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BRS 11 Gastroenterology > Large Bowel > Flashcards

Large Bowel Flashcards

1
Q

Label this diagram

A
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2
Q

What does the large bowel consist of?

A

Colon, caecum, appendix, rectum and anal canal

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3
Q

What is the caecum?

A

Blind pouch just distal to the ileocaecal valve

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4
Q

What is the appendix?

A

Thin, finger-like extension of the caecum
Not physiologically relevant

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5
Q

What are the principal functions of the large bowel?

A
  • Reabsorption of electrolytes and water
  • Elimination of undigested food and waste
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6
Q

What are the four sections to the colon?

A

Ascending colon, transverse colon, descending colon and sigmoid colon

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7
Q

Where does the ascending colon run from?

A

The caecum to the hepatic flexure

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8
Q

Where does the transverse colon run from?

A

The hepatic flexure to the splenic flexure

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9
Q

Where does the descending colon run from?

A

The splenic flexure to the sigmoid colon

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10
Q

Where does the sigmoid colon run from?

A

The descending colon to the rectum

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11
Q

Which band of tissue attaches the transverse colon to the stomach?

A

Greater omentum

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12
Q

What is the blood supply of the proximal and distal transverse colon?

A
  • Proximal – blood from middle colic artery
  • Distal third – blood from inferior mesenteric artery
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13
Q

What is the region between the proximal part and the distal third of the colon sensitive to?

A

Ischemia

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14
Q

What is the appendices epiplociae and what is their purpose?

A
  • Fatty tags
  • Have protective function against intra-abdominal infections
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15
Q

What is the name given to describe the pouched appearance of the muscle coat of the colon?

A

Haustra

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16
Q

What is the taeniae coli?

A

longitudinal muscle - 3 thick bands which are needed for large intestine motility

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17
Q

What immunological tissues are common in the walls of the distal small intestine and large intestines?

A

Small intestine - peyer’s patches
Large intestine - solitary nodules

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18
Q

How do haustra form?

A

The taenia coli is shorter than the small intestine which causes the formation of pouched ovoid segments called haustra

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19
Q

What does the colon reabsorb?

A

Electrolytes and water

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20
Q

In which part of the colon is more water and electrolytes absorbed?

A

More in the proximal colon

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21
Q

How does Na and Cl get absorbed?

A

Through exchange mechanisms and ion channels

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22
Q

How does K+ get reabsorbed?

A

Moves passively into the lumen

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23
Q

What happens when the large intestine absorbs more than 4.5L of water?

A

DIarrhoea

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24
Q

What histological feature distinguishes the rectum from the colon?

