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Block 1 > Anatomy and Physiology of the Large Intestine > Flashcards

Anatomy and Physiology of the Large Intestine Flashcards

1
Q

What are the three functions of the large intestine?

A

Extract Na+ and water from luminal contents

To make and store faeces

To move faeces towards the rectum

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2
Q

Which cells secrete alkaline mucus in the large intestine?

Where are these cells found?

A

Goblet cells

Luminal epithelium

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3
Q

What is an alkaline mucus in the large intestine for?

A

Protect the epithelium from acid, abrasion, and bacteria

Provide a medium to hold faecal matter together

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4
Q

How does sodium move into the luminal cell in the JEJUNUM?

A

Na+K+ ATPase pump moves sodium out of cell (active transport)

Na+ is reabsorbed in co-transport with glucose or galactose via SGLT1 (secondary active transport)

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5
Q

Which transporter absorbs fructose?

A

GLUT5

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6
Q

How does glucose, galactose and fructose move out of a luminal cell?

A

GLUT2

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7
Q

How does water move into the intestinal epithelium?

A

Down an osmotic gradient created by sodium.

Sometimes between cells, sometimes through (‘tight’ or ‘leaky’ junctions).

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8
Q

How is sodium moved into a COLONIC epithelial cell?

A

Na+ H+ exchanger

Electrogenic Na+ channel

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9
Q

Name 2 functions of the ileocaecal valve

A

Prevents back flow of faecal contents from the colon

Controls the rate at which chyme enters the colon.

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10
Q

What are the two categories of colonic movements?

A

Haustral contractions (mixing)

Mass movements (propulsive)

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11
Q

Name two functions of colonic motility

A

Facilitates absorption of water and salts.

Permits orderly evacuation of faeces.

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12
Q

The gastrocolic reflex:

A

Is mediated by gastrin and extrinsic autonomic nerves

Initiates mass movements in the colon

Pushes colonic contents to rectum

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13
Q

Name the two sphincters in the anal canal

A

Internal anal sphincter (smooth muscle)

External anal sphincter (skeletal muscle)

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14
Q

Why is the mechanism of sodium reabsorption different in the jejunum to the colon?

A

Because there is no more glucose to be reabsorbed to act as a co-transporter (SGLT1)

Na+ is absorbed in the colon in exchange for H+ or via an electrogenic Na+ channel

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15
Q

Is absorption of Na+ in the colon active or passive?

A

Active

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16
Q

What are the longitudinal muscles of the colon called?

A

Taeniae coli

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17
Q

Name the six steps of the defecation reflex

A
  1. Contraction of the rectum
  2. Relaxation of the internal anal sphincter
  3. Initial contraction of the external anal sphincter
  4. Increased peristaltic activity in the sigmoid colon
  5. Relaxation of the external anal sphincter
  6. Expulsion of faeces
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18
Q

What are the 4 parts of the Valsalva manoeuvre

A
  1. Full inspiration then forced expiration against a closed glottis, diaphragm moves downwards
  2. Abdominal and thoracic muscles contract
  3. Intra-abdominal pressure increases, faeces forced into rectum
  4. Defecation reflex initiated
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19
Q

What causes faeces to be brown?

A

Derivatives of bilirubin

20
Q

What causes the smell in faeces?

A

Products of bacterial action

21
Q

Name some functions of intestinal bacteria

A
  1. Provides immunity against common bacteria
  2. Forms secondary bile acids
  3. Digests mucus
  4. Degrades digestive enzymes
  5. Synthesises vitamin K
  6. Metabolises undigested polysaccharides
22
Q

What do purgatives do?

A

Accelerate transit through the intestine

23
Q

Define constipation

A

Infrequent or difficult evacuation of faeces

24
Q

What are 5 causes of constipation?

A 
Dietary 
Hormonal 
Anatomical
Medication side effect
Illness or disorder
25
Q

What are the four major classes of purgatives?

A

Bulk laxatives

Osmotic laxatives

Faecal softeners

Stimulant purgatives

26
Q

How do bulk laxatives work?

A

They are polysaccharide polymers that are not broken down.

Retain water in GI lumen, softening and increasing faecal bulk.

Increased bulk stimulates mechanoreceptors

27
Q

Give 2 examples of bulk laxatives

A

Methyl cellulose

Ispaghula husk

28
Q

How do osmotic laxatives work?

A

They are poorly absorbed solutes that maintain an increased volume of fluid in the GI tract, resulting in a high volume of fluid entering the colon.

Distention leads to purgation.

29
Q

Give 3 examples of osmotic laxatives

A

Magnesium sulphate, magnesium hydroxide

Macrogol

Lactulose

30
Q

How does lactulose work?

A

Moves into the large colon and mimics the action of lactulose in the small intestine.

Bacteria breakdown lactulose. The fermentation produces gases, lactic acid which causes increased bloating and motility

31
Q

When is lactulose particularly useful?

A

In treating constipation secondary to opioids

32
Q

Give 2 faecal softeners

A

Docusate

Arachis oil enema

33
Q

How do faecal softeners work?

A

They contain anionic surfactants that lower the surface tension at oil-water interface, allowing water or fat to enter the stool

34
Q

Give 2 stimulant purgatives

A

Bisacodyl

Senna

35
Q

How does bisacodyl work?

What class of laxative is it?

A

Stimulates the rectal mucosa, resulting in mass movements

Stimulant purgative

36
Q

How does senna work?

What class of laxative is it?

A

Contains derivatives of athracene which is absorbed into the colon and have an effect on the myenteric plexus.

Stimulates the longitudinal muscle of the colon

Stimulant purgative

37
Q

Give 4 causes of diarrhoea

A

Infectious agents
Toxins
Anxiety
Drugs

38
Q

What are the 4 types of diarrhoea?

A

Motility-related
Osmotic
Inflammatory
Secretory

39
Q

Describe secretory diarrhoea

A

Increased active secretion or inhibition of absorption

Cholera

40
Q

Describe osmotic diarrhoea

A

Loss of water due to heavy osmotic load e.g. maldigestion

Coeliac diseases

41
Q

Describe inflammatory diarrhoea

A

Damage to mucosal lining or brush border leads to passive loss of protein-rich fluids and decreased ability to absorb these fluids.

Bacterial infection
Viral infections
Autoimmune disease e.g. IBD

42
Q

Describe motility-related diarrhoea

A

High GI motility, less time available for absorption of nutrients and water.

Diabetic neuropathy

43
Q

Name the 3 treatments for diarrhoea

A

Maintenance of fluid/electrolyte balance (Na+/K+)

Anti-diarrhoeal agents

(Anti-infective)

44
Q

What is in oral rehydration therapy?

A

Glucose
NaCl

Isotonic or hypotonic solution

45
Q

How does oral rehydration therapy work?

A

Na+ gets reabsorbed with glucose via SGLT1, water follows

46
Q

Name 2 opioid anti-motility agents

A

Codeine

Loperamide

47
Q

How do opioid anti-motility agents work?

A

Act on mui-opioid receptors in myenteric plexus

Increases tone and rhythmic contractions of colon but diminishes propulsion

Block 1 (13 decks)

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