Lecture 20 - Physiology of the Large Intestine

Question 1

What are Hastra?

Answer 1

saccules/ lumps that give LI its segmented appearance

Question 2

Mechanical digestion in the large intestine

Answer 2

Chyme enters through ileocecal valve, haustral churning, low peristalsis

Question 3

Chemical digestion in large intestine

Answer 3

Very limited, bacterial enzymes ferment remaining carbohydrates to produce flatus, amino acids broken down

Question 4

What is flatus?

Answer 4

gas in or from the stomach or intestines

Question 5

Are segmental contractions more or less predominant in LI than propulsive movements?

Answer 5

more, propulsive movements only happen 3-4 times a day

Question 6

What are mass movements in LI?

Answer 6

giant migrating contraction, intense and prolonged peristalsis which can clear sections of colon of all contents

Question 7

Where do mass movements occur in GI Tract?

Answer 7

only LI

Question 8

What triggers motility of colon?

Answer 8

morning wakening, in response to stretch in stomach and digestion by products in SI

Question 9

What increases colon transit time?

Answer 9

eating fibres (increase faecal weight, reducing Transit time)
stress (may increase motility)

Question 10

What decreases colon transit time?

Answer 10

bad diet, immobility, old age, being a female (statistically have slower transit time compared to men)

Question 11

How much water is absorbed by LI everyday?

Answer 11

500-100ml (only 100ml reabsorbed)

Question 12

What is faeces made of?

Answer 12

undigested food, inorganic salts, sloughed off epithelial cells (cells moved of interior of mucosa), bacterial products and bacteria

Question 13

Where in LI is there a greater risk of faecal impaction?

Answer 13

descending colon

Question 14

Process of defaecation

Answer 14

• chyme moves down descending part of colon
• reflex initiated by distension of rectum
• parasympathetic input relaxes internal anal sphincter and contraction of external sphincter (involuntary)
• increased pressure in rectum, longitudinal muscle shortens
• voluntary contractions of diaphragm and abdomen
• external anal sphincter opens

Question 15

Causes of constipation

Answer 15

idiopathic (bad diet - low fibre, low fluid intake), gender (women more susceptible, psychiatric, disease, latrogenic (morphine, laxative abuse)

Question 16

Causes of Diarrhoea that don’t normally require treatment

Answer 16

dietary indiscretion, mild food poisoning

Question 17

Causes of diarrhoea usually requiring treatment

Answer 17

disease, drug-induced (cholinergic drugs), travel

Question 18

Causes of IBS

Answer 18

abnormal GI motility, psychological factors (anxiety), food allergens, bile acids, processed foods, luminal compounds, altered serotonin levels

Question 19

Cause of Haemorrhoids

Answer 19

excessive straining due to constipation

Question 20

What are haemorrhoids?

Answer 20

overdistended veins in submucosa of lower rectum

Question 21

Complications caused by haemorrhoids

Answer 21

thrombosis of local blood vessels

Question 22

What medications can be given to help with haemorrhoids?

Answer 22

bulk/lubricant laxatives to ease defaecation, topical preparations (anusoyl), local anaesthetics, anti-inflams such as hydrocortisone to relieve symptoms

Question 23

2 regions of the colon

Answer 23

proximal and distal

Question 24

What part of colon can be reached rectally?

Answer 24

distal

Question 25

What part of colon can only be reached via oral route?

Answer 25

proximal

Question 26

Where in LI is fluid enough for drug absorption?

Answer 26

only ascending colon (think descending is where impaction etc. can occur as fluid is drawn out from chyme)

Question 27

Some functions of gut microbacteria

Answer 27

metabolism of indigestible material, vitamin synthesis, neurochemical synthesis, anti-inflam affects, promote bone growth

Question 28

Factors affecting microbiome

Answer 28

diet, age, host genetics, exercise, antibiotics, smoking, geographical impacts

Question 29

Interventions to regulate microbiome in gut

Answer 29

probiotics, faecal microbiota transplant, phage (virus) therapy to selectively target bacteria