Large Bowel

Question 1

Facts about the caecum

Answer 1

Blind pouch just distal to the ileocecal valve - larger in herbivores

Question 2

Facts about the appendix

Answer 2

Thin, finger like extension of the caecum - not physiologiclaly relevant in humans

Question 3

What are the principal functions of the large bowel

Answer 3

Reabsorption of electrolytes and water

Elimination of undigested food and waste

1.5m long 6 cm diameter

Question 4

Differen parts of the colon

Answer 4

Asencding colon runs from caecum to hepatic flexure

Transerse colon runs from hepatic flexure to spelnic flexure, hangs off the stomach - attached by a wide band of tissue called greater omentum

Descending colon - splenic flexure to sigmoid colon

Sigmond colon runs from descneding colon to rectum

Question 5

Blood supply of colon

Answer 5

Supplied with blood by the middle colic artery (branch of superior mesenteric artery)

Distal third of colon perfused by inferior mesentric artery

Region between two is sensitive to ischemia

Question 6

What is taenia coli used for

Answer 6

Large intestine motility

Question 7

What are teh nodules of lymphoid tissue

Answer 7

Small intestine - peyers patches

Large intestine - solitary nodules

Question 8

What causes haustra

Answer 8

Taenia coli shorter than small intestine

Question 9

Colon function

Answer 9

Colon absorbs electrolyes and water

Na and Cl absorbed by exchange mechanisms

Water follows by osmosis

K moves passively into lumb

Large intestine can reabsobre 4.5 litres - above this threshold results in diarrhoea

Question 10

How is the rectum different to the colon

Answer 10

Transverse rectal folds in submucosa and absence of taenia coli

Question 11

What is the mucosal organisation of large bowel

Answer 11

Mucosa appears smooth at gross level because no villi

Enterocytes have short irregular mcirovilli with reabsorption of salts

Crypts dominated by goblet cells

Question 12

Goblet cells in large bowel

Answer 12

Mucus - facilitates passage of increasingly solid colonic contents

Acetylcholine - stimulates goblet cell secretion

Question 13

Difference between large bowel and small bowel

Answer 13

No paneth cells and enteroendocrine cells

Glycocalyx do not contain digestive enzymes

Question 14

What are the muscle layers of the large bowel

Answer 14

Circular muscles segmentally thickened

Logitudinal laeyrs concentrated in three badns -taenia coli

Between taenia longitudinal layer is thin

Bundles of teniae coli penetrate circular layer at irregular intervals

Question 15

Is movement of large bowel more or less complicated than small intestine

Answer 15

More complicated

Question 16

How does the chyme move in the large bowel

Answer 16

Kneading process - 5-10cm/hr

Promotes absorption of electrolytes and water

Proximal colon- antipropulsive patterns domiante to retian chyme

Increase in frequency following a meal

Short propulsive movements every 30 mins

Question 17

What is the mass movement in the large bowel

Answer 17

1-3 times daily

Propel contents 1/3-3/4 of length

Food that contains fibre promots rapid transport (through colon)

Question 18

What is the large bowel innervated by

Answer 18

Parasympathetic - Ascending colon and transfverse - vagus

Distally innervated by pelvic nerves

Sympathetic - lower thoracic and upper lumbar spinal cords

External anal sphincter controlled by somatic motor fibres in pudendal nerves

Afferent sensory neurons detect pressure

Enteric nervous system

Myenteric plexus ganglia

Question 19

How is the defecation reflex controlled

Answer 19

Sacral spinal cord - both reflex and voluntary actions

Distension of walls of rectum - pressure receptors send signals via myenetric plexus to initiate peristaltic waves

Internal anal sphincter inhibited

Weak intrinsic signal augmented by autonomic reflex

External anal sphincter under voluntary control

Urge resisted, sensation subsides

Question 20

Why is rectum known as the socila part

Answer 20

Distinguish between solid, liquid and gas

Can identify what can be passed appropriately in what circumstance

Question 21

What is faeces made up of

Answer 21

150g/day adult

two thirds water

solids: cellulose, bacteria, cell debris, bile pigments, salts (k+)

Bile pigments give colour

Bacterial fermentation gives odour

Question 22

How much does the microbiome of an average human weigh

Answer 22

1.5KG

Question 23

Role of the intestinal flora

Answer 23

Sythesis and excrete vitamins

Prevent colonization by pathogens by competiting for attachment sites or for essential nutrients

Antagonize otehr bacteria through production of substances which inhibit non-indigenous species

Stimulate production of cross-reactive antibodies which can cross react with certain related pathogens prevent infection

Stimulate development of certain tissues - caecum and lymphatic tissues

Fibre can be broken down by bacteria

Produces short cahin fatty acids - regulat gut hormone, energy source, influence food intake, insulin sensitivity

Question 24

What are the types of flora

Answer 24

Bacteroides - gram negative, anaerobic, non-spore forming bacteria - initiation colitis and colon cancer

Bifidobacteria - gram positive, non-sporeforming, lactic acid bacteria, frienly bacteria which prevents colonisation of other bacteria

Question 25

What are the recent research between gut bacteria and intestinal flora

Answer 25

Drug metabolism, insulin resistance, bile acid metabolism, lipid metabolism, obesity

Question 26

What is a fecal transplant

Answer 26

Help transfer the microbiota from one healthy individual to another