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Y1 Alimentary > Large intestine > Flashcards

Large intestine Flashcards

1
Q

What does the large intestine consist of?

A 
Colon
Cecum
Appendix
Rectum
Anal canal
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2
Q

What is the cecum? Where is it found?

A

It’s a blind pouch just distal to the ileocecal valve - larger in herbivores

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3
Q

What is the appendix?

A

A thin finger like extension of the cecum that is not physiologically relevant in humans

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4
Q

What are the functions of the colon?

A
  • reabsorption of electrolytes and water

- elimination of undigested food and waste

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5
Q

What is the length and diameter of the colon?

A

1.5 m long

6cm diameter

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6
Q

Where is the ascending colon found?

A

Right side of the abdomen, runs from the cecum to the hepatic flexure (the turn of the colon by the liver)

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7
Q

Where is the transverse colon found?

A

Runs from the hepatic flexure to the splenic flexure (the turn of the colon by the spleen). Hangs off the stomach, attached by a wide band of tissue called the greater omentum (posterior side, mesocolon)

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8
Q

Where is the descending colon found?

A

From the splenic flexure to the sigmoid colon

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9
Q

Where is the sigmoid colon found?

A

From descending colon to the rectum - s shaped

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10
Q

Where is blood supplied from in the transverse colon?

A

Middle colic artery - branch of the superior mesenteric artery

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11
Q

What is blood from the distal third of the transverse colon perfused by?

A

Inferior mesenteric artery

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12
Q

What region of the colon is sensitive to ischemia?

A

The region between the distal third and the proximal transverse colon

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13
Q

What are the properties of the peritoneum?

A
  • has fatty tags
  • muscle coat has 3 thick longitudinal bands
  • gut wall pouched in appearance
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14
Q

Where are the nodules of lymphoid tissue commonly found in the intestines?

A
  • walls of distal small intestine (Peyer’s patches)

- large intestine (solitary nodules)

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15
Q

What is the suggested function of the appendices epiploica?

A

Protective function against intra-abdominal infections

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16
Q

What is necessary for large intestine motility?

A

Taenia coli

- three seperate longitudinal ribbons of smooth muscle that are shorter than small intestine

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17
Q

What are the formation of pouched ovoid segments called in taenia coli?

A

Haustra

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18
Q

How are Na+, Cl-, Water and K+ transported in colon?

A

Na+ and Cl- absorbed by exchange mechanisms and ion channels
Water follows by osmosis
K+ moves passively into lumen

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19
Q

What is the histology of the rectum?

A

Similar to colon but distinguished by transverse rectal folds in it’s submucosa and the absence of taenia coli in it’s muscularis externa

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20
Q

What is the terminal portion of the rectum called? What is it surrounded by?

A

Anal canal

Surrounded by internal circular muscle and external striated muscle anal sphincters

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21
Q

What cells are abundant in the large intestine?

A

Like the small intestine, enterocytes and goblet cells are abundant. Abundant crypts and stem cells are found in crypts

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22
Q

Where are mucosa found in the large intestine?

A

Mucosa appears smooth at gross level because no villi, smaller SA than small intestine

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23
Q

What kind of microvilli do enterocytes in the large intestine have?

A

Short, irregular microvilli and primarily concerned with resorption of salts

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24
Q

How is water absorbed in the large intestine? What is the result?

A

It passively follows electrocytes resulting in more solid gut contents

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25
Q

Where are goblet cells prevalent in the large intestine?

A

More in crypts than along the surface and increases distally towards the rectum

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26
Q

What does the mucus do in the large intestine?

A

Facillitates the passage of increasingly solid colonic contents and covers bacteria and particulate matter

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27
Q

What hormone stimulates goblet cell secretion?

A

Acetylcholine - parasympathetic and enteric nervous system

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28
Q

Where are paneth cells found in the large intestine?

A

Bases of crypts

29
Q

What do paneth cells contain

A

Large acidophillic granules containing:
- antibacterial enzyme lysozyme which protects stem cells
- glycoproteins and zinc which are essential for some enzymes
they also engulf some bacteria and protozoa and may have role in regulating intestinal flora

30
Q

What do the muscularis and externa layer consists of?

A

An inner circular and an outer longitudinal layer

31
Q

What is special about the circular muscle layer of the large intestine?

A

Segmentally thickened

32
Q

What is special about the longitudinal muscle?

A

Concentrated in three bands - taenia coli. Between the taenia, longitudinal layer is thin. Bundles of muscle from the teniae coli penetrate the circular layer at irregular intervals

33
Q

What is special about the haustra?

A

Shorter than circular muscle layer, ovoid segments that can contract individually.

34
Q

What are the colonic contractions like?

A

Kneading process that is minimally propulsive 5-10cm/hr at most

35
Q

What does large intestine motility do?