A

Rectum has transverse rectal folds in its submucosa and absence of taenia coli

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25
Which two muscles surround the anal canal?
The internal sphincter and external sphincters
26
What type of muscle is the internal anal sphincter?
Circular muscle
27
What type of muscle is the external anal sphincter?
Striated muscle
28
What are the mucosal layers of the large bowel, starting with the inner most?
Mucosa Submucosa Muscularis Serosa
29
What does the serosa harbour?
Blood vessels and nerve endings
30
What are found in crypts?
Stem cells
31
Which cells are abundant in the large bowel?
Crypts with stem cells Goblet cells Enterocytes
32
Why does the mucosa appear smooth at gross level?
No villi
33
What are enterocytes primarily concerned with?
The reabsorption of salts via microvilli
34
What do enterocytes have on their surface?
Short, irregular microvilli
35
Does the large or small bowel contain more goblet cells?
Large bowel
36
Which cell dominates inside the crypts?
Goblet cells
37
What are the apical ends of the goblet cells packed with?
Mucus filled granules awaiting release
38
What is the role of mucus in the large bowel?
Mucus - facilitates the passage of the increasingly solid colonic contents and covers bacteria & particulate matter.
39
What neurotransmitter stimulates goblet cell secretion?
ACh
40
Are there paneth cells in the large bowel?
No
41
Does the glycocalyx of the large bowel contain digestive enzymes?
No
42
What makes up the brush border?
Microvilli
43
What is the surface of the microvilli covered in?
Glycocalyx
44
What does the glycocalyx do?
traps a layer of water & mucous known as “unstirred layer” - this regulates the rate of absorption from the intestinal lumen
45
What is the glycocaylx?
A rich carbohydrate layer on the apical membrane
46
What does the muscularis externa consist of?
an inner circular and outer longitudinal layer
47
How are the circular muscles thickened?
Segmentally thickened
48
Where are the longitudinal muscles of the large bowel concentrated?
In three bands - taenia coli
49
What is the thickness of the longitudinal layer between the taenia coli?
Thin
50
Where are the ovoid segments of the large bowel not seen?
Rectum and anal canal
51
What are haustra?
Ovoid segments, which are are shorter than circular muscle layer and can contract individually
52
What large bowel movements dominate in the chyme in order to retain chyme?
Anti-propulsive patterns
53
What causes back and forth mixing in the transverse and descending colon?
haustral contractions
54
What do colonic contractions promote?
Absorption of electrolytes and water
55
How does the motility of the large bowel change following a meal?
Increase in the frequency of colonic contractions following a meal in order to promote the reabsorption of electrolytes and water
56
What is mass movement?
High amplitude propagated contractios which resemble a peristaltic wave. Can propel the contants 1/3-3/4 of the length of the large intestine in a few seconds
57
What promotes the process of mass movement through the large intestine?
Food containing fibre (undigestible material)
58
What is the parasympathetic innervation of the ascending colon?
Vagus nerve
59
What is the parasympathetic innervation of most of the transverse colon?
Vagus Nerve
60
What is the parasympathetic innervation of the distal colon (descending and sigmoid)?
Pelvic nerves
61
What is the sympathetic innervation of the large bowel?
Lower thoracic and upper lumbar spinal nerves
62
What is the external anal sphincter controlled by?
Somatic motor fibres in the pudendal nerves
63
What is Hirschsprung's disease?
Lack of enteric intramural ganglia
64
Where are myenteric plexus ganglia concentrated?
Below the taenia coli
65
What can stimulate mass movement?
Presence of food in the stomach
66
How does aldosterone promote water and Na+ reabsorption?
Synthesis of Na+ ion channel and Na+/K+ pump
67
How does the rectum become filled with faeces?
Through mass movement in the sigmoid colon
68
What controls the defacation reflex?
Sacral spinal cord
69
Describe the defacation reflex
- Reflex to sudden distension of walls of rectum. - Pressure receptors send signals via the myenteric plexus to initiate peristaltic waves in the descending and sigmoid colon and rectum - This inhibits the internal anal sphincter - This weak, intrinsic signal is then augmented by autonomic reflex
70
How is the sensation for defacation able to subside?
External anal sphincter under voluntary control, so if the urge is resisted then the sensation subsides
71
Which part of the rectum can distinguish between solids, liquids and gas?
The "social" part of the rectum - last few cm of the rectum
72
How many grams of faeces do adults pass a day?
150g
73
What proportion of faeces is water?
2/3
74
What are the solid components of faeces?
Cellulose, bacteria, cell debris, bile pigments, salts (K+)
75
What gives faeces such a strong odor?
Bacterial fermentation
76
Describe the microbiome of an average adult?
* Diverse, highly metabolically active community * Comprises approximately 1.5 kg of live bacteria, with the active biomass equivalent to a major human organ
77
What are the 7 roles of the intestinal flora?
1. Synthesize and excrete vitamins 2. Prevent colonisation by pathogens through competitive inhibition 3. Produce substances which are toxic to non-indigenous species 4. Stimulate prouction of cross-reactive antibodies 5. Stimulate development of some tissues 6. Break down fibre 7. Produce short chain fatty acids
78
How do intestinal flora prevent colonisation by pathogens?
Competing for attachment sites or essential nutrients.
79
How does the production of cross reactive antibodies by intestinal flora prevent infection?
Antibodies produced against components of the normal flora can crossreact with certain related pathogens
80
Which tissues do intestinal flora stimulate the development of?
Caecum and lymphatic tissues
81
What is the purpose of intestinal flora producing short chain fatty acids?
* Regulate gut hormone release * Be absorbed to be used as an energy source * Influence functions such as food intake or insulin sensitivity directly
82
Recent research has shown links between gut bacteria and..
* Drug metabolism * Insulin resistance * Bile acid metabolism * Lipid metabolism * Obesity
83
What are the most prevalent types of bacteria in the gut?
* Bacteroides * Gram negative, anaerobic and non-spore forming bacteria
84
Describe bifidobacteria
* Gram-positive, non-sporeforming, lactic acid bacteria * Prevent colonization by potential pathogens

BRS 11 Gastroenterology (25 decks)

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