physiology of large intestine

Question 1

what happens in mechanical digestion in the large intestine

Answer 1

• chyme enters through the ileocaecal valve
• haustral churning
• peristalsis occurs slowly (mass movement)

Question 2

what happens in chemical digestion in the large intestine

Answer 2

• only bacterial enzymes are present
  
  • carbohydrates are fermented to produce flatus
  • break down remaining amino acids

Question 3

what is the predominant mixing in the large intestine

Answer 3

segmental contractions

Question 4

how do mass movements work

Answer 4

intense and prolonged peristaltic contraction which can clear sections of the colon of all contents

Question 5

are mass movements seen anywhere else in the digestive tract

Answer 5

no

Question 6

what stimulates colonic motility

Answer 6

morning wakening

Question 7

what does gastrocolic reflex cause

Answer 7

increased motility in colon in response to stretch in stomach and byproducts of digestion in the small intestine

Question 8

what influences transit

Answer 8

diet - eg fibre increases faecal weight and reduces transit time

stress can increase motility

Question 9

what does immobility lead to

Answer 9

constipation

Question 10

how does age affect colonic motility

Answer 10

can prolong transit time

Question 11

do women have slower or faster colonic transit time

Answer 11

women have slower transit time

Question 12

how much water enters large intestine per day and how much is reabsorbed

Answer 12

0.5-1L and all except 100ml is reabsorbed

Question 13

what does faeces consist of

Answer 13

• undigested food
• inorganic salts
• sloughed off epithelial cells
• bacterial products
• bacteria

Question 14

what is in the ascending (right) colon

Answer 14

it is relatively fluid

has the consistency of muesli with large aggregates beginning to form

Question 15

what is in the transverse colon

Answer 15

less water and some gas

Question 16

what is there a risk of in the descending colon

Answer 16

risk of impaction in faeces

Question 17

what initiates defecation reflex

Answer 17

distension of rectum
(parasympathetic input to open internal anal sphincter)

it is involuntary

Question 18

what does increased pressure in rectum cause

Answer 18

the longitudinal muscle to shorten

Question 19

are contractions of diaphragm and abdomen during defaecation voluntary or involuntary

Answer 19

voluntary

Question 20

last part of defaecation process

Answer 20

external anal sphincter opens

Question 21

what are the disorders of the large intestine

Answer 21

• disorders of motility (constipation and diarrhoea)
• ibs
• haemorrhoids

Question 22

what causes constipation

Answer 22

• idiopathic
• gender (women more likely)
• psychiatric (depression etc)
• disease
• iatrogenic (morphine etc)

Question 23

what causes diarrhoea
(that isn’t severe enough for treatment)

Answer 23

• diet
• mild food poisoning

Question 24

what causes diarrhoea
(that is severe enough for treatment)

Answer 24

• disease (neoplasia, UC etc)
• drug induced
• travel

Question 25

what causes IBS

Answer 25

- abnormal GI motility - psychological factors (anxious patients who worry excessively) - luminal compounds which may irritate the bowel (allergens etc) - altered serotonin levels

Question 26

what happens to veins when you have haemorrhoids

Answer 26

overdistended veins in submucosa of the lower rectum

Question 27

what causes haemorrhoids

Answer 27

excessive straining in constipation

Question 28

what complications can haemorrhoids cause

Answer 28

thrombosis of local blood vessels

Question 29

what can ease defaecation

Answer 29

bulk/lubricant laxatives

Question 30

what can relieve symptoms of haemorrhoids

Answer 30

topical preparations such as - preparation H - anusoyl - anaesthetics - anti inflammatories

Question 31

what are the two regions of the colon

Answer 31

proximal and distal

Question 32

how can the distal part of the colon be reached

Answer 32

rectally (useful when treating haemorrhoids)

Question 33

how can the proximal section of the colon be reached

Answer 33

via the oral route

Question 34

which part of the colon is sufficiently fluid for drug absorption

Answer 34

the ascending colon

Question 35

treatment for constipation

Answer 35

- diet changes - laxatives - motility enhancers

Question 36

treatment for diarrhoea

Answer 36

- oral rehydration - antimotility agents - adsorbents - antimicrobial therapy

Question 37

how to treat IBS

Answer 37

- patient support (reassure them to stop anxiety) - diet changes - antispasmodic - antidepressants/hypnotherapy

Question 38

how to change diet to treat IBS

Answer 38

for constipation - high fibre diet - laxatives for diarrhoea - avoid fresh fruits/salds - loperamide

Question 39

how do antidepressants/hypnotherapy treat IBS

Answer 39

strong brain/gut link new 5-HT receptor targeted drugs may prove beneficial

Question 40

what are some functions of the gut bacteria

Answer 40

- metabolism of indigestible material - vitamin synthesis - neurochemical synthesis - anti-inflammatory effects - promotion of bone growth - positive effects on brain and cardiovascular health

Question 41

what factors affect the gut microbiome

Answer 41

- diet - age - host genetics - exercise - antibiotics - smoking - geographical impact

Question 42

what are intervention strategies for the gut bacteria

Answer 42

- probiotics - faecal microbiota transplant - phage therapy to selectively target bacteria