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Gastroenetrology > Physiology and pharmacology of the large intestine > Flashcards

Physiology and pharmacology of the large intestine Flashcards

1
Q

How long is the Large intestine?

A

1.7m

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2
Q

What are the 4 parts of the large intestine?

A

Caecum and appendix
Colon
Rectum
Anal canal and anus

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3
Q

What are the four sections of the colon?

A

Ascending
Transverse
Descending
Sigmoid

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4
Q

What are the three smooth muscle layers in the caecum and colon?

A

Teniae Coli
Internal anal sphincter
External anal sphyincter

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5
Q

Do the caecum and appendix have a function in humans?

A

No

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6
Q

How many litres of fluid does the caecum normally receive from the ileum per day?

A

1-2L

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7
Q

How is entry from ileum to the caecum regulated?

A

The gastroileal reflex in response to gastrin and CCK through the ileocaecal valve

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8
Q

What is the appendix?

A

A blind ended tube with extensive lymphoid tissue connected to the distal caecum via the appendiceal orifice that may be obstructed by faecalith.

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9
Q

What are the 5 primary functions of the colon?

A 
Absorption of Na+, Cl- and H20
Absorption of short fatty acid chains
Secretion of K+, HC03 and mucus
Reservoir of colonic contents
Periodic elimination of faeces
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10
Q

Are there Villi in the mucosa of the colon?

A

No

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11
Q

What is present in the mucosa of the colon?

A

Colonic folds
Crypts
Microvilli

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12
Q

What do colonocytes mediate?

A

Electrolyte absorption by osmosis

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13
Q

What do crypt cells mediate?

A

Ion secretion

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14
Q

What do goblet cells secrete?

A

Copious mucus containing glycosaminoglycans

Trefoil proteins involved in host defense

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15
Q

What are Na+ absorption and K+ secretion mediated by?

A

Aldosterone

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16
Q

What might cause signifigant loss of K+ in the faeces?

A

Secretory diarrhoea

17
Q

How much ileocaecal material is absorbed by the colon each day?

A

0.1L

18
Q

What is Haustration?

A

Non-propulsive segmentation

19
Q

What is Peristaltic propulsive movements?

A

Mass movement

20
Q

What is Defaecation?

A

Periodic egestion

21
Q

What are Haurstra?

A

Saccules caused by alternating contraction of the circular muscle

22
Q

Where does haustration occur?

A

The proximal colon

23
Q

What generates haustration?

A

Slow wave activity

24
Q

Describe mass movement

A

simultaneous contraction of large sections (about 20 cm) of the circular muscle of the ascending and transverse colon (haustra disappear) - drives faeces into distal regions

25
Q

When does mass movement occur and what triggers it?

A

occurs about one to three times daily
typically triggered by a meal (often breakfast) via the gastrocolic response involving
gastrin
extrinsic nerve plexuses

26
Q

Describe the process of motility in the large intestine

A

Mass movement > Rectum fills with feacal matter > Activation of rectal stretch receptors and afferents to brain > Activation of parasympathetic efferents > Contraction of smooth muscle of sigmoid colon and rectum

27
Q

How would a beneficial resident bacteria in the gut be described?

A

Commensal

28
Q

What is the function of commensal bacteria?

A

increase intestinal immunity by competition with pathogenic microbes
promote motility and help maintain mucosal integrity
synthesise vitamin K2 and free fatty acids (from carbohydrate) that are absorbed
activate some drugs (e.g. used in treatment of IBD)

29
Q

How do gases in the large intestine arise?

A

swallowing air

30
Q

What is constipation and what causes it?

A

Presence of hard dried faeces within the colon (results from delay in defaecation and enhanced absorption of H2O)

31
Q

What are the causes of constipation?

A

ignoring, or suppressing, the urge to defaecate
decreased colonic motility (e.g. improper diet, drugs, metabolic disorders, old age)
obstruction of faecal movement
paralytic ileus following abdominal surgery
impairment of motility/defaecation reflex (e.g. Hirschprung disease, involving absence of a section of the enteric nervous system)

32
Q

What are the symptoms of constipation?

A

Abdominal discomfort
Headache
Loss of appetit
General malaise

33
Q

what drugs are used to treat constipation?

A

Laxatives

34
Q

What are Purgatives?

A

Agents that cause purging or cleansing of the bowel by promoting evacuation

35
Q

When should laxatives and purgatives not be used?

A

When there is a physical obstruction of the bowel

36
Q

What do laxatives do?

A

increase peristalsis and/or soften faeces causing, or assisting, evacuation

Gastroenetrology (17 decks)

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