Large intestine: structure and function

Question 1

where does the large intestine start?

Answer 1

ileocaecal valve

Question 2

what are the 4 parts of the large intestine?

Answer 2

ascending
transverse
descending
sigmoid

Question 3

what’s different about the muscularis externa of the large intestine compared with S.I?

Answer 3

The large intestine has a complete circular muscle layer but the longitudinal layer is in 3 separate strips throughout the length of the large intestine

Question 4

what gives the large intestine it’s puckered appearance?

Answer 4

contracted haustra

Question 5

Main function of goblet cells in the lining of crypts in large intestine

Answer 5

Goblet cells are interspersed between simple columnar epithelium producing mucus that provides lubrication for movement of faeces

Question 6

describe rectum structure:

mucosa, and muscula externa

Answer 6

The rectum is a straight, muscular tube

mucosa - simple columnar epithelium

muscularis externa - thicker to hold onto faeces

Question 7

what is the mucosa of L.I comprised of?

Answer 7

simple columnar epithelium

Question 8

what are teniae coli?

Answer 8

the ribbon-like parts of longitudinal smooth muscle - entire length of colon

Question 9

where is the anal canal found?

Answer 9

between distal rectum and anus

Question 10

is the muscularis thicker in the rectum or anal canal?

Answer 10

anal canal due to the internal anal sphincter

Question 11

which type of muscle is found in:-
External anal sphincter
Internal anal sphincter

Answer 11

external - skeletal muscle

internal - ring of smooth muscle

Question 12

what type of control is the anal canal under?

Answer 12

voluntary - you can hold a poo in if you can’t find a toilet

Question 13

what is the outermost layer of the large intestine?

Answer 13

Ascending and descending colon - adventitia

Transverse colon - serosa

Question 14

main functions of the colon

Answer 14

actively transports Na+ from lumen into blood which in turn pulls H20 across with it - dehydrates chyme and makes solid faecal pellets

bacterial fermentation of undigested carbohydrate

Question 15

what products are made from bacterial fermentation of undigested carbohydrate?

Answer 15

short chain fatty acids
vitamin K
gas - nitrogen, CO2, H2, CH4 etc

Question 16

What is Vitamin K important for?

Answer 16

blood clotting

Question 17

in a normal state, how is the anus kept closed?

Answer 17

internal anal sphincter (s.m under automatic control) and external anal sphincter (skeletal muscle under voluntary control)

Question 18

what is the wave of intense contraction called that follows eating a meal

Answer 18

mass movement contraction

Question 19

Describe the defaecation reflex?

Answer 19

reflex that gives us the urge to go for a poo

it is initiated by the contraction of the rectum. The internal anal sphincter relaxes whilst the external contracts. Increased peristaltic activity moves material along and increases pressure on ext anal sphincter. This then relaxes under voluntary control and expels faeces

when this reflex is triggered you can either choose to delay or defecate

Question 20

What control is there over the defaecation reflex?

Answer 20

parasympathetic control via pelvic splanchnic nerves (no sympathetic influence)

however, there is a voluntary delay of defaecation - descending pathways

Question 21

symptoms associated with constipation? (4) and main reason for these?

Answer 21

headaches
nausea
loss of appetite
abdominal distension

due to distension of rectum

Question 22

Causes of diarrhoea (5)

Answer 22

pathogenic bacteria
protozoans
viruses
toxins
food

Question 23

give 2 types of enterotoxigenic bacteria that commonly cause diarrhoea

Answer 23

vibrio cholerae

excherichia coli

Question 24

how do enterotoxigenic bacteria work?

Answer 24

These toxins turn on intestinal Cl- secretion from crypts - they elevate intracellular second messengers like cAMP, cGMP etc and ensure the CFTR channel is always open so therefore the crypts secrete H20 all the time as H20 moves with Cl- => profuse watery diarrhoea

Question 25

treatment of secretory diarrhoea

Answer 25

Give sodium/glucose solution
oral rehydration therapy - drives H20 absorption

must let diarrhoea run but keep hydrating them