A

Promotes absorption of electrolytes and water

36
Q

What happens in proximal colon- large intestine motility ?

A

Antipropulsive patterns dominate to retain chyme

37
Q

What happens in transverse and descending colon in large intestine motility?

A

Localised segmentation contractions of circular muscle called Haustral contractions cause back and forth mixing

38
Q

When do movements in the large intestine increase?

A

Short propulsive movements happen every 30 minutes but increase in frequency following a meal

39
Q

What does mass movement in large intestine resemble?

A

Peristaltic wave

40
Q

What kind of food promotes rapid transport through colon

A

Food containing fibre (indigestible material)

41
Q

What nerves control which parts of the large intestine parasympathetically?

A

Ascending colon and transverse colon - vagus nerve

More distal - pelvic nerve

42
Q

What nerves and parts of spinal cord control which parts of the large intestine sympathetically?

A

Lower thoracic and upper lumbar spinal cord

43
Q

How are the external anal sphincters controlled? What nerves?

A

Somatic motor fibres in pudendal nerves

44
Q

What disease is the enteric nervous system important in and what happens in this disease?

A

Hirschsprung’s disease - no enteric intramural ganglia

45
Q

Where are the myenteric plexus ganglia concentrated below?

A

Taenia coli

46
Q

What does aldosterone promote in the large intestine?

A

Sodium and water absorption by synthesis of Na+ ion channel, Na+/K+ pump

47
Q

How does defecation occur?

A

Rectum filled with faeces by mass movement into sigmoid colon and stores stool until convenient to void.

48
Q

What is the defecation reflex controlled by?

A

Primarily by sacral spinal cord - both reflex and voluntary actions

49
Q

What is defecation?

A

A reflex to sudden distension of walls of rectum

50
Q

What causes the reflex of defecation?

A

Pressure receptors sending signals via myenteric plexus to initiate peristaltic waves in descending sigmoid colon and rectum. Internal anal sphincter inhibited.

51
Q

What kind of control, autonomic or voluntary, does the external anal sphincter have? What about the intrinsic signal

A

Voluntary - external anal sphincter

Weak intrinsic signal augumented by autonomic reflex

52
Q

What are the last few centimetres of the rectum known as?

A

The social part of the rectum

53
Q

What ability does the social part of the rectum have? Why is this important?

A

Can distinguish between solid, liquid and gas. It is important in knowing what can be passed appropriately in what circumstance

54
Q

What solids are passed in the faeces?

A

Cellulose, bacteria, cell debris, bile pigments and salts (K+)

55
Q

What gives the colour and odour of faeces?

A

Bile pigments give colour

Bacterial fementation gives odour

56
Q

How much poop does an adult do a day?

A

150g

57
Q

How much of poop is water

A

2/3

58
Q

What is different in bacterial flora in stomach and small intestine vs large intestine?

A

Stomach and small intestine have few bacteria - protected

Large intestine contains many essential to normal function

59
Q

How much (in weight) live bacteria does an average adult human comprise of? What is the active biomass equivalent to?

A

1.5kg

major human organ

60
Q

What are the roles of intestinal flora in large intestine? (7)

A
  • make and excrete vitamins eg vit K
  • prevent pathogen colonization by competing for attachment sites or essential nutrients
  • antagonize other bacteria by the make stuff that inhibit or kill non indigenous species
  • stimulate making of cross reactive antibodies that prevent infection or invasion
  • stimulate development of certain tissues eg cecum and lymphatic tissues
  • break down fibre
  • make short chain FA
61
Q

What problems can germ free animals have?

A

Clotting problems

62
Q

How do cross reactive antibodies made in intestinal flora prevent infection or invasion?

A

Antibodies produced against components of the normal flora can cross react with certain related pathogens

63
Q

How is fibre broke down in the intestines?

A

By colonic bacteria

64
Q

What do short chain fatty acids do?

A

Regulate gut hormone release

Absorbed to be used as energy source or to influence functions eg food intake and insulin sensitivity directly

65
Q

What is a type of normal gram negative bacteria in gut? What are the qualities of this bacteria?

A

Bacteriodes - gram negative, anaerobic, non spore forming bacteria

66
Q

What do bacteriodes have implications on?

A

Initiation colitis and colon cancer

67
Q

What is a type of normal gram postive bacteria in gut? Properties?

A

Bifidobacteria

Gram positive, non sporeforming, lactic acid bacteria, described as friendly bacteria

68
Q

What do bifidobacteria do?

A

Prevent colonization by potential pathogens

69
Q

What are gut bacteria recently discovered to have a link with? (5)

A
  1. drug metabolism
  2. insulin resistance
  3. bile acid metabolism
  4. lipid metabolism
  5. obesity

Y1 Alimentary (21 decks)

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