity in colon

↑ Pressure on external anal sphincter - relaxes under voluntary control ⇒ expulsion of faeces
32
Q

What is constipation?

A

No absorption of toxins from faecal material following long periods of retention

33
Q

Does constipation lead to absorption of toxins?

A

no

34
Q

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

A

Frequency of bowel movements vary considerably from individual to individual

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

Due to distension of 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
first year medical exams…

39
Q

How much deaths occur per year due to diarrhoea?

A

Major killer of children under 5 years of age in developing countries

40
Q

What is E-coli an example of?

A

Enterotoxigenic Bacteria

41
Q

What are examples of enterotoxigenic bacteria?

A

Vibrio cholerae, Escherichia coli

42
Q

What does enterotoxigenic bacteria produce that causes diarrhoea?

A

Produce protein enterotoxins which maximally turn on intestinal chloride secretion from crypt cells

43
Q

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

A

↑ H2O secretion

Act by elevating intracellular second messengers:
cAMP
cGMP
calcium

44
Q

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

A

H2O secretion swamps absorptive capacity of villus cells → profuse watery diarrhoea (25 litres per day for cholera)

45
Q

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

A

25 litres

46
Q

Do enterotoxins damage villus cells?

A

don’t damage villus cells

47
Q

What is the treatment of secretory diarrhoea?

A

Give sodium/glucose solution

Drive H2O absorption ⇒ 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 (44 decks)

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